Lubrication system for screw compressors using an oil still

#In closed refrigeration and air conditioning systems, the refrigerant and lubricant are normally in contact. Because there is an affinity between lubricants and refrigerants, they are present in refrigeration and air conditioning systems as a mixture of varying composition. The composition will depend upon many factors such as the temperature, whether the system is running or not, whether oil is separated by flow through an oil separator or circuitous path, whether the refrigerant undergoes a phase change, etc. The lubricant in the refrigerant tends to coat the surfaces of the system and deteriorates the heat transfer properties of the system. The refrigerant not only dilutes the lubricant, but is subject to outgassing which results from a pressure reduction and produces a froth which can interfere with lubrication.

#A small heat exchanger is preferably located below the cooler or evaporator of a closed refrigeration or air conditioning system and defines an oil rich generator or still. Alternatively, the still may be located at a higher level but would require a pump, or the like. The oil rich generator takes mixed liquid made up of refrigerant and oil from the cooler. A portion of the relatively warm liquid from the condenser is diverted into the generator vessel. In flowing through the tubes in the generator vessel, heat is given up by the flow from the condenser causing the refrigerant in the generator vessel to boil. Alternatively, a supplemental heat source such as electric resistance heat may be used. The resulting refrigerant vapor is vented from the vessel and flows to the compressor suction due to the pressure differential between the compressor suction and the cooler. The boiling off of refrigerant results in an “oil rich” liquid. The oil rich liquid is supplied to the lubrication system via one, or more, ejectors which cause the oil rich liquid to be entrained in high pressure gas diverted from the compressor. The pressure driving the ejectors is, preferably, the higher of the discharge pressure or the last closed lobe rotor pressure.

#In passing through the generator, the refrigerant flow from the condenser is subcooled. This relatively high pressure, subcooled flow is supplied to the motor for cooling. In cooling the motor, the subcooled flow is heated and expanded and is subsequently supplied to the suction flow to the compressor.

#For a fuller understanding of the present invention, reference should now be made to the following detailed description thereof taken in conjunction with the accompanying drawings wherein:

#FIG. 1 is a schematic diagram of a closed refrigeration or air conditioning system employing the present invention;

#FIG. 2 is a more detailed schematic diagram of the FIG. 1 system;

#In FIG. 1, the numeral 10 generally designates a closed refrigeration or air conditioning system. As is conventional, there is a closed circuit serially including compressor 12, discharge line 14 connected to the discharge port, condenser 16, line 18 which contains expansion device 20, cooler or evaporator 22 and suction line 24 leading to the suction port. Compressor 12 is a multi-rotor, hermetic, screw compressor and is driven by electric motor 26 which is connected to a source of electric power (not illustrated). As is best shown in FIGS. 2 and 5, screw compressor 12 has a plurality of intermeshing rotors with three rotors 121, 131 and 141 being illustrated. Referring specifically to FIG. 3, rotor 121 has end shafts 1211 and 121-2 and an axial bore 121-3 extending the full length of rotor 121 and shafts 121-1 and 121-2. End shafts 121-1 and 121-2 are connected to rotor 121 through intermediate shafts 121-1a and 121-2a, respectively. Intermediate shafts 121-1a and 121-2a are in a tight clearance relationship with labyrinth seals 122 and 123. Labyrinth seal 122 seals rotor bore 12-1 from bearing chamber 12-2. Similarly, labyrinth seal 123 seals rotor bore 12-1 from bearing chamber 12-3. Shaft 121-1 is supported in bearing chamber 12-2 by a plurality of bearings 124-1, 124-2 and 124-3. Similarly, shaft 121-2 is supported in bearing chamber 12-3 by bearing 125-1.

#Rotor 121, as illustrated in FIG. 3, and described above, is representative of rotors 131 and 141 relative to bearing support and lubrication. The only differences would be that there are both male and female rotors and that one rotor would be driven by motor 26 and would, in turn, drive the other rotors. In gears the driving gear is the “sun” and the driven gears are the “planets”. The rotors can be driven through gears rather than directly through the rotors.

#Referring again to FIG. 1, according to the teachings of the present invention, a portion of the relatively warm liquid in condenser 16 passes via line 30 to generator vessel or still 32. Preferably, generator vessel or still 32 is located below or at a lower level than cooler 22. If necessary, or desirable, generator vessel or still 32 can be located at a higher level but would require pumping to supply the still. The liquid from condenser 16 supplied via line 30 passes through a plurality of tubes 34 in a heat exchange relationship with the refrigerant-oil mixed liquid which flows into generator vessel 32 from cooler 22 via line 36. After passing through the tubes 34, the flow is supplied via line 35 to motor 26 for cooling motor 26 and subsequently combines with the suction gas supplied via line 24. The diverted flow from the condenser 16 gives off heat to the refrigerant-oil mixture in generator 32 causing the refrigerant to boil while the flow from the condenser 16 is cooled. The vapor resulting from the boiling of refrigerant is vented out of generator vessel 32 via line 38 which connects to the compressor suction line 24 and flows into the compressor suction due to the pressure differential between the compressor suction and cooler 22.