Analysis Of Decoupling Control Of Air Quantity And Spraying Water In Combined Air Cooler

Fan and spraying-water pump are energy consumption devices in combined aircooler. Operation costs can be reduced by adjusting the motor frequency of the fan andpump, considering the environment temperature, humidity and the heat load.That the implicit functional relation of air quantity of the combined air cooler withtotal heat load, surrounding air temperature and humidity, and the junctional temperatureof hot fluid between finned coils and evaporative coils (JT) in the cooler was developedand analyzed. The curves of air demand with several main factors above were plotted bythe program. Finally the explicit function of air demand was fitted by calculating1000effective working conditions. The results show that the air demand increases linearlywith total heat load, and it increases linearly with environment humidity as well, but theinfluence of humidity was slight. The air demand increases or decreases faster when theenvironment temperature is above25℃, and slower at the temperature below10℃, Theair demand also decline with the rise of JT. The fitted function of air demand indicatesthe rules of air demand with the variables. The function may be references for design andoperation of combined air coolers, and may provide a proto model for the control systemof the air cooler as well.Based on the industrial operation of combined air cooler, took into account of thedemand of heat load and cost saving, the coupling relationship between the demand ofair, spraying water and the temperature of cooled hot fluid was analysed. The formulaof cost is given as well.According to the theory of heat and mass transfer, based on the model of heat andmass transfer between wet air and water film in the infinitesimal area, the optimization ofquantity of air and spraying water was programmed. When the ambient air temperature,relative humidity and hot fluid flow varies within a certain range, the program can beused to calculate the optimal quantity of air and spray water, and in the optimal condition,the task of heat transfer can be finished at the lowest operating cost.Asuming the heat fluid to be hot water,4500sets of data were calculated within therange: the hot water flow rate of40~90t/h, inlet air temperature of-5~35℃, inlet airrelative humidity of60%~90%, air quantity of5~30million m~3/h, spraying waterquantity of65~650m~3/h. The formula of solving the outlet temperature of hot fuild isfitted.The decoupling controller of quantity of air and spraying water is designed and could provide a reference for industrial computer control systems.