Numerical Simulation Optimization Research Of Integral Gravity Heat Pipe Heat Exchanger

Under the current trend of energy conservation and emission reduction,improving energy utilization and realizing multi-level utilization of energy,recovering boiler flue gas waste heat can not only improve boiler efficiency,but also save energy.As a kind of heat transfer equipment,gravity heat pipe is widely welcomed in the heat exchange equipment industry because of its unique phase change heat transfer mode,small heat transfer resistance,good isothermal,high heat transfer efficiency and good compactness.In this paper,taking the gravity heat pipe as the heat transfer element,an integral gravity heat pipe heat exchanger is designed to recover the flue gas waste heat of two WNS 14-1.25/115/70-q hot water boilers in the heating system.(1)Starting from the theoretical research,this paper theoretically analyzes the seven steps of gravity heat pipe heat transfer,and theoretically designs the integral gravity heat pipe heat transfer according to the actual boiler working conditions and specific design requirements.The heat transfer principle,heat transfer resistance,working temperature,heat pipe diameter,heat pipe working medium,liquid filling capacity,length ratio,arrangement mode,pipe spacing and total number of heat pipes of gravity heat pipe are theoretically calculated.According to the tube spacing,water side inlet velocity,fin type,fin spacing,thickness and fin inclination angle,the heat exchanger is numerically simulated.The simulation results of no fin,straight fin and corrugated fin are processed,the heat transfer and inlet and outlet pressure drop under different working conditions are compared and analyzed,and the heat transfer performance of integral gravity heat pipe is comprehensively analyzed by using comprehensive performance evaluation indexes.(2)Using fluent 19 0 software is used to simulate the heat pipe heat exchanger,and Tecplot is used to process the simulation results of various working conditions.The heat pipe spacing is 75 mm,70mm,65 mm and 60 mm,the inlet flow velocity at the water side is0.02m/s,0.04m/s,0.06m/s,0.08m/s,0.10m/s,0.12m/s,0.16m/s and 0.20m/s.The analysis shows that with the decrease of heat pipe spacing and the increase of water flow velocity,the heat exchange of heat pipe heat exchanger first increases rapidly and then increases slowly,and the inlet and outlet pressure drop first increases slowly and then increases rapidly.The heat exchange and pressure drop under various working conditions are analyzed.When the pipe spacing is reduced from 75 mm to 70 mm,65mm and 60 mm,the average increase of heat exchange is 4.9%,11.3% and 17.8% respectively.The average increase of pressure drop was27.8%,45.4% and 61.8% respectively.With the decrease of tube spacing,the heat exchange of heat pipe heat exchanger increases,but at the same time,the pressure drop at the inlet and outlet also increases rapidly.(3)The heat pipe spacing is 65 mm and the water flow velocity is 0.12m/s.The simulation calculation of flat fins with fin spacing of 4.5mm,5mm,5.5mm and 6mm and fin thickness of 0.2mm,0.4mm,0.6mm,0.8mm,1.0mm and 1.2mm shows that the heat exchange first increases and then decreases with the gradual thickening of fins,and decreases with the increase of fin spacing;The pressure drop increases with the increase of fin thickness and with the decrease of fin spacing.Compared with no fins,when the fin spacing is 5mm and the fin thickness is 0.4mm,the heat exchange increases by 10.77% and the pressure drop increases by 280%.(4)The corrugated fins with inclination angles of 7 °,8 °,9 °,10 °,11 °,12 ° and 13 °are numerically simulated,and the comprehensive performance evaluation index is introduced.It is found that when the fin inclination angle is 11 °,the comprehensive performance evaluation index PEC = 1.007,the lifting capacity is 0.67%,the heat exchange increases by11%,and the pressure drop increases by 110.5%.Under this parameter condition,considering the heat exchange and pressure drop,the performance of gravity heat pipe heat exchanger designed in this paper is the best.To sum up,this paper makes an in-depth study on the structure and heat transfer performance of the integral gravity heat pipe heat exchanger by using theoretical calculation and fluent numerical simulation.The relevant results have a certain reference for the waste heat recovery of low-temperature flue gas in China.