Thermal expansion valve

An expansion valve (also called a throttle valve ) is a means which decreases the pressure of the flowing fluid through a local constriction of the flow cross-section and thus causes a volume increase or expansion. The pressure reduction is carried out without removal of work and idealized without dissipating heat, that is thermodynamically isenthalpically.

Types

Expansion valves may be regulated or unregulated executed.

Thus, a constriction of the pipe an unregulated expansion valve represents a bottleneck such, also referred to as a throttle, and the capillary is in the household refrigerator with a piece of tube of very small diameter, called, realized.

In systems with higher power controlled expansion valves are used. Here, the cross section and thus, the pressure drop for a suitable reference value is regulated. In the case of a refrigerating machine can be, for example, the pressure in the subsequent evaporator such a command variable, which is then obtained an approximately constant temperature of the cooled medium.

Use in a compression chiller

In a cold-vapor compression refrigeration unit, as it is used for example in a refrigerator, or many types of the air conditioner, the expansion valve reduces the pressure of the working fluid ( refrigerant) entering normally be almost boiling liquid in the expansion valve. Here it undergoes a change of state, which can be assumed in a first approximation as adiabatic isenthalpically; which means that neither the heat is exchanged with the surroundings (adiabatic ) and not the enthalpy of the fluid changes ( isenthalpically ). A portion of the fluid vaporizes as it passes through the expansion valve, while the other part remains in the liquid state. Then the working fluid enters the evaporator, where the still liquid portion absorbs heat from the surroundings and so realized the actual benefit of the chiller.

In large systems, the expansion valve is replaced by a turbine. As the turbine mechanical power output is obtained, the state change is no longer isenthalpically during the passage through the turbine.

• Valve