制冷系统原理课件.ppt

* * * Discuss the construction and operation of an evaporative condenser (page 30). A typical evaporative condenser cell is represented in Figure 4?19 below. Each cell consists of the following major components: refrigerant condensing coils, fan, water sump, recirculation pump, drift eliminators, and water spray nozzles. The hot ammonia gas is fed into the top of the cooling coil. Water is evenly sprayed over the cooling coil by spray nozzles. The water is supplied by the recirculation pump from the condenser water sump. The water absorbs heat from the ammonia in the coils. Water evaporates from the wet coils and heat is carried away in the water vapor by the fan-induced airflow. Any water that does not evaporate falls back to the condenser sump. The sump is supplied with makeup water to replace the evaporated water and to control the amount of solids in the circulating water. Excess water return returns back to a tank or other source to be chemically retreated. The ammonia gas is continually cooled as it flows through the coil. When enough heat has been removed, the gas condenses to liquid ammonia. The liquid ammonia flows out of the coil and drains to the receivers. * * * * * Discuss glycol sub-loops (page 32). Some of cooling loads require glycol at above freezing temperatures. These cooling loads are supplied through sub-loops that mix locally recirculated glycol with cold glycol from the main system. Refer to Figure 4?22. In the above sub-loop, a recirculation pump supplies glycol at a constant 33?F to an air cooling coil by blending a portion of glycol return flow with cold glycol (27?F) from the main system. A temperature transmitter (TT) senses the glycol temperature to the cooler. Based on this temperature signal, a temperature control valve (TV) open/closes as necessary to adjust the amount of cold glycol being supplied to the pump. The cold glycol mixes with a portion of the warm glycol return flow at the pump suction. The warm glycol t