JP5790332B2 - 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.

  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.

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

  In order to achieve the above object, the heat exchanger for a thermoacoustic engine of the present invention is attached to an acoustic cylinder that generates acoustic vibrations in the axial direction, passes through the acoustic cylinder from the inside to the outside, and then returns to the inside at a different position in the axial direction. A vent pipe that returns to the inner side of the acoustic cylinder; and an outlet opening that faces the axial direction of the acoustic cylinder inside the acoustic cylinder; and an outlet opening that faces the radial direction of the acoustic cylinder inside the acoustic cylinder; It is what has.

  A plurality of the vent pipes may be provided, and the plurality of vent pipes may be arranged at intervals in the circumferential direction of the acoustic cylinder at the same position in the axial direction of the acoustic cylinder.

  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.

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.

  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 an acoustic cylinder 2 that generates acoustic vibrations in the axial direction, and from the inside to the outside of the acoustic cylinder 2. There is a vent pipe 3 that passes through and returns to the inside again at a different position in the axial direction.

  The ventilation pipe 3 has an inlet opening 4 facing the axial direction of the acoustic cylinder 2 inside the acoustic cylinder 2 and an outlet opening 5 facing the radial direction of the acoustic cylinder 2 inside the acoustic cylinder 2. The ventilation tube 3 is a thin tube having a diameter sufficiently smaller than that of the acoustic cylinder 2. The vent pipe 3 includes an elbow 6 extending from the inlet opening 4 to the inner periphery of the acoustic cylinder 2, an outward path 7 extending through the acoustic cylinder 2 from the inside to the outside and extending radially outward of the acoustic cylinder 2, and the acoustic cylinder 2 and a U-shaped part 8 extending in parallel with the acoustic cylinder 2 and a return path part 9 extending inward in the radial direction of the acoustic cylinder 2 and penetrating the acoustic cylinder 2 from the outside to the inside to reach the outlet opening 5.

  The elbow portion 6 bends an angle of 90 degrees from the inlet opening 4 facing the axial direction of the acoustic cylinder 2 to the inner periphery of the acoustic cylinder 2 in a curved manner. The length of the forward path part 7 is set to an appropriate value obtained by experiment, 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. The return path portion 9 does not protrude inward from the inner periphery of the acoustic cylinder 2, and the outlet opening 5 is formed on the same plane as the inner periphery of the acoustic cylinder 2.

  A plurality of vent pipes 3 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 3 are arranged at equal intervals in the circumferential direction of the acoustic cylinder 2.

  The heat exchanger 1 is filled with a heat storage material 10 formed by laminating a plurality of metal mesh materials at a position facing the outlet opening 5 inside the acoustic cylinder 2 (corresponding to a heating unit).

  In this embodiment, the heat exchanger 1 constitutes a heating side heat exchanger, and the vent pipe 3 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 is moving in the vicinity of the inlet opening 4 so as to face the inlet opening 4, the dynamic pressure acts on the inlet opening 4 as it is, and the pressure PA in the inlet opening 4 is ,
PA = static pressure + dynamic pressure. In the vicinity of the outlet opening 5, since the opening surface of the outlet opening 5 is along the moving direction of the working fluid, dynamic pressure does not act, and the pressure PB at the outlet opening 5 is
PB = static pressure.

In the state of FIG. 2B, since the working fluid is moving from the back side of the inlet opening 4 around the inlet opening 4, the pressure PA at the inlet opening 4 is
PA = static pressure-dynamic pressure x C2
C2 is a positive real number smaller than 1. The reason why the dynamic pressure component becomes small is that a part of the moving working fluid is caught in the inlet opening 4. In the vicinity of the outlet opening 5, since the opening surface of the outlet opening 5 is along the moving direction of the working fluid, dynamic pressure does not act, and the pressure PB at the outlet opening 5 is
PB = static pressure.

When the pressure PA at the inlet opening 4 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 at the inlet opening 4 is larger than the static pressure. On the other hand, since the average pressure MPB at the outlet opening 5 is equal to the static pressure, the average pressure MPA at the inlet opening 4 is larger than the average pressure MPB at the outlet opening 5. As a result, the working fluid moves from the inlet opening 4 toward the outlet opening 5 in the vent pipe 3.

