Two-stage centrifugal compressor

Details Two-stage centrifugal compressor Two-stage centrifugal compressor

2000-11-14

2002-04-23

Walberg, Teresa (Department: 3742)

Pumps

Motor driven

Including means utilizing pump fluid for augmenting cooling,...

C415S111000

Reexamination Certificate

active

06375438

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates, in general, to a two-stage centrifugal compressor used in refrigeration cycles and, more particularly, to an improvement in such a compressor to allow the electric motor to be cooled by refrigerant of a refrigeration cycle without having another external motor cooler, thus simplifying the refrigerant line of the refrigeration cycle thereby resulting in an improvement in both the operational performance and operational efficiency of the cycle.
2. Background Art
As well known to those skilled in the art, two-stage centrifugal compressors have been typically used in large-scaled refrigeration systems. However, it is necessary in recent days to actively study such a type of compressors to reduce the size of them since it is desired to use them with indoor air conditioners for houses or automobiles.
Conventional two-stage centrifugal compressors for refrigeration systems are composed of an electric motor set at the central portion within a motor housing, with the motor consisting of a rotor and a stator. An impeller having a plurality of blades is set on both ends of a rotating shaft of said rotor. First and second compression parts are provided to the opposite ends of the motor housing. In an operation of a refrigeration system, refrigerant circulates through a main refrigerant line of the system and is compressed at the first and the second compression parts by said impellers of the compressor. The compressed refrigerant from the compression parts passes through the main refrigerant line while absorbing heat from the electric motor and cooling the motor.
In the operation of the refrigeration system, the two-stage centrifugal compressor receives refrigerant from an evaporator and primarily compresses the refrigerant at the first compression part, and secondarily compresses the primarily compressed refrigerant at the second compression part, and so the refrigerant becomes highly heated and highly pressurized gas refrigerant. The gas refrigerant having high temperature and high pressure is fed from the compressor to a condenser. In order to suck refrigerant from the evaporator and to compress the refrigerant, and to circulate the pressurized refrigerant in the refrigeration system during a refrigeration cycle, it is necessary to rotate the electric motor at a high speed. Due to such a high speed rotating motion of the motor, much heat is generated from both the motor and its bearing parts and deteriorates the operational performance of the compressor in addition to a reduction in operational reliability of the compressor.
Therefore, it is necessary to appropriately and effectively cool the motor and the bearing parts. In an effort to accomplish the above object, the construction of both a motor cooling system and a refrigerant line of a two-stage centrifugal compressor has been actively studied. As a result of such active studies, several techniques for cooling the motor and the bearing parts of such a two-stage centrifugal compressor have been proposed as follows.
In a conventional two-stage centrifugal compressor of
FIG. 1
a,
gas refrigerant is sucked from an evaporator into the compressor C through a first refrigerant line L
1
. In such a case, the refrigerant is primarily compressed at the first compression part C
1
. The refrigerant is, thereafter, fed into the second compression part C
2
of the compressor C through an external refrigerant line L
2
so as to be secondarily compressed at that compression part C
2
, and so the refrigerant becomes highly heated and highly pressurized gas refrigerant. The gas refrigerant, having a high temperature and a high pressure, is fed from the compressor C into a condenser. In the above compressor C, a motor cooling cycle is separately provided in the fixed jacket M
j
of the electric motor M. In the motor cooling cycle provided in the jacket M
j
, refrigerant from the compressor C circulates through another refrigerant line L
3
under the control of a separate cooling unit Cu, thus cooling the motor M.
FIG. 1
b
shows a refrigerant cycle diagram of a conventional two-stage centrifugal compressor according to another embodiment of the prior art. In this compressor C, gas refrigerant is sucked from an evaporator into the compressor C through a first refrigerant line L
1
. The refrigerant is thus primarily compressed at the first compression part C
1
of the compressor C and is secondarily compressed at the second compression part C
2
prior to being fed into a condenser in the same manner as that described for the embodiment of
FIG. 1
a
. The condenser condenses the refrigerant so as to convert the phase of the refrigerant from a gas phase into a liquid phase prior to feeding the refrigerant to an evaporator. In this compressor C, a part of the condensed refrigerant is sucked into and flows in the fixed jacket M
j
of the electric motor M. The liquid refrigerant is evaporated while flowing in the jacket M
j
and is joined to an external refrigerant line L
4
prior to being sucked into the second compression part C
2
of the compressor C. At the second compression part C
2
of the compressor C, the gas refrigerant from the jacket M
j
is compressed to become a highly pressurized refrigerant.
FIG. 1
c
shows a refrigerant cycle diagram of a conventional two-stage centrifugal compressor according to a further embodiment of the prior art. In this compressor C, gas refrigerant is sucked from an evaporator into the compressor C through a first refrigerant line L
1
and flows in the interior of the compressor C while cooling the electric motor M. The refrigerant is, thereafter, sucked into the first compression part C
1
of the compressor C through an external refrigerant line L
2
, thus being primarily compressed at that compression part C
1
The refrigerant is sucked from the first compression part C
1
into the second compression part C
2
of the compressor C through the external refrigerant line L
2
, thus being secondarily compressed at that compression part C
2
prior to being fed into a condenser.
FIG. 1
d
shows a refrigerant cycle diagram of a conventional two-stage centrifugal compressor according to still another embodiment of the prior art. In the embodiment of
FIG. 1
d
, gas refrigerant is sucked from an evaporator into the compressor C through a first refrigerant line L
1
, and is primarily compressed at the first compression part C
1
of the compressor C. The refrigerant is, thereafter, fed into the second compression part C
2
of the compressor C through an external refrigerant line L
2
so as to be secondarily compressed at that compression part C
2
, and so the refrigerant becomes highly heated and highly pressurized gas refrigerant. The gas refrigerant, having a high temperature and a high pressure, is fed from the compressor C into a condenser. In the above compressor C, another refrigerant line L
5
extends through the interior of the compressor C prior to being joined to the external refrigerant line L
2
. Gas refrigerant, which is separated from liquid refrigerant at a vapor liquid separator of a refrigeration cycle, flows into the compressor C through the refrigerant line L
5
. On the other hand, an additional refrigerant line L
4
extends through the fixed jacket M
j
of the electric motor M prior to being joined to the external refrigerant line L
2
. The condensed liquid refrigerant from the condenser flows through the refrigerant line L
4
.
FIG. 1
e
shows a refrigerant cycle diagram of a conventional two-stage centrifugal compressor according to still another embodiment of the prior art. In the embodiment of
FIG. 1
e
, gas refrigerant is sucked from an evaporator into the first compression part C
1
of the compressor C through a first refrigerant line L
1
, and is primarily compressed at that compression part C
1
. The refrigerant, thereafter, flows through an external refrigerant line L
2
so as to pass through the interior of the compressor C while cooling the electric motor. The refrigerant is, thereafter, fed into the second co

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