JP5772399B2 - Heat exchanger for thermoacoustic engine - Google Patents

Description

  The present invention relates to a heat exchanger for a thermoacoustic engine that can increase heat transfer and suppress mass flow.

  In a thermoacoustic engine that performs a Stirling cycle that is an external combustion engine, a heat-side heat exchanger that performs heat exchange with an external high-temperature heat source and a heat cycle are performed in the longitudinal direction of the acoustic cylinder in which the working fluid is sealed. A cooling side heat exchanger is provided for discharging the waste heat later to the outside. A regenerator for maintaining a temperature gradient is disposed between the heating side heat exchanger and the cooling side heat exchanger.

Conventionally, a heat exchanger is configured to take heat from outside into an acoustic cylinder by heat conduction using a material having high thermal conductivity such as copper. The amount of heat transfer by heat conduction is expressed by the following equation.
Heat transfer amount = C1 x temperature difference x heat transfer area / heat transfer distance
C1 is a constant determined by the material

  FIG. 4 shows a part of a thermoacoustic engine in which the heat source is composed of an electric heater. In this thermoacoustic engine, the heating-side heat exchanger 41 has an electric heater 43 wound around the outer periphery of the acoustic cylinder 42 and internal fins 44 incorporated in the acoustic cylinder 42. The cooling side heat exchanger 45 includes a cooling cylinder 46 that allows cooling water to pass along the outer periphery of the acoustic cylinder 42, and internal fins 47 that are incorporated in the acoustic cylinder 42. The regenerator 48 includes a heat storage material 49 formed by laminating a plurality of metal mesh materials inside the acoustic cylinder 42 between the internal fins 44 of the heating side heat exchanger 41 and the internal fins 47 of the cooling side heat exchanger 45. Filled.

  In the heating-side heat exchanger 41 of FIG. 4, the temperature of the electric heater 43 can be freely adjusted, so that it is easy to increase the temperature difference. In addition, the heating side heat exchanger 41 has a short heat transfer distance because the electric heater 43 as a heat source is directly wound around the outer periphery of the acoustic cylinder 42. Thus, since the temperature difference is large and the heat transfer distance is short, a large amount of heat transfer can be expected.

JP 2011-122567 A

  By the way, the thermoacoustic engine does not use a heat source that generates heat by consuming energy like an electric heater, but if the waste heat generated in another system can be used, the energy saving effect is great.

  A part of a thermoacoustic engine using exhaust as a heat source is shown in FIG. In this thermoacoustic engine, the heating-side heat exchanger 51 has external fins 52 attached to the outer periphery of the acoustic cylinder 42 and internal fins 44 incorporated in the acoustic cylinder 42. The cooling side heat exchanger 45 and the regenerator 48 are the same as those in FIG.

  In the heating side heat exchanger 51 of FIG. 5, exhaust gas from an internal combustion engine, exhaust from a boiler, exhaust from an incinerator, etc. can be used as a heat source. However, since the temperature of the exhaust is lower than that of an electric heater, a large temperature difference Cannot be obtained.

  On the other hand, the outer fin 52 has a plurality of protrusions 53 extending radially from the outer periphery of the acoustic cylinder 42, and a plurality of branch protrusions 54 protruding from the surface of each protrusion 53. However, if the length of the protrusion 53 is increased in order to increase the heat transfer area to the exhaust, the heat transfer distance from the tip of the protrusion 53 or the branch-shaped protrusion 54 to the outer periphery of the acoustic cylinder 42 is increased. Further, when the number of the protrusions 53 is increased in order to increase the heat transfer area to the exhaust, the protrusion thickness (circumferential direction of the acoustic cylinder 42) decreases, and the heat flow path from the tip of the protrusion 53 toward the outer periphery of the acoustic cylinder 42 The heat transfer area becomes smaller. As described above, if the external fin 52 is increased in the heating-side heat exchanger 51 provided with the external fin 52 so as to take in more exhaust heat, the heat transfer distance becomes longer or the heat transfer area becomes smaller. There is a dilemma to do.

