EP3412991A1

EP3412991A1 - Heat exchange system and scale suppression method for heat exchange system

Info

Publication number: EP3412991A1
Application number: EP16894555.8A
Authority: EP
Inventors: Kazuhiro Shigyo; Takafumi Nakai; Kazuhiro Miya; Shuhei NAITO
Original assignee: Mitsubishi Electric Corp
Current assignee: Mitsubishi Electric Corp
Priority date: 2016-03-16
Filing date: 2016-11-28
Publication date: 2018-12-12
Anticipated expiration: 2036-11-28
Also published as: EP3412991A4; WO2017158938A1; JPWO2017158938A1; JP6239199B1; EP3412991B1

Abstract

A heat exchange system includes a first circulation circuit annularly provide to allow a first liquid to be circulated therein, a second circulation circuit annularly provided to allow a second liquid to be circulated therein, a heat exchanger configured to perform heat exchange between the first liquid and the second liquid, a pressure retention unit configured to pressurize and retain a portion of the second liquid, an opening and closing mechanism unit disposed on an inlet side of the heat exchanger, into where the second liquid is to flow, the opening and closing mechanism unit being provided to switch the second liquid to be made to flow into the heat exchanger, between the second liquid from the second circulation circuit and the second liquid from the pressure retention unit, and a controller which controls the amount of pressure to be applied to the second liquid retained by the pressure retention unit, and controls the switching operation of the opening and closing mechanism unit.

Description

Technical Field

The present invention relates to a heat exchange system which heats a to-be-heated liquid, for example, water to be applied to a shower or the like, and a scale reduction method for the heat exchange system.

Background Art

Water heaters which supply hot water to a bathroom or a kitchen are roughly divided into, for example, electric water heaters, gas-fired water heaters such as gas boilers, and oil-fired water heaters. Such a water heater is provided with a heat exchanger for transferring heat to water. Recently, of electric water heaters, in particular, heat pump water heaters, which are a heat-pump heat exchanger type of electric water heaters, have received attention from the viewpoint of saving energy and reduction of carbon dioxide, which is a countermeasure against global warming.
Such a heat pump water heater transfers heat of the atmosphere to a heat medium, and uses this heat to boil water. More specifically, the principle of a heat pump water heater is based on the following cooling energy cycle: heat generated when a heat medium is compressed to be in a gaseous form is transferred to water by a heat exchanger, and cold air generated when the heat medium is expanded is used to return the temperature of the heat medium to the atmospheric temperature.
In theory, it is not possible to extract more energy than the energy applied to operate the water heater. However, a heat pump water heater based on the above cooling energy cycle utilizes the heat of the atmosphere, and can thus use more energy than the energy required to operate the water heater.
A heat exchanger performs heat exchange between a heat medium flowing in the heat exchanger and a fluid such as water, which flows over the surface of the heat exchanger. It is therefore important to keep the surface of the heat exchanger, which serves as a heat transfer surface, clean at all times. This is because when the surface of the heat exchanger gets dirty, the effective heat transfer surface area decreases, resulting in reduction of a heat transfer capacity. Furthermore, if such dirt accumulates, it may clog a flow passage of water or the like.
Accordingly, in recent years, various methods have been proposed to solve the above problems arising due to adhesion of scale. For example, patent literatures 1 and 2 describe that generation of scale is restricted using a pulsating flow the amount of which is changed, and which is generated by applying pulsation to the pressure of water for hot water supply.
Heat pump water heaters described in patent literatures 1 and 2 each include a hot water tank, a heating circulation passage for drawing out hot water from a lower part of the hot water tank and returning the hot water to an upper part of the hot water tank, a heating heat exchanger which heats hot water in the heating circulation passage, a pulsation generating unit disposed upstream of the heating exchanger in the heating circulation passage to cause the hot water in the heating circulation passage to flow in a pulsational manner, a circulation unit which circulates the hot water in the heating circulation passage, and a controller which controls the pulsation generating unit and the circulation unit.
The controller causes the pulsation generating unit to operate to produce a pulsating flow, while heating is performed by the heating heat exchanger, and controls the circulation unit to make the flow quantity in the heating circulation passage greater than or equal to a predetermined value.
Such a heat pump water heater can reduce accumulation of scale in the heating heat exchanger even when water having a high hardness is boiled, and can also reduce the rate of clogging of pipes which is caused by scale, to thereby increase the life of the heat pump water heater.
Patent literature 3 describes that when water is pulsating, a greater shear stress acts when water flows at a constant rate, and it is possible to efficiently restrict adhesion of scale.
In heat pump water heaters described in patent literatures 1 to 3, the rotation speed of a motor which drives a pump for circulating water in a heat exchange system is controlled to apply pulsation to the water.

Citation List

Patent Literature

Patent Literature 1:	Japanese Unexamined Patent Application Publication JP 2010-145 037 A
Patent Literature 2:	Japanese Unexamined Patent Application Publication JP 2012-117 776 A
Patent Literature 3:	Japanese Unexamined Patent Application Publication JP 2014-016 098 A

Summary of Invention

Technical Problem

However, as described in patent literatures 1 to 3, in the case where the application of pulsation is controlled based on the rotation speed of the motor, since the rotation speed of the motor does not increase instantaneously, it takes some time that the rotation speed of the motor reaches a rotation speed at which the motor achieves a pump flow quantity at which a scale reduction effect is produced.
As a result, before the quantity of flowing water reaches a flow quantity at which the scale reduction effect is produced, the amount of scale-forming substance such as calcium ion that comes into contact with the heat exchanger per unit time increases as compared with the case where the quantity of flowing water is constant. Consequently, adhesion of scale is promoted, and the degree of a scale reduction effect to be obtained by application of pulsation is reduced.
The present invention has been made in view of the above problem of the related art, and an object of the present invention is to provide a heat exchange system and a scale reduction method for the heat exchange system, which can more efficiently and reliably restrict generation and growth of scale on the heat exchanger.

Solution to Problem

A heat exchange system according to an Embodiment of the present invention includes a first circulation circuit annularly provided to allow a first liquid to be circulated therein, a second circulation circuit annularly provided to allow a second liquid to be circulated therein, a heat exchanger which performs heat exchange between the first liquid and the second liquid, a pressure retention unit which pressurizes and retains a portion of the second liquid, an opening and closing mechanism unit disposed on an inlet side of the heat exchanger, into which the second liquid is to flow, the opening and closing mechanism unit being provided to switch the second liquid to be made to flow into the heat exchanger, from the second liquid from the second circulation circuit and the second liquid from the pressure retention unit, and a controller which controls the amount of pressure to be applied to the second liquid retained by the pressure retention unit, and controls the switching operation of the opening and closing mechanism unit.

Advantageous Effects of Invention

As described above, according to an Embodiment of the present invention, the heat exchanger is supplied at a preset timing with a secondary-side target liquid to which a preset pressure has been applied. Thereby, it is possible to more efficiently and reliably reduce generation and growth of scale on the heat exchanger.

Brief Description of Drawings

FIG. 1: FIG. 1 is a block diagram illustrating an example of the configuration of a heat exchange system according to Embodiment 1.
FIG. 2: FIG. 2 is a schematic diagram illustrating an example of the configuration of a pressure retention unit as illustrated in FIG. 1.
FIG. 3: FIG. 3 is a schematic diagram illustrating an example of the configuration of an opening and closing mechanism unit as illustrated in FIG. 1.
FIG. 4: FIG. 4 is a flowchart for explaining an operation of a pressure application unit as illustrated in FIG. 1.
FIG. 5: FIG. 5 is a graph illustrating an example of variation of a shear stress, which occurs with the passage of time, in the case where the rotation speed of a motor in a conventional pump is increased.
FIG. 6: FIG. 6 is a schematic diagram for explaining a relationship between a bubble adhering to the contact surface of a heat exchanger as illustrated in FIG. 1 and scale precipitating on the contact surface.
FIG. 7: FIG. 7 is a schematic diagram illustrating an example of scale which precipitates on the contact surface of the heat exchanger as illustrated in FIG. 1.
FIG. 8: FIG. 8 is a graph illustrating an example of a relationship between a shear stress and a diameter of each of bubbles at the time when each bubble is separated from the heat exchanger as illustrated in FIG. 1.
FIG. 9: FIG. 9 is a graph illustrating an example of variation of a shear stress, which occurs with the passage of time, in the case where the shear stress is applied to a secondary-side to-be-heated liquid in the heat exchange system as illustrated in FIG. 1.
FIG. 10: FIG. 10 is a graph illustrating an exemplary relationship between the number of times a shear stress pulse is applied and the average diameter of bubbles.
FIG. 11: FIG. 11 is a graph for explaining the amounts of scale adhering to the heat exchanger, which were measured by changing the timing of application of the shear stress pulse.
FIG. 12: FIG. 12 is a graph for explaining the amounts of scale adhering to the heat exchanger, which were measured by changing the shear stress of the shear stress pulse.
FIG. 13: FIG. 13 is a graph for explaining the amounts of scale adhering to the heat exchanger, which were measured by changing the pulse width of the shear stress pulse.
FIG. 14: FIG. 14 is a table for explaining the amounts of scale adhering to the heat exchanger, which were measured by changing the shear stress and pulse width of the shear stress pulse.
FIG. 15: FIG. 15 is a block diagram illustrating an example of the configuration of a heat exchange system according to Embodiment 2.
FIG. 16: FIG. 16 is a schematic diagram illustrating an example of the configuration of a second opening and closing mechanism unit as illustrated in FIG. 15.
FIG. 17: FIG. 17 is a graph for explaining the amounts of scale adhering to the heat exchanger, which were measured when first to third shear stress pulses were applied.
FIG. 18: FIG. 18 is a block diagram illustrating an example of the configuration of a heat exchange system according to Embodiment 3.
FIG. 19: FIG. 19 is a graph illustrating the amounts of scale adhering to the heat exchanger 2, which were measured when the first to third shear stress pulses were applied.

