Study On The Mechanism Of Enhanced Heat Transfer Of High-gravity Coupled With Microwave

As a typical chemical process intensification equipment,the high-gravity reactor has been successfully applied in many fields,such as distillation,absorption,wastewater treatment,nanomaterials preparation and so on.Because of its characteristics of strengthening mass transfer and mixing,it has been more and more widely recognized.However,the liquid is the dispersed phase and the gas is the continuous phase in the high-gravity reactor,the thermal conductivity inside the reactor is relatively low,which is not conducive to the heat transfer,and the heating process will have problems such as low heating efficiency and large energy consumption.In view of the fact that microwave can directly make polar molecules in solution vibrate and collide at extremely high frequency to realize rapid temperature rise,this paper proposes to carry out temperature distribution and application research in the coupled field of high-gravity and microwave.The main research contents and conclusions are as follows.(1)Experimental study on temperature-distribution law in the microwave reactor with multiple waveguides Three measuring sections were selected in the static reactor,and the temperature was measured by infrared thermometer and thermocouple respectively.The influence of the position and quantity of microwave source on the temperature-rise law and temperature-distribution law of each section and the whole water area was investigated.The results show that the water on the top surface of water is easier to be heated than the water on the bottom,and the temperature of the water on the top surface is 4-5? higher than that on the bottom.Waveguides are located in the upper half of the cavity,and result in the higher heating efficiency of the water at the upper field.When the total output power is the same,the heating efficiency of the dual microwave sources is lower than that of the single microwave source,because the electromagnetic waves emitted by the dual microwave sources will affect each other,thus weakening the heating efficiency of the microwave reactor.(2)Simulation study on temperature-distribution law in the microwave reactor with multiple waveguides.The temperature distribution in the static reactor was simulated by COMSOL multiphysics software.It was found that the temperature-rise law obtained by the simulation was in good agreement with the experimental results,and the error between the experimental results and the simulation results was 10%-20%.Therefore,the model can be used to predict the temperature distribution law in higee-microwave coupling field.In addition,the optimal structure of microwave reactor is obtained by simulating the heating effect of different relative positions and installation modes of microwave sources.In the same total output power,when the two microwave sources are parallel to each other,the heating efficiency and uniformity are significantly higher than that of the single microwave source and the mutually perpendicular double microwave sources.During this study,the heating efficiency is the highest and the uniformity of temperature distribution is the best when the angle between the two microwave sources is 120°.On the contrary,the heating efficiency is the lowest and the uniformity of temperature distribution is the worst when the angle is 150°.(3)Simulation study on temperature-distribution law in the coupled field of high-gravity and microwave.The temperature distribution of water flowing on the rotating disk during microwave heating was simulated by using HFSS and Fluent softwares.Among them,HFSS software is used to simulate the distribution of electromagnetic field and the electromagnetic power loss density of water in the reactor.Fluent software is used to simulate the flow state of water on the rotating disk.Then,the electromagnetic power loss density obtained from HFSS is substituted into Fluent as load,and finally the temperature distribution law of water flowing on the rotating disk by microwave heating is obtained.The results show that the temperature of water does not rise too much on the rotating disk because of its fast velocity,and the temperature rise is higher near the overflow weir.Therefore,increasing the action time of microwave is important for the design of the reactor.