JPH06147791A - Heat exchanger of apparatus with regenerator - Google Patents

Abstract

PURPOSE:To improve an efficiency by eliminating a useless temperature distribution in a heat exchanger in an apparatus having a regenerator such as a Stirling engine and heat exchangers at both ends of the regenerator. CONSTITUTION:Channels 7', 8' of operation fluids in heat exchangers 2, 3 at both ends of a regenerator 4 are so formed as to be continuously or stepwisely reduced in sizes (diameters, gaps, etc.) toward the generator.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The invention of the present application relates to a device having a regenerator (heat storage device, cooler) such as a Stirling engine, a Stirling refrigerator, a Gifford McMahon refrigerator, that is, a machine or device using the Stirling engine ( Automobiles, heat pumps, etc.), Stirling refrigerators, GM
The present invention relates to a heat exchanger at both ends of a regenerator in an applied device of a refrigerator that uses a refrigerating machine such as a refrigerator (a cryopump, a refrigerator for a linear car, a cooling device for a super-electric device).

[0002]

2. Description of the Related Art A typical Stirling engine, Stirling refrigerator or the like is a machine that transports heat or amplifies (generates) heat by reciprocating a fluid using a regenerator. The regenerators of these machines have heat exchangers at both ends that always let heat in and out with the outside world, and are described in, for example, SAE Technical Paper Series 859423. FIG. 1 shows a block diagram of a conventional Stirling engine equipped with a heat exchanger. Reference numerals 1 and 6 are called a compression piston and an expansion piston, respectively, and cause pressure fluctuation and fluid movement in the system. 2 and 3 are the heat exchangers that we are interested in here. Reference numeral 2 is a low temperature side heat exchanger that radiates heat by cooling water from the outside. Reference numeral 3 denotes a high temperature side heat exchanger which is a portion for taking in heat from the outside, but in the example of this figure, heating is performed by a flame. The high temperature part and the low temperature (room temperature) part are connected by the heat storage device, that is, the regenerator 4, and work is amplified and heat is transferred in the heat storage device. A device with such a regenerator will function as heat enters and leaves the regenerator. Most of the heat exchanger structures are 2 in Fig. 1.
Alternatively, the working fluid flows through the fine flow passages 7 or 8 as in 3, and the heating source 5 or the cooling source (cooling water or the like) comes into contact with the outside of the flow passage.

Considering this heat exchanger thermodynamically, it is as follows. It is assumed that the heat exchanger is considered as a bundle of flow passages having a certain diameter, and the fluid inside is heated or radiated from the fluid inside with a constant heating and heat radiation density. now,
As an example, consider the case of a Stirling engine. In the engine, the high temperature side of the regenerator is the heating side and the low temperature side is the heat radiating side. The heat supplied from the high temperature side heat exchanger is transferred to the regenerator and used for generating work in the regenerator. The transport of heat to the regenerator in this heat exchanger is important and problematic. If heat is supplied to the fluid at a uniform density from the wall surface of the flow path of the high temperature side heat exchanger, the heat is transferred to the regenerator in the flow path to the regenerator. As it gets closer, its heat flux must grow. By the way, as a conclusion obtained from thermoacoustic theory, it has been shown that the heat flux Q carried by the fluid that vibrates (reciprocates) is the sum of the three heat fluxes obtained by the following equations 1, 2, 3, and 4. There is.

[0004]

[Equation 1]

[0005]

[Equation 2]

[0006]

[Equation 3]

[0007]

[Equation 4]

Here, the meanings of the symbols in the above equations are as follows. Qprog: Heat flux carried by traveling wave component Qstand: Standing wave component QD: Heat flux carried only by positional displacement of fluid Fs: Quantity related to heat capacity of flow passage of heat exchanger χ ': Reversible change Degree χ ”: degree of irreversible change ω: angular frequency of vibration β: coefficient of thermal expansion Tm: average temperature of working fluid ρm: average density of working fluid Cp: specific heat of working fluid ▽ Tm: temperature gradient of flow passage wall ξ ₀ , Prog: Traveling wave component of displacement amplitude ξ ₀ , stand ² : Standing wave component of displacement amplitude

