US2649696A - Evaporating-condensing heat transfer system - Google Patents

Description

Aug. 25, 1953 V J. G. TANDBERG 2,649,695

EVAPORATING-CONDENSING HEAT TRANSFER SYSTEM Filed Nov. 23, 1945 FIG. I.

INV; 1\ I TOR. BY

Patented Aug. 25,1953

EVAPORATING- CONDENSING HEAT TRANSFER SYSTEM John Gudbrand Tandberg, Stockholm, Sweden,

assignor to Aktiebolaget Elektrolux, Stockholm, Sweden, a corporation of Sweden Application November 23, 1945, Serial No. 630,273 In Sweden December 22, 1944 4 Claims.

This invention relates to an arrangement in evaporating and condensing heat transfer systems, especially hermetically closed heat transfer systems and its general object is to eliminate certain inconveniences which have appeared in evaporating and condensing systems, especially in such systems which are utilized for heat transfer at'small differences in temperature between the heat absorbing and the heat dissipat- 'ing parts of the system.

For the transfer of heat from an object to be cooled to a cold source it is previously known to utilize hermetically closed evaporating and condensing heat transfer systems usually containing methyl chloride and the like as a heat transfer medium, possibly in addition to an inert gas. It often occurs that the difference in temperamm between the compartment to be cooled and the cold source for cooling the compartment with the'aid of such a heat transfer system is small and in a range of ten degrees more or less and in such cases certain difliculties have appeared in obtaining a constant and reliable vaporization of the heat transfer medium in the system. When the cold source is thermostatically controlled and arranged to maintain a certain temperature in the cooling compartment, for example, it often appears that when the'thermostat, after a shut down period, restarts the refrigerating apparatus, the heat transfer medium in the heat absorbing part of the heat transfer system cannot be brought to a boil at the relatively small differences in temperature which appear in the system. The liquid will instead be superheated without any boiling taking place.

The object of the invention is to facilitate the starting of the vaporization of the heat transfer medium with rise in temperature and is substantially characterized by a branch communicating with the system, such branch having a higher temperature than the operating temperature of the heat absorbing part of the system.

The invention will be hereinafter more fully described with reference to the embodiment diagrammatically shown in the accompanying drawing, and in this connection further characteristic features of the invention will be set forth.

In the drawing Fig. 1 diagrammatically shows a so-called cooling box in which an absorption refrigerating apparatus is embodied and arranged to absorb heat from the cooling compartment of the box with the aid of an evaporating and condensing heat transfer system;

and Fig. 2 is a fragmentary view of a cooling box like that shown in Fig. 1 illustrating a modification of the invention.

In the drawing reference character Ill denotes the heat-insulation of the cooling box, such insulation surrounding the cooling compartment denoted by II. This compartment is defined by a sheet lining l2, forming the heat-absorbing surface of the cooling compartment. The outer surface of the sheet is heat-conductively connected to the heat absorbing part I 3 of an hermetically closed evaporating and condensing heat transfer system having the form of a pipe coil, the heat dissipating part I I of which, being suitably arranged as a pipe coil, is closely heat-conductively connected with a cold source. In the embodiment shown the cold source comprises a primary evaporator of an absorption refrigerating apparatus l5, for example, of the inert gas type. The primary evaporator may suitably be formed as a pipe coil in good thermal exchange relation with the pipe coil M of the: heat transfer system.

The heat absorbing part or secondary evap-- orator [3 of the heat transfer system absorbs heat from the cooling box, the heat transfermedium contained therein being vaporized by such abstracted heat. The vapour flows through the system and enters the heat dissipating part or condenser 14 of the system where the vapour is condensed and gives up heat to the primary evaporator associated with the part I 4. The condensate returns by gravity flow through a conduit I6 back to the heat absorbing part of the system. It will be assumed that the heat absorbing part or secondary evaporator [3 has a temperature of -20 C. and that the primary evaporator associated with the part H1 at the same time has a temperature of 25 C. This small difference in temperature is in many cases insufficient to achieve the boiling of the liquid in the heat absorbing part l3 of the heat transfer system. For this purpose a difference in temperature of 15 C. may be required to instigate boiling, for example. This means that the variations in temperature in the cooling compartment II are important, especially when the compartment is thermostatically controlled.

