JP2009222038A - Heat exchanger for stirling engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the heat exchange efficiency of a heat exchanger by improving the contact efficiency between working gas and fins. <P>SOLUTION: A number of fins are formed on an inner surface of a ring-shaped base toward the center of the ring. The width of working gas passages formed of the fins is set to be constant. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a heat exchanger for a Stirling engine.

The Stirling engine is attracting attention as a heat engine that does not cause destruction of the ozone layer because it uses a natural refrigerant such as helium, hydrogen, or nitrogen as a working gas instead of Freon.
FIG. 4 is a schematic diagram showing the configuration of the Stirling engine. In the Stirling engine 1 used as a refrigerator, when the piston 12 is reciprocated by a power source such as a linear motor 20, the displacer 13 is synchronously reciprocated with a predetermined phase difference with respect to the piston 12 due to the flow resistance of the working gas. . By the operation of the piston 12 and the displacer 13, the working gas moves back and forth between the compression space 45 and the expansion space 46, the temperature of the working gas increases in the compression space 45, and the temperature of the working gas decreases in the expansion space 46. . The heat of the compression space (high-temperature space) 45 is radiated through the high-temperature heat transfer head 40 to achieve isothermal compression change, and the external heat is absorbed into the expansion space (low-temperature space) 46 through the low-temperature heat transfer head 41 to change isothermal expansion. If this is realized, a reverse Stirling cycle is formed.
Since the heat of the compression space (high temperature space) 45 is transmitted to the high temperature heat transfer head 40 and external heat is absorbed by the expansion space (low temperature space) 46 through the low temperature heat transfer head 41, the high temperature heat transfer head 40 and the low temperature heat transfer head are absorbed. Heat exchangers 42 and 43 are arranged inside the head 41, respectively. Increasing the heat exchange efficiency and heat transfer efficiency of the heat exchangers 42 and 43 has been a concern in the art.

As a conventional technique related to this heat exchanger, Patent Document 1 describes a heat exchanger in which a flat plate-like material provided with a large number of fins is shaped into a ring shape with the fins inside.
JP 2007-85641 A

When considering the flow rate of the working gas passing through the heat exchanger, if a flat plate-like material provided with a large number of fins is formed into a ring shape with the fins inside, the flow path shape is usually trapezoidal as shown in FIG. .
In general, the relationship between the pressure loss (differential pressure) ΔP and the flow velocity v of the fluid flowing through the flow path is expressed as follows: fluid density is ρ, flow coefficient of friction is f, flow path length is l, and hydraulic diameter of the flow path is If d, it is expressed by the following equation.

  Equation 1 is transformed into an equation for obtaining the flow velocity v.

  Next, assuming that the short channel side is w and the long channel side is h in the case of a rectangular channel (not including the side walls at both ends), the hydraulic diameter d is expressed by the following equation.

  Substituting equation 3 into equation 2,

Thus, it can be seen that the flow velocity v is proportional to the route of the flow path short side w. That is, the flow velocity v decreases as the flow path short side w decreases, and the flow velocity v increases as the flow path short side w increases.
From the above, when the short side of the channel changes like a trapezoidal channel, the flow velocity distribution gradually changes in the fin direction, and the flow velocity distribution is as shown in FIG. If the flow velocity of the working gas is different in the fin direction as described above, the flow of the working gas in the heat exchanger is disturbed, and the contact efficiency between the working gas and the fin is lowered.
In such a case, as described in Patent Document 1, even if heat is likely to flow toward the outer circumferential direction of the heat exchanger by gradually increasing the cross-sectional area of the fin toward the outer circumferential direction of the heat exchanger, Since the heat of the working gas is not transmitted well, the effect cannot be exhibited effectively. That is, to improve the heat exchange efficiency of the heat exchanger, it is necessary to improve the heat flow of the heat exchanger without reducing the contact efficiency between the working gas and the fins.
The present invention has been made in view of the above points, and provides a heat exchanger for a Stirling engine in which heat transfer between a working gas and a heat transfer head is stable, and a Stirling engine using the same. The purpose is to provide.

The invention according to claim 1 is a Stirling engine heat exchanger that transfers heat transferred between the compression space and the working gas traveling between the expansion space to the heat transfer head, and is in contact with the inner periphery of the heat transfer head. A plurality of fins extending toward the center of the ring are provided on the inner surface of the ring-shaped base so that the width of the working gas flow path formed by the fins is constant.
The invention according to claim 2 is the invention according to claim 1, characterized in that the fins are tapered toward the center.

