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Intro to Marine Engineering 2E Episode 7

Tham khảo tài liệu 'intro to marine engineering 2e episode 7', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 170 Refrigeration air conditioning and ventilation Figure 9.5 Evaporator stores in which the fan and coil unit are one and a larger version in direct expansion cargo or air conditioning systems where the fan or fans may be remote. A more elaborate design is used for secondary refrigerant cooling which takes the form of a shell and tube vessel. Such a type is illustrated in Figure 9.5 and employs direct expansion. In this case the refrigerant passes through the tubes and the secondary refrigerant is passed over the tube bank. The refrigerant is sprayed into the tubes so as to ensure an even distribution through all the tubes. Any oil present is not sprayed and drains away. In this type of evaporator two features are employed to improve heat transfer efficiency. On the refrigerant side there is a centre tube with a spiral fin fitted around it as illustrated or the insert may be in the form of an aluminium star which has a spiral twist on it. Also baffles are arranged on the brine side to deflect the brine across the tube bank. Refrigerant flow control valves It is usual to have a solenoid valve in the liquid line prior to the expansion valve or regulator. This shuts or opens as determined by the thermostat in the space or the secondary refrigerant being cooled. It may also be used to shut off various circuits in a cooler when the machine is operating on part-load conditions. The expansion valve regulator is a more complex piece of equipment which meters the flow of refrigerant from the high-pressure to the low-pressure side of the system. This may be of the thermostatic type as shown in Figure 9.6. The bulb senses the temperature of the refrigerant Refrigeration air conditioning and ventilation Ỉ7Ỉ Capillary tube Tube and space screw Figure 9.6 Thermostatic expansion valve or regulator Bulb Evaporator at the outlet from the evaporator and opens or closes the valve accordingly. The design of the valve is critical and is related to the pressure difference between the .