GB2029948A - Refrigeration apparatus with improved oil separation - Google Patents

Abstract

To improve the efficiency of oil separation in refrigeration apparatus having a compressor (1), a condenser (2,4), an evaporator (6) and an oil separator (3), the oil separator (3) is disposed downstream of a first condenser stage (2) and before a second condenser stage (4). <IMAGE>

Description

SPECIFICATION Refrigeration apparatus with improved oil separation The invention relates to a method of improving the efficiency of oil separation in refrigeration plants.

The invention is particularly applicable to refriger ation plants incorporating screw compressors which have quantities of oil injected to them in order to improve the efficiency of the sealing against vapour leakage within the compressor. A disadvantage associated with the injection of oil for sealing purposes is that very efficient oil separation methods are required in the discharge of the com pressor in order to prevent the carry over of unacceptable quantities of oil into the rest of the refrigeration system where it would impair the efficiency of heat transfer. The refrigerant evapor ator is particularly vulnerable to impairment of heat transfer because of unacceptable quantities of oil.

In conventional screw compressor refrigerating systems there is usualy provided a large and effi cient oil separator in the compressor discharge. The separated oil is returned to the compressor through an oil cooler which may be water cooled or cooled directly by refrigerant. Significant quantities of heat relative to the refrigerating capacity may be re moved from the oil at this stage. In other screw compressor designs liquid refrigerant is injected at high pressure into the compressor discharge, thus cooling the oil by direct contact between evaporat ing refrigerant and hot oil.

It is an object of the present invention to provide a refrigeration apparatus with improved oil separation means.

The present invention provides a refrigeration apparatus having a compressor, a condenser, an evaporator and an oil separator characterised in that the oil separator is disposed downstream of a first condenser stage and before a second condenser stage.

Further, preferred, details of the invention will appear from the following description of one embo diment of a refrigeration apparatus according to the present invention illustrated with reference to the accompanying schematic drawing.

The apparatus comprises a screw compressor 1 which is followed in the downstream direction of refrigerant fluid circulation by a first condenser stage 2, an oil separator 3, a second condenser stage 4, an expansion valve 5 and an evaporator 6.

Some specific and latent heat is removed from the mixture of oil and refrigerant in the first condenser stage condenser 2. Within this stage, there is considerable condensation of oil vapour on the cold condensing surfaces. The resulting mixture of re frigerant vapour and oil is then passed from the first stage condenser 2 to an oil separator 3 whose I efficiency is considerably increased compared to the efficiency of a separator place immediately down stream of the compressor discharge before the condenser, for various reasons. Firstly the specific volume of the refrigerant oil mixture is considerably reduced due to the lowering of the temperature of the mixture and some condensation of refrigant.

Secondly, the oil will be more readily separated because a significant proportion of it will have coalesced on the cold surfaces within the first stage condenser. As a result of this the oil separator can be made significantly smallerthan one used in conventional refrigeration apparatus in which the separator is placed immediately downstrean at the compressor discharge.

The oil collected in the separator 3 is normally returned to the screw compressor 1 through an oil return line 7. Any small quantities of condensed refrigerant which are returned with the oil to the compresor 1 do not affect the pumping capacity of the compressor 1 because they are returned to the compression space after compression has begun.

These small quantities of refrigerant may evaporate within the compressor 1 and the oil to some extent and provide additional cooling to the compressor 1.

The substantially oil-free refrigerant issuing from the oil separator 3 is fed into a second stage condenser 4 where it is substantially condensed to high pressure liquid refrigerant which may then be fed to the evaporator 6 through the expansion valve 5 in conventional manner. Within the evaporator 6 the refrigerant extracts heat by vaporisation thereof providing cooling in conventional manner and is then returned to the inlet side of the compressor 1.

1. A refrigeration apparatus having a compressor, a condenser, an evaporator and an oil separator characterised in that the oil separator is disposed downstream of a first condenser stage and before a second condenser stage.

