Exploration Of A Heat Exchanger And Mechanism Of Heat Transfer Enhancement Based On Complex Flow Cross Tube Bundles

As China’s economic development has entered the new normal,energy-centered environmental problems are becoming more and more serious.As the most widely used heat exchanger in the petrochemical energy field,the design and development of highefficiency energy-saving shell-and-tube heat exchangers has always been a research hotspot.Based on the research of complex flow cross tube bundle shell-and-tube heat exchanger,the author proposes a special-shaped inclined baffle heat exchanger with complex flow state.The shell side flow and heat transfer of heat exchanger were studied by theoretical analysis,numerical simulation and experimental verification.The research contents and conclusions are as follows:1.A special-shaped inclined baffle heat exchanger is proposed based on the complex flow state of fluid,and compared with conventional baffle heat exchanger and profiled baffle heat exchanger.The results show that the Reynolds number is in range of 6000~10000,the shell side heat transfer coefficient,pressure drop and comprehensive performance of the special-shaped inclined baffle heat exchanger are higher than those of the conventional baffle heat exchanger and the profiled baffle heat exchanger.The special-shaped inclined baffle heat exchanger has a compact structure,the jet formed by baffles and heat exchange tube and the spiral flow of fluid through the sinusoidal baffles improve fluid turbulence,weaken the boundary layer,and enhance heat transfer.Moreover,the inclined baffles change the fluid flow flow path,strengthen the speed transfer effect,increase the diagonal flow area,and improve the utilization rate of the heat exchange area.Due to the compact layout,when fluid flushes the baffle,the fluid resistance of the shell side will be increased,resulting in a large pressure loss,and the shell-side pressure drop increases.The field synergy analysis shows that shell side fluid temperature field and velocity field of special-shaped inclined baffle heat exchanger are better,so it has better heat transfer enhancement characteristics.2.Based on the periodic model,the effects of different baffle arrangement,inclined angle of baffle,baffle spacing and baffle angle on heat transfer performance of special-shaped inclined baffle heat exchanger are studied.The results show that the shell heat transfer coefficient and comprehensive performance of the compact parallel arrangement heat exchanger are increased by 12.7%~14% and 3.6%~7.9%,and the pressure drop of staggered arrangement heat exchanger is lowest;With the increase of inclination angle of baffle,the pressure drop of shell side of heat exchanger increases,the heat transfer coefficient and comprehensive performance increase first and then decrease,and the heat transfer performance is optimal when the inclination angle is 25°;As the increase of baffle spacing,the shell side heat transfer coefficient and the pressure drop of heat exchanger decrease,and the comprehensive performance improves.The continuity of fluid velocity and the separation frequency of the boundary layer are reduced,the number of baffles in the shell-side unit and the flow resistance are reduced.Therefore,the heat exchanger with a 190 mm baffle spacing has the best comprehensive performance;With the increase of baffle angle,the heat transfer coefficient and pressure drop of shell side increase,and the comprehensive performance decreases.The smaller angle of baffles,the more uniform shell-side fluid velocity distribution,the greater turbulent kinetic energy of the fluid,and the stronger heat transfer.However,the change of baffle angle has a more pronounced effect on the pressure drop of shell side.Therefore,the heat transfer has a better comprehensive performance when the angle of baffle is 60°;According to dimensionless analysis method,the shell side heat transfer coefficients and fluid resistance criterion correlation of different structural parameters of special-shaped inclined baffle heat exchangers are given to guide the engineering design.Based on correlation,the genetic algorithm is used to optimize the specific parameters.Compared with initial parameters,the entropy production of the new structural parameters is reduced by 5.3%,which indicates that optimized heat exchanger has more useful functions and better performance.3.Design the same cold model experimental device as numerical model,laser Doppler velocimeter is used to measure the velocity of special measuring points on the shell side of special-shaped inclined baffle heat exchanger.Comparing the experimental data with simulation results,the results show that error between the experimental results and imulated values is not more than 23%,which verifies the accuracy of the numerical simulation method and results.