US2116100A - Refrigerating apparatus - Google Patents

Description

May 3,1938. RJ. CRACKNLL REFRIGERATING APPARATUS Filed March 7, 1936 Patented May 3, 1938 REFRIGERATING APPARATUS Richard John Cracknell, London, England, assignor to U. D'. Engineering Company Limited, London, England, a British company Application March 7, 1936, Serial No. 67,672 In Great Britain A ugustS, 1935 6 Claims.

This invention comprises improvements'in or relating to refrigerating apparatus of thetype in which the refrigerant evaporates in pipes or coils.

It is known that the rate of heat transmission in such evaporators is improved by increasing the relative amount of liquid refrigerant in the pipes or coils. This can be provided for by admitting the refrigerant liquid after passing the expansion valve into a cylindrical vessel called a separator which must be xed at a certain height above the levell of 'the evaporator coils to which it is connected. In this vessel the gas formed when the liquid passes the expansion valve is separated from the liquid and only the liquid passes into the coils. The height above the evaporator coils at which the separator must be fixed depends on the form or length of the coils, it being necessary to provide a sufficient head to feed the liquid to the coils by gravity. In some cases owing to the length of theV coils in order to provide a sufficient head to overcome the friction' or resistance in the coils it would be necessary lto fix the separator at such a height above the coils as to make this method impracticable. In such cases a pump is sometimes used to force the liquid from the separator into the coils. This arrangement has the disadvantages that it involves the cost of a pump and motor to drive 30 it, also the cost of running the motor and in addition it involves a gland on the pump spindle which must be kept gas tight.

Itis an object of the present invention to provide means whereby the quantity of refrigerant in the evaporator coils is increased and at the same` time it is unnecessary to provide either a pump or a gravity head to ensure the flow of the refrigerant through the evaporator.

According to the present invention in an evap- A on `4K0 orative refrigerator there is provided between the condenser and the evaporator a heat exchanger through which the refrigerant passes on its way to the evaporator, incombination. with a pressure reducing expansion valve (for example, a 45 float-operated expansion valve) between the condenser and the heat exchanger and a second pressure reducing valve between the heat exchanger and the evaporatorand means to ref turn the refrigerantirom the evaporator to the 50 heat exchanger so as to extract heat from the refrigerant passing through the heat exchanger to the evaporator.

In accordance with this arrangement the refrigerant from the condenser is not' allowed to 55 fall to the evaporator pressure while it ls in the heat exchanger so that its temperature when it enters the heat exchanger element will be higher than that of the liquid surrounding it and While still under the excess pressure it is cooled in the heat exchanger to such a temperature that 5 when it passes through the second pressure reducing valve only a small amount of evaporation due to loss of pressure at the valve will take place. 'I'his ensures that the refrigerant entering the evaporator coils is mainly in the liquid form. 10 The heat exchanger receives from the evaporator a mixture of still-liquid refrigerant and of refrigerant which has been evaporated. In the heat exchanger such part of the refrigerant coming from the evaporator as is still in the liquid 15 form will be gasied by receiving heat from the refrigerant which is passing through the heat exchanger to the evaporator. Consequently only the vapor will pass to the compressor which is used to deliver it to the condenser and therefore not only is the evaporator itself rendered more efficient by the reduction of vapor therein but the risk of knocking in the compressor is obviated.

The heat exchanger conveniently takes the form of a separating vessel having an inlet for a mixture of liquid and gases from the evaporator, an outlet in the upper part to the separator and a heat exchange element in the lower part through which the refrigerant from the condenser to the evaporator passes, said heat exchange element being so located as to be in Contact with liquid refrigerant which separates from gasesin the separator. The refrigerant, therefore, does not enter the body of the separator until it has passed through the evaporator. Around the coil forming the heat exchange element within the separator is a free space which is lled with liquid refrigerant coming from the evaporator and the purpose of the separator is, therefore, in part, to separate this liquid from the vapor which is going to the compressor.

The pressure reducingv expansion valve for controlling the outflow from the condenser is conveniently of known type comprising a iloat-operated expansion valve capable of delivering liquid refrigerant to the heat exchanger coil whilst stopping the passage of -gaseous refrigerant. At the outlet from the heat exchanger the coil is provided with an automatic pressure reducing valve capable of maintaining a pressure of, say, by way of example, 60 lbs. in the heat exchanger when there is a pressure of, say, 20 lbs. in the evaporator. As a result the float valve will reduce from the condenser pressure to the intermediate pressure of 60 lbs. or so which is maintained in the heat exchanger. This reduction of pressure at the float valve will be accompanied by a corresponding reduction of temperature and f by some evaporation but the vapor is recondensed in the heat exchanger and the temperature further reduced to such a level that only a small amount of vapor is produced at the second pressure reducing valve. As the liquid passes the pressure reducing valve under considerable pressure it is unnecessary to provide a pump or any gravity head to force the refrigerant through the evaporator, so that the separator and heat exchanger can be fixed at any level in relation to the evaporator.

The accompanying drawing illustrates diagrammatically and by way of example o'ne arrangement of apparatus in accordance with the invention.