Description of Embodiments

Embodiment

1

A heat exchange system according to Embodiment 1 of the present invention will be described below.
The heat exchange system heats or cools a secondary-side liquid such as water, with the heat of a primary-side liquid heated or cooled by a heat pump. The heat exchange system restricts adhesion of scale which occurs on a contact surface of the heat exchanger, which contacts the secondary-side liquid, when it heats or cools of the secondary-side liquid.
It should be noted that the following description is given by referring to by way of example a heat exchange system which produces hot water by heating a to-be-heated liquid such as water for use in a shower, with the heat of a to-be-heated liquid heated by a heat pump.

Configuration of heat exchange system

FIG. 1 is a block diagram illustrating an example of the configuration of a heat exchange system 1 according to Embodiment 1 of the present invention.
As illustrated in FIG. 1, the heat exchange system 1 includes a primary-side circulation circuit 10 serving as a first circulation circuit, a secondary-side circulation circuit 20 serving as a second circulation circuit, and a heat exchanger 2 disposed between the primary-side circulation circuit 10 and the secondary-side circulation circuit 20. In the heat exchange system 1, by the heat exchanger 2, heat is exchanged between a primary-side to-be-heated liquid serving as a first liquid, which circulates in the primary-side circulation circuit 10, and a secondary-side to-be-heated liquid serving as a second liquid, which circulates in the secondary-side circulation circuit 20. The heat exchange system 1 heats the secondary-side to-be-heated liquid with the heat of the primary-side to-be-heated liquid.
In Embodiment 1, for example, the temperature of the primary-side to-be-heated liquid flowing in the primary-side circulation circuit 10 is controlled to be 60 degrees C, and the temperature of the primary-side to-be-heated liquid on an outlet side of a heat pump 11 is controlled to be 65 degrees C. As to the secondary-side to-be-heated liquid in the secondary-side circulation circuit 20, suppose the temperature of the secondary-side to-be-heated liquid on an outlet side of the heat exchanger 2 is 57 degrees C. In the secondary-side circulation circuit 20, a sterilization operation which raises the temperature of the secondary-side to-be-heated liquid on the outlet side of the heat exchanger 2 to 65 degrees C is performed for just one hour, for example, once every two weeks for the purpose of removing bacteria from the secondary-side to-be-heated liquid.
The primary-side circulation circuit 10 includes the heat pump 11, a heater 12, a flow switching device 13, a first pump 14, a radiator 15, an expansion vessel 16, and the heat exchanger 2.
In the primary-side circulation circuit 10, the heat pump 11, the heater 12, the expansion vessel 16, the flow switching device 13, the heat exchanger 2, and the first pump 14 are connected annularly by a pipe 17. The radiator 15 is connected by a pipe 18, which is disposed between the flow switching device 13 and the first pump 14, and is different from the pipe 17. The pipe 17 and the pipe 18 are connected such that the two pipes are branched off from the flow switching device 13, and join together at a point between the heat exchanger 2 and the first pump 14.
In the heat pump 11, for example, a refrigeration cycle is provided. The heat pump 11 heats the primary-side to-be-heated liquid supplied by the first pump 14.
The heater 12 is provided to further heat the primary-side to-be-heated liquid supplied from the heat pump 11. The heater 12 heats the primary-side to-be-heated liquid supplied from the heat pump 11, and supplies the heated primary-side to-be-heated liquid to the flow switching device 13.
The flow switching device 13 is, for example, an electromagnetic three-way valve including one inlet and two outlets. One of the outlets of the flow switching device 13 is selected to supply the primary-side to-be-heated liquid supplied from the heat pump 11 via the heater 12 to either the heat exchanger 2 or the radiator 15, thereby effecting switching between flow passages.
The first pump 14 is driven by a motor (not illustrated), and causes the primary-side to-be-heated liquid to be supplied from either the heat exchanger 2 or the radiator 15 to the heat pump 11.
The radiator 15 is, for example, a heat exchanger. The radiator 15 performs heat exchange between the primary-side to-be-heated liquid flowing in the pipe 18 and indoor air in indoor space which is space to be air-conditioned, and heats the indoor air with the heat of the primary-side to-be-heated liquid.
The heat exchanger 2 performs heat exchange between the primary-side to-be-heated liquid flowing in the primary-side circulation circuit 10 and the secondary-side to-be-heated liquid flowing in the secondary-side circulation circuit 20, and heats the secondary-side to-be-heated liquid with the heat of the primary-side to-be-heated liquid.
The expansion vessel 16 is provided to temporarily store the primary-side to-be-heated liquid flowing out from the heater 12.
The secondary-side circulation circuit 20 includes a tank 21, a second pump 22, a scale trap 23, a pressure application unit 30 and the heat exchanger 2. In the secondary-side circulation circuit 20, the tank 21, the second pump 22, the heat exchanger 2 and the scale trap 23 are annularly connected by a pipe 24 and a pipe 25.
The pressure application unit 30 is disposed in a flow passage which serves as a bypass circuit made up of a pipe 36 and a pipe 37, and which is different from a flow passage made up of the pipes 24 and 25 and located between the tank 21, the second pump 22 and the heat exchanger 2.
The tank 21 is supplied with the secondary-side to-be-heated liquid heated in the heat exchanger 2, and stores the secondary-side to-be-heated liquid. The tank 21 is also supplied with tap water or the like from the outside via a feed pipe 21a, and the supplied tap water or the like is made to flow out from the tank 21 as the secondary-side to-be-heated liquid, and is then supplied to the second pump 22. The heated secondary-side to-be-heated liquid stored in the tank 21 is discharged to the outside via a hot water pipe 21b, and used as hot water for a shower or the like.
The second pump 22 is driven by a motor (not illustrated), and causes water, which is the secondary-side to-be-heated liquid, to be suppled from the tank 21 to the heat exchanger 2. The second pump 22 can change the quantity of the secondary-side to-be-heated liquid to be supplied to the heat exchanger 2, in accordance with the rotation speed of the motor. For example, the second pump 22 can increase the quantity of the secondary-side to-be-heated liquid to be supplied to the heat exchanger 2, by increasing the rotation speed of the motor.
The scale trap 23 is provided to trap scale which adhered to and was then removed from a contact surface of the heat exchanger 2 that contacts the secondary-side to-be-heated liquid. The larger the number of times the secondary-side to-be-heated liquid is circulated, the greater a scale-trapping effect of the scale trap 23. Therefore, a boiling system in which the secondary-side to-be-heated liquid is circulated only once can hardly be expected to obtain the scale-trapping effect, and thus it does not have to include the scale trap 23.
The pressure application unit 30 is supplied with the secondary-side to-be-heated liquid from the tank 21. The pressure application unit 30 applies a preset pressure to the secondary-side to-be-heated liquid supplied thereto, and then supplies the secondary-side to-be-heated liquid to the heat exchanger 2.
The pressure application unit 30 includes a third pump 31, a pressure retention unit 32, an opening and closing mechanism unit 33 and an opening and closing control unit 34.
The third pump 31 is driven by a motor (not illustrated), and causes a to-be-heated liquid to be supplied from the tank 21 to the pressure retention unit 32.
The pressure retention unit 32 is supplied with the secondary-side to-be-heated liquid from the tank 21 via the third pump 31. The inside of the pressure retention unit 32 is filled with the secondary-side to-be-heated liquid at all times, and is subjected to application of a pressure higher than the pressure of the secondary-side to-be-heated liquid flowing in the pipe in the secondary-side circulation circuit 20.
FIG. 2 is a schematic diagram illustrating an example of the configuration of the pressure retention unit 32 as illustrated in FIG. 1.
As illustrated in FIG. 2, the pressure retention unit 32 includes a cylinder structure unit 32a which is formed in the shape of a hollow cylinder. The cylinder structure unit 32a is provided with a solenoid valve 32b, a solenoid valve 32c, a water-quantity sensor 32d, a pressure sensor 32e, and a pressurizing unit 32f. The solenoid valve 32b to the pressurizing unit 32f are connected to the opening and closing control unit 34 via a signal line 35.
After the secondary-side to-be-heated liquid flows into the cylinder structure unit 32a via the pipe 36, the pressure retention unit 32 applies a preset pressure to the secondary-side to-be-heated liquid in the cylinder structure unit 32a. The pressure retention unit 32 then causes the secondary-side to-be-heated liquid to flow out toward the opening and closing mechanism unit 33 to be described later via the pipe 37.
The solenoid valve 32b is disposed at the inlet of the pressure retention unit 32, through which the secondary-side to-be-heated liquid flowing through the pipe 36 via the third pump 31 flows. The solenoid valve 32b supplies information indicating its open/closed state to the opening and closing control unit 34 via the signal line 35. The open/closed state of the solenoid valve 32b is controlled based on a control signal supplied from the opening and closing control unit 34 via the signal line 35.
The solenoid valve 32c is provided at, for example, an upper part of the pressure retention unit 32. The solenoid valve 32c supplies information indicating its open/closed state to the opening and closing control unit 34 via the signal line 35. The open/closed state of the solenoid valve 32c is controlled based on a control signal supplied from the opening and closing control unit 34 via the signal line 35.
Under normal conditions, the solenoid valve 32b and the solenoid valve 32c are in "open" state. The open/closed state of each of these valves is controlled by the opening and closing control unit 34 based on the result of detection which is supplied from the water-quantity sensor 32d to be described later. When the water-quantity sensor 32d detects that the inside of the cylinder structure unit 32a is filled with the secondary-side to-be-heated liquid, the solenoid valve 32b and the solenoid valve 32c are controlled to be in "closed" state based on control by the opening and closing control unit 34.
The water-quantity sensor 32d detects the quantity of secondary-side to-be-heated liquid stored in the cylinder structure unit 32a, and supplies the result of this detection to the opening and closing control unit 34 via the signal line 35.
The pressure sensor 32e detects the pressure of the secondary-side to-be-heated liquid stored in the cylinder structure unit 32a, and supplies the result of this detection to the opening and closing control unit 34 via the signal line 35.
The pressurizing unit 32f is formed in the shape of a rod. When pushed into the cylinder structure unit 32a based on a control signal supplied from the opening and closing control unit 34 via the signal line 35, the pressurizing unit 32f applies a preset pressure to the secondary-side to-be-heated liquid stored in the cylinder structure unit 32a.
When the pressure sensor 32e detects that the pressure of the secondary-side to-be-heated liquid in the cylinder structure unit 32a reaches a preset pressure, the cylinder structure unit 32a holds a state in which the pressure is applied to the secondary-side to-be-heated liquid, based on control by the opening and closing control unit 34. As a result, the secondary-side to-be-heated liquid in the cylinder structure unit 32a is kept subjected to the currently applied pressure.
The following description is given by re-referring to FIG. 1. The opening and closing mechanism unit 33 is, for example, a three-way valve. The opening and closing mechanism unit 33 selects one of the secondary-side to-be-heated liquid which flows in the pipe 37 connected to the pressure retention unit 32 and the secondary-side to-be-heated liquid which flows in the pipe 24 connected to the second pump 22, and causes the selected secondary-side to-be-heated liquid to flow toward the heat exchanger 2.
It should be noted that under normal conditions, the opening and closing mechanism unit 33 is adapted to keep the pressure application unit 30 and part of the secondary-side circulation circuit 20 which is located beside the tank 21, isolated from each other in pressure.
FIG. 3 is a schematic diagram illustrating an example of the configuration of the opening and closing mechanism unit 33 as illustrated in FIG. 1.
As illustrated in FIG. 3, the opening and closing mechanism unit 33 includes a solenoid valve 33a and a solenoid valve 33b.
The solenoid valve 33a is provided at the pipe 37 connected to the pressure retention unit 32. The solenoid valve 33a supplies information indicating its open/closed state to the opening and closing control unit 34 via a signal line 38. The open/closed state of the solenoid valve 33a is controlled based on a control signal supplied from the opening and closing control unit 34 via the signal line 38.
The solenoid valve 33a is provided with a metal shutter 33c. The metal shutter 33c is operated based on control by the opening and closing control unit 34, and determines whether the solenoid valve 33a is to be in the open or closed state. The metal shutter 33c includes, for example, a through hole located close to its center part. When the through-hole is aligned with the pipe 37, the solenoid valve 33a enters the "open" state.
The solenoid valve 33b is provided at the pipe 24 connected to the second pump 22. The solenoid valve 33b supplies information indicating its open/closed state to the opening and closing control unit 34 via the signal line 38. The open/closed state of the solenoid valve 33b is controlled based on a control signal supplied from the opening and closing control unit 34 via the signal line 38.
The solenoid valve 33b is provided with a metal shutter 33d. The metal shutter 33d is operated based on control by the opening and closing control unit 34, and determines whether the solenoid valve 33b is to be in the open or closed state. The metal shutter 33d includes, for example, a through hole located close to its center part. When the through hole is aligned with the pipe 24, the solenoid valve 33b enters the "open" state.
The opening and closing mechanism unit 33 is operated based on control by the opening and closing control unit 34 such that the solenoid valve 33a and the solenoid valve 33b operate in interlock with each other.
For example, in the opening and closing mechanism unit 33, the metal shutter 33d is moved to cause the solenoid valve 33b to enter the "closed" state at the same time as the metal shutter 33c is moved to cause the solenoid valve 33a to enter the "open" state.
By virtue of the above operation of the solenoid valve 33a and the solenoid valve 33b, two secondary-side to-be-heated liquids which respectively flow in the pipe 37 and the pipe 24 can be prevented from flowing out simultaneously; and the pressure applied to the secondary-side to-be-heated liquid flowing on a pressure retention unit 32-side can be prevented from being applied toward the tank 21.
It should be noted that the above configuration of the solenoid valve 33a and the solenoid valve 33b is intended to enable them to more quickly respond to the control by the opening and closing control unit 34.
The following description is given by re-referring to FIG. 1. The opening and closing control unit 34 controls elements of the pressure retention unit 32 and those of the opening and closing mechanism unit 33.
The opening and closing control unit 34 receives the result of detection which is obtained by the water-quantity sensor 32d of the pressure retention unit 32 as illustrated in FIG. 2. Based on information indicated by this result, the opening and closing control unit 34 supplies a control signal for controlling the opening and closing of the solenoid valve 32b and the solenoid valve 32c to the pressure retention unit 32 via the signal line 35.
The opening and closing control unit 34 receives from the pressure retention unit 32, the result of detection which is obtained by the pressure sensor 32e as illustrated in FIG. 2. Based on information indicated by this result, the opening and closing control unit 34 supplies a control signal for controlling the operation of the pressurizing unit 32f to the pressure retention unit 32 via the signal line 35.
Furthermore, the opening and closing control unit 34 supplies at a preset timing, a control signal for controlling the opening and closing of the solenoid valve 33a and solenoid valve 33b of the opening and closing mechanism unit 33 as illustrated in FIG. 3, to the opening and closing mechanism unit 33 via the signal line 38.