  It is also conceivable to provide a heat pipe instead of the external fin 52. However, the heat pipe uses water as a working fluid for carrying heat inside. For this reason, a use temperature range is limited to normal temperature to 200 degreeC. The temperature of the exhaust heat is not only from room temperature to 200 ° C. but may be 200 ° C. or more, and the temperature is not stable. Therefore, heat pipes are not suitable for conveying exhaust heat.

  The thermoacoustic engine has the following mass flow problem apart from the heat transfer problem described so far.

  As shown in FIG. 6, in the thermoacoustic engine 61, a prime mover 63 is provided in an acoustic cylinder 62 that is closed in a loop shape. The prime mover 63 includes a heater 64, a regenerator 65, and a cooler 66. Acoustic vibration is generated in the axial direction of the acoustic cylinder 62 due to the temperature gradient from the heater 64 to the cooler 66.

  At this time, the working fluid expands by heating in the heater 64. Since the right side of the heater 64 is a space, there is no resistance, but the left side of the heater 64 is a resistance because the heat storage material of the regenerator 65 occupies the left side. Therefore, the expanded working fluid is more easily moved toward the space than the heat storage material. The working fluid expanded by the heater 64 is repeatedly moved toward the space, and a flow of the working fluid swirling clockwise as shown in the drawing is generated as the entire acoustic cylinder 62 closed in a loop shape. Such an overall working fluid flow is called mass flow (streaming).

  When the mass flow occurs, the heated working fluid leaves the heater 64, and when the working fluid cooled by the cooler 66 flows into the heater 64 through the regenerator 65, the working fluid in the prime mover 63 is equalized. The temperature gradient becomes loose and the generation of acoustic vibration is hindered. Mass flow is a major factor that hinders the output improvement of thermoacoustic engines.

  The thermoacoustic engine 61 is provided with a rubber film 67 as a member for suppressing mass flow at a position appropriately separated from the prime mover 63 in the axial direction of the acoustic cylinder 62. The rubber film 67 is capable of transmitting the acoustic vibration in the axial direction of the acoustic cylinder 62 and interrupting the mass flow by vibrating to swell alternately in one and the other in the axial direction accompanying the acoustic vibration. Can do.

  In the thermoacoustic engine 71 shown in FIG. 7, a jet nozzle (taper nozzle) 73 is provided in addition to the prime mover 72. That is, a prime mover 72 including a heater 75, a regenerator 76, and a cooler 77 is provided in the acoustic cylinder 74 closed in a loop shape, and the jet nozzle 73 is appropriately separated from the prime mover 72 in the axial direction of the acoustic cylinder 62. Is installed.

  The jet nozzle 73 is inclined and protrudes inwardly in the radial direction of the acoustic cylinder 74 from the inner circumference of a certain position (one position) in the axial direction of the acoustic cylinder 74 to another position (the other position) in the axial direction. A plate is formed continuously in the circumferential direction of the acoustic cylinder 74. The jet nozzle 73 has a large-diameter opening at one position in the axial direction of the acoustic cylinder 74, a small-diameter opening at the other position, and a tapered shape in which a space between the large-diameter opening and the small-diameter opening is hollow. It becomes the member of.

  The action of the jet nozzle 73 is to generate a mass flow from the large diameter opening toward the small diameter opening. The jet nozzle 73 is installed with the small-diameter opening facing the heater 75 so as to cancel out the mass flow due to the expansion of the working fluid by the generated mass flow.

  As described above, in the thermoacoustic engine 61, the mass flow is blocked by the rubber film 67, and in the thermoacoustic engine 71, the mass flow is canceled by the jet nozzle 73.

  However, the rubber film 67 is a problem because it is the only movable member in the thermoacoustic engine 61 and reduces the durability of the thermoacoustic engine 61. Since the jet nozzle 73 causes a loss in the acoustic vibration, the output of the thermoacoustic engine is not always improved even if the mass flow is canceled out, which is a problem.

