US 2888809 A
Description (OCR text may contain errors)
J1me 1959 s. J. RACHFAL GAS COMPRESSION APPARATUS Filed Jan. 27, 1955 INVENTOR.
STANLEY J. RACH FAL GAS COMPRESSION APPARATUS Stanley J. Rachfal, Syracuse, N.Y., assignor to Carrier Corporation, Syracuse, N.Y., a corporation of Delaware Application January 27, 1955, Serial No. 484,416
2 Claims. (Cl. 62-196) One particular application of such a machine is in a mechanical refrigeration system where the gaseous refrigerant passing from the evaporator is compressed and forwarded to the condenser.
In refrigeration systems of the kind under consideration a volatile refrigerant is circulated through a circuit including a centrifugal compressor and a discharge line permitting flow of compressed Vaporous refrigerant to a condenser where the refrigerant is changed to the liquid phase as heat is extacted therefrom by an exchange of heat between the Vaporous refrigerant and a cooling medium. A liquid line, provided with valve means for allowing passage of liquid refrigerant from the relative high pressure side of the system to the low pressure side of the system in a predetermined sequence permits flow of liquid refrigerant to the evaporator where an exchange of heat occurs between the liquid refrigerant and a medium to be cooled. In this instance the liquid refrigerant absorbs heat from the medium so as to change its form to a vapor. The Vaporous refrigerant then flows to the compressor to complete the circuit.
Through the agency of the valve means and the compressor the system is maintained at different pressures such that the temperature of the mediums passed in heat exchange relation with the refrigerant is suflicient to cause the required change of state to occur.
During the operation of the system as described there may occur a reduction in the load on the evaporator. This manifests itself in a reduced volume of Vaporous refrigerant in the suction line. In order, however, for a constant speed centrifugal compressor to operate above the surge limit it is necessary that a minimum Volume of Vaporous refrigerant be continuously supplied to the inlet end of the compressor. It will be understood that the surge limit in this instance, defines that operating point of the compressor, below which unstable action occurs. In other words it is necessary, in order to achieve positive operation of the system in which the centrifugal compressor is a component, that the flow of refrigerant in the system be non-reversing or uni-directional in the desired manner. Accordingly, it is desirable that a volume of Vaporous refrigerant suflicient to prevent any reversal of flow be continuously supplied to the compressor.
It is therefore, an object of this invention to provide an arrangement for assuring the flow through the compressor of a volume of gas sufficient to prevent unstable operation of the refrigeration system. In achieving this object a bypass line, having a valve therein, connected 2,888,809 Patented June 2, 1959 between the condenser and the suction line, is provided.
Another object of the invention involves the provision of a control for the valve in the bypass line that will reflect a condition necessitating an increased volume of Vaporous refrigerant at the entrance to the compressor.
Other objects and advantages of the invention will be apparent upon a consideration of the ensuing specification and drawings in which:
The figure of the drawing is a diagrammatic view of a centrifugal refrigeration system using a control scheme illustrating the invention. As shown, the system is shutdown and the suction damper closed.
Referring more particularly to the drawing, for an illustration of one use of the invention, 10 represents a conventional centrifugal compressor of the type widely used in refrigeration systems. The compressor 10 is mechanically connected through its power shaft and a coupling to a constant speed motor 11. Vaporous refrigerant compressed in the compressor passes through discharge line 12 to a condenser 13 including coil 16' where it is converted to a liquid as heat is extracted therefrom by a cooling agent flowing in coil 13. Float valve 14 permits passage of liquid from the condenser to the liquid line 14. Economizer 15 equipped with a float valve 15' operates to permit passage of liquid refrigerant to line 16 leading to the evaporator or cooler 17. Thus it will be apparent that liquid flows from the higher pressure in the condenser to the lower pressure in the evaporator through the two float valves. The liquid refrigerant in the evaporator is passed in heat exchange relation with a medium such as water, for example, flowing in the coil 18. The water may be used as a cooling medium in an air conditioning system. As heat from the entering Water is transferred to the cooler liquid refrigerant, the latter changes state and flows as vapor to the compressor. Any vapor formed in the economizer due to a flashing action as the liquid passes to a zone of lower pressure flows back to a stage of the compressor through line 40.
