Rotary expansible chamber devices – Heat exchange or non-working fluid lubricating or sealing – Non-working fluid passage in inner working or reacting member
Patent
1997-12-15
1999-07-20
Thorpe, Timothy S.
Rotary expansible chamber devices
Heat exchange or non-working fluid lubricating or sealing
Non-working fluid passage in inner working or reacting member
4182011, F04C 2904
Patent
active
059248556
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
In screw-spindle compressors, as disclosed by EP-A 472933, the pressure difference attainable depends to a considerable extent on the leakage losses between the peripheral surfaces, moving relative to one another, of the rotors and the pump-chamber housing. In view of this, the aim will be to keep the clearance between these surfaces as small as possible. However, the operating safety, with due regard to the temperature-induced thermal expansion of the rotors, requires greater clearance.
It is known to directly cool rotors of twin-shaft compressors (EP-A 290664) by a heat-transfer medium (lubricating oil) being provided in a bearing hollow space of the rotor, which heat-transfer medium is cooled by a stationary cooling coil projecting into the bearing hollow space. This has the disadvantage that the bearing hollow space of the rotor has to be sealed off. However, the seals required for this are trouble-prone, in particular at a high number of revolutions. High losses which lead to the generation of heat and jeopardize the cooling effect also arise in the heat-transfer medium, which is swirled between the rotating rotor and the stationary cooling coil.
It is conventional practice to cool the delivered medium by liquid coolant, for example, being injected (U.S. Pat. No. 4,515,540) or by some of the delivered medium being fed back after cooling (DE-A 25 44 082). Such cooling may also be provided in combination with the invention; however, the aim of the invention is to cool the rotor so that the rotor, in particular in the area of the sensitive bearings, can assume a temperature which is below the pressure-side temperature of the delivered medium.
SUMMARY OF THE INVENTION
The object of the invention is therefore to create a screw-spindle compressor of the type described, in which the rotors are cooled independently of the delivered medium in such a way that good preconditions for a small clearance between the rotors themselves as well as between the rotors and the pump-chamber housing are created without requiring trouble-prone seals.
The solution according to the invention is composed of two components, namely firstly the feature that the displacement rotors are cooled to a greater extent on the pressure side than on the suction side and secondly a cooling technique utilizing the special type of construction of the rotor bearing arrangement.
The idea of cooling the rotors to a greater extent on the pressure side than on the suction side is based on the fact that, in these machines, most of the compression heat arises in the pockets located closer to the pressure side and enclosed by the rotors and the pump-chamber housing, since, as a result of the leakage losses and possibly also the preadmission at possibly the same volume, they contain a greater gas mass than the pockets closer to the suction side. If the heat is preferably dissipated from the rotor area close to the pressure side, constant diameter ratios of the rotors over their entire length will be achieved more easily than if the rotors are cooled over their entire length. Here, multi-stage rotors mean those whose screw turns forming the compression pockets orbit the rotor several times, so that a plurality of compression pockets separated from one another in each case on the suction and pressure side are formed over the rotor length. In a three-stage arrangement, the screw turns orbit the associated rotor three times in each case. The stage number may be established in accordance with the respective range of pressure application. At least five stages are preferably used.
For the cooling, the invention uses a special technique adapted to the type of construction. This type of construction requires each displacement rotor to be mounted in a floating manner on a stationary bearing tube surrounding the rotor shaft and at least one rotor-side bearing and projecting into the rotor. Only the bearing tube is directly cooled, while the cooling of the rotor takes place indirectly by the peripheral surfaces, opposite one another
REFERENCES:
patent: 3289600 (1966-12-01), Whitfield
patent: 3795117 (1974-03-01), Moody, Jr. et al.
patent: 4515540 (1985-05-01), Pillis
patent: 4917583 (1990-04-01), Frings et al.
patent: 5269667 (1993-12-01), Mauney
patent: 5295798 (1994-03-01), Maruyama et al.
Dahmlos Christian
Rook Dietmar
Steffens Ralf
Gartenberg Ehud
SIHI Industry Consult GmbH
Thorpe Timothy S.
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