Operation of heat exchange system

The primary-side to-be-heated liquid is supplied to the heat pump 11 by the first pump 14, and is then heated. The heated primary-side to-be-heated liquid is re-heated by the heater 12, and then flows into the flow switching device 13.
In the flow switching device 13, in the case where the outlet for the flow toward the radiator 15 is selected, the primary-side to-be-heated liquid flows out from the flow switching device 13 through the outlet for the flow toward the radiator 15. After flowing out from the flow switching device 13, the primary-side to-be-heated liquid flows into the radiator 15, where the primary-side to-be-heated liquid exchanges heat with indoor air, thereby heating the indoor air. Then, after flowing out from the radiator 15, the primary-side to-be-heated liquid flows into the first pump 14.
By contrast, in the flow switching device 13, in the case where the outlet for the flow toward the heat exchanger 2 is selected, the primary-side to-be-heated liquid flows out from the flow switching device 13 through the outlet for the flow toward the heat exchanger 2. After flowing out from the flow switching device 13, the primary-side to-be-heated liquid flows into the heat exchanger 2, where the primary-side to-be-heated liquid exchanges heat with the secondary-side to-be-heated liquid, thereby heating the secondary-side to-be-heated liquid. Then, after flowing out from the heat exchanger 2, the primary-side to-be-heated liquid flows into the first pump 14.
The secondary-side to-be-heated liquid such as water which is supplied to the tank 21 flows out from the tank 21, and is then made to flow into the heat exchanger 2 by the second pump 22 via the pressure application unit 30. In the heat exchanger 2, the secondary-side to-be-heated liquid is heated by heat exchange with the primary-side to-be-heated liquid, and then flows out from the heat exchanger 2.
After flowing out from the heat exchanger 2, the secondary-side to-be-heated liquid flows into the tank 21 via the scale trap 23, and is stored in the tank 21. The secondary-side to-be-heated liquid stored in the tank 21 is mixed with, for example, water, and used as hot water for a shower or the like.
Also, the secondary-side to-be-heated liquid stored in the tank 21 is supplied to the pressure application unit 30. The secondary-side to-be-heated liquid supplied to the pressure application unit 30 is made to flow into the pressure retention unit 32 by the third pump 31 of the pressure application unit 30.
After the secondary-side to-be-heated liquid flows into the pressure retention unit 32, a preset pressure is applied to the secondary-side to-be-heated liquid based on control by the opening and closing control unit 34, and the secondary-side to-be-heated liquid then flows out from the pressure retention unit 32. After flowing out therefrom, the secondary-side to-be-heated liquid flows into the opening and closing mechanism unit 33.
After the secondary-side to-be-heated liquid flows into the opening and closing mechanism unit 33, when the solenoid valve 33a, which is opened/closed based on control by the opening and closing control unit 34, is made to be in the "open" state, the secondary-side to-be-heated liquid flows out of the opening and closing mechanism unit 33 and flows into the heat exchanger 2.
At this time, in the opening and closing mechanism unit 33, the solenoid valve 33a disposed beside the pressure retention unit 32 and the solenoid valve 33b disposed beside the second pump 22 operate in interlock with each other such that one of the solenoid valve 33a and the solenoid valve 33b is controlled to be in the "open" state. Therefore, when the solenoid valve 33a is in the "open" state, only the secondary-side to-be-heated liquid present in the pressure retention unit 32 flows into the heat exchanger 2. At this time, the opening/closing operation of the solenoid valve 33a and the pressure to be applied to the secondary-side to-be-heated liquid in the pressure retention unit 32 are controlled to cause the secondary-side to-be-heated liquid flowing out from the pressure retention unit 32 to flow into the heat exchanger 2 at a preset timing and with a preset pressure.
FIG. 4 is a flowchart illustrating the operation of the pressure application unit 30 as illustrated in FIG. 1.
With reference to FIG. 4, descriptions will be given regarding operations from supplying of the secondary-side to-be-heated liquid from the tank 21 to the pressure application unit 30 to flowing of the secondary-side to-be-heated liquid retained by the pressure application unit 30 into the heat exchanger 2.
First, based on control by the opening and closing control unit 34, the solenoid valve 32c is made to be in the "open" state, and the solenoid valve 32b is made to be in the "open" state (steps S1 and S2). Then, the secondary-side to-be-heated liquid stored in the tank 21 is supplied to the pressure retention unit 32 by the third pump 31 (step S3). When the secondary-side to-be-heated liquid is supplied to the pressure retention unit 32, the solenoid valve 32c is made to be in the "closed" state, and the solenoid valve 32b is made to be in the "closed" state, based on control by the opening and closing control unit 34 (steps S4 and S5).
In the pressure retention unit 32, based on control by the opening and closing control unit 34, a preset pressure is applied by the pressurizing unit 32f to the secondary-side to-be-heated liquid in the pressure retention unit 32 (step S6). The pressure applied to the secondary-side to-be-heated liquid in the pressure retention unit 32 is held (step S7).
Next, a control signal is transmitted from the opening and closing control unit 34 to the solenoid valve 33b of the opening and closing mechanism unit 33 (step S8). In the opening and closing mechanism unit 33, the metal shutter 33d is slid based on the control signal to cause the solenoid valve 33b to be in the "closed" state (step S9).
Furthermore, a control signal is transmitted from the opening and closing control unit 34 to the solenoid valve 33a of the opening and closing mechanism unit 33 (step S10). In the opening and closing mechanism unit 33, the metal shutter 33c is slid based on the control signal to cause the solenoid valve 33a to be in the "open" state (step S11).
As a result, the secondary-side to-be-heated liquid in the pressure retention unit 32 flows out from the pressure retention unit 32 and flows into the heat exchanger 2 (step S12).
Next, a control signal is transmitted from the opening and closing control unit 34 to the solenoid valve 33a of the opening and closing mechanism unit 33 (step S13). In the opening and closing mechanism unit 33, the metal shutter 33c is slid based on the control signal to cause the solenoid valve 33a to be in the "closed" state (step S14).
Furthermore, a control signal is transmitted from the opening and closing control unit 34 to the solenoid valve 33b of the opening and closing mechanism unit 33 (step S15). In the opening and closing mechanism unit 33, the metal shutter 33d is slid based on the control signal to cause the solenoid valve 33b to be in the "open" state (step S16).

