A thermal expansion valve or thermostatic expansion valve (often abbreviated as TEV, TXV, or TX valve) is a component in vapor-compression refrigeration and air conditioning systems that controls the amount of refrigerant released into the evaporator and is intended to regulate the superheat of the refrigerant that flows out of the evaporator to a steady value. Although often described as a "thermostatic" valve, an expansion valve is not able to regulate the evaporator's temperature to a precise value. The evaporator's temperature will vary only with the evaporating pressure, which will have to be regulated through other means (such as by adjusting the compressor's capacity).Get more news about Condenser Expansion Machine,you can vist our website!
Thermal expansion valves are often referred to generically as "metering devices", although this may also refer to any other device that releases liquid refrigerant into the low-pressure section but does not react to temperature, such as a capillary tube or a pressure-controlled valve.
A thermal expansion valve is a key element to a heat pump; this is the cycle that makes air conditioning, or air cooling, possible. A basic refrigeration cycle consists of four major elements: a compressor, a condenser, a metering device and an evaporator. As a refrigerant passes through a circuit containing these four elements, air conditioning occurs. The cycle starts when refrigerant enters the compressor in a low-pressure, moderate-temperature, gaseous form. The refrigerant is compressed by the compressor to a high-pressure and high-temperature gaseous state. The high-pressure and high-temperature gas then enters the condenser. The condenser cools the high-pressure and high-temperature gas allowing it condense to a high-pressure liquid by transferring heat to a lower temperature medium, usually ambient air.
In order to produce a cooling effect from the higher pressure liquid, the flow of refrigerant entering the evaporator is restricted by the expansion valve, reducing the pressure and allowing isenthalpic expansion back into the vapor phase to take place at a lower temperature. A TXV type expansion device has a sensing bulb filled with a liquid that has similar thermodynamic properties to the refrigerant. This bulb is thermally connected to the output of the evaporator so that the temperature of the refrigerant that leaves the evaporator can be sensed. The gas pressure in the sensing bulb provides the force to open the TXV, therefore dynamically adjusting the flow of refrigerant inside the evaporator and, as a result, the superheat acquired by the refrigerant that exits the evaporator.[1]
The superheat is the excess temperature of the vapor above its boiling point at the evaporating pressure. No superheat indicates that the refrigerant is not being fully vaporized within the evaporator and liquid may end up recirculated to the compressor. On the other hand, excessive superheat indicates that there is insufficient refrigerant flowing through the evaporator coil, and thus a large portion of it does not contain any liquid refrigerant to evaporate and is not providing significant cooling in that portion. Therefore, by regulating the superheat to a small value, typically only a few °C, the heat transfer of the evaporator will be near optimal, without excess saturated refrigerant being returned to the compressor.
Some thermal expansion valves are also specifically designed to ensure that a certain minimum flow of refrigerant can always flow through the system, while others can also be designed to control the evaporator's pressure so that it never rises above a maximum value.
