Numerical Reserach On Enhanced Heat Transfer Characteristics Of The Y-shaped Inner-Ribs Tubes

With the rapid development of society,problems such as energy shortages and environmental pollution have become increasingly prominent.How to improve energy utilization rate and achieve energy conservation and emission reduction has become the focus of attention.Heat transfer enhancement technology is an important way to solve a series of problems,such as energy shortage and environmental pollution.Longitudinal vortex enhanced heat transfer technology is a kind of passive heat transfer enhancement technology.Based on longitudinal vortex enhanced heat transfer technology,a new type of inner rib heat transfer tube structure is proposed in this paper,which mainly studies the fluid flow and heat transfer characteristics in the heat exchange tube.In this paper,ANSYS CFD15.0 software is used to simulate the fluid flow and heat transfer characteristics of Y-shaped inner rib heat exchange tube.The effects that different Y-shaped inner ribs structural parameters on heat transfer characteristics are analyzed.Then,the fluid flow and heat transfer characteristics of Y-shaped inner rib heat transfer tubes under unsteady state pulsating flow are studied.Finally,based on the genetic algorithm,the structural parameters of Y-shaped inner rib heat transfer tubes are optimized.The main results of this paper are as follows:Firstly,the numerical simulation of Y-shaped inner rib heat transfer tube is carried out with the Fluent 15.0 software.The fluid flow characteristics in the tubes are analyzed.The effects of different structural parameters on the fluid flow and heat transfer in the tubes were studied.The results show that the Y-shaped inner ribs generate multiple longitudinal vortexes in the tube,the fluid in the tube is severely turbulent,the fluid mixing in the near-wall area and core area is more fully,the viscous bottom layer in the near-wall area is destroyed,and the heat exchange capability is enhanced.When the Reynolds number is3500~17500,the comprehensive evaluation factor is1.4~1.85.When the Y-shaped inner rib angle?and the distance P are constant,the PEC increases with the length L of the inner rib,and the maximum value is obtained at L=8mm.When the inner rib length L and the ditance P are constant,with the increase of the angle?,the PEC first increases and then decreases,and at the?=90°,the PEC obtains the maximum value.When the inner rib angle?and the length L are constant,the larger the distance is,the smaller the PEC value.Based on the extremum principle of entransy dissipation theory,the effects of different included angles and inner rib lengths on the thermal dissipation are analyzed.Secondly,when the pulsating inlet velocities is sinusoidal periodic variation,the effects on fluid flow and heat transfer characteristics of Y-shaped inner rib heat exchange tube are studies.And then the effect of the pulsation amplitude A_u,frequency f and Reynolds number Re on the heat transfer effect is analyzed.The results show that with the increase of the pulsation amplitude A_u,the Nusselt number is also increased significantly,and the heat transfer effect is obviously enhanced.When Re=10500 and the amplitude A_u=0.5,the pulsating flow frequency f=1Hz is the critical frequency.When f<1Hz,Nu increases gradually with the increase of frequency,but the change is small.When f>1Hz,with the increase of frequency,Nu also increases gradually and the rate of increase is larger.The effect is improved significantly.When the amplitude A_u=0.5 and the frequency f=5Hz,Nu increases as the Reynolds number increases,and heat transfer increases.The influence of amplitude and frequency on the field synergy angles in two periods,and the variation with time of the entransy dissipation in one cycle under different amplitudes.Finally,according to the numerical simulation results on the steady state,the linear regression of Nu and f in the Y-shaped inner rib heat transfer tube,the correlation of integrate evaluation factors of PEC is obtained.And then the mathematical model of the optimal design of the heat transfer tubes is established,using the genetic algorithm and the Fimicon Function of MATLAB to obtain the optimal parameters of the Y-shaped inner rib structure.