Combined Air Cooler Experiment And Its Control System Debugging And Water Film Flow Numerical Simulation

With the water film evaporation air cooler in petrochemical industry in thebackground, a small combined air-cooling test rig is built to measure correspondingparameters as well as the heat and mass transfer performance. The temperature of hotwater inside the tubes, water film temperature as well as temperature and humidity of airoutside the tubes are measured under different conditions by changing the entrance windvelocity, spray water density, temperature and velocity of hot fluid inside the tubes. Theheat transfer performance and the relationships between various working parameters areanalyzed, and the change of heat and mass transfer coefficient of water film and air isobtained. Meanwhile, VOF simulation of water film outside horizontal tube is studiedwith CFD method and the threshold for “wriggle wave” of water film outside the tube isobtained, which is referencial valuable for determining spray volume.The testing and control system of the test rig are designed and studied. AKeithley2700data inspector and a250Ω resistor box are used to collect the data ofthermocouples, RTD, air volume, spray volume and hot water flow rate. Thecommunication between Keithley2700board and PC is realized by a program compiledwith VC++6.0, and data display and processing can work through the program too.The controlling program is written, through which the operating frequency of fan motorand pump motor can be regulated by changing temperature deviation and the controlvoltage, and thus the spray amount, air volume and the temperature of the outlet air canbe controlled and a stable temperature of the outlet hot fluid is obtained. Temperaturedeviation is got by the incremental PID algorithm, which is realized by controllingvoltage increment as a function of the temperature deviation.The temperature of hot water along the tubes, temperature of water film outside thetubes, humidity and temperature of air outside the tubes and the flow pressure drop arestudied under different air volumes and spray volumes. The influence of air volume andspray volume on heat transfer amount, spray water temperature, heat transfer coefficient, air state outside the tubes, water film mass transfer coefficient and the air pressure dropoutside the pipe are also studied.