  Then, the objective of this invention is providing the heat exchanger for thermoacoustic engines which can solve the said subject, can enlarge heat transfer, and can suppress mass flow.

  In order to achieve the above object, a heat exchanger for a thermoacoustic engine according to the present invention is attached to the outside of an acoustic cylinder that generates acoustic vibration in the axial direction, and is located at a different position in the axial direction of the acoustic cylinder inside the acoustic cylinder. A vent pipe formed with a leading inlet opening and an outlet opening; and a slanting inward in the radial direction of the acoustic cylinder from an inner periphery of the acoustic cylinder on one axial side of the inlet opening to an axially opposite side of the inlet opening. And a rectifying plate protruding.

  A plurality of the vent pipes are provided, and the plurality of vent pipes are arranged at intervals in the circumferential direction of the acoustic cylinder at the same position in the axial direction of the acoustic cylinder, and the rectifying plate is arranged in the circumferential direction of the acoustic cylinder May be formed continuously.

  You may have a thermal storage material in the position which faces the said exit opening inside the said acoustic cylinder.

  The present invention exhibits the following excellent effects.

  (1) The amount of heat transfer can be increased.

  (2) Mass flow can be suppressed.

It is a block diagram of the heat exchanger for thermoacoustic engines of this invention. It is a figure explaining the principle of this invention, (a) represents the half period of acoustic vibration, (b) represents the remaining half period of acoustic vibration. (A)-(d) is a block diagram of the vent pipe which shows other embodiment of this invention. It is a partial block diagram of the conventional thermoacoustic engine. It is a partial block diagram of the conventional thermoacoustic engine. It is a block diagram of the conventional thermoacoustic engine. It is a block diagram of the conventional thermoacoustic engine.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

  As shown in FIG. 1, a heat exchanger (hereinafter referred to as a heat exchanger) 1 for a thermoacoustic engine according to the present invention is attached to the outside of an acoustic cylinder 2 that generates acoustic vibration in the axial direction. A vent pipe 5 in which an inlet opening 3 and an outlet opening 4 leading to the inside of the acoustic cylinder 2 are formed at different positions, and an axial direction of the inlet opening 3 from the inner periphery of the acoustic cylinder 2 on one axial side of the inlet opening 3 It has the baffle plate 6 which inclines and protruded inward in the radial direction of the acoustic cylinder 2 toward the opposite side.

  The inlet opening 3 and the outlet opening 4 of the ventilation pipe 5 are formed on the same plane as the inner periphery of the acoustic cylinder 2 and are directed in the radial direction of the acoustic cylinder 2. The vent pipe 5 is formed of a thin tube having a diameter sufficiently smaller than that of the acoustic cylinder 2. The vent pipe 5 extends from the inlet opening 3 through the acoustic cylinder 2 and extends outward in the radial direction of the acoustic cylinder 2, a U-shaped part 8 extending in parallel with the acoustic cylinder 2, and the radial direction of the acoustic cylinder 2. A return path portion 9 extending inward and penetrating through the acoustic cylinder 2 to reach the outlet opening 4.

  The lengths of the forward path portion 7 and the return path portion 9 of the ventilation pipe 5 are set to appropriate values obtained through experiments, for example. The U-shaped portion 8 is bent into a U-shape or a U-shape and extends a predetermined length in a direction parallel to the axis of the acoustic cylinder 2. The length of the U-shaped portion 8 is set to an appropriate value obtained through experiments, for example.

  A plurality of vent pipes 5 are arranged at intervals in the circumferential direction of the acoustic cylinder 2 at the same position in the axial direction of the acoustic cylinder 2. Here, twelve vent pipes 5 are arranged at equal intervals in the circumferential direction of the acoustic cylinder 2.