Restriction of generation of scale on heat exchanger

Next, restriction of generation of scale the heat exchanger 2 will be described.
FIG. 5 is a graph illustrating an example of variation of a shear stress, which occurs with the passage of time in the case where the rotation speed of a motor in a conventional pump is increased.
In Embodiment 1, for example, tap water is used as the secondary-side to-be-heated liquid to be stored in the tank 21. Such a secondary-side to-be-heated liquid contains scale components such as oxides or carbonate compounds of metal ions represented by calcium. Therefore, when the secondary-side to-be-heated liquid is caused to exchange heat with the primary-side to-be-heated liquid by the heat exchanger 2, the scale components contained in the secondary-side to-be-heated liquid precipitate and adhere onto a contact surface of the heat exchanger 2 that contacts the secondary-side to-be-heated liquid. When the precipitating scale adheres onto the heat exchanger 2, the scale clogs the flow passage, thus reducing the heat exchange efficiency.
As described in the "Background Art" section, in the related art, a pulsating flow is generated in a to-be-heated liquid, or the speed at which the to-be-heated liquid passes through a heat exchanger is increased, thereby generating a shear stress between the to-be-heated liquid and a contact surface of the heat exchanger which contacts the to-be-heated liquid. Also, in the related art, scale precipitating on the contact surface of the heat exchanger is peeled off by the shear stress, to thereby restrict the growth of the scale.
In this case, for example, in order that the speed of the to-be-heated liquid be increased, in general, it is done by increasing the rotation speed of the motor driving the pump which feeds the to-be-heated liquid. However, it takes some time to cause the rotation speed of the motor which drives the pump to reach a target rotation speed. Thus, as illustrated in FIG. 5, for example, two seconds are required to obtain a target shear stress by increasing the rotation speed of the motor.
That is, in the above conventional method, it takes some time to cause the quantity of the to-be-heated liquid to reach a flow quantity at which a scale reduction effect is produced, and the growth of scale is promoted, thus reducing the scale reduction effect.
In Embodiment 1, in order to restrict the growth of scale, the secondary-side to-be-heated liquid subjected to application of a preset pressure is made to flow into the heat exchanger 2 at a preset timing, thereby giving a shear stress which can remove scale precipitating on the contact surface of the heat exchanger 2 that contacts the secondary-side to-be-heated liquid.

Precipitation of scale

FIG. 6 is a schematic diagram for explaining a relationship between a bubble adhering to the contact surface of the heat exchanger 2 as illustrated in FIG. 1 and scale precipitating on the contact surface.
FIG. 7 is a schematic diagram illustrating an example of scale precipitating on the contact surface of the heat exchanger 2 as illustrated in FIG. 1.
As illustrated in FIG. 6, if a bubble 40 contained in the secondary-side to-be-heated liquid adheres to the contact surface of the heat exchanger 2 that contacts the secondary-side to-be-heated liquid, a micro layer 41 is formed at an interface between the bubble 40 and the contact surface of the heat exchanger 2, and in the micro layer 41, ions concentrate such that the concentration thereof is approximately 1.5 times greater than those in areas other than the interface. In the micro layer 41, a larger number of scale nuclei, which are starting points of scale growth, precipitate than in areas to which no bubble 40 adheres. As illustrated in FIG. 7, at the interface between the bubble 40 and the contact surface of the heat exchanger 2, a scale nucleus precipitates so as to conform to the shape of the bubble 40.
The scale precipitating in the above manner can be removed by applying a shear stress. At this time, if the nuclei of the scale adhering to the contact surface of the heat exchanger 2 have not yet grown, the scale can be removed by a smaller shear stress than that required to remove grown scale.
Furthermore, since the scale nuclei are minute as compared with grown scale, there is no risk that such scale nuclei will re-adhere to the surface of the heat exchanger 2, pipes or the like, or deposit on parts of the pipes which stagnate liquid flow. Accordingly, scale adhering in the form of scale nuclei can be removed efficiently with a lower flow quantity and a smaller shear stress than those required to remove grown scale.

Relationship between shear stress and diameter of bubble at bubble separation time

FIG. 8 is a graph illustrating an example of a relationship between a shear stress and the diameter of each of bubbles 40 at the time when each bubble 40 is separated from the heat exchanger 2 as illustrated in FIG. 1.
It can be seen that as illustrated in FIG. 8, the greater the shear stress applied to the secondary-side to-be-heated liquid, the smaller the diameter of the bubble 40 separated from the contact surface of the heat exchanger 2 that contacts the secondary-side to-be-heated liquid. For example, if a shear stress of 50 Pa is applied to the secondary-side to-be-heated liquid, a bubble 40 having a diameter of approximately 100 µm can be separated from the contact surface of the heat exchanger 2.
FIG. 9 is a graph illustrating an example of variation of a shear stress, which occurs with the passage of time, in the case where the shear stress is applied to the secondary-side to-be-heated liquid in the heat exchange system 1 as illustrated in FIG. 1. In FIG. 9, the variation of the shear stress, which is indicated by a dotted line, corresponds to the variation of the shear stress which occurs with the passage of time as illustrated in FIG. 5.
As illustrated in FIG. 9, in Embodiment 1, a shear stress is applied in the manner of pulses to the secondary-side to-be-heated liquid (the shear stress applied in the manner of pulses will be hereinafter referred to as "shear stress pulses"). In this case, the applied shear stress rises steeply as compared with the case illustrated in FIG. 5, as a result of which a target shear stress can be applied in a shorter time period to the bubbles 40 and scale nuclei that adhere to the heat exchanger 2. It is therefore possible to efficiently remove the scale nuclei and restrict the growth of the scale, as compared with the case illustrated in FIG. 5.
As described above, when shear stress pulses are applied as illustrated in FIG. 9, bubbles 40 adhering to the contact surface of the heat exchanger 2 that contacts the secondary-side to-be-heated liquid are moved in accordance with the applied shear stress. For example, in an example as illustrated in FIG. 8, in the case where a shear stress of 50 Pa is applied for 0.5 seconds, a bubble 40 having a diameter of approximately 100 µm can be moved.
FIG. 10 is a graph illustrating an example of a relationship between the number of times a shear stress pulse is applied and the average diameter of the bubbles 40. FIG. 10 illustrates by way of example the case where a shear stress of 50 Pa is applied to the secondary-side to-be-heated liquid at intervals of 0.5 seconds.
As illustrated in FIG. 10, the average diameter of the bubbles 40 adhering to the contact surface of the heat exchanger 2 that contacts the secondary-side to-be-heated liquid increases as the number of times a shear stress pulse is applied increases. For example, in the case where the shear stress pulse is applied three times, the average diameter of the bubbles 40 is 1000 µm or greater. This is because when the shear stress pulse is applied a number of times, a plurality of bubbles 40 aggregate into a single larger bubble 40.
Furthermore, as illustrated in FIG. 8, the greater the diameter of the bubble 40, the smaller the shear stress required to remove the bubble. For example, when a shear stress pulse of 3.3 Pa is applied, it is possible to remove a bubble 40 of approximately 1000 µm into which a number of bubbles are aggregated.
That is, according to Embodiment 1, such a great shear stress pulse as to have a great shear stress reaching a target shear stress is applied a number of times, to thereby cause the bubbles 40 to move and aggregate into a larger bubble, and then shear stress pulses to act a smaller shear stress than the above shear stress are applied. Thereby, it is possible to efficiently remove the bubbles 40 and scale nuclei which adhere to the heat exchanger 2, and restrict the growth of the scale.

Investigation of scale reduction effect

An investigation of the scale reduction effect for scale adhering to the heat exchanger 2 will be described.
The following description is given with respect to investigations of scale reduction effects which are obtained in the case where the timing at which the shear stress pulse is applied is changed, the case where the pulse width which is the time period in which the shear stress pulse is applied is changed, and the case where the shear stress and pulse width of the shear stress pulse are changed..

