Pressure temperature relationship for liquid refrigerants air

pressure temperature relationship for liquid refrigerants air

The evaporator then transfers the heat from the air to a cool fluid medium called Ra refrigerant . Pressure / temperature relationship: As the pressure on a. This controlled flow is necessary to prevent the return of liquid refrigerant to the The TXV is not designed to control air temperature, head pressure, capacity. For example, when the pressure increases then the temperature also increases. The refrigerant air is pressurized into the compressor meaning the pressure as the refrigerant releases latent heat by turning from a gas to a liquid as it cools.

In our diagram, the dashed line going through both the compressor and TX valve does this. Above and to the right of that line the refrigerant exists at high pressure — typically one hundred to several hundred pounds per square inch gauge psig.

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Evaporators can have various forms, but the type shown is typical. It consists of a back-and-forth length of copper tubing to which metal fins have been attached.

As the cold liquid refrigerant enters the evaporator it cools the tubing and the fins. A fan blows air across the fins. The cold fins remove heat from the air, thereby lowering the air temperature in the cooled space. The removed heat is conducted through the metal to the refrigerant where it is absorbed. As this happens, the refrigerant gradually changes from liquid to gas.

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To make the refrigerant ready to do further cooling, it is necessary to get rid of that heat and convert the refrigerant back to a cold liquid again. A motor-driven mechanical compressor does this — and serves at the same time as a vapour pump that keeps the refrigerant circulating around the loop. As the gas is compressed its temperature goes up, and at the compressor output we have high-pressure very-hot gas. In fact, the compressor has added even more heat.

It is the condenser that saves the day by letting the system dump that excess heat into the atmosphere.

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Typical condensers are built much like evaporators, and they, too, have fans that blow air across their fins. Here, the passing air picks up heat from the refrigerant — just the opposite of what happens at the evaporator. As the blend changes phase, more of one component will transfer to the other phase faster than the rest. This property is called fractionation.

pressure temperature relationship for liquid refrigerants air

The changing composition of the liquid causes the boiling point temperature to shift as well. The overall shift of temperature from one side of the heat exchanger to the other is called the temperature glide.

Zeotropic blends cannot be defined by a single pressure-temperature relationship.


The temperature glide will cause different values for temperature at a given pressure, depending on how much refrigerant is liquid and how much is vapor. The most important values for checking superheat and subcool are the end points of the glide or the pressure-temperature relationship for saturated liquid and saturated vapor.

The saturated liquid condition is often referred to as the bubble point. Imagine a pot of liquid sitting on a stove; as it begins to boil it forms bubbles in the liquid. The saturated vapor condition is referred to as the dew point. Imagine a room full of vapor and dew drops forming on the furniture. PT charts for the zeotropic blends list two columns next to each temperature: For these blends, the vapor and liquid pressures are only separated by 1 or 2 psi.

Because the difference is quite small between the two values some manufacturers' PT charts will only list one column for these blends. Using a two-column PT chart When checking a superheat or subcool temperature the procedure is the same as for a single-component refrigerant.

Superheat is checked by measuring the temperature of the vapor line, measuring the pressure, then subtracting the saturated temperature from the measured temperature.

pressure temperature relationship for liquid refrigerants air