4.4: Gas Laws
Click play on the following audio player to listen along as you read this section.
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
Pressure is directly proportional to the force , in (N) newton’s and inversely proportional to the area , in (m 2 ) 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 (cm 3 ) 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:
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.