Plate heat transfer has the advantages of high heat transfer coefficient, compact structure, light weight, convenient installation, maintenance and combination. It has been widely used in recent decades and has become an indispensable equipment in heat transfer process. In the field of central air conditioning, it can be used as the evaporator and condenser of water-cooled chilled water refrigeration unit or as the evaporator of air-cooled chiller, which can effectively enhance heat transfer, reduce the size of refrigeration unit, improve the operating efficiency of the system, etc., and the application prospect is very broad. .
The heat transfer mechanism of the plate heat exchanger is complicated. This problem is particularly prominent for the plate evaporator with phase change heat. Therefore, there are few research reports on the use of plate heat exchangers as evaporators. A few universities such as Xi'an Jiaotong University have conducted preliminary research on the plate evaporator. So far, the evaporation heat transfer coefficient has not been determined by reliable methods. Several companies in Sweden and Germany have conducted a large number of experiments, but the actual test data is not published, and empirical data is used in the selection.
The refrigeration system is in partial load operation for most of the time. In order to save the running cost, the central air conditioning water system generally reduces the flow of cold water flowing through the evaporator by the frequency conversion adjustment of the bypass or the water pump, thereby causing the cold water flow rate and the plate type. The heat transfer performance of the evaporator changes. In this paper, the matching relationship between plate heat exchanger coefficient, refrigerant side heat transfer coefficient and water flow rate during partial load is studied. The relationship between flow velocity and heat transfer coefficient is obtained, which provides the correct selection of plate heat exchanger. A reference, which is of great significance to the variable frequency control of the water pump and the operation and energy saving of the entire air conditioning system.
1. Experimental method In order to effectively measure the heat transfer coefficient of the refrigerant side of the plate evaporator, the water-water heat transfer method is first used to measure the water side heat transfer coefficient, and then the refrigerant-water heat exchange method is used to measure the same water flow rate. The heat transfer coefficient of the lower refrigerant side and the total heat transfer coefficient, and the relationship between the two heat transfer coefficients and the water flow rate are obtained.
The specific method is: using the same flow rate to heat the hot water of about 50 ° C and the normal temperature water of about 30 ° C, adjust the water flow on both sides of the plate heat exchanger to make it reach a preset value, and make the flow on both sides the same. The water flow rates on both sides are equal. Since the temperature of the hot and cold water on both sides is not much different, the heat transfer coefficient of the water on both sides can be approximated. The total heat transfer amount can be calculated according to the temperature difference and flow rate of the water inlet and outlet, and the total heat transfer coefficient and the water at the flow rate can be calculated. The heat transfer coefficient of the side changes the flow rate of the water to obtain the heat transfer coefficient of the water side at different flow rates. Then, the plate heat exchanger is connected to the refrigeration system, and instead of the evaporator, the flow rate of the cold water is respectively set to a set of flow rates during water-water heat exchange, and the heat transfer coefficient can be obtained by the heat exchange amount on the water side, according to The water side heat transfer coefficient is used to obtain the refrigerant side heat transfer coefficient, and the relationship between the heat transfer coefficient, the refrigerant side heat transfer coefficient and the water flow rate is obtained.
The heat transfer mechanism of the plate heat exchanger is complicated. This problem is particularly prominent for the plate evaporator with phase change heat. Therefore, there are few research reports on the use of plate heat exchangers as evaporators. A few universities such as Xi'an Jiaotong University have conducted preliminary research on the plate evaporator. So far, the evaporation heat transfer coefficient has not been determined by reliable methods. Several companies in Sweden and Germany have conducted a large number of experiments, but the actual test data is not published, and empirical data is used in the selection.
The refrigeration system is in partial load operation for most of the time. In order to save the running cost, the central air conditioning water system generally reduces the flow of cold water flowing through the evaporator by the frequency conversion adjustment of the bypass or the water pump, thereby causing the cold water flow rate and the plate type. The heat transfer performance of the evaporator changes. In this paper, the matching relationship between plate heat exchanger coefficient, refrigerant side heat transfer coefficient and water flow rate during partial load is studied. The relationship between flow velocity and heat transfer coefficient is obtained, which provides the correct selection of plate heat exchanger. A reference, which is of great significance to the variable frequency control of the water pump and the operation and energy saving of the entire air conditioning system.
1. Experimental method In order to effectively measure the heat transfer coefficient of the refrigerant side of the plate evaporator, the water-water heat transfer method is first used to measure the water side heat transfer coefficient, and then the refrigerant-water heat exchange method is used to measure the same water flow rate. The heat transfer coefficient of the lower refrigerant side and the total heat transfer coefficient, and the relationship between the two heat transfer coefficients and the water flow rate are obtained.
The specific method is: using the same flow rate to heat the hot water of about 50 ° C and the normal temperature water of about 30 ° C, adjust the water flow on both sides of the plate heat exchanger to make it reach a preset value, and make the flow on both sides the same. The water flow rates on both sides are equal. Since the temperature of the hot and cold water on both sides is not much different, the heat transfer coefficient of the water on both sides can be approximated. The total heat transfer amount can be calculated according to the temperature difference and flow rate of the water inlet and outlet, and the total heat transfer coefficient and the water at the flow rate can be calculated. The heat transfer coefficient of the side changes the flow rate of the water to obtain the heat transfer coefficient of the water side at different flow rates. Then, the plate heat exchanger is connected to the refrigeration system, and instead of the evaporator, the flow rate of the cold water is respectively set to a set of flow rates during water-water heat exchange, and the heat transfer coefficient can be obtained by the heat exchange amount on the water side, according to The water side heat transfer coefficient is used to obtain the refrigerant side heat transfer coefficient, and the relationship between the heat transfer coefficient, the refrigerant side heat transfer coefficient and the water flow rate is obtained.
The valve is a series of gas emergency shut off solenoid valves, specially designed as gas pipe breaker for emergency use. It can be connected with gas leaking detection sensor, fire alarm circuit or other intelligent sensor modules so that on site or remote shut down on gas supply (manually or automatically) is possible, hence ensuring the safety on gas usage. The valve features an auto-close when strong vibration is detected. After close, manual operation is required to turn on the valve. This feature meets safety regulations in the event of an accident.
Gas Solenoid,Solenoid Valve,Gas Solenoid Valve,Solenoid Operated Valve
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