  The rectifying plate 6 is in contact with the inner periphery of the acoustic cylinder 2 on one side of the inlet opening 3 in the axial direction, and is separated from the inner periphery of the acoustic cylinder 2 on the opposite side of the inlet opening 3 in the axial direction. Thus, the rectifying plate 6 forms an axial opening 10 facing the axial direction of the acoustic cylinder 2 on the opposite side of the inlet opening 3 in the axial direction.

  The rectifying plate 6 is formed continuously in the circumferential direction of the acoustic cylinder 2. Thereby, the baffle plate 6 becomes a taper-shaped ring which covers each inlet opening 3 inclining from the inner side. At the same time, this tapered ring is a jet nozzle having a small-diameter opening facing the heating unit 11 formed at a position facing the outlet opening 4 inside the acoustic cylinder 2 and a large-diameter opening facing the opposite direction. Equivalent to.

  The heat exchanger 1 is filled with a heat storage material 12 formed by laminating a plurality of metal mesh materials in a position facing the outlet opening 4 inside the acoustic cylinder 2, that is, the heating unit 11.

  In this embodiment, the heat exchanger 1 constitutes a heating side heat exchanger, and the vent pipe 5 outside the acoustic cylinder 2 is arranged in an exhaust atmosphere. The exhaust passage is not particularly limited here. The cooling side heat exchanger 45 and the regenerator 48 are the same as those shown in FIGS.

  The principle of the heat exchanger 1 of this invention is demonstrated using FIG.

  In the acoustic cylinder 2, acoustic vibration is generated in the axial direction. Acoustic vibration is that the working fluid repeatedly reverses. The period in which the working fluid moves in one axial direction of the acoustic cylinder 2 as shown in FIG. 2A and the period in which the working fluid moves in the opposite axial direction of the acoustic cylinder 2 as shown in FIG. Are repeated alternately.

In the state of FIG. 2A, since the working fluid moves in the vicinity of the inlet opening 3 so as to face the axial opening 10, the dynamic pressure acts on the axial opening 10 as it is. Pressure PA is
PA = static pressure + dynamic pressure. In the vicinity of the outlet opening 4, since the opening surface of the outlet opening 4 is along the moving direction of the working fluid, dynamic pressure does not act, and the pressure PB at the outlet opening 4 is
PB = static pressure.

In the state of FIG. 2B, since the working fluid is moving from the back side of the axial opening 10 toward the rectifying plate 6 around the inlet opening 3, the pressure PA in the axial opening 10 is
PA = static pressure-dynamic pressure x C2
C2 is a positive real number smaller than 1. The reason why the dynamic pressure component is small is that a part of the moving working fluid is caught in the axial opening 10. In the vicinity of the outlet opening 4, since the opening surface of the outlet opening 4 is along the moving direction of the working fluid, dynamic pressure does not act, and the pressure PB at the outlet opening 4 is
PB = static pressure.

When the pressure PA in the axial opening 10 is averaged for a time sufficiently longer than the period of the acoustic vibration, the average pressure MPA is
MPA = static pressure + dynamic pressure × (1-C2) / 2
It becomes. Since C2 is a positive real number smaller than 1, (1-C2) / 2 is a positive real number, and the average pressure MPA in the axial opening 10 is larger than the static pressure. On the other hand, since the average pressure MPB at the outlet opening 4 is equal to the static pressure, the average pressure MPA at the axial opening 10 is larger than the average pressure MPB at the outlet opening 4. Thereby, in the vent pipe 5, the working fluid moves from the axial opening 10 to the outlet opening 4 via the inlet opening 3.

