Temperature Field Measurement Of Liquid Film Based On Laser-induced Fluorescence

Due to the high heat and mass transfer efficiency and low consumption,liquid film is widely applied in the evaporating process of large evaporators and in the cooling process of microelectronic devices.It's important to make clear the flowing process and transfer characteristics in liquid film,which can improve the industrial equipment,make it perform better and predict the heat damage.Therefore,it is very important to study the temperature field and its distribution.Based on high-speed photography and laser induced fluorescence(PLIF),which was a non-invasive and high temporal resolution method,the measurement of liquid film temperature field and the analysis of heat transfer performance were carried out.An extraction method of fluorescence intensity based on the optimized average gray values was presented,and a temperature field measurement method based on the two-dimensional planar laser calibration was proposed,which improved the measurement accuracy effectively.At the same time,the temperature field of the liquid film and the factors that influenced the heat transfer performance of the liquid film were experimentally analyzed.Specific work includes the following aspects:The importance of liquid film in the industrial process of heat transfer was analyzed.The significance of temperature field measurement of liquid film and analysis of heat transfer performance was also discussed.It was concluded that it was difficult to measure the temperature field and analyze the heat transfer mechanism of liquid film.The PLIF temperature measurement technology was introduced briefly,and the advantages of temperature field measurement of liquid film were described.Based on the PLIF temperature measurement and high-speed photography,a temperature measurement system of liquid film was built.The hardware and software of the liquid film temperature control system were designed,and the PC software system was developed by VB.The temperature measurement system of liquid film based on PLIF could form constant temperature liquid film and simultaneously capture the corresponding fluorescence image of liquid film,which provided the experimental device basis for subsequent system calibration,temperature field measurement,heat transfer research and so on.The calibration experiment was completed and the temperature measurement system of liquid film was calibrated.An extraction method of fluorescence intensity based on the optimized average gray values was presented,and a temperature field measurement method based on the two-dimensional planar laser calibration was proposed,which improved the measurement accuracy effectively.The temperature-fluorescence intensity curve was fitted by the least square method,and the fitting error was analyzed in detail.Temperature field of the thermostat liquid film and heated liquid film was obtained by the experiment respectively.The comparison between the temperature measurement results of PLIF and PT1000 was made and the relative error of PLIF temperature measurement was analyzed.At the same time,heat transfer coefficient was calculated by the temperature field distribution of the heated liquid film.Then effects of flow rate and initial temperature on the heat transfer performance were analyzed.