Pressure temperature relationship for liquid refrigerants

Basic Refrigerant Circuit With Pressure and Temperature Relationships

pressure temperature relationship for liquid refrigerants

Pressure-temperature relation, Superheat & sub-cooling relationship between the pressure and temperature of a refrigerant holds good only when some liquid . the saturated liquid temperature (also called the bubble point temperature). At a given pressure, single component refrigerants, such as. CFC and. This article demonstrate the proper use of the pressure-temperature This P-T relationship will hold true when refrigerant liquid and vapor are.

Imagine a room full of vapor and dew drops forming on the furniture.

Basic Refrigerant Circuit With Pressure and Temperature Relationships

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.

pressure temperature relationship for liquid refrigerants

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. In the case of a blend, you Simply read the saturated temperature next to the pressure in the vapor dew point column of the chart.

When checking the subcool condition the technician will measure the temperature of the liquid line, the pressure at that point and subtract the measured temperature from the saturated temperature at the end of the condenser.

With the blend you read the saturated temperature next to the pressure in the liquid bubble point column of the chart. For a single-component or azeotropic refrigerant, the operating pressure for the low side of a system can be found by cross referencing the desired coil temperature on the PT chart.

For high-glide blends, however, the desired coil temperature is the average or midpoint temperature of the coil. The problem with two-column PT charts is that the conditions a t the endpoints of the temperature glide are listed, not the midpoint.

How to read a pressure temperature chart for super-heat and sub-cooling calculations

If the vapor column is read directly at the desired temperature, then the end of the evaporator will be the correct temperature, but the re st of the coil will be too cold. If the liquid column is used directly, then the beginning of the coil will be the correct temperature, but the rest of the coil will be too warm.

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Two-column PT charts are every bit as useful as the traditional ones. The charging and service procedures are very similar for both single-component refrigerants and zeotropic blends, and the specialized liquid and vapor data correct for the effects of the blends' temperature glide. For example, when the pressure increases then the temperature also increases.

pressure temperature relationship for liquid refrigerants

When the pressure decreases, then the temperature decreases. There are two examples that demonstrate this principle. The first is that of a spray can. The volume of the can is constant. When contents are removed from the can, then the mass of the contents will be reduced in the can.

PRESSURE AND TEMPERATURE RELATIONSHIP

Because there is less mass in the can with a constant volume, the pressure will decrease. This pressure decrease in the can results in a temperature decrease. The contents coming out of the can also cool in temperature but for another reason. Outside of the can the volume is not held constant. Thus the contents are free to expand when they move from the high pressure in the can to the low pressure outside of the can. Expansional cooling causes the contents coming out of the can to cool.