Mechanical Cooling
32 Gas Laws
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Before we can examine the inner workings of direct expansion cooling systems, it will help to have a basic understanding of how fluids and gasses behave under different conditions. Specifically we are concerned with how changes in pressure, temperature or volume will affect our cooling systems.
Pressure is defined as a force acting upon an area. Expressed mathematically
[latex]\text{Pressure}=\dfrac{\text{Force}}{\text{Area}}[/latex]
Pressure is directly proportional to the force, in (N) newton’s and inversely proportional to the area, in (m2) square meters, upon which it acts. By changing either the force or the area, we can vary the pressure of a system.
Temperature is the thermal energy contained by a material as its atoms collide with each other. It is a representation of kinetic energy. The hotter an object is, the more kinetic energy it atoms have, and the more collisions will occur.
It takes energy to heat something, and a hot object will slowly cool by dissipating its kinetic energy to the outside environment.
Temperature is measured in either degrees Celsius (C°) or degrees kelvin (K°) . Kelvin is the base unit of temperature in the SI system.
Volume represent the given space that something occupies. When describing gasses or liquids we often describe the volume that they take up. measured in cubic centimetres (cm3) or more commonly, (L) liters.
When compared, we find that the temperature of a system is directly proportional to its pressure and inversely proportional to the volume that it occupies.
Expressed mathematically:
[latex]\text{Temperature}=\dfrac{\text{Pressure}}{\text{Volume}}[/latex]
This equation is a simplification of more complex gas laws, but will serve to illustrate the relationships that we wish to focus on.
In our DX cooling systems we will control the volume and pressure of a medium, the refrigerant, to transfer heat from one place to another.
A mechanical cooling system that uses the evaporation and condensation of a refrigerant to remove heat from an area.
The force acted upon an object or medium by the surrounding environment. Often measured in PSI or Pascal’s.
A measure of the average molecular kinetic energy of a system on a definite scale. Measured in degrees Fahrenheit, Celsius or Kelvin.
The amount of space that an object or medium takes up. Measured in cubic units (cm3) or liters.
A pushing or pulling on an object, that when unopposed will result in a change in that objects velocity.
The surface of an object or medium. Measured in square units (m2).
The kinetic energy possessed by an object or mediums atoms and perceived as heat.
A material used in DX cooling systems that boils below room temperature, and is used to transfer thermal energy from one point to another.