Refrigeration – Processes – Lubricant handling
Patent
1986-11-12
1988-09-27
Wayner, William E.
Refrigeration
Processes
Lubricant handling
62471, F25B 4302
Patent
active
047732296
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a method for a refrigeration system for cooling, sealing and lubrication of the working chamber of a screw compressor forming a part of the system, which screw compressor together with a condenser, an expansion valve and an evaporator forms a circulation circuit, in which a refrigerant and a small amount of oil are circulating.
In a refrigeration system of this or a similar type, in which oil for lubrication of the compressor's working chamber can flow out into the circulation system via an oil separator situated on the compressor's high pressure side, the oil will sooner or later end up in the evaporator. Because the refrigerant evaporates from the liquid surface, an enrichment of the oil will occur in liquid form. This impairs the evaporators efficiency, partly through the shifting boiling point, partly through the impaired coefficient of heat transfer.
In practice this is handled today through different systems of oil returning, for example, pumping to a closed thread in a screw compressor. In an oil injected compressor, this flood must, however, not be so large that the compressor's discharge temperature begins to come close to the condensing temperature with the ensuing risk for condensation of the refrigerant in the oil separator and dilution of the oil.
The object of the invention is to completely or partly eliminate these drawbacks in a simple way. This has, according to the invention, been achieved in that the outlet of the compressor is connected directly to the inlet of the condenser for supplying the refrigerant and the total amount of oil from the compressor to the condenser. Refrigerant liquid containing oil with a pressure and temperature lower than the pressure and temperature of the refrigerant and oil in the condenser, preferably close to or the same pressure and temperature as in the evaporator, is supplied to the low pressure side of the compressor with such amounts per unit of time, that essentially all of the intended cooling and sealing is secured by means of the refrigerant liquid, the amount of oil present being restricted to a value which is required for proper lubrication of the rotors. A collection of refrigerant liquid containing oil takes place, preferably, in a pipe between the expansion valve and the evaporator, or from the evaporator, after which the refrigerant liquid and oil is transported to the compressor's low pressure side through a particular pipe, preferably to a thread with reduced pressure in relation to the inlet pressure, which can be achieved by delaying the opening of the thread towards the inlet.
The idea of the invention is consequently to have a thorough reduction of the oil flow passing through the compressor and also a thorough increase of the amount of refrigerant injected into the compressor.
By means of the reduced oil flood, the oil separator can be dispensed with and, consequently, a meaningfully lower discharge temperature can therefore be allowed. A larger amount of refrigerant liquid can therefore be injected in the compressor for sealing and temperature control. This liquid is undercooled in relation to the inlet temperature and can therefore be injected into the compressor's low pressure side without the risk of worsening of the volumeter.
The result of this is an improved efficiency because of better sealing and cooling than what is normally achieved during oil injection for the same goal. Besides a controlled low discharge temperature is achieved which gives a smaller difference in thermal deformation between inlet and outlet and even improved lifetime for the oil and refrigerant. An improved efficiency for the evaporator which counteracts the oil enrichment can even be achieved.
The invention is further clarified in the following with reference to the attached drawing, which schematically shows a refrigeration system, with which an example of the method according to the invention is applied.
The drawing shows a screw compressor 1 with inlet 2 and outlet 3 which later is directly connected to a condenser 4 which, toge
REFERENCES:
patent: 3150277 (1964-09-01), Chubb et al.
patent: 3931718 (1976-01-01), Haselden
patent: 4261180 (1981-04-01), Nozawa et al.
patent: 4375156 (1983-03-01), Shaw
Pamlin Roland
Sjoholm Lars
Svenska Rotor Maskiner AB
Wayner William E.
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