Characteristic Analysis And Structure Optimization In The Shell Side Of Helical-like Heat Exchanger

Shell-and-tube heat exchanger is a kind of equipment widely used in the industrial field.With the continuous advancement of energy conservation and emission reduction,the optimization and improvement of traditional shell-and-tube heat exchangers have received much attention.Helical flow is the ideal flow pattern in shell and tube heat exchangers,but the traditional helical baffles are complicated to manufacture.The helical-like heat exchanger developed based on the above situation can not only induce the shell-side fluid to generate an approximate helical flow but also has a simple process of machining and installation of the baffle,which has great potential for industrial application.In this paper,the flow characteristics and heat transfer performance of helical-like heat exchangers are studied by numerical method.The main contents are as follows:(1)The Realizable k-ε turbulence model is selected to numerically solve the flow and heat transfer characteristics in the helical-like heat exchanger and quarter sector helical baffle heat exchanger,and the results are compared with the results of Laser Doppler Velocimeter experiments and related literature.The results indicate that the numerical results are in good agreement with the experimental results,which verifies the reliability of the numerical method in this paper.(2)Statistical analysis of fluid velocity in helical-like heat exchanger and quarter sector helical baffle heat exchanger is performed using tools such as user-defined functions(UDF).The results show that the axial and radial velocity distribution trends of the fluid in the two heat exchangers are similar,and the difference in velocity is mainly concentrated in the longitudinal component.The flow patterns at different heat exchange tubes of the helical-like heat exchanger are relatively uniform,and the scouring effect on the tube bundle is better than that of the quarter sector helical baffle heat exchanger.Multiple jets are generated at the baffle of the helical-like heat exchanger,which improves the turbulent flow intensity on the shell side and makes its heat transfer performance 6.75%～10.66% higher than that of the quarter sector helical baffle heat exchanger.(3)The effects of angle,width,two-group spacing,and two-baffle spacing on the shell-side performance of the helical-like heat exchanger were investigated,and a fourfactor and three-level test scheme was determined according to the center composite surface design method.The regression model of heat transfer coefficient,pressure drop,and comprehensive performance of helical-like heat exchanger is established by using Response Surface Methodology.The model indicated that the baffle angle has the greatest influence on the heat transfer coefficient and pressure drop,and the two-group spacing has the greatest influence on the comprehensive performance.In addition,the optimal parameter combination of the helical-like heat exchanger is predicted by the regression model.Compared with the initial structure,the heat transfer performance is improved by 15.06%,and the comprehensive performance is improved by 5.79%.(4)A streamlined orthogonal elliptical tube was designed based on the shell-side flow pattern of the helical-like heat exchanger.The results show that the use of orthogonal elliptical tubes can improve the heat transfer performance and reduce the flow resistance of helical-like heat exchanger at small flow rates.Among them,the orthogonal elliptical tube with an axial ratio of 1.5 has the best performance,the heat transfer coefficient is 0.43%～4.39% higher than that of the smooth tube,and the comprehensive performance is 0.52%～4.03% higher than that of the smooth tube.With the increase of the axial ratio,the streamlined degree of the orthogonal elliptical tube increases,and the flow resistance decreases significantly.The results of field synergy analysis indicate that the reason for the enhanced heat transfer of the orthogonal elliptical tube is to improve the synergy between the shell-side velocity field,temperature field,and pressure field.