  Returning to FIG. 1, the operation of the thermoacoustic engine will be described. The working fluid that moves through the vent pipe 5 as described above receives heat from the external exhaust via the pipe wall of the vent pipe 5 and reaches a high temperature. Considering the amount of heat transfer from the exhaust to the working fluid, the heat transfer area corresponds to the surface area of the vent pipe 5, and the heat transfer distance corresponds to the wall thickness of the vent pipe 5. Therefore, the amount of heat transfer from the external exhaust to the working fluid in the vent pipe 5 is sufficiently large. At this time, the amount of heat obtained by the working fluid in the vent pipe 5 is carried into the acoustic cylinder 2 by the movement of the working fluid. In the acoustic vibration of the thermoacoustic engine, the displacement amplitude of the working fluid is large and the frequency is high. Therefore, the moving speed of the working fluid in the vent pipe 5 is large. As described above, the heat exchanger 1 of the present invention has a large amount of heat transfer from the external exhaust to the working fluid in the vent pipe 5 compared to the heating side heat exchanger 51 of FIG. Since the moving speed of the working fluid is high, the amount of heat transferred from the outside into the acoustic cylinder 2 is improved.

  When the working fluid that has reached a high temperature in the vent pipe 5 returns from the outlet opening 4 into the acoustic cylinder 2, the vicinity of the outlet opening 4 becomes hot, and the vicinity of the outlet opening 4 serves as the heating unit 11 and contributes to the operation of the thermoacoustic engine. . At this time, if the heat storage material 12 is provided in the heating unit 11, the heat storage material 12 receives heat from the working fluid and maintains a high temperature, and thus the operation of the thermoacoustic engine is stabilized.

  As described above, according to the heat exchanger 1 of the present invention, it is attached to the outside of the acoustic cylinder 2 that generates acoustic vibration in the axial direction, and leads to the inside of the acoustic cylinder 2 at different positions in the axial direction of the acoustic cylinder 2. A vent pipe 5 in which an inlet opening 3 and an outlet opening 4 are formed, and radially inward of the acoustic cylinder 2 from the inner circumference of the acoustic cylinder 2 on one axial side of the inlet opening 3 to the opposite side of the inlet opening 3 in the axial direction. Since it has the baffle plate 6 which inclines and protruded, the external fluid is delivered to the heating part 11 of a thermoacoustic engine because the working fluid of the acoustic cylinder 2 moves through the ventilation pipe 5, and the amount of heat transfer can be increased.

  The tapered ring formed of the rectifying plate 6 continuously formed in the circumferential direction of the acoustic cylinder 2 corresponds to a jet nozzle that faces the heating unit 11 with a small-diameter opening and a large-diameter opening in the opposite direction. To do. Therefore, the mass flow suppression effect due to thermal expansion can be obtained in the heating unit 11 as described in FIG.

  3 (a) to 3 (d) show another embodiment of the vent pipe.

  As shown in FIG. 3A, the vent pipe 31 is bent while extending radially from the acoustic cylinder 2, and the vent pipes 31 become parallel. The vent pipe 31 is effective when the installation space for the heat exchanger 1 is narrow on the left and right in the drawing.

  As shown in FIG. 3 (b), the vent pipe 32 is repeatedly bent in the circumferential direction of the acoustic cylinder 2 while extending radially from the acoustic cylinder 2 to have a zigzag shape. The ventilation pipe 32 can increase the heat transfer area in an installation space having a small diameter.

  As shown in FIG. 3 (c), the vent pipe 33 is repeatedly bent in the axial direction of the acoustic cylinder 2 while extending radially from the acoustic cylinder 2 to form a zigzag shape. The ventilation pipe 33 is effective for an installation space extending in the axial direction of the acoustic cylinder 2.

  As shown in FIG. 3 (d), the vent pipe 34 is repeatedly bent in the radial direction of the acoustic cylinder 2 while extending in the axial direction of the acoustic cylinder 2, and exhibits a zigzag shape.

  The shape of the vent pipe 5 is preferably selected according to the shape of the exhaust passage.

  In the embodiments so far, no fins are formed on the vent pipe 5, but the surface area may be increased by forming fins on the outer peripheral surface or inner peripheral surface of the vent pipe 5 or by forming grooves. .