First investigation: the case where the timing of application of the shear stress pulse is changed

First of all, as to the first investigation, the amount of scale adhering to the heat exchanger 2 in the case of changing the timing of application of the shear stress pulse will be described.
FIG. 11 is a graph for explaining the amount of scale adhering to the heat exchanger 2 in the case of changing the timing of application of the shear stress pulse.
In this example, to a secondary-side to-be-heated liquid with a shear stress of 1 Pa, which is a shear stress acting when the flow quantity is normal, a shear stress pulse cycle was applied under conditions described below, and the shear stress pulse cycle is a combination of a first shear stress pulse having a preset shear stress and a second shear stress pulse having a smaller shear stress than that of the first shear stress. Then, the adhesion amount of scale on the heat exchanger 2 in the case where the heat exchange system 1 was operated for 100 hours while changing the intervals of application of the shear stress pulse cycle was measured.
(a) First shear stress pulse

Shear stress: 50 [Pa]

Application duration (pulse width): 0.5 [sec]

Non-application duration: 0.5 [sec]

Number of times it is applied: 3

(b) Second shear stress pulse

Shear stress: 3.3 [Pa]

Application duration (pulse width): 0.5 [sec]

Non-application duration: 0.5 [sec]

Number of times it is applied: 1
FIG. 11 illustrates by way of example the adhesion amounts of scale which were measured when the shear stress pulse cycle was applied at intervals of 3 minutes, at intervals of 5 minutes and at the intervals of 7 minutes, respectively, the amounts being each expressed as a percent on the assumption that the adhesion amount of scale which was measured in the case of applying no shear stress pulse is 100%. Also, for reference, FIG. 11 illustrates results obtained in a pulsation operation involving pulsation produced by increasing the rotation speed of the motor in the conventional pump.
As illustrated in FIG. 11, in the case where the shear stress pulse cycle was applied at intervals of three minutes, the amount of scale adhering to the heat exchanger 2 was 50% of that in the case where no shear stress pulse was applied. In the case where the shear stress pulse cycle was applied at intervals of five minutes, the amount of scale adhering to the heat exchanger 2 was 61% of that in the case where no shear stress pulse was applied. In the case where the shear stress pulse cycle was applied at intervals of seven minutes, the amount of scale adhering to the heat exchanger 2 was 65% of that in the case where no shear stress pulse was applied. It should be noted that in the conventional pulsation operation, the amount of scale adhering to the heat exchanger 2 was 73% of that in the case where no shear stress pulse was applied.
According to these results, in the case where the shear stress pulse cycle was applied at intervals of three minutes, the adhesion amount of scale is the smallest, and the scale reduction effect is the greatest in all the above cases where the shear stress pulse cycles were applied at the intervals of the above different time lengths.
In other words, the shorter the intervals of application of the shear stress pulse cycle, the smaller the amount of scale deposition on the heat exchanger 2, and the higher the scale reduction effect.
It is known that the surface temperature of the heat exchanger 2 lowers, and the heat exchange efficiency lowers, as the number of times a first shear stress which is a great shear stress pulse is applied increases or the time period in which it is applied increases. It is therefore necessary to determine the number of times the first shear stress pulse in the shear stress pulse cycle and the time period in which the first shear stress pulse is applied, in such a way as to further improve the heat exchange efficiency, in accordance with the amount of scale adhering to the surface of the heat exchanger 2.

Second investigation: the case of changing the shear stress of the shear stress pulse

Next, as the second investigation, the amount of scale adhering to the heat exchanger 2 in the case of changing the timing of the shear stress of the shear stress pulse will be described.
FIG. 12 is a graph for explaining the amount of scale adhering to the heat exchanger in the case of changing the shear stress of the shear stress pulse.
In this example, to a secondary-side to-be-heated liquid with a shear stress of 1 Pa, which is a shear stress acting when the flow quantity is normal, the shear stress pulse cycle is applied under conditions indicated below. Then, the adhesion amount of scale on the heat exchanger 2 in the case where the heat exchange system was operated for 100 hours on the condition that the shear stress pulse cycle was applied at intervals of five minutes was measured.
(a) First shear stress pulse

Shear stress: 0 [Pa] to 70 [Pa]

Application duration (pulse width): 0.5 [sec]

Non-application duration: 0.5 [sec]

Number of times it is applied: 3

(b) Second shear stress pulse

Shear stress: 3.3 [Pa]

Application duration (pulse width): 0.5 [sec]

Non-application duration: 0.5 [sec]

Number of times it is applied: 1
FIG. 12 illustrates by way of example the adhesion amounts of scale which were measured when first shear stress pulses having shear stresses 0 Pa to 70 Pa were applied, the amounts being each expressed on the assumption that the amount of scale adhered which was measured in the case of applying no shear stress pulse is "100".
As illustrated in FIG. 12, in the case where the shear stress of the first shear stress pulse was greater than or equal to 5 Pa, the amount of scale adhering to the heat exchanger 2 was reduced as compared with the case where no shear stress pulse was applied. By contrast, in the case where the shear stress of the first shear stress pulse was greater than or equal to 50 Pa, the adhesion amount of scale was unchanged, and the scale reduction effect tended not to be further improved.
In such a manner, when the shear stress of the first shear stress pulse is greater than or equal to 5 Pa, the scale reduction effect can be obtained, and when the shear stress of the first shear stress pulse is greater than or equal to 50 Pa, the scale reduction effect is not further improved. That is, it is preferable that the shear stress of the shear stress pulse be set to fall within the range of 5 to 50 Pa.
Furthermore, since the shear stress of the second shear stress pulse is 3.3 Pa, it is more preferable that the ratio between the shear stress of the first shear stress pulse and that of the second shear stress pulse be set to fall within the range "5:3.3" to "50:3.3".

Third investigation: the case where the pulse width of the shear stress pulse is changed

Next, as the third investigation, the amount of scale adhering to the heat exchanger 2 in the case of changing the pulse width of the shear stress pulse will be described.
FIG. 13 is a graph for explaining the amount of scale adhering to the heat exchanger 2 in the case of changing the pulse width of the shear stress pulses.
In this example, to a secondary-side to-be-heated liquid with a shear stress of 1 Pa, which is a shear acting when the flow quantity is normal, a shear stress pulse cycle was applied under conditions indicated below. Then, the adhesion amount of scale on the heat exchanger 2 in the case where the heat exchange system 1 was operated for 100 hours on the condition that the shear stress pulse cycle was applied at intervals of five minutes was measured.
(a) First shear stress pulse

Shear stress: 30 [Pa]

Application duration (pulse width): 0 [sec] to 5.0 [sec]

Non-application duration: 0.5 [sec]

Number of times it is applied: 1

(b) Second shear stress pulse

Shear stress: 3.3 [Pa]

Application duration (pulse width): 0.5 [sec]

Non-application duration: 0.5 [sec]

Number of times it is applied: 1
FIG. 13 illustrates by way of example the adhesion amounts of scale which were measured when first shear stresses having pulse widths of 0 to 5.0 seconds were applied, the amounts being each expressed on the assumption that the adhesion amount of scale which was measured in the case of applying no shear stress pulse is "100".
As illustrated in FIG. 13, the amounts of scale adhering to the heat exchanger 2 which were measured when the first shear stresses having pulse widths of 0 to 5.0 seconds were applied were all reduced as compared with that in the case where no shear stress pulse was applied.
In particular, when the first shear stress pulses having pulse widths of 0.1 to 1.0 second were applied, the measured amount of scale adhered were less than or equal to 70%, and the scale reduction effect tends to be further improved.
In such a manner, in the case where the pulse width of the first shear stress pulse is set to fall within the range of 0 to 5.0 seconds, an improved scale reduction effect can be obtained as compared with the case where no shear stress pulse is applied. In particular, in the case where the pulse width is set to fall within the range of 0.1 to 1.0 second, a further improved scale reduction effect can be obtained.
Furthermore, in the case where the pulse width of the shear stress pulse is set in the above manner, the scale can be reduced in a shorter time period, whereas it takes approximately 2 seconds to reduce the scale with such a control of the pump as described above.

Fourth investigation: the case of changing the shear stress and pulse width of the shear stress pulse

Next, as the fourth investigation, the amount of scale adhering to the heat exchanger 2 in the case of changing the shear stress and pulse width of the shear stress pulse will be described. The fourth investigation is a combination of the second investigation and the third investigation.
FIG. 14 is a table for explaining the amount of scale adhering to the heat exchanger 2 in the case of changing the shear stress and pulse width of the shear stress pulse.
In this example, to a secondary-side to-be-heated liquid with a shear stress of 1 Pa, which is a shear stress acting when the flow quantity is normal, a shear stress pulse cycle was applied under conditions described below. Then, the adhesion amount of scale on the heat exchanger 2 in the case where the heat exchange system 1 was operated for 100 hours on the condition that the shear stress pulse cycle was applied at intervals of five minutes was measured.