Since Qprog and Qstand are unrelated to the sound gradient of the flow passage and are determined by the frequency of vibration and the size of the flow passage, there is no great displacement along the flow passage. On the other hand, since QD is an amount proportional to the temperature gradient, the size of QD may change if the size of the temperature gradient changes. Since the heat flux becomes larger as it gets closer to the regenerator along the heat exchanger, Qpr
Since ong and Qstand cannot be changed, there is no choice but to rely on the remaining QD. That is, the temperature gradient changes along the flow path of the heat exchanger, and as a result, the QD changes along the heat exchanger, so that uniform heat supply from the flow path wall can be dealt with.
The distribution of the temperature gradient at that time, that is, the temperature distribution along the fluid of the heat exchanger, is that the QD is proportional to the temperature gradient, and in order for the QD to increase uniformly along the flow path, the temperature distribution is along the flow path. It is easily sought to make parabolic changes. That is, in a heat exchanger having a uniform diameter flow path, heat flows in and out uniformly from the flow path wall, so that a parabolic temperature distribution is inevitably attached along the flow path.
FIG. 2 shows such a temperature distribution, FIG. 2 (a) shows the case of an engine, and FIG. 2 (b) shows the case of a refrigerator. The temperature gradient shown in this figure causes the following problems. Considering the case of the engine,
As shown in (a), there is a nearly uniform temperature gradient in the regenerator (heat accumulator), but the heat exchangers at both ends have a parabolic temperature distribution as shown in the figure, and the heating temperature is A Point temperature (T
A), the cooling temperature is the temperature at point D (TD), but the temperature difference between both ends of the regenerator is TB-TC. In the Stirling engine, the larger the temperature difference between both ends of the regenerator, the higher the output and the efficiency. Since the heating source has the temperature TA and the cooling source has the temperature TD, ideally, the temperature difference TA-TD is expected.

Similarly, the regenerator of the refrigerator is shown in FIG.
As shown in (b), the heat exchanger on the high temperature side and the heat exchanger on the low temperature side each have a parabolic temperature distribution curve opposite to that of the engine as shown in the figure. It is easily understood that this temperature distribution is also disadvantageous for the refrigerator. That is, the regenerator high temperature end (the temperature at the B'point and TB ') is higher than the heat radiation temperature on the high temperature side (the temperature at the A'point, TA'), and the freezing generation temperature (D 'at the low temperature portion is high. Point temperature, TD ') is higher than the regenerator low temperature end temperature (C' point temperature, TC '), resulting in an excessive temperature gradient in the regenerator, resulting in reduced efficiency. Has become.

In this way, the generation of useless temperature distribution at both ends of the regenerator is an essential problem in the conventional heat exchanger having a uniform flow passage cross-sectional area, and as a result, this is caused in the engine and the refrigerator. It was a major cause of reduced efficiency.

[0012]

The problem to be solved by the invention of claim 1 of this application is to eliminate the temperature distribution in this useless heat exchanger.

Further, the problem to be solved by the invention of claim 1 of this application is to obtain a practical constitution for solving the above problem.

[0014]

According to the invention of claim 1 of the present application, a Stirling engine, a Stirling refrigerator, a Gifford-McMahon refrigerator, and other devices having a regenerator (heat storage device, storage device) are provided. In the heat exchangers at both ends of the regenerator, the flow passage dimensions (diameter, gap, etc.) of the working fluid inside the regenerator were reduced continuously or stepwise as it came closer to the regenerator.

Further, in the invention of claim 2 of this application, in the above-mentioned structure, a large number of wire nets and perforated plates are packed in the flow path of the working fluid, and the fineness of the meshes is sequentially changed to form the flow path dimension. Was changed in stages.

[0016]

As described above, the role of the heat exchanger is to transfer heat to and from the outside world and transport the heat to the regenerator. The transport amount (heat flux) also needs to increase toward the downstream side, and the change in the heat flux magnitude was realized by applying a temperature gradient in a form that depends on the temperature gradient dependency of QD. However, in order to give a heat flux distribution without a temperature gradient, it is necessary to impose a heat flux distribution in addition to QD. The candidates are Qprog and Qstand, and they have distributions according to their positions, so that χ ′ and χ ″ are distributed as shown in Equations 2 and 3. χ ′ and χ ″ are the figures. 3 is a function of ωτ, ω is the operating angular frequency of the refrigerator, and τ is the thermal relaxation time between the fluid and the heat exchange wall, which is defined by Equation 5 below.