In the drawing: I I is a pipe carrying a refrigerant from the condenser to a float-operated expansion valve I2 which may, for example, be of the type described in my United States Patent SpecicationNo. 2,024,721. From the expansion valve liquid refrigerant passesby the pipe I3 to a heat exchanger coil I4 disposed in the lower part of a separating vessel I5 so that it is immersed in liquid refrigerant I6 in the vessel. 'Ihe outlet of the heat exchanger coil I4 passes to the reducing valve I'I and thence to the evaporator coil I8.

The return pipe I9 from the evaporator coil enters the upper part of the separating chamber I5 and here the mixture of liquid and gaseous refrigerant which cornes from the evaporator separates out. Only gaseous refrigerant is returned by the pipe 20 to the compressor.

It will be appreciated that the liquid refrigerant I6 in the separating vessel I5 cools the refrigerant passing from the heat exchanger coil Il and therefore is itself gradually evaporated, and also continuously replenished by the supply from the evaporator coil. In due course the liquid refrigerant in the separating vessel I5 strikes a balance of level and temperature at which it remains constant. As the evaporator coil is more filled with liquid than when the separator I5 and heat exchanger coil are omitted, it is necessary to allow suflicent extra quantity of refrigerant in the system to keep the evaporator coil so filled and also to allow for the extra refrigerant which occupies the lower part of the separator I5.

The amount of heat removed from the liquid coming from the condenser will depend upon the difference of temperature between the condenser and evaporator. Under average conditions with ammonia as the refrigerant' it may be sufficient to evaporate in the heat exchanger from 10 to 15% of the total flow of refrigerant passing .into the evaporator. In that case 10 to 15% of the total amount of liquid entering the evaporator will pass through the evaporator coils unevaporated and return to the heat exchanger where it is separated from the vapor and used to cool the liquid going into the evaporator. A continuous supply of liquid is thus maintained in the heat exchanger. There is no gain or loss in this exchange of heat but it provides a simple means of increasing the amount of liquid in the evaporator coils.

This arrangement has, furthermorefthe advantage that it can readily be lincorporated in existing refrigerating systems of the evaporator type without modification of the evaporator or condenser units and will serve to increase the capacity of the plant. It also has the important advantage that the separator and heat exchanger can be located at any level in relation to the evaporator.

I claim:

1. In an evaporative refrigerator the provision between the condenser and the evaporator of a heat exchanger comprising a conduit having a heat-exchanging wall through which conduit the refrigerant passes on its way to the evaporator and a refrigerant space adjacent to said conduit, in combination with a pressure reducing expansion valve between the condenser and the conduit of the heat exchanger and a second pressure reducing valve between the conduit of the heat exchanger and the evaporator and means to return the spent refrigerant from the evaporator to the refrigerant space of the heat exchanger so as to extract heat from the refrigerant passing through the heat exchanger to the evaporator.

2. In an evaporative refrigerator the provision between the condenser and the evaporator of a heat exchanger comprising a conduit having a heat-exchanging wall through which conduit lthe refrigerant passes o n its way to the evaporator and a refrigerant space adjacent to said conduit, in combination with a pressure reducing floatoperated expansion valve between the condenser and the conduit of the heat exchanger and a second pressure reducing valve between the conduit of the heat exchanger and the evaporator and means to return the spent refrigerant from the evaporator to the refrigerant space of the heat exchanger so as to extract heat from the refrigerant passing through the heat exchanger to the evaporator.

- 3. Apparatus as claimed in claim 1 wherein the heat exchanger takes the form of a separating vessel having an inlet for a mixture of liquid and gases from Ithe evaporator, an outlet in the upper part to the compressor and a heat exchange element in the lower part through which the refrigerant passes from the condenser to the evaporator, said heat exchange element being so located as to be in contact with liquid refrigerant which separates from gases in the separator.

4. Apparatus as claimed in claim 2 wherein the heat exchanger takes the form of a separating vessel having an inlet for a mixture of liquid and gases from the evaporator, an outlet in the upper part to the compressor and a heat exchange element in the lower part through which the refrigerant passes from the condenser to the evaporator, said heat exchange element being so located as to be in contact with liquid refrigerant which separates from gases in the separator.

5. In an evaporative refrigerator, the combination of a condenser, a pressure-reducing valve at the outlet yof the condenser such as to retain uncondensed gases and pass condensed liquid therefrom, a heat exchange vessel, a conduit passing through the lower part of the heat exchange vessel ,from the pressure reducing valve, a second pressure-reducing valve beyond the heat exchange vessel in the said conduit, an evaporator beyond the second pressure-reducing Valve, a connection from the return pipe of the evaporator to the heat exchanger so as to return unevaporated liquid refrigerant thereto, a compressor, a connection from the upper part of the heat exchange vessel to the compressor, and a connection from the compressor to the condenser.

6. An evaporative refrigerating system including a compressor, a condenser, a float-operated expansion valve, a heat exchange element.- a pressure-reducing valve, a separator vessel in the lower part of which said element is disposed and an evaporator, a conduit for the passage of liquid refrigerant from said condenser through said oat-operated expansion'valve to said heat exchange element, a conduit from said heat exchange element for the passage of liquid refrigerant from said element through said pressurereducing valve to said evaporator, saidpressurereducing valve being adapted to maintain a pressure in said element greater than the evaporator pressure but less than the condenser pressure, a conduit from said evaporator to aid separator for compressor for delivery of compressed gaseous 1U refrigerant to said condenser.

RICHARD JOHN CRACKNELL.

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