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>>>in Freon PH chart there are (liquid line) and (gas line) .the two lines shapes like a pyramid (there intersection point is called the critical point...
>>>if the freon condition (pressure , temp.) located on the gas line that mean the freon is saturated gas
>>>>if the freon condition (pressure , temp.) located on the liquid line that mean the freon is saturated liquid
>>>if the freon condition (pressure , temp.) located between the liquid and gas lines that mean the freon is mixed
>>>if the freon condition (pressure , temp.) located after the liquid line that mean the freon is sup-cooled
>>>>if the freon condition (pressure , temp.) located after the gas line that mean the freon is super heated
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the sub-cooling increase the performance if it happen before the expansion valve by cooling the freon pipe before it .to be sure that all enter the compressor is liqid
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super heat increase the performance if it happen before the compressor to be sure that all enter the compressor is gas
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we usually make heat exchange between the pipe that enter the valve and the compressor...the the pipe that enter the valve are suppose to be cooled off by the pipe that entering the compressor
Most materials can exist in three forms: solids, liquids, and gases. Water is a common example. Water can exist as a solid (ice), a liquid, or a gas or vapor (steam). Only a gas or vapor (these are interchangeable terms) can be superheated. Let's use water as an example as we explain these terms.
Water at sea level boils at212 degrees F. When heated to212 degrees F, the molecules that make up water are moving at a high enough speed that they overcome the air pressure above the water. As additional heat is added to liquid water at212 degrees, the water begins to boil. As the water boils it is changing state from a liquid to a gas. In addition, during the boiling process the temperature remains the same (212 degrees F). There is no change in temperature during a change of state.
This phenomenon is true for all substances as they change state no matter how much heat is added. As long as the water is still boiling and not all the water has completely changed to a gas (steam) the temperature remains at212 degrees F. This means that a thermometer placed in boiling water will remain at212 degrees throughout the boiling process even though heat is added to cause the water to boil. This heat of boiling is called latent heat. The word "latent" is a Latin word for "hidden." The heat added to the water is hidden from the thermometer since the temperature remains unchanged during the boiling process.
After all the water has changed to a gas or vapor (steam), then the addition of still more heat to the vaporized water or steam will cause the temperature of the steam to increase above its boiling temperature of212 degrees. Any increase in temperature of the steam above its boiling point is called "superheat." Steam at213 degrees F is superheated by1 degree F.
Superheat is then any temperature of a gas above the boiling point for that liquid. When a refrigerant liquid boils at a low temperature of40 degrees in a cooling coil and then the refrigerant gas increases in temperature, superheat has been added. If this refrigerant changed from a liquid to a gas or vapor at40 degrees and then the refrigerant vapor increased in temperature to50 degrees F, it has been superheated by10 degrees.
Subcooling is now easy to understand. Only liquids and solids can be subcooled. Subcooling is any temperature of a liquid or solid below its saturation temperature. Let's use water as an example again. Liquid water at sea level has a saturation (boiling) temperature of212 degrees F. If we were to add heat to the saturated water, it would first boil away with no change in temperature (remember latent heat?) and then become superheated if still more heat were added to the vapor (steam) after it had all turned to a vapor.
Instead of boiling our212 degree water by adding heat, we shall remove heat from the212 degree water. As heat is removed from the liquid water, its temperature will drop below its boiling (saturation) temperature. Water at211 degrees has been subcooled by1 degree F. If the temperature of the water is decreased to180 degrees, the water has been subcooled from212 to180 degrees. That is, it has been subcooled by32 degrees. When you drink180 degree coffee, you are drinking a subcooled liquid!
sub cooling is the condition of liquid refrigerant in colder than minimum temperature ( saturation temperature) required to keep it from boiling and hence change from liquid to a gas state while supeheat is the temperature of vapor above the boiling point at particular pressure.
