US2617271A - Refrigerating system with downwardly evaporating secondary circuit - Google Patents

Description

Nov. 11, 1952 w. G. NOLCKEN REFRIGERATING SYSTEM WITH DOWNWARDLY EVAPORATING SECONDARY CIRCUIT iled March 3 1949 INVENTOR.

N E K m 0 N. E O F R A M E D L O Y B ATTORNEY use of ebullition promoters and the like.

Patented Nov. 11, 1952 REFRIGERATING SYSTEM WITH DOWN- WARDLY EVAPORATING SECONDARY CIRCUIT Woldemar George Nolcken, Headington, Oxford, England, assignor to Pressed Steel Company Limited, Oxford, England, a British company Application March 3, 1949, Serial No. 79,481 In Great Britain March 16, 1948 2 Claims.

The present invention relates to refrigerating systems, and concerns particularly a system in which a secondary cooling system is employed to cool directly, for example, the walls of a refrigerator cabinet.

In secondary systems of the type where a condenser is in direct or indirect thermal contact with a source of cold, such as the primary evaporator of a refrigerating apparatus, and an evaporator is in direct or indirect thermal contact with the refrigerated space, it is customary to induce a closed unidirectional gravity circulation of the secondary refrigerant through the system by placing the secondary condenser at a higher elevation than the secondary evaporator.

More particularly, withinthe heat absorbing section of the system, i. e. the secondary evaporator, a circulation of refrigerant is maintained by the difference in density between liquid in the descending limb and vapour or mixed vapour and liquid in the rising limb or limbs, the type of circulation depending on details of size and shape of the evaporator. Thus, in the so-called fully flooded type of evaporator, the boiling refrigerant is contained in conduits of relatively wide bore. Vapour is formed on the heat absorbing walls of the conduits and rises through the liquid to the surface in the shape of small bubbles, wherefrom it escapes into the condenser, is liquified and returns to the evaporator. In evaporators of this type the heat transfer from the heat-absorbing surface to the stagnant liquid is poor, and satisfactory operation is seldom possible without the On account of the relatively wide piping used, such evaporators are inconvenient and expensive for some applications, such as cooling the liner of a domestic cabinet.

In the re-circulating type of evaporator, on the other hand, the heat absorbing pipes are of small bore in order to prevent, as much as possible, the rise of vapour bubbles through the liquid and to induce gas lifting of the liquid by the vapour to the higher level of the condenser, wherefrom it is returned to the evaporator through a short, preferably vertical, heat-insulated liquid supply pipe.

This evaporator functions as a U tube, of which one limb is straight and short and serves the purpose of feeding the liquid condensate back to the bottom of the other limb, whilst the second, or rising limb, constitutes the evaporator proper and has the shape and dimensions required for absorption of the quantity of heat for which it is designed at its working temperature, as well as for satisfactory gas-lift circulation. As is known, these two conditions are not always compatible.

Depending on the size and temperature differ,- ence of the heat flow through the secondary system, the bore of the evaporator tube and its shape, e. g. the angle of rise, the degree of bending and so forth, must be carefully selected to secure, particularly when starting-up, a satisfactory circulation free from gas locks, which will not collapse and become of the flooded type before the lowest temperature difference has been reached at Which the machine is expected to operate.

In practice, the actual shape of the refrigerated space defined, for example, by the liner of the domestic cabinet, and the direct distribution of cooling tubes on its surface for uniform cooling as well as the amount of cooling surface required to secure the desired temperature difference, may not agree with the best conditions for circulation.

A compromise has then to be reached between the two conflicting demands of heat transfer and circulation as a result of which both processes fail to operate at conditions of highest efficiency. In order to avoid these difi'iculties, according to the present invention, there is provided an evaporator with non-gas lift gravity circulation, which is substantially free from the construction restrictions imposed by the gas lift process and which cannot gas lock or stop circulating at low temperature differences.

In general, 1. e. with primary evaporators of the so-called dry expansion type, it is known to circulate the refrigerant through the evaporator in a downward direction, this method having the advantage of smooth operation and more uniform temperature distribution than the opposite method of evaporating the refrigerant upwards.

According to the invention, this method of evaporating downwards is now applied to secondary systems.

The invention is illustrated in the accompanying drawing, which is a perspective view from the rear, with parts broken away, of a domestic refrigerator incorporating the secondary system of the invention.

The refrigerator comprises the outer casing H and inner liner i 2, defining the food storage compartment, the space between them being filled with insulation, as indicated at I4. A hermetically sealed motor-compressor unit l5, mounted at the bottom of the cabinet, circulates compressed vapour refrigerant to the condenser I6, wherein it is condensed before passing, via the capillary tube H, to the evaporator [8, shown as a coil 19 and an evaporator box 20. Refrigerant returns to the suction side of the compressor from the header I3, via the pipe 2|, in heat-exchange relationship with the capillary tube 11. This circuit comprises the usual primary system of a refrigerator and will include the usual control devices such as thermostats, overload switches and so forth.