Ratio between first and second shear stress pulses: "3:1" to "30:1"
Pulse widths of first and second shear stress pulses: 0.1 [sec] to 2.0 [sec]
Duration of non-application of first and second shear stress pulses: 0.5 [sec]
1. (a) Number of times first shear stress pulse is applied: 3
2. (b) Number of times second shear stress pulse is applied: 1

FIG. 14 illustrates by way of example results of scale reduction effects on the assumption that the adhesion amount of scale in the case of applying no shear stress pulse is "100". In FIG. 14, "-" denotes results that the scale reduction effect was greater than or equal to 20%, that is, results that the adhesion amount of scale was less than or equal to 80%, and "+" denotes results that the scale reduction effect was less than 20%, that is, results that the amount of scale deposition exceeded 80%.
As illustrated in FIG. 14, in the case where the ratio between the shear stress of the first shear stress pulse and that of the second shear stress pulse was greater than or equal to "5:1", and the pulse width of the shear stress pulse was less than or equal to 1.0 second, obtained scale reduction effects were greater than or equal to 20%.
Furthermore, in the case where the ratio between the shear stress of the first shear stress pulse and that of the second shear stress pulse was greater than or equal to "10:1", and the pulse width of the shear stress pulse was less than or equal to 1.5 seconds, obtained scale reduction effects were greater than or equal to 20%.
Also, in the case where the ratio between the shear stress of the first shear stress pulse and that of the second shear stress pulse was greater than or equal to "20:1", and the pulse width of the shear stress pulse was less than or equal to 2.0 seconds, obtained scale reduction effects were greater than or equal to 20%.
It can be seen from these results that if the ratio between the shear stress of the first shear stress pulse and that the second shear stress pulse is great, even if the pulse width of the shear stress pulse is set short, a scale reduction effect for scale adhering to the heat exchanger 2 can be obtained.
In such a manner, in Embodiment 1, there are provided; the primary-side circulation circuit 10 which is annularly provided, and in which the primary-side to-be-heated liquid is circulated; the secondary-side circulation circuit 20 which is annularly shaped, and in which the secondary-side to-be-heated liquid is circulated; the heat exchanger 2 which performs heat exchange between the primary-side to-be-heated liquid and the secondary-side to-be-heated liquid; the pressure retention unit 32 which pressurizes and retains a portion of the secondary-side to-be-heated liquid; the opening and closing mechanism unit 33 disposed on a side of the heat exchanger 2, into which the secondary-side to-be-heated liquid flows, the opening and closing mechanism unit 33 being provided to switch the secondary-side to-be-heated liquid to be made to flow into the heat exchanger 2 between the secondary-side to-be-heated liquid from the secondary-side circulation circuit 20 and the secondary-side to-be-heated liquid from the pressure retention unit 32; and the opening and closing control unit 34 which controls the amount of the pressure to be applied to the secondary-side to-be-heated liquid retained by the pressure retention unit 32, and also control the switching operation of the opening and closing mechanism unit 33.
In such a manner, a pressurized secondary-side to-be-heated liquid is supplied to the heat exchanger 2, whereby generation and growth of scale can be efficiently and reliably restricted.
The opening and closing control unit 34 controls the pressure retention unit 32 and the opening and closing mechanism unit 33 such that a secondary-side to-be-heated liquid to which a shear stress pulse cycle is applied is supplied to the heat exchanger 2, the shear stress pulse cycle being a combination of a plurality of shear stress pulses having different shear stresses.
To be more specific, the shear stress pulse cycle is a combination of a first shear stress pulse and a second shear stress pulse having a smaller shear stress than that of the first shear stress pulse, which is achieved such that the first and second shear stress pulses are combined in this order.
Therefore, after the bubbles 40 adhering to the contract surface of the heat exchanger 2 are moved and aggregated into a large bubble by applying the first shear stress pulse, the large bubble can be removed by applying the second shear stress pulse. Thus, it is possible to efficiently remove the bubbles 40 and scale nuclei adhering to the contact surface of the heat exchanger 2 that contacts the secondary-side to-be-heated liquid.

Embodiment 2

Next, a heat exchange system according to Embodiment 2 of the present invention will be described.
The heat exchange system according to Embodiment 2 is different from that of Embodiment 1 on the point that it includes a second pressure-application unit. In Embodiment 2, the secondary-side to-be-heated liquid is boiled up when it is circulated a number of times between the tank 21 and the heat exchanger 2 (this will be hereinafter referred to as "multiple-boiling system" as appropriate).

Configuration of heat exchange system

FIG. 15 is a block diagram illustrating an example of the heat exchange system 1 according to Embodiment 2. In the following description, elements identical to those of Embodiment 1 mentioned above will be denoted by the same reference signs, and their detailed descriptions will be omitted.
As illustrated in FIG. 15, the heat exchange system 1 includes the primary-side circulation circuit 10, the secondary-side circulation circuit 20, and the heat exchanger 2. The secondary-side circulation circuit 20 is provided with a second pressure-application unit 50, in addition to components similar to those of Embodiment 1.
The second pressure application unit 50 includes a fourth pump 51, a second pressure retention unit 52 connected to the fourth pump 51 by a pipe 56, and a second opening and closing mechanism unit 53 connected to the second pressure retention unit 52 by a pipe 57. The fourth pump 51 has a similar configuration and a similar function to those of the third pump 31. The second pressure retention unit 52 also has a similar configuration and a similar function to those of the pressure retention unit 32.
FIG. 16 is a schematic diagram illustrating an example of the configuration of the second opening and closing mechanism unit 53 as illustrated in FIG. 15.
As illustrated in FIG. 16, the second opening and closing mechanism unit 53 includes a solenoid valve 53a and a solenoid valve 53b.
The solenoid valve 53a is provided at the pipe 57 connected to the second pressure retention unit 52. The solenoid valve 53a supplies information indicating its open/closed state to the opening and closing control unit 34 via a signal line 58. Furthermore, the open/closed state of the solenoid valve 53a is controlled based on a control signal supplied from the opening and closing control unit 34 via the signal line 58.
The solenoid valve 53a is provided with a metal shutter 53c. The metal shutter 53c is operated based on control by the opening and closing control unit 34, and determines whether the solenoid valve 53a is to be in the open or the closed state. The metal shutter 53c includes, for example, a through hole located close to its central part. When the through hole is aligned with the pipe 57, the solenoid valve 53a is made to be in the "open" state.
The solenoid valve 53b is provided at the pipe 25 connected to the tank 21. The solenoid valve 53b supplies information indicating its open/closed state to the opening and closing control unit 34 via the signal line 58. Furthermore, the open/closed state of the solenoid valve 53b is controlled based on a control signal supplied from the opening and closing control unit 34 via the signal line 58.
The solenoid valve 53b is provided with a metal shutter 53d. The metal shutter 53d is operated based on control by the opening and closing control unit 34, and determines whether the solenoid valve 53b is to be in the open or the closed state. The metal shutter 53d includes, for example, a through hole located close to its central part. When the through hole is aligned with the pipe 25, the solenoid valve 53b is made to be in the "open" state.
The second opening and closing mechanism unit 53 is operated based on control by the opening and closing control unit 34 such that the solenoid valve 53a and the solenoid valve 53b operate in interlock with each other.
For example, in the second opening and closing mechanism unit 53, the metal shutter 53d is moved to cause the solenoid valve 53b to be in the "closed" state at the same time as the metal shutter 53c is moved to cause the solenoid valve 53a to be in the "open" state.
By virtue of the above operation of the solenoid valve 53a and the solenoid valve 53b, it is possible to prevent the secondary-side to-be-heated liquid flowing out from the second pressure retention unit 52 via the pipe 57 from flowing toward the tank 21. Tit should be noted that the solenoid valve 53a and the solenoid valve 53b are formed to have the above configurations in order that these valves can more quickly respond to control by the opening and closing control unit 34.
The following description is given by re-referring to FIG. 15. In addition to control similar to that in Embodiment 1, the opening and closing control unit 34 controls components of the second pressure retention unit 52 and components of the second opening and closing mechanism unit 53.
For example, the opening and closing control unit 34 supplies a control signal for controlling an operation of the second pressure retention unit 52 to the second pressure retention unit 52 via a signal line 55. Furthermore, the opening and closing control unit 34 supplies, at a preset timing, a control signal for controlling the opening and closing of the solenoid valve 53a and solenoid valve 53b of the second opening and closing mechanism unit 53 provided as illustrated in FIG. 16, to the second opening and closing mechanism unit 53 via the signal line 58.
In the present example, unlike in Embodiment 1, the opening and closing control unit 34 is provided independently from the pressure application unit 30. However, the opening and closing control unit 34 is not limited to that of the example. For example, the opening and closing control unit 34 may be included in the pressure application unit 30 as in Embodiment 1, or may be included in the second pressure-application unit 50.

Operation of heat exchange system

In the heat exchange system 1 according to Embodiment 2, the flow of the primary-side to-be-heated liquid in the primary-side circulation circuit 10 and the flow of the secondary-side to-be-heated liquid in the secondary-side circulation circuit 20 are similar to those in Embodiment 1. The operation of the pressure application unit 30 is also similar to that in Embodiment 1.
The secondary-side to-be-heated liquid stored in the tank 21 is supplied to the second pressure-application unit 50. The secondary-side to-be-heated liquid supplied to the second pressure-application unit 50 is made to flow into the second pressure retention unit 52 by the fourth pump 51 of the second pressure-application unit 50.
The secondary-side to-be-heated liquid in the second pressure retention unit 52 is subjected to application of a preset pressure based on control by the opening and closing control unit 34, and then flows out from the second pressure retention unit 52. After flowing out from the second pressure retention unit 52, the secondary-side to-be-heated liquid flows into the second opening and closing mechanism unit 53.
The secondary-side to-be-heated liquid in the second opening and closing mechanism unit 53 flows out from the second opening and closing mechanism unit 53 and flows into the heat exchanger 2, when the solenoid valve 53a, which is opened/closed based on control by the opening and closing control unit 34, is made to be in the "open" state.
At this time, the opening/closing operation of the solenoid valve 53a and the pressure to be applied to the secondary-side to-be-heated liquid in the second pressure retention unit 52 are controlled, to thereby cause the secondary-side to-be-heated liquid flowing out from the second pressure retention unit 52 to flow into the heat exchanger 2 at a preset timing and with a preset pressure.
The secondary-side to-be-heated liquid flowing from the second pressure retention unit 52 into the heat exchanger 2 is subjected to application of a shear stress pulse within the heat exchanger 2, which is performed in an opposite direction to the direction of application of a shear stress pulse to the secondary-side to-be-heated liquid flowing from the pressure retention unit 32 into the heat exchanger 2. In Embodiment 3, the above shear stress pulse in the opposite direction is applied as a third shear stress pulse between the first shear stress pulse and the second shear stress pulse having a smaller shear stress than that of the first shear stress pulse, which are described above with respect to Embodiment 1. In this case, suppose the third shear stress pulse is equivalent to the first shear stress pulse except for the direction of application of the shear stress pulse.
As described above, the first shear stress pulse, which acts to push bubbles in a direction toward the interior of the heat exchanger 2, is applied to cause the bubbles to be moved and aggregated, and the third shear stress pulse, which acts to pull the bubbles back in a direction away from the interior of the heat exchanger 2, is applied. Thereby, it is possible to increase the efficiency of formation of a large bubble into which bubbles are moved and aggregated by applying the first shear stress pulse.
In this case, the bubbles 40 and scale nuclei adhering to the surface of the heat exchanger 2 that contacts the secondary-side to-be-heated liquid are more efficiently removed than in the case where only the first and second shear stress pulses are applied.

