Refrigerants such as ammonia are used for low-temperature systems. These include food and process cooling, ice rinks, and so forth. Propane has been used for some special applications. Now that chlorinated hydrocarbons have been determined to be harmful to the earth’s ozone layer, R-11 (CCl3F), R-12 (CCl2F2), and other similar compounds that were in common …
Read More…Category: Refrigeration
Refrigeration Capacity
Refrigeration machines are rated in tons of refrigeration. This rating indicates the size and ability to produce cooling energy in a given period. One ton of refrigeration has cooling energy equal to that produced by 1 ton of ice melting in 24 hours. Since it takes 288,000 Btu of heat to melt 1 ton of …
Read More…Basic Refrigeration Cycle
A substance changes state when the inherent amount of heat is varied. Ice is water in a solid state and steam is a vapor state of water. A solid is changed to a liquid and a liquid to a vapor by applying heat. Heat must be added to vaporize or boil a substance. It must …
Read More…Refrigeration from Vaporization
The perspiration on your body evaporates and cools your body. Water kept in a porous container is cooled on a hot day. The water seeps from the inside. There is a small amount of water on the outside surface. The surface water is vaporized—it evaporates. Much of the heat required for vaporization comes from the …
Read More…Latent Heat
The heat required to change the state of a substance without changing its temperature is called its latent heat, or hidden heat. Theoretically, any substance can be a gas, liquid, or solid, depending on its temperature and pressure. It takes heat to change a substance from a solid to a liquid or, from a liquid …
Read More…Heat Content
Every substance theoretically contains an amount of heat equal to the heat energy required to raise its temperature from absolute zero to its temperature at a given time. This is referred to as heat content, which consists of sensible heat and latent heat. Sensible heat can be felt because it changes the temperature of the …
Read More…Specific Heat
Every substance has a characteristic called specific heat. This is the measure of the temperature change in a substance when a given amount of heat is applied to it. One Btu (British thermal unit) is the amount of heat required to raise the temperature of 1 lb of water by 1° at 39º F. With …
Read More…Temperature and Heat
The production of excess heat in a system will cause problems. Normally, matter expands when heated. This is the principle of thermal expansion. The linear dimensions increase, as does the volume. Removing heat from a substance causes it to contract in linear dimensions and in volume. This is the principle of the liquid in a …
Read More…Atmospheric Pressure
The layer of air that surrounds the earth is several miles deep. The weight of the air above exerts pressure in all directions. This pressure is called atmospheric pressure. Atmospheric pressure at sea level is 14.7 psi, which converts to 1.013 × 105 N/m2. The instrument used to measure atmospheric pressure is called a barometer. …
Read More…Pressure-Indicating Device
Pressure-indicating devices are most important in the refrigeration field. It is necessary to know the pressures in certain parts of a system to locate trouble spots. The diaphragm is a flexible sheet of material held firmly around its perimeter so there can be no leakage from one side to the other (see Fig. 4-5). Force …
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