The secondary system comprises the evaporator 30, made up of a tube of any diameter, size'or shape convenient for efliciently cooling the refrigerated space and shown enveloping the liner 12, but preferably so arranged that the mean gradient of descent is continuous throughout. The evaporator is connected with'a condenser 3| of any type or convenient shape which is in thermal contact with the box of the primary evaporator 18. The evaporator is further connected with a liquid-vapour separator vessel 32, between which and the condenser extends a vapour'return pipe 33. The total charge of secondary refrigerant is such that all liquid can be held by the liquidvapour separator vessel 32 without blanking ofl the evaporator and the vapour return pipe 33.

The operation is as follows:

In the first place, assuming all liquid refrigerant is in the liquid-vapour separator vessel 32,

then when the primary circuit begins to function, the box 20 of the primary evaporator I8 chills the walls of the secondary condenser 3| causing condensation of the secondary refrigerant vapour to take place therein, at the same time lowering the pressure throughout the system. Refrigerant now distils over from the liquid-vapour separator vessel 32 into the secondary condenser-3| and, at the same time, condensate flows from the latter, via the pipe 34, into the secondary evaporator 30, where it is re-evaporated, the vapour escaping via the vapour return pipe 33 back to the condenser 3l. Inasmuch as the liquid-vapour separator vessel absorbs any heat at all, it will, in course of time, evaporate its liquid into the circulatory system until there is equilibrium between the amount which evaporates and the amount flowing back as liquid from the secondary evaporator. This latter amount, of course, corresponds with the rate of heat absorption by the liquid-vapour separator vessel. The pipe connections between the secondary evaporator 30, and the liquid-vapour separator vessel 32, functions with the vapour return pipe 33 as a U-tube, of which the former contains vapour and liquid and the-latter vapour only, thereby assuring the necessary gravity circulation throughout the system. It may be noted that the vapour return pipe is free from the restrictions which apply to the corresponding (liquid supply) pipe in the other systems, i. e. to be straight, short and not to absorb heat. Furthermore, the height of the condenser from inlet to outlet is irrelevant and does not appreciably increase the gas lifting head as in other systems. I i

The evaporator may have any convenient shape but preferably rising portions in the direction of flow should be avoided. The bore is irrelevant within reasonable limits. It should not be so narrow that frictional resistance, combined with acceleration, causes liquid topile up in the condenser to an undesirable extent.

The liquid-vapour separator vessel 32 should absorb some heat from the refrigerated space. The greater the proportion of heat absorbed thereby compared with the evaporator 30, the shorter will be the delay after starting up before the evaporator is fully wetted, and the wetter will be the circulation therethrough.

The liquid-vapour separator vessel may be in the form of a container of any suitable shape and size ormay consist of one or more interconnected pipes. In the'same way, the condenser may be of any of the'usual well-known types.

If desired, an independent thermostatic or pressure controlcan be incorporated in the secondary system.

LI claim:

1. A refrigerator including a cabinet, a liner defining the cold storage space, a primary refrigcrating system including a motor compressor unit, a condenser and an evaporator, said evaporator being arranged within said liner, a secondary condenser-evaporator system, the secondary condenser of which is in thermal contact with the primary evaporator, the secondary evaporator being in the form of a tube embracing said liner and at a lower level than said secondary condenser and connected thereto by a liquid refrigerant pipe to ensure circulation of secondary refrigerant downwardly in said secondary evaporator, a liquid/vapour separator'vessel connected at the bottom of the secondary evaporator in thermal contact with the liner and a rising vapour refrigerant pipe connecting said separator vessel with the secondary condenser.

2. A refrigerator including a cabinet, a liner defining the cold storage space, a primary refrigerating system including a motor-compressor unit, a condenser and an evaporator, said evaporator being arranged within said liner, a secondary condenser-evaporator system, the secondary condenser of which is in thermal contact with the primary evaporator, the secondary evaporator being in the form of a tube embracing said liner, the mean gradient of descent of said tube being continuous throughout its length and arranged at a lower level than said secondary condenser and connected thereto by a liquid refrigerant pipe to ensure circulation of secondary refrigerant downwardly in said secondary evaporator, a liquid/vapour separator vessel connected at the bottom of the secondary evaporator in thermal contact with the liner and a rising vapour refrigerant pipe connecting said separator vessel with the secondary condenser.

WOLDEMAR GEORGE NOLCKEN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,013,469 Knight Sept. 3, 1935 2,361,792 Philipp Oct. 31, 1944 2,401,613 Charland June 4, 1946 2,455,850 Atchison Dec. 7, 1948 FOREIGN PATENTS Number Country Date 575,535 Germany Apr. 28, 1933

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