Investigation of scale reduction effect

Next, reduction of scale adhering to the heat exchanger 2 will be described.
In Embodiment 2, a shear stress pulse cycle which is provided by adding a third shear stress pulse to the first and second shear stress pulses according to Embodiment 1 is applied to the heat exchanger 2, the third shear stress pulse being applied to the heat exchanger 2 in the opposite direction to the direction in which the first and second shear stress pulses are applied.
FIG. 17 is a graph for explaining the amount of scale adhering to the heat exchanger 2 in the case where the first to third shear stress pulses are applied.
In this example, to a secondary-side to-be-heated liquid with a shear stress of 1 Pa, which is a shear stress acting when the flow quantity is normal, a shear stress pulse cycle was applied under conditions given below, and the applied shear stress pulse cycle is a combination of the first shear stress pulse having a preset shear stress, the second shear stress pulse having a smaller shear stress than that of the first shear stress pulse, and the third shear stress pulse which is equivalent to first shear stress pulse, and is applied to the heat exchanger 2 in the opposite direction to that of the first shear stress pulse. Then, the adhesion amount of scale on the heat exchanger 2 in the case where the heat exchange system 1 was operated for 100 hours while changing the intervals of application of the shear stress pulse cycle was measured. It should be noted that the first shear stress pulse, the third shear stress pulse and the second shear stress pulse are applied in this order.
(a) First shear stress pulse

Shear stress: 50 [Pa]

Application duration (pulse width): 0.5 [sec]

Non-application duration: 0.5 [sec]

Number of times it is applied: 3

(b) Third shear stress pulse

Shear stress: 50 [Pa]

Application duration (pulse width): 0.5 [sec]

Non-application duration: 0.5 [sec]

Number of times it is applied: 3

(c) Second shear stress pulse

Shear stress: 3.3 [Pa]

Application duration (pulse width): 0.5 [sec]

Non-application duration: 0.5 [sec]

Number of times it is applied: 1
FIG. 17 illustrates by way of example the adhesion amounts of scale which were measured when the shear stress pulse cycle is applied at intervals of 3 minutes, the amounts being each expressed as a percent on the assumption that the adhesion amount of scale which was measured when no shear stress pulse was applied is 100%. In this figure, the case of applying no shear stress pulse is referred to as "comparative example 1", and the case of applying a shear stress pulse cycle in which the first shear stress, the third shear stress and the second shear stress were applied in this order is referred to as "example 1". Furthermore, the case of applying a shear stress pulse cycle in which the first shear stress pulse and the second shear stress pulse were applied in this order as in Embodiment 1 is referred to as "comparative example 2".
As illustrated in FIG. 17, in comparative example 2 in which the shear stress pulse cycle was applied such that the first shear stress pulse and the second shear stress pulse were applied in this order, the adhesion amount of scale on the heat exchanger 2 was 50% of that of comparative example 1 in which no shear stress pulse was applied. Furthermore, in example 1 in which the shear stress pulse cycle was applied such that the first shear stress pulse, the third shear stress pulse and the second shear stress pulse were applied in this order, the adhesion amount of scale on the heat exchanger 2 is 35% of that of comparative example 1.
According to these results, in the case where the shear stress pulse cycle was applied such that the first shear stress pulse, the third shear stress pulse and the second shear stress pulse were applied in this order, the adhesion amount of scale on the heat exchanger 2 was reduced, and the scale reduction effect was improved, as compared with the case where the shear stress pulse cycle was applied such that the first shear stress pulse and the second shear stress pulse were applied in this order.
As described above, in Embodiment 2, the heat exchanger 2 is supplied with a secondary-side to-be-heated liquid subjected to application of a shear stress pulse cycle in which the first shear stress pulse, the third shear stress pulse and the second shear stress pulses are to be applied in this order. Thereby, it is possible to further efficiently and further reliably restrict generation and growth of scale.

Embodiment 3

Next, a heat exchange system according to Embodiment 3 of the present invention will be described.
The heat exchange system according to Embodiment 3 is different from Embodiment 2 in that the scale trap 23 provided in the secondary-side circulation circuit 20 is omitted. In Embodiment 3, the secondary-side to-be-heated liquid is circulated between the tank 21 and the heat exchanger 2 once, whereby it is boiled up (this will be hereinafter referred to as "single-boiling system").
In the case where the secondary-side to-be-heated liquid is circulated between the tank 21 and the heat exchanger 2 once, the degree of a scale trapping effect obtained by the scale trap 23 as illustrated in FIG. 15 is smaller than that in the case where the secondary-side to-be-heated liquid is circulated a number times between the tank 21 and the heat exchanger 2, and the above single circulation can be hardly expected to reduce adhesion of scale on the heat exchanger 2. As a result, the adhesion amount of scale on the heat exchanger 2 is larger than that in the same amount of secondary-side to-be-heated liquid as in the above case is circulated a number of times to be boiled up. In view of this point, in Embodiment 3, a shear stress pulse cycle similar to that in Embodiment 2 is applied also in the single-boiling system, to thereby reduce the adhesion amount of scale on the heat exchanger 2.
The number of times the secondary-side to-be-heated liquid needs to be circulated until it is boiled up depends on, for example, energy characteristics which varies in accordance with the kind of refrigerant for use in the heat pump. For example, if fluorocarbon gas such as R410 is used as a secondary-side to-be-heated liquid, when the secondary-side to-be-heated liquid is circulated a number of times, it is boiled up with a high energy efficiency. On the other hand, if a natural refrigerant such as carbon dioxide (CO₂) is used as a secondary-side to-be-heated liquid, when the secondary-side to-be-heated liquid is circuited once, it is boiled up with a higher energy efficiency than when it is circulated a number of times.

Configuration of heat exchange system

FIG. 18 is a block diagram illustrating an example of the heat exchange system 1 according to Embodiment 3 of the present invention. In the following description, elements identical to those of embodiments 1 and 2 mentioned above will be denoted by the same reference signs, and their descriptions will be omitted.
As illustrated in FIG. 18, the heat exchange system 1 includes the primary-side circulation circuit 10, the secondary-side circulation circuit 20 and the heat exchanger 2. However, unlike the heat exchange system 1 according to Embodiment 2 illustrated in FIG. 15, the scale trap 23 is removed.

Investigation of scale reduction effect

Next, reduction of scale adhering to the heat exchanger 2 will be described.
In Embodiment 3, a shear stress pulse cycle including first to third shear stress pulses is applied to the heat exchanger 2 as in Embodiment 2.
FIG. 19 is a graph for explaining the adhesion amounts of scale on the heat exchanger 2 in the case where the first to third shear stress pulses are applied.
In this example, to a secondary-side to-be-heated liquid with a shear stress of 1 Pa, which is a shear stress acting when the flow quantity is normal, a shear stress pulse cycle is applied under conditions given below, and the shear stress pulse cycle is a combination of a first shear stress pulse having a preset shear stress, a second shear stress pulse having a smaller shear stress than that of the first shear stress pulse and a third shear stress pulse which has a shear stress equal to that of the first shear stress pulse, and which is applied to the heat exchanger 2 in the opposite direction to the direction of application of the first shear stress pulse. In the above application, the first shear stress pulse, the third shear stress pulse and the second shear stress pulse are applied in this order.
As to the adhesion amount of scale on the heat exchanger 2, the adhesion amount of scale at the time when 2000 liters (L) of secondary-side to-be-heated liquid was boiled up was measured. This is because the adhesion amount of scale on the heat exchanger 2 at the time when for example, 200 liters of secondary-side to-be-heated liquid which corresponds to the capacity of a single tank 21 was boiled up was not sufficient for evaluation, and thus in order to properly evaluate the adhesion amount of scale, it was necessary to measure the adhesion amount of scale at the time when the above quantity of secondary-side to-be-heated liquid, which corresponds to the capacity of ten tanks 21, was boiled up.
(a) First shear stress pulse

Shear stress: 50 [Pa]

Application duration (pulse width): 0.5 [sec]

Non-application duration: 0.5 [sec]

Number of times it is applied: 3

(b) Third shear stress pulse

Shear stress: 50 [Pa]

Application duration (pulse width): 0.5 [sec]

Non-application duration: 0.5 [sec]

Number of times it is applied: 3

(c) Second shear stress pulse

Shear stress: 3.3 [Pa]

Application duration (pulse width): 0.5 [sec]

Non-application duration: 0.5 [sec]