[0017]

[Equation 5]

In the above equation 5, r ₀ is the representative length of the flow path,
(Radius for circular tubes, half the spacing for parallel plates),
α is a temperature spread coefficient of the fluid, and is a constant if the temperature is constant. In order to generate a distribution in χ ′, χ ″ without a temperature distribution, it is a method that gives a distribution to r _0. The invention of claim 1 is the dimension of the flow path of the heat exchanger (representative length, etc.). ), Qprog, Qs
It is possible to realize the heat flux distribution without causing temperature distribution by causing tan position dependency.

According to the second aspect of the invention, a heat exchanger having a practical structure can be obtained.

[0020]

FIG. 4 shows a concrete example, that is, an example of a Stirling engine. Since it is effective to rely on Qprog in the three-ring engine because it has relatively many traveling wave components,
It is desirable to increase χ'in the direction of increasing heat flux. That is, the representative length of the flow path is reduced along the heat flux direction. As shown in FIG. 4, in the heat exchanger 3 on the high temperature side, the dimensions (diameter, etc.) of the passage 8 ′ become smaller as it gets closer to the regenerator 4, and the heat exchanger 2 at the low temperature side also has passages closer to the regenerator 4. The size of 7'is reduced. Since it is practically difficult to continuously change the diameter and gap of the flow passage, as shown in Fig. 5, the flow passage 7 "of a certain size in the heat exchanger is filled with the wire mesh, and the fineness of the wire mesh is reduced. A, B,
The same effect can be obtained by the method of gradually changing the C, D, and E positions in a step-wise rough manner. These methods are basically the same both for the engine and for the refrigerator. However, since the amount of heat and temperature flowing in and out of the heat exchanger differ depending on the difference in engine and refrigerator and the capacity, it is natural that it is necessary to decide how to change the flow path dimensions or the distribution of the wire mesh according to it. is there.

[0021]

As described above, according to the first aspect of the present invention, the operation of the heat exchanger is changed by changing the Qprog according to the change in the amount of heat of the working fluid transported in the heat exchanger. By eliminating the temperature gradient along the flow direction of the fluid, the efficiency of the equipment as a heat engine can be improved. Further, according to the invention of claim 2, it is possible to provide a heat exchanger having a practical configuration.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a conventional Stirling engine including a heat exchanger.

FIG. 2 is a diagram showing a temperature distribution over a heat exchanger and a regenerator (a heat storage device, a storage device), (a) shows a case of a Stirling engine, and (b) a storage cooling type refrigeration such as a Stirling refrigerator. Machines are shown respectively.

FIG. 3 is a diagram showing ωτ dependence of χ ′ and χ ″ (when a flow channel is a circular tube).

FIG. 4 is a diagram showing an embodiment of the invention of this application.

5 is a diagram showing a detailed configuration of a heat exchanger in FIG.

[Explanation of symbols]

 1 compression piston 2 low temperature heat exchanger 3 high temperature heat exchanger 4 regenerator (heat storage device) 5 heat source 6 expansion piston 7 working fluid flow path in low temperature heat exchanger 7'working fluid flow path in low temperature heat exchanger 7 "Working fluid flow path in low temperature heat exchanger 8 Working fluid flow path in high temperature heat exchanger

Claims (2)

[Claims] 1. The internal operation of a heat exchanger at both ends of a regenerator in a device having a regenerator (heat storage, cooler) such as a Stirling engine, a Stirling refrigerator, a Gifford McMahon refrigerator. The structure of the heat exchanger is characterized in that the flow passage of the fluid is reduced in size or diameter in a continuous or stepwise manner as it is closer to the regenerator. 2. The flow path dimension is changed stepwise by packing a large number of wire nets or perforated plates in the flow path of the working fluid and sequentially changing the fineness thereof. The heat exchanger described in 1).