Research On Direct Contact Heat Transfer Performance Driven By Stable Heat Flo

Direct contact heat exchangers have great potential in the field of waste heat utilization because of the advantages of low temperature differential drive and simple structure.However,due to the complex heat transfer process of mixed fluid,difficult measurement of two-phase contact area and temperature,uneven mixing and difficult separation of hot and cold fluids,direct contact heat exchangers have been affected by the wide range of commercial applications.In view of the problems existing in direct contact heat exchangers,such as the difficult measurement of two-phase contact area and two-phase temperature,and uneven mixing of hot and cold fluids,this paper investigated the heat exchange performance in different working conditions,established the microelement layer model,and studied the relationship between the uniformity of temperature field and the efficiency of heat exchanger.Based on the electromagnetic tomography system,the inclination Angle algorithm is applied to quantify the mixing uniformity in the direct contact heat transfer process,which provides a new idea for improving the utilization efficiency of waste heat and the optimization of heat exchanger.Firstly,by establishing the microelement layer model of heat exchanger,the uniformity factor of temperature difference field is introduced into direct contact heat exchanger.The uniformity of temperature difference field of direct contact heat exchanger running with continuous heat source is analyzed.The heat transfer height is proposed and its influence on volume heat transfer coefficient and heat exchanger efficiency is analyzed.The results show that the error between the theoretical heat transfer height and the actual heat transfer height is within 5% and the variation trend of both is the same.The bubble uniformity is proportional to the temperature field uniformity factor,and the positive correlation coefficient between heat exchanger efficiency and temperature field uniformity is +0.975,which accords with the principle of temperature field uniformity.Secondly,this study presents a new method for quantifying the mixing uniformity of fluids in direct contact heat exchangers using electromagnetic tomography(EMT)with the inclination Angle algorithm.Nano-scale iron powder(Fe),ferric oxide(Fe2O3)and ferric oxide(Fe3O4)were dissolved in the continuous phase as tracer particles.Electromagnetic tomography was used to measure magnetic distribution at different flow rates in the dispersed phase,and EMT images were processed by the inclination Angle algorithm to quantify the mixing uniformity of the fluid.The influence of mixing uniformity on heat exchanger efficiency is further analyzed.Experiments respectively set three kinds of the dispersed phase of nano fluid velocity of 0.03 kg/s,0.06 kg/s,0.09 kg/s,0.12 kg/s,0.15 kg/s,0.18 kg/s.The results show that the inclination Angle of each group oscillates between-1.5° and +1.5°,and the oscillation rate of the inclination Angle decreases with the passage of time.The negative correlation coefficient between the heat exchanger efficiency and the tilt Angle is-0.94,and the correlation coefficient obtained by this method is 2% higher than that of the traditional uniformity judgment method.With the increase of the flow velocity of the dispersed phase,the mixing uniformity of the continuous phase and the dispersed phase increases first and then decreases,and the growth rate of the heat exchanger efficiency increases first and then decreases.When the flow velocity of the dispersed phase is0.12kg/s,the mixing uniformity of the two-phase flow and the heat exchanger efficiency in the temperature field reach the peak.