  Returning to FIG. 1, the operation of the thermoacoustic engine will be described. The working fluid moving through the vent pipe 3 as described above receives heat from the external exhaust via the pipe wall of the vent pipe 3 and becomes high temperature. Considering the amount of heat transfer from the external exhaust to the working fluid, the heat transfer area corresponds to the surface area of the vent pipe 3, and the heat transfer distance corresponds to the wall thickness of the vent pipe 3. Therefore, the amount of heat transferred from the external exhaust to the working fluid in the vent pipe 3 is sufficiently large. At this time, the amount of heat obtained by the working fluid in the vent pipe 3 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, so that the moving speed of the working fluid in the vent pipe 3 is large. Thus, the heat exchanger 1 of the present invention has a larger amount of heat transfer from the external exhaust to the working fluid in the vent pipe 3 than 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 having a high temperature in the vent pipe 3 returns from the outlet opening 5 into the acoustic cylinder 2, the vicinity of the outlet opening 5 becomes high temperature, and the vicinity of the outlet opening 5 serves as a heater and contributes to the operation of the thermoacoustic engine. At this time, if the heat storage material 10 is provided so as to face the outlet opening 5, the heat storage material 10 receives heat from the working fluid and maintains a high temperature, so that the operation of the thermoacoustic engine is stabilized.

  As described above, according to the heat exchanger 1 of the present invention, the heat exchanger 1 has the vent pipe 3 that passes from the inner side to the outer side of the acoustic cylinder 2 and returns to the inner side at different positions in the axial direction. Since it has the inlet opening 4 facing the axial direction of the acoustic cylinder 2 inside the cylinder 2 and the outlet opening 5 facing the radial direction of the acoustic cylinder 2 inside the acoustic cylinder 2, the working fluid of the acoustic cylinder 2 passes therethrough. By moving the trachea 3, external heat is delivered to the heater of the thermoacoustic engine, and the amount of heat transfer can be increased.

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

  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 3 is preferably selected according to the shape of the exhaust passage.

  In the embodiments so far, no fins are formed on the vent pipe 3, but the surface area may be increased by forming fins on the outer peripheral surface or inner peripheral surface of the vent pipe 3 or by forming grooves. .

  If the distance between the inlet opening 4 and the outlet opening 5 of the vent pipe 3 is long, the working fluid moves from the vicinity of the outlet opening 5 (heater of the thermoacoustic engine) to the inlet opening 4 from the outlet opening 5 to the inlet opening 4. The acoustic cylinder 2 takes the heat of the working fluid and releases it to the outside of the acoustic cylinder 2 (outside the exhaust passage), and the temperature of the working fluid flowing into the vent pipe 3 is lowered. Since the amount of heat from the exhaust in the vent pipe 3 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 4 and the outlet opening 5 should be as short as possible. However, the distance between the inlet opening 4 and the outlet opening 5 is set to a predetermined length so that the high-temperature working fluid flowing into the acoustic cylinder 2 from the outlet opening 5 sufficiently conducts heat to the heat storage material 10 and is sucked into the inlet opening 4. It is preferable to ensure the above.

Considering the diameter of the vent pipe 3,
Vent pipe diameter = acoustic cylinder diameter × π / the number of vent pipes−the gap between the vent pipes. Since the portion of the inlet opening 4 gathers most densely in the vent pipe 3, it is preferable to set a gap so that the vent pipes 3 do not interfere with each other.

As the design condition of the vent pipe 3, the amount of heat that enters from the outside through the pipe wall of the vent pipe 3 is equal to the amount of heat that the working fluid flowing in the vent pipe 3 acquires.
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 3 is 12. However, the present invention is not limited to this, and the number of the vent pipes 3 may be 1 to 11, or 13 or more. When the diameter of the ventilation pipe 3 is constant, if the number of the ventilation pipes 3 is large, the amount of working fluid flowing into the heating unit of the thermoacoustic engine increases, and the amount of heat transfer to the heating unit increases. Further, when the moving speed of the working fluid in the vent pipe 3 is constant, if the number of vent pipes 3 is large, the amount of working fluid flowing into the heating section increases, and the amount of heat transfer to the heating section increases.

  In the embodiment of FIG. 1, the heat storage material 10 is provided at a position facing the outlet opening 5 inside the acoustic cylinder 2, but instead of the heat storage material 10, 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 Vent pipe 4 Inlet opening 5 Outlet opening 10 Heat storage material

Claims (3)

It is attached to an acoustic cylinder that generates acoustic vibration in the axial direction, and has a vent pipe that passes from the inside of the acoustic cylinder to the outside and returns to the inside again at a different position in the axial direction.
The vent pipe is
An inlet opening facing the axial direction of the acoustic cylinder inside the acoustic cylinder;
A heat exchanger for a thermoacoustic engine having an outlet opening facing the radial direction of the acoustic cylinder inside the acoustic cylinder. A plurality of the vent pipes;
2. The heat exchanger for a thermoacoustic engine according to claim 1, wherein 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 or 2, further comprising a heat storage material at a position facing the outlet opening inside the acoustic cylinder.