  According to the present invention, it is possible to obtain a heat exchanger for a Stirling engine capable of stably transferring heat from a working gas.

FIG. 1 is a plan view of a heat exchanger for a Stirling engine according to the present invention, and FIG. 2 is a sectional view taken along line AA shown in FIG.
A heat exchanger 100 for a Stirling engine according to the present invention is formed by forming a large number of fins 102 at a constant pitch on the inner surface of a thin ring-shaped base 101 extending in the axial center direction of the base 101. A region surrounded by the base 101 and the fins 102 becomes a working gas flow path. The heat exchanger 100 is in contact with the inner periphery of a high-temperature heat transfer head or a low-temperature heat transfer head (not shown) on the outer periphery of the base 101, and transfers heat through the heat transfer head.
FIG. 3 is a partially enlarged view of a plan view of the heat exchanger. As shown in FIG. 3, the fins 102 are narrowed toward the center of the base 101 so that the circumferential width w of the flow path is constant in the radial direction. As a result, the flow velocity is constant throughout the flow path, and the working gas flows smoothly, and heat can be efficiently exchanged with the fins 102.
Furthermore, the cross-sectional area of the fin 102 gradually increases toward the outer periphery of the heat exchanger 100. As a result, the thermal resistance decreases toward the outer peripheral side, and heat easily flows toward the outer peripheral direction of the heat exchanger 100, thereby increasing the amount of heat exchanged with the heat transfer head.
The heat exchanger 100 is made of copper, copper alloy, aluminum, aluminum alloy or the like having high heat transfer efficiency.

From the above, it can be understood that the heat transfer efficiency is better than that of the prior art, but further, the difference in the heat release caused by the difference in flow velocity distribution between the rectangular flow path and the trapezoidal flow path will be examined.
Generally, the heat dissipation amount Q is defined by the following equation using the temperature difference ΔT between the gas and the fin, the heat transfer coefficient hy, and the surface area A.

  In addition, the heat transfer coefficient hy under constant wall surface temperature conditions is λ for the gas thermal conductivity, L for the flow direction length of the flat plate (fin), Num for the average Nusselt number, Pr for the Prandtl number for the gas, and the flow direction When the Reynolds number based on the distance is ReL, the following formula is used.

  If the parameters other than the flow velocity v in Expressions 6 to 8 are constant, the following relationship is established between the heat release amount Q and the flow velocity v.

  Here, in order to easily obtain the heat dissipation amount Q in the trapezoidal channel, the trapezoidal channel is considered as a set of rectangular channels divided into n. Assuming that the cross-sectional area of the flow path is A and the constant that does not depend on the flow path is K, the heat radiation amount is expressed as follows.

In order to grasp the difference specifically, when the average hydraulic diameter d is 0.6, that is, when the average flow path width w is 0.3, in the rectangular flow path and the trapezoid flow path (a set of divided rectangular flow paths) Compare the heat dissipation amount Q.
As shown in FIG. 7, the trapezoidal flow path is divided into five flow paths (I to V), and the hydraulic diameter of each section is defined as section I.
: 0.2, section II: 0.4, section III: 0.6, section IV: 0.8, section V: 1.0, and the flow velocity v is determined by the above equation 4, a trapezoidal channel ( The heat release amount Q5 of the rectangular flow path divided into five is as follows.

  When the heat radiation amount of the rectangular channel when the channel short side w is 0.3 is Q1, the result is as follows.

  From the above, by comparing Q1 and Q5, it can be seen that the heat dissipation efficiency is higher in the rectangular channel.

  The present invention is applicable to all Stirling engines.

The top view of the embodiment concerning the present invention AA sectional view of an embodiment concerning the present invention. The elements on larger scale of the embodiment concerning the present invention Outline diagram showing the structure of a Stirling engine Plan view of conventional heat exchanger for Stirling engine Flow chart of trapezoidal flow path Conceptual diagram of replacing trapezoidal flow path with 5-divided rectangular flow path

Explanation of symbols

101 Base 102 Fin

Claims (2)

In a heat exchanger for a Stirling engine that transfers heat transferred between the compression space and the working gas moving back and forth to the expansion space to the heat transfer head,
A large number of fins extending toward the center of the ring are provided on the inner surface of the ring-shaped base in contact with the inner periphery of the heat transfer head so that the width of the working gas flow path formed by the fins is constant. thing,
A heat exchanger for Stirling engines. The heat exchanger for a Stirling engine according to claim 1, wherein the fins are tapered toward the center.

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