According to the invention the difference in temperature required to instigate vaporization of the heat transfer medium in the second evaporator or part I3 can be substantially reduced by providing the system with a part I! in the form of a dead-end branch connected to the lower portion of the heat-absorbing part I 3 of the heat transfer system. This branch I! extends through the insulation Iii of the box and may reach the outer lining or shell l8 with which it possibly can be heat-conductively connected. In certain cases it may even be desirable for the branch I! to extend outside the box, as shown in Fig. 2, so that it can be maintained at the temperature of ambient air and at a substantially higher temperature than the other parts of the system.

A certain vapor expulsion though of course very small, may continually take place in this branch, and the vapour bubbles will little by little penetrate and pass intg the pipe coil it, where they will cause a lively vapor expulsion of the heat transfer medium, ii the difierence in temperature intended is at hand. No superheating of the liquid will thus take place. In order that the vapour will flow in the intended direction, that is to say, in a direction upward through the pipe coil 13, the lowest part of the coil is provided with a U-shaped trap 19.

It is, however, not necessary for continuous Vapor expulsion to take place in the branch 11. most cases it is quite sufficient if in certain relatively long intervals of time gas bubbles are formed in the branch and penetrate into the system. In order to obtain a vapour expulsion which to a certain degree is intermittent, the

branch can be extended upwards, its upper end :1.

being closed. In this way a gas bubble will be formed which grows larger and larger whereby the heat supply to the liquid will become less and less because, owing to the growing gas bubble, the heat absorbing surface in contact with the liquid will become smaller and smaller.

The branch Il may be arranged in such a way that, only after a relatively long interval of time, the gas bubble will become large enough to allow gas to penetrate down to the coil opening and into the pipe coil 13. In this way the deadeend branch will substantially be filled with vapour at least as long as the difference in temperature between the heat transfer system and the outside atmosphere is sufiiciently great. The presence of this vapour quantity freely communicating with the system has proven extremely satisfactory and effectively prevents superheating which is due to lack of heat transfer medium in vapor phase.

This invention is not to be limited to the embodiment shown but may be varied in several ways within the scope of the basic inventive concept. This is applicable not only to the form of the branch and its connection to the heat transfer system but also to the method of supplying heat to the branch. In certain cases especially in larger compartments, it may be desirable to provide the branch with a separate, possibly thermostatically controlled heat source, which will effect boiling and vaporization of liquid in the branch, substantially at the initial phase of the starting of the primary refrigerating system. Also, the invention is not to be limited to the utilization of a particular cold source or any definite temperature range for which the heat transfer system is intended to operate.

I claim: 7

1. In combination with refrigeration apparatus comprising a cabinet having inner and outer walls and insulation therebetween, said inner wall defining a space, and primary cooling means, a secondary heat transfer circuit adapted to contain a vaporizable heat transfer agent, said circuit including a heat absorbing portion arranged to abstract heat from the space and a heat rejecting portion, said heat rejecting portion being arranged to be cooled by the primary cooling means to effect vaporization of said agent in said heat absorbing portion and condensation of the vaporized agent in said heat rejecting portion, and a part connected to receive condensed agent from said heat absorbing portion below the liq.- uid level normally maintained therein during operation of said circuit, said part extending in the gap between said inner and outer walls and being constructed and arranged to promote evaporation of condensed agent therein and deliver such vapor to said heat absorbing portion.

2. Refrigeration apparatus as set forth in claim 1 in which said heat absorbing portion in.- cludes a coil in thermal exchange relation with said inner wall, and said part comprises a deadend branch communicating with such coil.

Refrigeration apparatus as, set forth in claim 1 in which said part comprises a deadend hollow member having one end communicating with said heat absorbing portion and its opposite closed end in thermal exchange r lation with said outer wall.

4. Refrigeration apparatus as set forth in claim 1 in which said part extending in the gap between said inner and outer walls includes a portion projecting exteriorly of said outer wall.

JOHN GUDBRAND TANDBERG.

References Cited in the file of this patentv UNITED STATES PATENTS Number Name Date 2,138,612 Philipp Nov. 29, 1938 2,157,012 Philipp May 2, 1939 2,230,342 May Feb. 4, 1941 2,257,447 Atchison Sept. 30, 1941 2,331,898 Kleen Oct. 19, 1943 2,390,085 Kleen Dec. 4, 1945

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