  If the distance between the inlet opening 3 and the outlet opening 4 of the vent pipe 5 is long, the acoustic cylinder from the outlet opening 4 to the inlet opening 3 is moved when the working fluid moves from the vicinity of the outlet opening 4 (heater 11) to the inlet opening 3. 2 takes the heat of the working fluid and releases it to the outside of the acoustic cylinder 2 (outside the exhaust flow path), and the temperature of the working fluid flowing into the vent pipe 5 decreases. Since the amount of heat from the exhaust in the vent pipe 5 is consumed to compensate for the temperature drop of the working fluid, it is a loss for the thermoacoustic engine. Therefore, the distance between the inlet opening 3 and the outlet opening 4 should be as short as possible. However, the distance between the inlet opening 3 and the outlet opening 4 is set to a predetermined length so that the high-temperature working fluid flowing into the acoustic cylinder 2 from the outlet opening 4 is sufficiently conducted to the heat storage material 12 and then sucked into the inlet opening 3. It is preferable to ensure the above.

Considering the diameter of the vent pipe 5,
Vent pipe diameter = acoustic cylinder diameter × π / the number of vent pipes−the gap between the vent pipes.

The design condition of the vent pipe 5 is that the amount of heat entering from the outside through the pipe wall of the vent pipe 5 is equal to the amount of heat acquired by the working fluid flowing in the vent pipe 5.
Thermal resistance coefficient x Vent pipe surface area / pipe wall thickness x (exhaust temperature-working fluid temperature)
= Cross section of vent pipe x Flow velocity in vent pipe x Heat capacity per unit volume of working fluid x (Outlet opening temperature-Inlet opening temperature)
It is preferable to satisfy the relationship.

  In the embodiment of FIG. 1, the number of the vent pipes 5 is 12. However, the present invention is not limited to this, and the number of the vent pipes 5 may be 1 to 11, or 13 or more. When the diameter of the vent pipe 5 is constant, if the number of the vent pipes 5 is large, the amount of working fluid flowing into the heating unit 11 increases, and the amount of heat transfer to the heating unit 11 increases. Further, when the moving speed of the working fluid in the vent pipe 5 is constant, if the number of vent pipes 5 is large, the amount of working fluid flowing into the heating unit 11 increases and the amount of heat transfer to the heating unit 11 increases. .

  In the embodiment of FIG. 1, the heat storage material 12 is provided at the position facing the outlet opening 4 inside the acoustic cylinder 2. However, instead of the heat storage material 12, an internal fin similar to the conventional one may be provided. .

  In the embodiment of FIG. 1, the heat exchanger 1 is used as a heating side heat exchanger, but the heat exchanger 1 can also be used as a cooling side heat exchanger 45. In this case, the heat exchanger 1 is provided inside the cooling cylinder 46 (see FIG. 4), and performs heat exchange between the cooling water and the working fluid.

DESCRIPTION OF SYMBOLS 1 Heat exchanger 2 Acoustic cylinder 3 Inlet opening 4 Outlet opening 5 Vent pipe 6 Current plate 12 Heat storage material

Claims (3)

A vent pipe attached to the outside of the acoustic cylinder that generates acoustic vibration in the axial direction, and having an inlet opening and an outlet opening leading to the inside of the acoustic cylinder at different positions in the axial direction of the acoustic cylinder;
And a rectifying plate that protrudes from the inner periphery of the acoustic cylinder on one side in the axial direction of the inlet opening to the axially opposite side of the inlet opening to incline radially inward of the acoustic cylinder. Engine heat exchanger. A plurality of the vent pipes;
The plurality of vent pipes are arranged at intervals in the circumferential direction of the acoustic cylinder at the same position in the axial direction of the acoustic cylinder,
The heat exchanger for a thermoacoustic engine according to claim 1, wherein the current plate is formed continuously in a circumferential direction of the acoustic cylinder.   The heat exchanger for a thermoacoustic engine according to claim 1 or 2, further comprising a heat storage material at a position facing the outlet opening inside the acoustic cylinder.