View Answer. Refrigeration compressors provide a refrigerant circulation in the system and, unlike gas compressors, are not used independently out of the refrigeration system. Moisture reacts with the refrigerant to form an acidic solution. Back pressure valves are usually fitted at warmer rooms where the temperature is set at 4°C to 5°C or higher for eg. A filter drier installed in the liquid line at the condenser coil outlet to filter or trap minute foreign particles and absorb any moisture or water present in the system. E-mail. Suction line filter-driers are a temporary installation to clean up the system, after service, we must discard if the pressure drops below the set pressure. The rate of heat absorption by the evaporator differs from different cargoes carried and the outside air temperature. Chapter 10-11 Multipurpose refrigeration systems A refrigerator with a single compressor can provide refrigeration at several temperatures by throttling the refrigerant in stages. The lube oil pressure needs to be more than the suction pressure for the lube oil to come out of the bearings. Each stage operates on an ideal vapor-compression refrigeration cycle Cold refrigerant leaving the evaporator coil outlet can be used to under cool the warm liquid refrigerant leaving from the condenser outlet by using a heat exchanger as shown in the diagram known as suction to the liquid heat exchanger. You perfectly explain each thing to me and I recommend this to be read. Such systems … Refrigerants, are chemical compounds that are alternately compressed and condensed into a liquid and then permitted to expand into a vapor or gas as they are pumped through the mechanical refrigeration system to cycle. One reason for this could be the a] system is low on refrigerant b] high pressure cut out is improperly adjusted c] discharge valves are leaking slightly d] discharge valves are leaking excessively. If there is no back pressure valve, then it can lead to low temperatures or over flooding of the evaporator which could cause a problem like freezing in water coolers and spoilage of perishable items like vegetables and fruits. Large refrigerating compressors are running with 2 to 3 units in a v or w type arrangement, provided with an unloading mechanism. Back pressure valve may sometimes be fitted into the system to hold back a high evaporator pressure, where two to three evaporator outlet feeds into a common compressor suction line. Hot gas bypass valves used in compressors do not have a capacity reduction device like compressor unloader. Since the motor, as well as the compressor, is not accessible for repair or maintenance, a failure of the inbuilt motor winding like short circuit can cause decomposition of the refrigerant and serious contamination to the crankcase lubricating oil. 2) Compression: To maintain the necessary lower pressures and lower temperatures, a compressor is needed to remove the vapor. The purpose of the compressor in the refrigeration cycle is to accept the low-pressure dry gas from the evaporator and raise its pressure to that of the condenser. It maintains 6°C to 7°C of superheat at the outlet of the evaporator. The discharge valve body is held in place by a safety spring as shown in the image which is fitted to allow the complete discharge valve to lift in the event of liquid carry over to the compressor. It gives uniform torque, therefore, the smaller flywheel may be used 5. Purpose of … Sometimes cargo/stores are freshly located in a warm climate, the cooling load on the system increases significantly. In some plants, relief devices are arranged to discharge toward the low-pressure side of the system. Commercial refrigeration compressors are divided into three main categories: In turn, the intermediate systems (liquid) with coolant can be performed as a coolant for both open and closed circuits. Bursting discs, which comprise thin metal diaphragms designed to burst at a pressure equal to the MWP. Compression refrigeration systems require a cooling water circulation rate of approximately 3 gpm per ton of refrigeration, with a 10°F temperature drop across the cooling tower. A fluid-filled bulb connected through a capillary to a bellows. The compressor in a refrigeration system is normally selected to be able to satisfy the highest possible cooling load. In the vertical position, the refrigerant gas bubbles goes anywhere in the sight glass/moisture indicator. The electric motor is directly connected to the compressor with a single shaft avoiding the use of any coupling or mechanical seal and leaving no chance of refrigerant leaking into the atmosphere. A comparative study has been carried out of R-12, 22, 125, 134a, 152a, 218, 245, 500, 502, 507 and 717 as working fluids in a vapour-compression refrigeration system. Mechanical refrigeration, is the utilization of mechanical components arranged in a "refrigeration system" for the purpose of transferring heat. Some high-pressure switch controls the restart of the compressor automatically on a drop in pressure; others have a manual reset mechanism. This acidic solution dissolves copper tubings and extracts copper from copper-based alloys like brass or bronze present in different parts of an air conditioning system. An alternative possibility is to increase … Compressor Selection Criteria Evaporator Operating Conditions Refrigerant Type Ambient Conditions Required Refrigeration Capacity Compression Ratio Flow Rate through the compressors of the designed system (Free Air Delivery, FAD) Compressor Cooling System Total Required Power Input 4. It reduces leakage of refrigerant 4. Bypass valve regulates the cooling capacity by injecting discharge gas back into the suction. Thermostatic expansion valve acts as a regulator where the refrigerant is metered from the high-pressure side to the low-pressure side of the system. There is always pressure drop across the evaporator in practical, and it’s even higher in large evaporators. These refrigerants take on different forms as they change temperature and pressure. Commonly used materials for sight glass are brass metals and for ammonia, it’s steel or cast iron. In a vapour absorption refrigeration system, the compressor of the vapour compression system is replaced by Absorber, generator and liquid pump Join The Discussion. Refrigeration is the process of removing heat from a closed body or space enclosed so that its temperature is first lowered and then maintained at a required level which is below the temperature of surroundings. Hermetic compressor mostly used in household refrigerators, both motor and compressor are enclosed in a steel housing also known as a hermetic container where no gas or liquid can enter or escape from the welding seals welded around the container. Fusible plugs, which contain a metal alloy, melts when the temperature in the system corresponding to the MWP. It keeps the evaporator pressure constant regardless of the load. This sometimes leads to very shallow and clumsy rotors. Vegetable storeroom or lobby. 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