DE2063555A1 - Cold gas chiller - Google Patents

Description

PHA. 20526.

FaientMwalt

kmettet: N. V »Philips' Gloeitqmpenfabriekeo

File Να _Λ PHA-20.526
Registration from »21 Des. 1970

KaltgaskHltemsohine.

The invention relates to a Kaltgaskttltemaaohine, the one compression space of variable volume and higher medium temperature as well as an expansion space connected with the aem contains lower mean temperature, its volume can be changed by a displacer movable in a cylinder, whereby the connection between the spaces mentioned a regenerator is located, which the working medium on its way from the compression to the expansion room and vice versa.

Cold gas sutures of the ax mentioned above are known. The efficiency of machines of this type, as well as the tiefeteireiohbara Temperature depended to a large extent on the heat capacity of the regenerator and of the flow losses occurring in the regenerator. To have a satisfactory heat capacity of the regenerator, materials such as steel wool, gauze made of phosphorus oxonze or lead are used in known regenerators

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balls used, the heat capacity per unit volume depends on the degree of compression of these materials in the housing of the regenerator. With an increasing degree of compression, however, the flow resistance increases, so that the As the flow increases, the pressure difference across the regenerator increases. This flow resistance has the consequence that the maximum permissible Limited flow speed of the working medium is, so that the speed of the drive motor is limited

k is. This means that the usual motors are relatively have to be big. Another Naohteil the regenerators this type is the one that it is a result of the materials used and manufacturing processes are costly.

I'm another disadvantage, especially for small machines, is that there must be a seal between the displacer and the cylinder wall to ensure that the whole amount of working medium through the regenerator back and forth flows. This seal incurs material and manufacturing costs and also brings the disadvantage of frictional losses

P with itself.

SiQ invention aims to provide a KaltgaakBltemasohine create in which the above-mentioned disadvantages are avoided. To achieve this, the cold gas refrigerator is according to the invention characterized in that the regenerator passes through an annular gap between the displacer and the one with this cooperating cylinder wall is formed, .With at least one of the two facing surfaces of the displacer and the cylinder with a surface layer of high heat capacity is provided, and where the hydraulic diameter of the

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mentioned annular gap of the condition:

corresponds to, in the ) Ί = viscosity of the medium; O = specific density of the medium; M = molar weight of the medium; H = Gaa constant; T ■ mean temperature in the gap; 1 = length of the gap; η »number of cycles per second; D »diameter of the displacer,

while the hydraulic diameter d. roughly equal to twice the gap width is.

The cold gas refrigeration machine according to the invention has the advantage of a simple and cheap regenerator design, with through the lack of a seal between the displacer and the cylinder also greatly reduces the friction loss.

The displacer can be formed by a body made of plastic, such as Teflon, which is attached to the outer circumference with a Layer of metal, e.g. stainless steel, provided 1st.

It has been proven that when the gap width is chosen such that the hydraulic diameter dee Gap is within the specified limits, a satisfactory heat transfer from the working medium to the gap walls and The other way round is feverish, while also the flow resistance The working medium in the gap is low. The latter means that a high flow velocity is permissible, so that

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the number of cycles per second can be large, whereby the Dimensions of the electric motor driving the machine are small become a

Another favorable form of execution is the Regenerator fill factor lower than 10% and preferably less than $ 1. This is what the term "fill factor" means here To understand the relationship between the "free volume" in the regenerator and the total regenerator volume, i.e. free volume plus the volume used by the regenerator material.

The invention is described below with reference to the enclosed Drawing explained in more detail. Show it:

Fig. 1, partially in section, a known cold gas refrigeration machine;

2 shows a partially schematic section of a cold gas refrigeration machine with a gap regenerator;

3 schematically shows a two-stage cold gas refrigerator with a gap regenerator.

Fig. 1 partially shows a known Kaltgaskkühlaaschine 10. This machine contains a cylinder 10a made of stainless steel with a small wall thickness, so that heat conduction in the The longitudinal direction is limited to a minimum. A displacer 14 is arranged in this cylinder. This displacer 14 contains a base part 15 with passed through this part axial channels 16 which adjoin a regenerator 11b which is received in the displacement part 11. The regenerator 11 b consists of a material with a high heat capacity, such as steel wool, gauze made of phosphor bronze or lead balls. Regenerators of this Art have a very high regenerative capacity, but also one

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relatively large flow resistance for the working medium. A seal 18 made of plastic is around the Base part 15 of the VerdrSngars attached to the occurrence of To prevent leakage along the displacer, so that the working medium only through the channels 16 and the regenerator 11b of the Compression space 13 can flow to the expansion space 19 and vice versa. The expansion space I9 is through a freezer plate limited, through which the generated cold can be removed from the space 19. The whole cold part is covered by one envelope 21 surrounded by a heat-insulating vacuum space 22 *

