Introduction of Expansion Valve in Industrial Chiller

Introduction of Expansion Valve in Industrial Chiller

In the chiller refrigeration system, the expansion valve is one of the four major components of the refrigeration system (compressor, condenser, expansion valve, evaporator).

The function of the expansion valve:

The expansion valve is one of the throttling devices. Its function in the refrigeration system of the chiller is to throttle the saturated liquid (or subcooled liquid) under the condensation pressure in the condenser or liquid receiver to the evaporation pressure and evaporate Temperature, while adjusting the flow of refrigerant entering the evaporator according to changes in load.

The composition of the expansion valve:

Simply put, the expansion valve is composed of three parts: the valve body, the temperature sensor and the balance tube.
temperature sensor bag

The temperature-sensing bag is filled with refrigerant in a saturated gas-liquid equilibrium state, and this part of the refrigerant is not connected to the refrigerant in the system. It is generally tied to the outlet pipe of the evaporator, and is in close contact with the pipe to sense the temperature of the superheated steam at the outlet of the evaporator. Since the refrigerant inside it is saturated, it transmits the saturated state pressure to the valve body according to the temperature.

Balance tube

One end of the balance tube is connected to the outlet of the evaporator slightly away from the temperature-sensing bulb, and is directly connected to the valve body through a capillary tube. The function is to transmit the actual pressure at the outlet of the evaporator to the valve body. There are two super-large industrial fans with diaphragms in the valve body, and the diaphragms move upward under the action of pressure to reduce the refrigerant flow through the expansion valve, seeking balance in dynamics.

Quality judgment

Generally speaking, the higher the degree of superheat set by the thermal expansion valve, the lower the heat absorption capacity of the evaporator, because increasing the degree of superheat will take up a considerable part of the heat transfer surface of the evaporator, so that the saturated steam can be superheated here. It occupies a part of the heat transfer area of the evaporator, so that the area of the refrigerant vaporizing and absorbing heat is relatively reduced, that is to say, the surface of the evaporator is not fully utilized. However, if the degree of superheat is too low, the refrigerant liquid may be brought into the compressor, causing the unfavorable phenomenon of liquid hammer.

Therefore, the superheat adjustment of the expansion valve should be appropriate, which can not only ensure that enough refrigerant enters the evaporator, but also prevent liquid refrigerant from entering the compressor. When the resistance of the refrigerant flowing through the evaporator is small, it is best to use an internally balanced thermal expansion valve. Conversely, when the resistance of the evaporator is large, generally exceeding 0.03MPa, an externally balanced thermal expansion valve should be used.

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