US 3315481 A
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April 25, 1967 D. R. CHECK ETAL 5,
APPARATUS AND METHOD FOR CONTROLLING REFRIGERANT FLOW IN A REFRIGERATION MACHINE Filed Feb. 16, 1966 20 FIG. 2
OOOOOOO O OOOOOOOOOOO OOOOOOOOOOOOO OOOOOOOOOOO FIG! INVENTORS. DONALD R. CHECK. WILLIAM E. CLARK.
United States Patent 3,315,481 APPARATUS AND METHOD FOR CONTROLLING REFRIGERANT FLOW IN A REFRIGERATION MACHINE Donald R. Check, Minneapolis, Minn., and William E.
Clark, Syracuse, N.Y., assignors to Carrier Corporafion, Syracuse, N.Y., a corporation of Delaware Filed Feb. 16, 1966, Ser. No. 527,86 9 Claims. (Cl. 62-115) This invention relates broadly to a refrigeration machine. More particularly, this invention relates to the control of refrigerant flow in a refrigeration machine. Still more particularly, this invention relates to a liquid refrigerant metering device particularly equipped to provide a minimum head within the refrigeration machine under abnormal conditions and in addition, provide for passage of a mixture of liquid and gaseous refrigerant to the evaporator of a refrigeration machine at low load conditions to improve the efficiency of the evaporator.
In high tonnage refrigeration machines, a compressor is arranged to extract gaseous refrigerant from an evaporator and pump the compressed refrigerant to a condenser where the refrigerant is cooled and condensed. In communication with the condenser, there is normally provided a receiver for collecting liquid refrigerant formed in the condenser prior to its passage to the evaporator. The receiver usually contains refrigerant both in the liquid and gaseous phases. In some machines, a portion of the liquid refrigerant is utilized to cool the motor dn'ving the refrigerant compressor. To insure suflicient refrigerant flow to the motor being cooled, a minimum refrigerant pressure differential between the receiver and motor casing is required.
To maintain a liquid seal in the receiver, a metering device is employed to regulate refrigerant flow from the condenser to the evaporator.
Under normal operating conditions, the level of the liquid refrigerant collected in the receiver is a function of the pressure difference between the high pressure side of the machine and the low pressure side of the machine and the load on the machine, it being understood the condenser is disposed in the high pressure side and the evaporator in the low pressure side of the machine. Refrigerant flow from the condenser to the evaporator occurs in an amount related to the loading on the machine and automatic controls such as suction guide vanes are provided for the purpose of maintaining flow rates corresponding to machine loading. Refrigerant metering devices are designed to pass a predetermined amount of refrigerant in accordance with the level of liquid refrigerant collected to maintain a liquid seal in the receiver.
The liquid from the receiver is passed through the metering device to the evaporator. The evaporator contains a multiplicity of tubes usually referred to as a tube bundle through which the medium to be cooled is passed in heat transfer relation with the refrigerant in the evaporator. Under normal operating conditions, the heat supplied to the refrigerant from the medium being cooled is sufiicient to cause the liquid refrigerant in the evaporator to boil vigorously. The boiling refrigerant thus wets all the tubes in the evaporator, providing optimum heat transfer between the medium and the refrigerant. However, at low loads a relatively small quantity of heat is given off by the medium. The refrigerant, under these conditions, does not boil vigorously enough to wet all the tubes, causing the efliciency of the evaporator to decrease. Therefore, to maintain evaporator efliciency at low load, the liquid refrigerant therein must be agitated. To accomplish this, a part of the high pressure gaseous refrigerant from the condenser is passed through the liquid in the evaporator.
Under abnormal conditions, such as start up, there is usually insufiicient pressure on the system to force liquid refrigerant to the refrigerant compressor motor. It is, therefore, desirable to provide a rapid build up of pressure in the high pressure side (receiver) when the machine is started and to maintain a minimum pressure difference in the machine under abnormal conditions.
The chief object of this invention is to provide an improved refrigerant flow control device. It is an additional object of this invention to provide a refrigerant control device which will maintain a constant level of liquid refrigerant in the receiver under normal operating conditions. A further object of this invention is to provide a control for passing liquid and gaseous refrigerant to the evaporator to provide agitation of the liquid refrigerant therein under low load conditions. A still further object of this invention is to provide a refrigerant control device which will provide for rapid build up of pressure in the machine at start up and maintain a minimum pressure therein under abnormal operating conditions. Another object of this invention is to provide an improved method for controlling refrigerant flow in a refrigeration machine between the high pressure and the low pressure sides thereof.