Fig. 2 shows schematically a cold gas refrigeration machine, the corresponds on the whole to the machine according to FIG. In this cold gas refrigerator, however, the regenerator 11b is omitted * The housing 23, the case 24 and the compression space 25 are the same as those of FIG. The displacer 26 is made of a poorly thermally conductive plastic, which is of a thin stainless steel sheath 27 surrounded iflt. Between the cylinder, which is also made of stainless steel 28 and the displacer 26, an open gap 29 is provided. On its way from the compression space 25 to the expansion space JO, the working medium now flows through the gap 29 »whereby it gives off heat to the metal bands 28 and 27. When the working medium flows in the opposite direction, it takes the one in the walls 28 and 27 stored heat again. In order to achieve a satisfactory effect of the Maaohine, the dimensions must be dea Gap 29 can be chosen such that the heat transfer number X ^ .2OO and the pressure difference across the gap as a result of the Ströraungsvorlusta Λρ ^ Ο, Ι ρ, where ρ is the mean pressure in

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the machine represents. Ea turned out to be this Both conditions are met when the hydraulic durometer of the gap is equal to twice the gap width is the condition:

3

240 η nD ² l- ~ ^ d,

corresponds in the?

ri »viscosity of the working medium;

/ 0 " specific view of the medium;

M = molar weight of the medium; R χ gas constant; T = mean temperature in the gap;

1 - length of the gap;

η ■ number of cycles per second;

D ■ Diameter of the displacer

In a practical example in which helium as the working fluid in the engine is present at an average pressure of 20 atmospheres and in which the average cracking temperature of 200 ⁰ K, R Ri are Diesi 8000 M - 4 T - 200

η - 10 ~ ⁵

/ θ- 4.Θ,

furthermore the diameter of the displacer is 10 mm and the speed is η - 10 revolutions / second. Furthermore, a gap length of 1 - 200mm is selected. Dtr maximum hydraulic through «- meases dee gap is then

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4.8 x 10 100 χ With these dimensions is then obtained for the heat transfer!

Nu

Re.Pr * S PUr an annular gap and for Pr * 0.75 then »

7.5 _t 2 ^ pl _m 40

Re. 0.75 XD. ^ D _h Re

Where Re - /) id _h ^ _{2 / Oi}

so A _e 40 Ή 3t D 1

2 / D i d. / η

where i is the mean volume flow on the cold side of the Represents regenerator, so that i «2nVo =

For machines of this type, the stroke is S · "*? D, while the middle one

Current is the current at the end in the regenerator is approximately equal to the half, so that

_Λ 4Ο.4 η * D 1 80 η

D ⁵ d _h / OnD ² d _fa

If the condition is inserted, this gives ι

. 80 χ 10 " ⁵ 200 _on _

/ \ - / ·. j, ■

4.8 χ 10 χ 100 χ 10 16 χ 10, which makes a satisfactory heat transfer sioher, the pressure difference occurring across the gap slid

η ^{10 3} ^ ^1Q " ^{2 X 20} ° ^{X 10} " ⁵ -8000 kg / a *

(16.10 " ² ) ³ χ 10" ⁹

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Since ρ - 20 ata - 2.1O ⁵ kg / m ² - ^ - - 0.04, which is far below the value of 0.1 which is still permissible for a satisfactory effect of a machine.

So in this way is a cold gas refrigerator obtained particularly simple design with a satisfactory heat transfer in the regenerator and very low flow losses.

Fig. 3 shows a cold gas refrigerator of the two-stage type, i.e. with two expansion spaces 31 and -30, their volumes can be changed by the displacer 26. This displacer again consists of a plastic body with a thin metal jacket An open gap 29 is again provided between the displacer and the cylinder, in the same way as in the case of the Kaltgaskältenaachine acts as a regenerator according to Fig. 2. The mode of operation of this cold gas refrigerator is based on the description above emerged.

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Claims (2)

PHA. 20526 PATENT CLAIMS λ. / Cold gas refrigeration machine with a compression chamber of variable volume and higher average temperature and an expansion chamber of lower average temperature connected to this, the volume of which can be changed by a displacer movable in a cylinder, with a regenerator located in the connection between the mentioned chambers which the working medium flows on its way from the compression chamber to the expansion chamber and vice versa, characterized in that the regenerator is formed by an annular gap between the displacer and the cylinder wall cooperating with it, with at least one of the two mutually facing surfaces of the displacer and deo cylinder a surface layer of high heat capacity is provided, and wherein the hydraulic office knife of the aforementioned annular gap of the condition corresponds to η - viscosity of the medium? /) ■ specific diohte of the working medium ·} M »molar weight of the working medium; R »Gaskons tanti; T «■ medium temperature in the gap} 1 * length of the gap, η ■ number of cycles per second » D «diameter of the displacer, while "'a ~~" ι is about the same as the double fan of the split side, 10 9829/1150 PHA. 20526 2. KaltgaskSltemeschine according to claim 1, characterized in that the fill factor of the regenerator is lower ala and is preferably less than $ 1. 109829/1 ISO Blank page