A suction damper 36) having an actuating motor 31 operable in response to the temperature of the chilled water leaving the cooler coil is shown placed in line 20. Bulb 32, containing a thermal responsive fill may be used to regulate operation of the damper motor in any known manner.
The invention herein contemplated comprises modifying the basic cycle as described above to the extent that a volume of Vaporous refrigerant suflicient to prevent a reversal of refrigerant flow in the system is always available at the inlet to the compressor. Accordingly, a line 21 connecting the condenser and the suction line is provided. A valve 22 responsive to a predetermined temperature rise of the Vaporous refrigerant or gas as it passes through the compressor permits passage of vaporous refrigerant to the suction line to supplement a reduced volume of gas as occasioned by a reduction in the load on the cooler.
Line 21 has a restriction in the form of a plate 33 having an opening therein for causing a pressure drop in the gas flowing from the condenser to the suction line. Line 34 permits flow of liquid refrigerant from the condenser to the line 21, downstream from the restriction. The liquid refrigerant flashes off as it enters the zone of lower pressure creating a cooling effect. Thus, it will be noted that restriction 33 and line 34 lower the pressure and temperature of the gas in the bypass line to substantially the pressure and temperature in the suction line.
It has been found that in the case of a centrifugal compressor operating at constant speed that the volume of gas necessary to prevent operation in the unstable range is related to the change in the temperature of the gas as it passes through the compressor. For illustration as the load on the cooler, as represented by the amount of heat necessary to be extracted from the water to achieve a desired temperature of water leaving coil 20 varies, the volume of gas generated by the exchange of heat will also vary. The head developed by the compressor when divided by the efiiciency will provide the input of energy per pound of refrigerant gas. This valve is proportional to the enthalpy rise across the compressor which in turn, is directly related to the temperature rise of the gas across the compressor. It has been found that the head increases with a decrease in volume of gas handled, therefore, in view of the facts mentioned above, the temperature difference across the compressor will increase. The control scheme described above will sense the condition and supplement the volume in the suction line by causing the valve in the bypass line to open.
Thus it is evident that an arrangement for preventing a reduction in the volume of gas or vaporous refrigerant of a magnitude sufficient to cause reversal of refrigerant flow Within the system is provided.
While I have described my invention as it pertains to the problem of surge protection in a refrigeration system utilizing a centrifugal compressor it will be apparent that the invention may be used in other applications involving turbo compressors wherev it is necessary to maintain constant volume load. For illustration in the operation of an air blast furnace, a damper for throttling air feed may be controlled through an arrangement responsive to the temperature rise of the gas as it passes through the compressor.
Other constructions and arrangements designed to measure the temperature rise under consideration and relay this information to the control apparatus involved will suggest themselves to those skilled in the art without departure from the spirit or scope of the invention as defined in the appended claims.
1. A refrigeration machine comprising a centrifugal compressor, a constant speed motor operating the centrifugal compressor, a condenser, a discharge line connecting the compressor and the condenser, for transmitting compressed gaseous refrigerant to the condenser, an evaporefer, a suction line connecting the evaporator and the compressor for supplying gaseous refrigerant formed in the evaporator to the compressor, a conduit connecting the discharge line with the suction line for the purpose of releasing gas pressure in the discharge line while increasing gas pressure in the suction line when the load on the machine is reduced to the extent that the gas pressure developed by the compressor is insufficient to overcome the pressure in the discharge line and resist reverse flow of gaseous refrigerant through the compressor, a valve controlling flow of refrigerant through the conduit, and control means responsive to a predetermined difference in the temperature of the gas at the inlet and at the outlet of the compressor for regulating the operation of the valve.
2. The invention set forth in claim 1 including a line connecting the condenser with the conduit for conducting liquid refrigerant into the line for the purpose of cooling the gaseous refrigerant flowing in the line.
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