These objects are attained by providing a spring loaded or weighted metering valve in the refrigerant line between the condenser and evaporator to regulate the refrigerant flow therethrough. The spring or weight is selected so as to prevent the metering valve from opening until the desired minimum pressure difference between the high pressure and low pressure sides of the machine has been attained, or stated another way, until a preselected minimum pressure is developed in the condenser and receiver. When the refrigeration machine is operating above this minimum pressure requirement, a pilot trap is operable to modulate the metering valve in response to liquid level in the receiver line to maintain a seal therein under changes encountered in normal operating conditions. A pilot trap control line valve is operable in response to machine characteristics indicative of low load conditions to reduce refrigerant flow to the pilot trap, reducing pressure therein which in turn opens the metering valve, allowing liquid and gaseous refrigerant to flow to the evaporator under low load conditions to provide agitation of the liquid-refrigerant collected in the evaporator.
Other objects and features of this invention will be apparent upon a consideration of the ensuing specification and drawing in which:
FIGURE 1 is a schematic view of a refrigeration machine incorporating the preferred embodiment of the refrigerant flow control mechanism forming the subject of this invention.
FIGURE 2 is a sectional view of the pilot trap utilized in the control mechanism of the invention showing the pilot trap closed.
Referring more particularly to the drawing there is shown a refrigeration machine 1 for cooling a large quantity of water such as may be employed in air conditioning installation. The machine 1 having a refrigerant motor-compressor 1' includes a shell 2 for housing the heat transfer units associated with the machine. The shell 2 has a partition 3 therein for separating the high pressure condenser section 4 from the low pressure evaporator section 5. Tube bundle 6 in evaporator section 5 is provided for passing the water to be chilled therethrough.
A refrigerant metering control mechanism 7 is provided to control refrigerant fiow through receiver line 8 from the condenser section 4 to the evaporator section 5.
7 sure in line 11 downstream Refrigerant metering valve 9 which is biased toward a closed position by minimum head spring 9 controls the flow of refrigerant through line 8. The pilot trap as- 'sembly 10, under normal operating conditions, maintains a constant refrigerant level in line 8 by varying the pressure on valve 9. The pilot trap assembly communicates with receiver line 8 through line ll which has an orifice 12 therein.
Motor cooling is accomplished by providing the motor compressor '1' withliquid refrigerant'from the receiver line 8 through motor refrigerant line 21. The refrigerant is then routed to the low pressure side of the refrigeration machine through return line 22;
Under low load conditions a pilot trap valve 13' operable in response to changes in pressure across a cooler refrigerant distribution means restricts flow of refrigerant through line 11 to override pilot trap assembly and allow metering valve 9 to pass liquid and gaseous refrigerant therethrough. This agitates the liquid refrigerant in-the evaporator 5 under low load conditions. A cooler distribution means of the kind contemplated is described in detail in United States Patent application Ser. No. 281,- 400 filed May 20, 1963, and assigned to the assignee of this application.
Considering the operation of this control system, at start up, spring 9' will maintain metering valve 9. closed until'sufficient pressure is built up in the high side of the refrigeration machine and applied via line 8 to the underside of valve 9 to override the spring force. When the machine has reached its normal operating range, cooler refrigerant distribution pressure drop is relatively constant. This pressure difierence which is communicated to pressure differential control 13 on pilot trap valve 13' through lines 14 and 15 maintains valve 13v open. Gaseous refrigerant flowing through line 11 into the pilot trap assembly 10 through poppet valve 16 collects under the bucket 17 causing it to rise in the chamber 18 which has liquid refrigerant therein. The bucket 17 pushes lever 19 upward, closing pilot trap orifice 20 communicating with the evaporator; As liquid level in line 8 rises in response to changes in operating conditions, liquid refrigerant will flow through line 11 into the gaseous refrigerant is .no longer provided under bucket 17, it will start to sink, opening pilot trap orifice 20. Since pilot trap orifice 20 is larger than orifice 12, presfrom orifice 12 will decrease opening metering valve 9 to a greater extent to pass sufficient refrigerant therethrough to lower the liquid level in line 8 below the junction of lines'11 and 8. Thus, a substantially constant liquid level and seal is maintained within the machine operating range.
