Rotary expansible chamber devices – Heat exchange or non-working fluid lubricating or sealing – Non-working and working fluids intermix in working chamber
Patent
1990-06-05
1991-08-06
Vrablik, John J.
Rotary expansible chamber devices
Heat exchange or non-working fluid lubricating or sealing
Non-working and working fluids intermix in working chamber
4182011, F04C 1816, F04C 2902
Patent
active
050372823
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a rotary screw compressor for a gaseous working fluid comprising a male rotor and a female rotor mounted in a causing composed of a high pressure end section, a low pressure end section and a barrel section extending therebetween, said casing forming a working spaced generally in the shape of two intersecting parallel bores surrounded by barrel and end walls, each of said rotors having helical lobes and intermediate grooves through which the rotors intermesh forming chevron-shaped compression chambers in said working space, each of said bores housing one of said rotors, said casing being provided with an inlet port and an outlet port, each of said rotors being provided with shaft extensions mounted in bearings in said end sections and extending into first chambers in the low pressure end section and into second chambers in the high pressure end section, said low pressure end section having means for supply of liquid to aid first chambers and said high pressure end section having means for supply of liquid to said second chambers.
In compressors of this type the liquid, e.g. oil, supplied to the chambers in the end sections for bearing lubrication and other purposes usually has been drained to the low pressure channel of the compressor, as shown for instance in U.S. Pat. No. 3,314,597.
As the oil drained from the chambers in the end sections circulates within the compressor plant and gets a maximum temperature corresponding to the temperature of the working fluid in the high pressure channel, it has to be cooled down before recirculation into the compressor. However, owing to the temperature of the available cooling fluid and the practically possible size of the cooler, the oil introduced into the compressor will have a considerably higher temperature than the temperature of the working fluid to be compressed. The contact between the working fluid and the oil of the higher temperature during the inflow phase result in a healthy of the working fluid and thus is a decrease of the volumetric efficiency. There is also a considerable power required for the inflow of the oil from the low pressure channel through the low pressure port into the working space. Furthermore, a certain amount of the oil flows through the bore of the male rotor and has to be accelerated to the high speed of the tips of the lobes thereof.
A special problem arises in compressorsm forming a part of a refrigeration cycle using a working fluid of the type being dissolvable to a considerable extent in the oil, such as fluids of the type normally referred to as Freon, and commercially known for instance as R-12 and R-22. The oil supplied to the chambers in the end sections for bearing lubrication, shaft sealing, thrust balancing and similar purposes, normally has a pressure exceeding the presence in the high pressure channel of the compressor and the amount of working fluid dissolved therein is considerable. When the chambers are drained to the low pressure channel most of the working fluid is evaporated out of the oil as the solubility decreases with decreasing pressure. The amount of working fluid in this way supplied to the low pressure channel is so large that it will need a very considerable portion of the displacement volume of the compressor. The same amount of working fluid is during the compression dissolve in the oil. Owing to this fact the amount of working fluid passing through the compressor and circulating within the complete cycle will be mush less than the nominal capacity of the compressor or in other words thee volumetric efficiency of the compressor will be low.
All of the factors mentioned above will be more accentuated the smaller the dimensions of the compressr are as the amount of oil supplied to the chambers in the end sections cannot be reduced in the same proportion as the reduction of the amount of working fluid passing through the compressor.
U.S. Pat. No. 3,462,072 discloses a rotary screw compressor in which the above described problems are avoided in t
REFERENCES:
patent: 3314597 (1987-04-01), Schibbye
patent: 3462072 (1969-08-01), Schibbye
patent: 4211522 (1980-07-01), Pidgeon
patent: 4758136 (1988-07-01), Pamlin et al.
Svenska Rotor Maskiner AB
Vrablik John J.
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