2. A refrigeration apparatus as claimed in claim 1 wherein is provided an oil return line extending from the separator to the compressor.

3. A refrigeration apparatus according to claim 1 substantially as described hereinbefore with particular reference to the accompanying drawing.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (3)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Refrigeration apparatus with improved oil separation The invention relates to a method of improving the efficiency of oil separation in refrigeration plants. The invention is particularly applicable to refriger ation plants incorporating screw compressors which have quantities of oil injected to them in order to improve the efficiency of the sealing against vapour leakage within the compressor. A disadvantage associated with the injection of oil for sealing purposes is that very efficient oil separation methods are required in the discharge of the com pressor in order to prevent the carry over of unacceptable quantities of oil into the rest of the refrigeration system where it would impair the efficiency of heat transfer. The refrigerant evapor ator is particularly vulnerable to impairment of heat transfer because of unacceptable quantities of oil. In conventional screw compressor refrigerating systems there is usualy provided a large and effi cient oil separator in the compressor discharge. The separated oil is returned to the compressor through an oil cooler which may be water cooled or cooled directly by refrigerant. Significant quantities of heat relative to the refrigerating capacity may be re moved from the oil at this stage. In other screw compressor designs liquid refrigerant is injected at high pressure into the compressor discharge, thus cooling the oil by direct contact between evaporat ing refrigerant and hot oil. It is an object of the present invention to provide a refrigeration apparatus with improved oil separation means. The present invention provides a refrigeration apparatus having a compressor, a condenser, an evaporator and an oil separator characterised in that the oil separator is disposed downstream of a first condenser stage and before a second condenser stage. Further, preferred, details of the invention will appear from the following description of one embo diment of a refrigeration apparatus according to the present invention illustrated with reference to the accompanying schematic drawing. The apparatus comprises a screw compressor 1 which is followed in the downstream direction of refrigerant fluid circulation by a first condenser stage 2, an oil separator 3, a second condenser stage 4, an expansion valve 5 and an evaporator 6. Some specific and latent heat is removed from the mixture of oil and refrigerant in the first condenser stage condenser 2. Within this stage, there is considerable condensation of oil vapour on the cold condensing surfaces. The resulting mixture of re frigerant vapour and oil is then passed from the first stage condenser 2 to an oil separator 3 whose I efficiency is considerably increased compared to the efficiency of a separator place immediately down stream of the compressor discharge before the condenser, for various reasons. Firstly the specific volume of the refrigerant oil mixture is considerably reduced due to the lowering of the temperature of the mixture and some condensation of refrigant. Secondly, the oil will be more readily separated because a significant proportion of it will have coalesced on the cold surfaces within the first stage condenser. As a result of this the oil separator can be made significantly smallerthan one used in conventional refrigeration apparatus in which the separator is placed immediately downstrean at the compressor discharge. The oil collected in the separator 3 is normally returned to the screw compressor 1 through an oil return line 7. Any small quantities of condensed refrigerant which are returned with the oil to the compresor 1 do not affect the pumping capacity of the compressor 1 because they are returned to the compression space after compression has begun. These small quantities of refrigerant may evaporate within the compressor 1 and the oil to some extent and provide additional cooling to the compressor 1. The substantially oil-free refrigerant issuing from the oil separator 3 is fed into a second stage condenser 4 where it is substantially condensed to high pressure liquid refrigerant which may then be fed to the evaporator 6 through the expansion valve 5 in conventional manner. Within the evaporator 6 the refrigerant extracts heat by vaporisation thereof providing cooling in conventional manner and is then returned to the inlet side of the compressor 1. CLAIMS

1. A refrigeration apparatus having a compressor, a condenser, an evaporator and an oil separator characterised in that the oil separator is disposed downstream of a first condenser stage and before a second condenser stage.

2. A refrigeration apparatus as claimed in claim 1 wherein is provided an oil return line extending from the separator to the compressor.

3. A refrigeration apparatus according to claim 1 substantially as described hereinbefore with particular reference to the accompanying drawing.