Analysis And Optimization Of Heat Transfer Performance In Flue Gas-water Heat Exchange Tube

Flue gas waste heat recovery is an effective way to improve energy efficiency.The key equipment that affects waste heat recovery is heat exchanger.In order to improve the effect of flue gas heat transfer,domestic and foreign countries have carried out extensive research,and constantly put forward a variety of enhanced heat transfer structure.Based on the same purpose,in order to improve the tube type gas water heat exchanger efficiency,the inner fin type,jet type,combination type jet inner fin pipe condensation was simulated.(1)Firstly,the model validation of convection and condensation heat transfer in tubes is carried out.Based on the convection heat transfer experiment in the literature,the numerical simulation is carried out according to the experimental conditions,and the calculated data are compared with the experimental data.The numerical simulation results are in good agreement with the experimental data and the empirical theory.(2)Three different types of inner finned tubes(Inner fin tube with core block,rectangular finned tubes and hoval tubes)were established.The temperature,pressure,convective heat transfer coefficient,Nusselt number,drag coefficient and PEC efficiency value of the single phase convective heat transfer and condensing transformation heat transfer were studied by means of numerical means.The results show that the convection heat transfer coefficients of the three inner fin tubes are larger than those of the tubes under the same Reynolds number,and the PEC is less than 1,whether or not the phase change is condensed.The Nusselt number and the resistance coefficient of the three tubes when condensed are all larger than those of the single phase without condensation.The condensation PEC of the core tube is greater.The single phase PEC of the inner fin tube in the rectangle is larger,and the condensing PEC of the hoval tube is almost the same as that of the single-phase PEC.(3)The feasibility and comprehensive performance of jet impingement heat transfer enhancement in flue gas heat exchangers were studied.From the temperature,pressure,turbulent kinetic energy,the local heat flux and the Nusselt number and resistance coefficient and PEC performance analysis of several aspects of the opening angle,hole size,hole effect of axial spacing of three basic structural parameters on heat transfer.The results show that the PEC value of jet impingement tube is greater than 1.At the opening hole angle of 45 degrees,the hole diameter is 2mm,and the axial distance between the holes is 16 mm,the PEC is the highest,and the PEC value at different Reynolds numbers is between 1.25-1.7.(4)Two heat transfer enhancement methods,inner fin and jet impingement,were combined to improve the heat transfer performance of the tube heat exchanger.By numerical method,the heat transfer capability of two kinds of tube heat exchangers,Inner fin tube of round tube jet and special jet inner fin tube are analyzed and optimized.Changes of temperature,pressure,turbulent kinetic energy,the local heat flux and the Nusselt number and resistance coefficient and efficiency of PEC with the structure parameters and flow parameters were investigated.The results show that the heat transfer capacity of the inner fin tube of the two structures is stronger than that of the light tube and jet impingement tube,and the resistance increases little.In the range of Reynolds number studied,the PEC value of the inner fin tube in the tube jet is between 2-2.25,and the inner fin tube in the jet is between 1.15-2.1.