Under low capacity conditions, distribution pressure drop decreases. This modulatespilot trap valve 13' to restrict flow of refrigerant through line 11 which causes valve 9 to open and pass liquid and gaseous refrigerant therethrough to agitate the collected liquid refrigerant in evaporator 5.
It is to be understood that the pilot trap valve 13 could be actuated manually or by a solenoid rather than pressure drop as described above as well as by any other combination of system operating characteristics indicative of low capacity conditions.
While we have described a preferred embodiment of our invention, it is to be understood that the invention is not limited thereto since it may be otherwise embodied within the scope of the following claims.
1. In a refrigeration machine having a high pressure side and a low pressure side and including a condenser in the high pressure side of the system forliquifying gaseous refrigerant and an evaporator in the low pressure side of the system receiving liquid refrigerant from the condenser, a refrigerant metering device for regulating flow of refrigerant from the condenser to the evaporator comprising:
pilot trap. Since means for actuating said meteringvalve in response to V the level of liquid refrigerant in the high pressure side of the refrigeration machine under normal operating conditions to maintain a liquid seal at said metering valve, and
means responsive to an machine indicative of low load conditions to hold said metering valve open irrespective of the liquid level in the high side of the machine to pass liquid and gaseous refrigerant to the low pressure side of the machine.
2. In a refrigeration machine having a high pressure side and a low pressure side and including a condenser in the high pressure side of the system for liquifying gase ous refrigerant and an evaporator in the low pressure side of the system receiving liquid refrigerant from the condenser, a refrigerant metering device for regulating flow of refrigerant from the condenser to the evaporator comprising:
a metering valve between the condenser and evaporator for metering the flow of refrigerant therethrough,
a pilot trap having an inlet communicating with the high pressure refrigerant from said condenser up stream from said metering valve and an outlet com municating with the low pressure side of the refrigeration system; and
a control line from said pilot trap communicating withsaid metering valve, the refrigerant pressure in said disposed between the high pressure 3 wherein said pilot trap valve is actuated by a pressure differential control responsive to cooler refrigerant distribution pressure drop.
. 5. A refrigerant metering device according 'to claim 2 further including:
biasing means operably associated with said metering valve to maintain said metering valve closed until v the desired minimum refrigerant pressure is built up in the machine.
6. A refrigerant metering device according to claim 5 wherein said biasing meansis a spring.
7. A refrigerant metering device according to claim 2 further including:
a pilot trap valve disposed between the high pressure side ofthe system and the pilot trap inlet operable in response to predetermined demand on the refrigerationmachine to regulate the flow of refrigerant to said pilottrap, and I biasing means operably associated with said metering valve to maintain said metering valve closed until the desired minimum refrigerant'pressure is built up in the machine.
8. A refrigerant metering further including:
a pilot trap valve disposed between the high pressure side of the system and the pilot trap inlet,
a pressure differential control, responsive to cooler refrigerant distribution pressure drop, operably associated with said pilot trap valve to regulate the floW of refrigerant to said pilot trap, and
device according toclaim 2 a spring operably associated with said metering valve to maintain said metering valve closed until the desired minimum refrigerant pressure is built up in the machine.
9. A method of controlling refrigerant flow in a refrigeration machine which consists in the steps of:
regulating the passage of liquid refrigerant from the operating characteristic of the.
inlet, to reguhigh pressure side of the machine to the low pressure References Cited by the Examiner side of the machine by a mechanism operable in re- UNITED STATES PATENTS sponse to the level of liquid refrigerant collected in the high pressure side of the machine, and 2,589,859 3/1952 Phlnlps 62 '174 overriding the action of said mechanism at a predeter- 5 2,715,317 8/1955 P 62 149 mined load on the machine so that a mixture of gase- 2,871,673 2/1959 Rlchards et 62509 ous and liquid refrigerant from the high pressure side 2,921,446 1/1960 Zuhnke 62 117 may pass to the low pressure side unimpeded by the v action of the mechanism. LLOYD L. KING, Primary Examiner.