Heat Transfer Enhancement And Optimization Design On Shell Side Of Shell And Tube Heat Exchanger

Energy is the foundation of the development of the society and technology,and it also is the powerful assurance of the sustainable development.Since China is not the energy-efficient country in the world,the energy-saving is one of the important topics.Heat exchanger is widely used in all fields of industries as a kind of the heat transfer equipment,and it is the key equipment for the energy utilization.In all kinds of heat exchangers,the shell and tube heat exchanger(STHX)is the most widely used one.Therefore,improving the comprehensive performance of STHXs would be helpful to improve the energy efficiency.It also is meaningful for the energy saving and emission reduction,and it is expected to reduce energy consumption per unit of GDP.Based on existing theories,the present dissertation employs the numerical,experimental,and optimization methods to enhance the heat transfer of STHXs,which could further provide the guidance for developing the novel high-performance STHXs.Based on the heat transfer enhancement mode of uniformizing fluid temperature through fluid mixing(UFTTFM)in the tube side,its application in the shell side is analyzed in the present dissertation.The shell-side baffle structure is considered as a kind of technologies of the fluid-based heat transfer enhancement.According to this mode,the shell-side baffle structure disturbs the fluid flow to uniformize the temperature distribution of the working fluid,which leads to the increasing temperature gradient neat the tube walls,so the convective heat transfer performance is improved.The effects of UFTTFM of baffle rods with circular,elliptical,and square cross-sections are numerically investigated for ripple rod baffle heat exchangers(RRBHXs).The results indicate that the RRBHX with the elliptical cross-section present the most uniform temperature distribution and highest heat transfer coefficient,which verifies the shell-side heat transfer enhancement mode of UFTTFM.A novel double shell-pass rod baffle heat exchanger(DS-RBHX)is proposed in this dissertation.A sleeve is set in the single shell-pass rod baffle heat exchanger(SS-RBHX)to divide the shell side into two passes,which is expected to improve the heat transfer performance by increasing the flow velocity and flow distance.The numerical results indicate that the heat transfer rate of the DS-RBHX is around 27.9% higher than that of the SS-RBHX under the same power consumption,while the power consumption of the DS-RBHX decreases by 54.2% compared with the SS-RBHX under the same heat transfer rate.Therefore,the comprehensive heat transfer performance of the DS-RBHX is better than that of the SS-RBHX.Moreover,the pressure drops of the inlet and outlet zone account for 57% and 40% in the shell-side pressure drops of the SS-RBHX,while the proportions for the DS-RBHX are 37%and 24%,respectively.Therefore,inlet and outlet zones,particularly the inlet zone,are the key parts for reducing the flow resistance.On the other hand,the heat transfer coefficients of the inlet zone are higher than those of the main zone and outlet zone.It can be deduced that improving the heat transfer performance of the main zone and outlet zone is more effective for enhancing the overall heat transfer performance.Subsequently,experiments are carried out for the SS-RBHX and DS-RBHX.As a result,the correlation formula of the Nusselt number is summarized.The experimental results indicate that under the same flow rate the shell-side heat transfer coefficient and pressure drop of the DS-RBHX are higher than those of the SS-RBHX by 33.5%-54.0% and 34.2%-74.3%,respectively.Under the same pressure drop,the heat transfer coefficients of DS-RBHX increase by 14.4%-24.3% than those of SS-RBHX.The numerical simulation is conducted for the DS-RBHX tested in the experiments.The numerical model of the DS-RBHX is proved to be accurate by comparing the numerical and experimental results.Finally,it is safe to conclude that the DS-RBHX significantly improves the heat transfer performance relative to the SSRBHX,which is meaningful for further extending the application of rod baffle heat exchangers.To decrease the flow resistance of the inlet zone of the SS-RBHX,a curved flow guiding structure is set in the guide shell of the inlet.Numerical method is employed to investigate its effects of reducing flow resistance.The numerical results indicate that the curved flow guiding structure decreases the pressure drop of inlet zone and overall shell side by around 9.5% and5.7%,respectively,while it has little influence on the heat transfer performance.Besides,the flow resistance is effectively reduced by the curved flow guiding structure without increasing the cost.Therefore,the curved flow guiding structure is supposed to have the potential for the wide application.According to the velocity distribution,there is a clear flow dead zone in the outlet zone of the DS-RBHX.The traditional guide shell,the guide shell with a big rectangular opening(GSs BRO),and the guide shell with small rectangular openings are designed to eliminate the dead zone and enhance the heat transfer for the outlet zone of the DS-RBHX.The numerical results suggest that the GSs BRO has more significant effects on disturbing the fluid flow and improving the heat transfer performance than the other two guide shells.Under the same power consumption,the heat transfer rate of the outlet zone of the DS-RBHX with GSs BRO increases by around 9% compared to the DS-RBHX.Based on the STHX with segmental baffles(STHXs SG),a shell and tube heat exchanger with staggered baffles(STHXs SB)is proposed,in which the helical flow is generated by staggered baffles.Its flow and heat transfer performance are numerically compared with the STHXs SG and the STHX with continuous helical baffles.Among the three STHXs,the STHXs SB gets the highest heat transfer rate at the same power consumption.The heat transfer coefficient of the STHXs SB increases with the baffle cut decreasing and the staggered angle increasing.Moreover,a novel optimization procedure with the surrogate model is employed to simultaneously optimize the baffle number,staggered angle,and baffle cut of the STHXs SB.The orthogonal design,artificial neural network,genetic algorithm,and CFD are adopted in the procedure where the heat transfer rate and pressure drop are defined as the optimization objectives.After obtaining the Pareto fronts by the multi-objective optimization,the best compromise solution of STHXs SB is obtained by the multi-objective decision-making technique while the baffle cut,staggered angle,and baffle number are 0.45,79°,and 11,respectively.Furthermore,the Pareto fronts of the STHXs SBs and STHXs SGs are compared,which provides the evidence that the best compromise solution of STHXs SBs could effectively balance two conflicting objectives and further improve the comprehensive performance compared with the optimal STHXs SGs.From the point view of heat transfer enhancement,the dissertation develops the novel STHXs with longitudinal flow and helical flow by the numerical and experimental investigations,which provide more various and effective options for the applications of the STHXs.It is quite meaningful for improving the energy efficiency.