DiSCUSSION 4

1)      Give examples with appropriate diagrams and explanations of actual loads in refrigeration practice in a factory.

 

 

 

 

Figure 1: Batch continuous air blast freezer with counter flow air circulation

 

 

 

Figure 2: Batch continuous air blast freezer with cross flow air circulation

Figure 3: Batch continuous air blast freezer with cross flow air circulation

(Also constructed with counter current series flow air circulation

           

            As we know, the refrigerator is use to keep all the things cold by lowering their original temperatures; instead, an evaporating gas called a refrigerant draws heat away, leaving the surrounding area much colder. Refrigerators work on the principle of cooling through evaporation.

            A refrigerator consists of two storage compartments - one for frozen items and the other for items requiring refrigeration but not freezing. These compartments are surrounded by a series of heat-exchanging pipes. Near the bottom of the refrigerator unit is a heavy metal device called a compressor. The compressor is powered by an electric motor. More heat-exchanging pipes are coiled behind the refrigerator. Running through the entire system is pure ammonia, which evaporates at -27 degrees Fahrenheit (-32 Celsius). This system is closed, which means nothing is lost or added while it is operating. Because liquid ammonia is a powerful chemical, a leaking refrigerator should be repaired or replaced immediately.

            The same goes with the refrigeration practice (with actual loads) in a factory. As the example we can see from Figure 1, 2, 3 that the refrigerator fills with fish. The refrigeration process begins with the compressor. The process start when Ammonia gas is compressed until it becomes very hot from the increased pressure. This heated gas flows through the coils behind the refrigerator, which allow excess heat to be released into the surrounding air. This is why users sometimes feel warm air circulating around the fridge. Eventually the ammonia cools down to the point where it becomes a liquid. This liquid form of ammonia is then forced through a device called an expansion valve. Essentially, the expansion valve has such a small opening that the liquid ammonia is turned into a very cold, fast-moving mist, evaporating as it travels through the coils in the freezer. Since this evaporation occurs at -27 degrees F (-32 degrees Celsius), the ammonia draws heat from the surrounding area. This is the Second Law of Thermodynamics in effect. Cold material, such as the evaporating ammonia gas, tends to take heat from warmer materials, such as the water in the ice cube tray.

            As the evaporating ammonia gas absorbs more heat, its temperature rises. Coils surrounding the lower refrigerator compartment are not as compact. The cool ammonia still draws heat from the warmer objects in the fridge, but not as much as the freezer section. The ammonia gas is drawn back into the compressor, where the entire cycle of pressurization, cooling and evaporation begins anew.