What are the similarities and differences between the thermostatic expansion valve TXV refrigeration

The thermostatic expansion valve realizes the throttling flow from the condensation pressure to the evaporation pressure, and controls the flow of refrigerant at the same time. Its.

Although the DAO body volume is small, but the effect is huge, its working rights directly determine the working quality of the whole system, in the best way to supply liquid to the evaporator, to ensure the evaporator outlet refrigerant vapor superheat stability, the temperature sensor package must be in good contact with the suction pipe of the compressor to accurately sense the suction temperature of the compressor, usually filled with the same refrigerant as the refrigeration system, so as to realize the pressure fed back through the temperature sensing package is the saturation pressure of this type of refrigerant corresponding to the suction temperature of the compressor. The charge of the temperature sensor is only corrected according to the complete evaporation of the liquid refrigerant in the complete temperature sensing package at a specific temperature, which is equivalent to setting an upper limit for the pressure fed back by the temperature sensing bag acting on the diaphragm of the expansion valve, because if the surface temperature of the pipe wall continues to increase, it will only increase the temperature of the gaseous refrigerant inside the temperature sensing package (in a superheated state). And the pressure basically doesn't change anymore.

Expansion valves mainly play the role of throttling pressure reduction and regulating flow.

At the same time, it also has the function of preventing wet compression and liquid shock, protecting the compressor and abnormal overheating.

Many people like to use the expansion valve in the Dongluyang chiller.

Introduction to the basics of expansion valves:

The expansion valve consists of a valve body, a temperature sensing bag, and a balance tube.

It is composed of three parts, which are installed at the inlet of the evaporator, and the temperature sensing bag is wrapped at the outlet of the evaporator, and the opening of the expansion valve is adjusted according to the temperature of the evaporator outlet to control the flow of refrigerant.

The expansion valve is an indispensable part of the refrigeration system, mainly playing the role of expansion and throttling, as follows:

The refrigerant liquid at medium temperature and high pressure throttles through the expansion valve and becomes wet steam at low temperature and low pressure, which enters the evaporator for evaporation and heat absorption to complete the refrigeration process;

The expansion valve is a kind of throttling device, and its function in the chiller refrigeration system is to throttle the saturated liquid (or supercooled liquid) under the condensation pressure in the condenser or liquid reservoir to the evaporation pressure and evaporation temperature, and at the same time, adjust the flow rate into the evaporator refrigerant according to the change of load.

Generally speaking, the higher the superheat set by the thermostatic expansion valve, the lower the heat absorption capacity of the evaporator, because to increase the superheat heat, a considerable part of the heat transfer surface at the tail of the evaporator is taken up, so that the saturated vapor can be superheated here, which occupies a part of the heat transfer area of the evaporator, and the area of refrigerant vaporization heat absorption is relatively reduced, that is to say, the surface of the evaporator is not fully utilized. However, if the superheat is too low, the refrigerant liquid may be brought into the compressor, resulting in the unfavorable phenomenon of liquid shock. Therefore, the superheat of the expansion valve needs to be properly regulated to ensure that enough refrigerant enters the evaporator and prevents 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 thermostatic expansion valve; On the contrary, when the resistance of the evaporator is large, it is generally exceeded, and the thermal expansion valve of external equilibrium should be used.

Throttling and depressurizing.

The function of the expansion valve in the refrigeration system is to throttle and depressurize the liquid medium-temperature and high-pressure refrigerant in the supercooled state from the condenser, and reduce the temperature of the refrigerant at the same time, and the liquid refrigerant after throttling and depressurization enters the evaporator to evaporate and absorb heat.

Expansion valves are one of the key components of a refrigeration system.

See if it's blocked or not, if it's not blocked, it won't have much impact, if it's blocked. The automatic adjustment ability of the expansion valve will be invalid, and the opening of the expansion valve will be basically unchanged, and it will not play an adjustment role.

Anatomical diagram of the expansion valve.

The high pressure is too high, the low pressure is too low, and the cooling capacity is not.

I think that in general, the electronic system is better than the thermal system, the electronic expansion valve has a wider range of adaptation, and the adjustment is faster, and the only disadvantage is that the control system needs to be added, and the cost is higher.

The development of the interception mechanism: capillary tube - thermal expansion valve - electronic expansion valve, the adjustment range is getting larger and larger, the reaction speed is getting faster and faster, and the control amount is getting more and more accurate.

The thermal expansion valve of the refrigeration unit is composed of a temperature sensing bag, a capillary, a section, a flow valve needle, a push rod, a fixed value spring and an adjusting screw. According to the gas pressure at the lower part of the diaphragm, it can be divided into internal balance type and external balance type.

The gas pressure at the lower part of the diaphragm is the refrigerant pressure after the throttling of the expansion valve, and the needle valve is driven to move up and down through the push rod by using the deformation of the bellows, so that the opening of the valve increases or decreases, so as to adjust the flow of refrigerant.

In the case of an externally balanced expansion valve, the gas pressure at the lower part of the diaphragm is the refrigerant pressure at the outlet of the evaporator. The difference is that the lower space of the metal diaphragm is not connected with the outlet of the expansion valve, but an external balance pipe is connected from the outlet end of the evaporator to the lower side of the diaphragm of the valve, and the equilibrium pressure is taken from the outlet of the evaporator, which can compensate for the excessive pressure drop caused by the long process of the evaporator, so as to reduce the superheat and ensure the effective area and refrigeration effect of the evaporator.

The liquid supply method is different, NH3 refrigeration system uses gravity liquid supply, and some uses ammonia pump liquid supply (low circulation barrel) and so on. That's all I know, I haven't played with the ammonia system in years.

The thermodynamic expansion valve is large, the liquid supply is large, the evaporation pressure is high, the evaporation temperature is also high, and the temperature cannot be lowered. The chiller can not zhi

Complete evaporation, large amount of liquid return, serious wear of the compressor oil run, excessive liquid return, resulting in compressor liquid shock.

The thermostatic expansion valve is small, the liquid supply is small, the refrigerant is insufficient, and the heat cannot be carried away enough, and the cooling is slow, or even cannot be lowered. The return air temperature is high, and the compressor motor cannot be cooled in time and is easy to burn.