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How does Kelly|Technology select a matching thermal expansion valve for the refrigeration system?
The thermal expansion valve is one of the four major components in the refrigeration system. It is responsible for reducing the refrigerant from the condensing pressure to the evaporating pressure and proportionally controlling the flow rate of the refrigerant. The quality of the thermal expansion valve in a system will directly affect the operating performance of the entire system, so the selection of a suitable thermal expansion valve is of great significance to the operating life, cooling effect and operating cost of the air conditioning system.
First, the purpose of thermal expansion valve selection
The selection of the thermal expansion valve plays an important role in the performance of the entire system. Proper selection of the thermal expansion valve will maximize the use of the evaporator and always match the evaporator to the thermal load.
Second, the phenomenon that the thermal expansion valve does not match the system
When the thermal expansion valve does not match the system, the refrigerant flow rate of the system will be reduced for a long time, and the cooling capacity of the thermal expansion valve will be large and small. When the cooling capacity is too small, the evaporator will supply insufficient liquid and generate excessive heat, which will adversely affect the performance of the system. When the cooling capacity is too large, it will cause oscillation and intermittently make the evaporator supply excessive. The suction pressure of the compressor fluctuates drastically, and even liquid refrigerant enters the compressor, causing a liquid stroke (wet stroke).
Third, the basis of thermal expansion valve selection
The selection of the thermal expansion valve is based on the type of refrigerant in the refrigeration system, the evaporating temperature range, and the magnitude of the evaporator superheating load.
1 thermal expansion valve selection method and general steps are as follows:
1) Determine the refrigerant type of the system.
2) Determine the evaporation temperature, condensation temperature and cooling capacity of the evaporator.
3) The pressure difference between the inlet and outlet of the thermal expansion valve.
2 expansion valve selection example
There is an evaporation coil (4DW4/10F-50x50.3A), the refrigerant is R407C, the cooling capacity is 96KW, the evaporation temperature is 8 °C, the condensation temperature is 50 °C, what type of thermal expansion valve is selected (based on Danfoss products) example). First, the pressure difference PΔ at both ends of the inlet and outlet of the expansion valve is determined.
In the formula:
P k is the condensing pressure.
P 0 is the evaporation pressure.
1 PΔ is the pressure drop of the liquid supply copper pipe.
2 PΔ is the pressure drop of the dispenser and the dispensing capillary.
P k (condensation pressure), P0 (evaporation pressure) can be found in the wetting diagram by the known parameters given.
P k =17.5 5 10×P a, P0=6.5 5 10×P a
The pressure drop of the liquid supply copper pipe, due to the coil selection software used, has a pressure drop of the supply pipe in the calculated data. Therefore, 1 PΔ = 0.0031 5 10 × Pa is known. The pressure drop of the liquid separator copper pipe of the re-dispenser takes an empirical value of 2 PΔ=1 5 10×Pa.
When the refrigerant is R407C, the cooling capacity is 96KW, the evaporation temperature is 8°C, the condensation temperature is 50°C, and the 1 PΔ is 10bar. The model is TDEZ26 thermal expansion valve (taking Danfoss products as an example).
Cooling capacity (KW) R407C
Evaporation temperature +15 ° C evaporation temperature +10 ° C
The pressure drop across the expansion valve is ΔP (bar) model and nominal cooling capacity.