Numerical Investigation And Optimization Design On Heat Transfer And Flow Performance In Shell Side Of Shell And Tube Heat Exchanger

With the improvement of the global industrialization level,countries in the world have an increasing demand for energy,and the problem of energy shortages is become more and more severe.In addition to adjusting the energy structure and vigorously developing renewable clean energy,improving the utilization rate of existing energy is of great significance to China’s sustainable development.Heat exchanger is a kind of common heat exchange equipment,which is widely used in industrial production,and shell and tube heat exchanger(STHX)is the most widely used one.Therefore,improving the heat transfer efficiency of the STHX is an effective measure to improve the energy utilization efficiency.Based on the characteristics of trefoil-hole baffles to effectively scour the pipe wall,this thesis combines the trefoil-hole baffles with the oblique flow and spiral flow respectively to design two new structures of the STHXs,in order to achieve the heat transfer enhancement in the shell side of the STHXs.In the meantime,numerical simulation and optimization methods are used to study the flow and heat transfer performance in the shell side of the two new STHXs.The STHX with inclined trefoil-hole baffles(STHX-IT)is designed by combining the trefoil-hole baffles and the oblique flow.Numerical results show that the STHX-IT can significantly eliminate the flow dead zone and greatly reduce the pressure drop in the shell side,while the heat transfer performance is reduced,but the overall performance is enhanced.Meanwhile,the effect of geometric parameters,which are the inclination angle,the trefoilhole number,and the baffle cut,on the shell side performance of the STHX-IT is explored.Results show that the inclination angle has little effect on the shell side performance;while with the increase of the trefoil-hole number and the baffle cut,the heat transfer coefficient and pressure drop of the STHX-IT are both decreasing,but the overall performance is increasing.In addition,the structure of the STHX-IT is optimized by the optimization method with the surrogate model,which combines numerical simulation,artificial neural network,and genetic algorithm.And the best solution of the obtained Pareto front is selected by the TOPSIS(Technique for Order Preference by Similarity to Ideal Solution)method.The inclination angle,the trefoil-hole number,and the baffle cut of the optimal structure are 5.38°,6 and 43%,respectively.When compared with the STHX with segmental baffles(STHX-SG),the optimal solution has worse heat transfer performance and smaller pressure drop,but it shows better overall performance.The STHX with staggered trefoil-hole baffles(STHX-ST)is designed by combining the trefoil-hole baffles and the spiral flow.Numerical results show that the STHX-ST can effectively reduce the flow resistance and make the overall velocity distribution and temperature distribution of the shell side more uniform.Although the heat transfer performance of the STHX-ST reduces,its overall performance improves.At the same time,the effect of geometric parameters,i.e.the baffle number,the trefoil-hole number,and the baffle cut of baffles,on the shell side performance of the STHX-ST is explored.Simulation results show that when the baffle number increases,both the heat transfer coefficient and pressure drop of the STHX-ST increase,but its comprehensive performance increases firstly and then decreases,and the value reaches the maximum when the baffle number is 6.When the STHX-ST has larger baffle cut and larger trefoil-hole number,its heat transfer coefficient and pressure drop are smaller,while the comprehensive performance is better.Additionally,the flow and heat transfer performance of five kinds of STHX,i.e.STHX-SG,STHX with trefoil-hole baffles,STHX with staggered baffles,STHX-IT and STHX-ST,are compared and analyzed,in order to compare the effect on shell side performance of three methods adopted for the STHX in this thesis,that is,setting the inclined angle for baffles,setting the trefoilholes for baffles and setting the staggered baffles.Results indicate that all of these three methods can improve the shell performance of the STHX.Among them,the inclination angle has minimal influence on the shell side performance,while the trefoil-hole has the maximum influence;at the same time,the trefoil-hole improves the shell side performance mainly by reducing the pressure drop loss intensely.In this thesis,two new STHX structures are designed to enhance the heat transfer on shell side of the STHX.The flow and heat transfer performance of these STHXs are explored through numerical simulation and optimization design,which has a positive effect on improving the heat transfer efficiency of the STHX.