Study On Heat Transfer Characteristics Of Liquid-Vapor Separation Plate Condenser

Condensers are very important and essential components in many industries,such as energy and power,petrochemical,refrigeration and heating,food and medicine.Improving the heat exchange efficiency of condenser and reducing the sizes of condenser can not only decrease the weight of equipment and improve the efficiency of energy utilization.but also save the installation space and reduce the operation cost.As a result,the research on heat transfer mechanism and mechanical structure innovation of condenser has practical engineering value.In this doctoral dissertation,according to the condensation heat transfer characteristics of the plate condenser,liquid-vapor separation is applied to the plate condenser The mechanism,the realization structure and the influence factors in liquid-vapor separation plate condenser(LVSPC)are studied in depth.The following is the summary of this paper:Firstly,the basic principle of heat transfer enhancement of LVSPC is described.By appropriate liquid-vapor separation,the condensate can be discharged from the flow channel as soon as possible,which can reduce the thickness of the condensate film in the lower flow channel of the plate condenser,which is helpful to improve the overall heat transfer coefficient(HTC)of the condenser.Thin liquid film is helpful to improve the overall HTC of condenser This paper provides a detailed introduction of the construction and liquid separation fundamentals of LVSPC.The innovative improvement is to add a discharge port in the middle of the plate condenser,which divide the heat exchanger plate into two condensing areas.The condensate in the first condensation area is discharged through the discharge port,and the pure vapor enters into the second condensing area and continue to condenseBased on the idea of subsection calculation,the lumped parameter model for LVSPC was established.By means of multi-stage iterative method,a performance parameter calculation program for LVSPC is written with Visual Basic 6.0.The experimental correlations of condensation heat transfer coefficient(HTC_r)and pressure drop(?P_r,f)of plate heat exchanger developed by Yan,Han,Kuo are used in this program.The results show that the Kuo correlation has the smallest deviation and the highest reliability.Therefore.Kuo correlation is used to establish the mathematical model of heat transfer performance prediction of LVSPC.The performance of LVSPC with specific size were calculated and compared with common plate condenser(CPC).The results show that the HTC_r and the ?P_r,f of LVSPC are smaller than those of CPC.It can be seen that although the inlet vapor quality of the second condensing area of LVSPC(Xin,r,2)is improved,the mass flux of the second condensing area of LVSPC(G_r.2)is significantly reduced.Because the influence of the Xin,r,2 and the G_r,2 on HTC is opposite,and the decrease of G_r.2 has a greater influence,the HTC_r of the second condensing area of LVSPC is decreased significantly.Therefore,the structure of the second condensation area must be optimized.Taking the length ratio(LR)and corrugation height ratio(AR)as the key parameters of structural optimization.HTC_r,Pr,f,heat exchanger performance evaluation criterion(PEC),penalty factor(PF)and system exergy efficiency(?)are took as optimization evaluation indexes,the optimal values of LR and AR were solved by performance prediction model.The results show that when the LR and AR are around 0.5,the comprehensive thermal performance of LVSPC reaches the highest,and is better than CPC under the same conditions.According to the results of optimization,the structure size of LVSPC is determined by LR=0.5,AR=0.5.The influence of operating parameters such as G_r.Xin,r,l and heat flux(qr)on the heat transfer performance and comprehensive thermal performance of LVSPC is studied.The results show that HTC_r,qr and PF increase with the increase of G_r,Xin,r,l and qr,?P_r,f and PEC are magnified by the enlargement of G_r and Xin,r,l and reduced when qr is bigger.? is magnified by the enlargement of qr and Xin,r,l and reduced when qr raise.Experimental research is also carried out in this paper.Taking R134a as refrigerant,the heat transfer performance of LVSPC and CPC was compared.The experimental results can be concluded as follows:(1)under the same initial conditions,the HTC_r and the total heat transfer coefficient(Ktocai)of LVSPC are greater than those of CPC,and the total heat transfer of LVSPC is greater than that of CPC;(2)In all cases,the ?P_r,f of LVSPC is less than that of CPC,which indicates that LVSPC can reduce the flow resistance and pump power.Mass flux,vapor quality,pressure,heat flux and vapor superheat are taken as the research objects to study the influence of their changes on the heat transfer coefficient and pressure drop of LVSPC.The experimental results show that:(1)With the increase of mass flux,the Ktotai and ?P_r,f increase.(2)With the increase of vapor quality,the Ktotal has no obvious change,and the ?Pr increases slightly.(3)When the pressure goes up,the Ktotal goes up as well until the pressure rise to a certain value,and then Ktotal begain to goes down.(4)When the heat flux rise,the Ktotal rise and the ?P_r,f drop.(5)With the accretion of vapor superheat,the Ktotal and ?P_r,f will decline.According to the experimental data,the performance prediction model of LVSPC was verified again.The results show that all the predicted values of HTC_r and ?P_r,f are greater than the experimental values.Through the modification of the experimental correlation,the deviation of the predicted HTC_r values are less than 15%and the deviation of the predicted?P_r,f values are less than 20%.It shows that the calculation accuracy of the modified performance prediction model has been greatly improved.