By Dave Bird, Dyer Appliance Academy
In order to understand how refrigeration works, we first have to review a little science. There are currently 5 states of matter. For our discussion we will only consider 3. Those are solid state, liquid state and gas state.
A solid will retain its shape and volume without a container. A liquid will take on shape of its container without losing any volume if not under pressure. A gas will take on the shape and volume of its container and will expand to fill it.
There are 5 principles regarding how matter can change from one state to another. When matter is either heated or cooled or if pressure changes, matter will change from one state to another.
These 5 principles are:
Liquefaction occurs when a solid changes into a liquid. This is what happens when an ice cube is heated.
Solidification is when matter changes from a liquid to a solid. This is like when heat is removed from water and it turns to ice.
Vaporization happens when a liquid is heated and transforms into vapor. When water is heated it turns into steam which is a vapor or gas.
Condensation is when a vapor transforms into a liquid. An example of this is when you have an iced beverage. The cold of the drink causes the moisture in the air to change back to a liquid. The outside of the container will sweat.
Last we have sublimation which occurs when a solid turns directly into a gas state without passing through the liquid state. An example of sublimation is dry ice placed into water. The water warms the ice which then changes directly into a vapor.
Energy is the ability to do work. Energy exists in many forms such as light, heat chemical, mechanical and electrical energy. We also need to consider a couple of “Laws of Thermodynamics” as they apply to refrigeration.
The first law (as any good Star Trek fan knows) is that matter can neither be created or destroyed. It can only be changed from one form to another.
The second law of thermodynamics states that heat energy can only travel in one direction, from hot to cold. When 2 objects are placed together, heat will travel from the warmer object to the cooler one. The transfer will continue until the temperature of both objects are equal. This is a critical process in refrigeration.
Heat energy can be measured with a thermometer. There are 2 scales used to measure temperature. They are Fahrenheit and Celsius. On the Fahrenheit scale water freezes at 32 degrees and boils at 211 degrees. On the Celsius scale water freezes at 0 degrees and freezes at 100 degrees.
Another way to measure heat energy is in units of British Thermal Units (BTUs). One BTU is equal to the amount of heat required to raise the temperature of one pound of water 1 degree Fahrenheit at sea level.
Heat energy is an important factor in refrigeration. Refrigerators must be able to remove heat from inside the cabinet and send it to an area outside the cabinet.
Heat can be transferred by using one or more of the following methods:
Convection occurs when heat transfers are caused by air or fluid movement whether naturally or by forced air movement. In refrigeration, cold air absorbs any heat from food and air inside the cabinet. Forced air movement brings the air across the colder evaporator coils and the heat is transferred into the coils. Convection can also happen when heat transfers into and out of a liquid like the refrigerant used in a refrigerator or air conditioner.
Radiation is the travel of heat energy through the atmosphere by means of radiant waves (either light or radio frequency). This type of heat transfer is encountered when a refrigerator door is opened allowing heat to enter the cabinet.
Refrigeration is the process of lowering the temperature of a substance. The product that absorbs the heat from a substance to be cooled is known as a refrigerant. Refrigerants are chemical compounds that absorb heat by evaporating or boiling which changes the refrigerant from a liquid to a vapor.
The most common method of refrigeration is known as a vapor compression cycle (a refrigeration cycle using a compressor). This method relies on the evaporation of a liquid.
Refrigerants have a much lower boiling point than water. The most common refrigerant used in domestic refrigerators today is R-134A. R-134A boils at -15 degrees Fahrenheit. It can remove heat from a freezer compartment that has a temperature of 0 degrees Fahrenheit.
Now that we have learned the science of basic refrigeration come on back next month when we’ll talk about the sealed system. You will learn about the refrigeration cycle, the components in the sealed system and how they do their magic. Until then, be safe.