Number of times it is applied: 6
In the example illustrated in FIG. 19, the case in which the scale trap 23 was provided and the multiple-boiling system was adopted as in Embodiment 2, and no shear stress pulse was applied is referred to as the above "comparative example 1", and the adhesion amount of scale on the heat exchanger 2 in this case is defined as 100%. In this case, the secondary-side to-be-heated liquid was circulated 100 times between the tank 21 and the heat exchanger 2.
In this case, the case where the scale strap 23 was not provided, the single-boiling system was adopted, and a shear stress pulse cycle in which the first shear pulse, the third shear pulse and the second shear pulse were applied in this order was applied is referred to as "example 2". In this case also, the multiple-boiling system was adopted and a shear stress pulse cycle in which the first shear pulse, the third shear pulse and the second shear stress pulse were applied in this order was applied as in Embodiment 2 is referred to as "example 1". Furthermore, the case in which the single-boiling system was adopted as in Embodiment 3 but no shear stress pulse is applied is referred to as "comparative example 3".
As illustrated in FIG. 19, in comparative example 3 in which no scale trap 23 was provided, the single-boiling system was adopted, and no shear stress pulse was applied, the adhesion amount of scale on the heat exchanger 2 increased to 215% of that in comparative example 1. In example 2 in which no scale trap 23 was provided, the single-boiling system was adopted, and the first shear stress pulse, the third shear stress pulse and the second shear stress pulse were applied in this order, the adhesion amount of scale on the heat exchanger 2 was 58% of that in comparative example 1.
From the above results, it can be seen that in the case where shear stress pulses are applied in the single-boiling system, the adhesion amount of scale can be greatly reduced as compared with the case where no shear stress pulse is applied; that is, it is reduced from 215% to 58%. Also, in the multiple-boiling system, the adhesion amount of scale is reduced from 100% to 35% by applying shear stress pulses; that is, a reduction effect of 65% can be obtained. In contrast, in the single-boiling system, by applying shear stress pulses, the adhesion amount of scale is reduced from 215%, which is the adhesion amount of scale in comparative example 3, to 58%, which is the adhesion amount of scale in example 2, and a reduction effect of 157% can be obtained. That is, a greater reduction effect can be attained for the one-time boiling system than in the multiple-boiling system.
As described above, in Embodiment 3, the heat exchanger 2 is supplied with a secondary-side to-be-heated liquid subjected to application of a shear stress pulse cycle in which the first, third, and second shear stress pulses are applied in this order as in Embodiment 2. As a result, it is possible to efficiently and reliably restrict generation and growth of scale as in Embodiment 2.
That is, a reduction effect in which generation and growth of scale is restricted by applying such a shear stress pulse cycle as described above to the heat exchanger 2 can be obtained not only in the case where the secondary-side to-be-heated liquid is circulated a number of times in the secondary-side circulation circuit 20 as in embodiments 1 and 2, but also in the case where, for example, the secondary-side to-be-heated liquid is circulated once.
Although the above descriptions refer to embodiments 1 to 3 of the present invention, the present invention is not limited to embodiments 1 to 3 described above, and can be modified or applied in various ways without departing from the scope of the present invention.
For example, although the foregoing description of embodiments 1 to 3 refers to by way of example the heat exchange system 1 in which the heat of the primary-side to-be-heated liquid heated by the heat pump 11 is used to heat the secondary-side to-be-heated liquid, the heat exchange system 1 is not limited to such an example. For example, a heat exchange system 1 in which the heat of the primary-side liquid cooled by the heat pump 11 is used to cool the secondary-side liquid may be applied.
Furthermore, for example, the heat exchange system 1 may include no tank 21. In this case, for example, the heat exchange system 1 is provided with a passage into which a passage allowing the secondary-side to-be-heated liquid to be circulated in the secondary-side circulation circuit 20 branches. The pressure application unit 30 is supplied with the secondary-side to-be-heated liquid flowing in the passage provided as the above branch. Thereby, it is possible to efficiently remove bubbles 40 and scale nuclei adhering to the contact surface of the heat exchanger 2, in the same manner as described above.

Reference Signs List

1: heat exchange system
2: heat exchanger
10: primary-side circulation circuit
11: heat pump
12: heater
13: flow switching device
14: first pump
15: radiator
16: expansion vessel
17, 18: pipe
20: secondary-side circulation circuit
21: tank
21a: feed pipe
21b: hot water pipe
22: second pump
23: scale trap
24, 25: pipe
30: pressure application unit
31: third pump
32: pressure retention unit
32a: cylinder structure unit
32b, 32c: solenoid valve
32d: water quantity sensor
32e: pressure sensor
32f: pressurizing unit
33: opening and closing mechanism unit
33a, 33b, 53a, 53b: solenoid valve
33c, 33d, 53c, 53d: metal shutter
34: opening and closing control unit
35, 38, 55, 58: signal line
36, 37, 56, 57: pipe 40 bubble
41: microlayer
50: second pressure-application unit
51: fourth pump
52: second pressure retention unit
53: second opening and closing mechanism unit

Claims

A heat exchange system comprising:
- a first circulation circuit annularly provided to allow a first liquid to be circulated therein;

- a second circulation circuit annularly provided to allow a second liquid to be circulated therein;

- a heat exchanger configured to perform heat exchange between the first liquid and the second liquid;

- a pressure retention unit configured to pressurize and retain a portion of the second liquid;

- an opening and closing mechanism unit disposed on an inlet side of the heat exchanger, into which the second liquid is to flow, the opening and closing mechanism unit being configured to switch the second liquid to flow into the heat exchanger between the portion of the second liquid which flows from the pressure retention unit and an other portion of the second liquid which flows from the second circulation circuit; and

- a controller configured to control a pressure to be applied to the second liquid retained by the pressure retention unit, and control a switching operation of the opening and closing mechanism unit.
The heat exchange system of claim 1,
wherein a bypass circuit is provided between the opening and closing mechanism unit and the second circulation circuit, and
the pressure retention unit is disposed in the bypass circuit.
The heat exchange system of claim 2,
wherein the second circulation circuit is provided with a tank configured to store the second liquid, and
the bypass circuit is disposed between the opening and closing mechanism unit and the tank.
The heat exchange system of any one of claims 1 to 3,
wherein the controller controls the pressure retention unit and the opening and closing mechanism unit to cause the heat exchanger to be supplied with the second liquid to which a shear stress pulse cycle has been applied, the shear stress pulse cycle being a combination of a plurality of shear stress pulses having different stresses.
The heat exchange system of claim 4,
wherein the shear stress pulse cycle is a combination of a first shear stress pulse and a second shear stress pulse, the second shear stress pulse having a greater stress than that of the first shear stress pulse, and
the first stress pulse and the second shear stress pulse are combined in this order.
The heat exchange system of claim 5,
wherein the opening and closing mechanism unit includes:
- a first valve disposed in a flow passage which joins the second circulation circuit and the pressure retention unit; and

- a second valve disposed upstream of a point in the second circulation circuit where the flow passage joins, and
wherein the opening and closing mechanism unit is configured to:
- close the second valve and open the first valve, based on control by the controller; cause the second fluid pressurized in the pressure retention unit to flow into the heat exchanger as one of the first shear stress pulse and the second shear stress pulse, and

- close the first valve and open the second valve, based on control by the controller.
The heat exchange system of any one of claims 1 to 3, further comprising:
- a second pressure retention unit configured to pressurize and retain a location of the second liquid; and

- a second opening and closing mechanism unit disposed on an outlet side of the heat exchanger, and configured to switch flowing of the second liquid retained by the second pressure retention unit between flowing of the retained second liquid from the outlet side of the heat exchanger and flowing of the retained second liquid into the outlet side of the heat exchanger,
wherein the controller controls the pressure retention unit, the opening and closing mechanism unit, the second pressure retention unit and the second opening and closing mechanism unit to cause the heat exchange to be supplied with the second liquid to which a shear stress pulse cycle has been applied, the shear stress pulse cycle being a combination of a plurality of shear stress pulses to be supplied to the heat exchanger (2) in different directions.
The heat exchange system of claim 7,
wherein the shear stress pulse cycle includes a first shear stress pulse, a second shear stress pulse and a third shear stress pulse, the second shear stress pulse having a smaller stress than that of the first shear stress pulse, the third shear stress pulse having a stress equal to that of the first shear stress pulse, the third shear stress pulse being to be applied in an opposite direction to a direction of application of the first shear stress pulse, and
wherein the first shear stress pulse, the third shear stress pulse and the second shear stress pulse are combined in this order.
The heat exchange system of claim 8,
wherein the opening and closing mechanism unit includes:
- a first valve disposed in a first flow passage which joins the second circulation circuit and the pressure retention unit; and

- a second valve disposed upstream of a point in the second circulation circuit where the first flow passage joins,
wherein the second opening and closing mechanism unit includes:
- a third valve disposed in a second flow passage which joins the second circulation circuit and the second pressure retention unit; and

- a fourth valve disposed downstream of a point in the second circulation circuit where the second flow passage joins,
wherein the opening and closing mechanism unit is configured to:
- close the second valve and open the first valve, based on control by the controller;

- cause the second fluid pressurized in the pressure retention unit to flow into the heat exchanger as one of the first shear stress pulse and the second shear stress pulse; and

- close the first valve and open the second valve, based on control by the controller, and
wherein the second opening and closing mechanism unit is configured to:
- close the fourth valve and open the third valve, based on control by the controller;

- cause the second fluid pressurized in the second pressure retention unit to flow into the heat exchanger as the third shear stress pulse; and

- close the third valve and open the fourth valve, based on control by the controller.
A scale reduction method for a heat exchange system, the heat exchange system including a first circulation circuit annularly provided to allow a first liquid to be circulated therein, a second circulation circuit annularly provided to allow a second liquid to be circulated therein, and a heat exchanger configured to perform heat exchange between the first liquid and the second liquid, the scale reduction method reducing precipitation of scale on a contact surface of the heat exchanger that contacts the second liquid, the scale reduction method characterized by comprising:
- pressurizing and retaining a portion of the second liquid; and

- switching the second liquid to be made to flow into the heat exchanger, between the second liquid from the second circulation circuit and the second liquid from the pressure retention unit.