Optimum Spacing For Maximum Heat Transfer In A Bundle Of Tubes At Low Reynolds Number

Present project mainly investigates the effect of tubes spacing on the heat transfer between tube group and fluid at low Reynolds number.Meanwhile,the effect of spacing on the aerodynamics is also investigated.The tube group has two models,Model A(staggered)and Model B(in-line).Two models both consist of seven identical isothermal tubes(d = 0.04m).The simulations are proceeded at various range of spacing ratios(g*= gld,g*changes from 0.1 to 5 and g is the spacing between two adjacent tubes)for fixed Reynolds number(Re = 100,based on d)and Prandtl number(Pr =0.74).Finite volume method is used in the simulations and the main objective focuses on the spacing ratio effects on the total heat transfer ratio((?)/A*represents the heat transfer ratio,(?) is the mean value of all tubes Nusselt numbers,A*is the dimensionless area of tubes group).The heat transfer ratio of single tube((?)),other aerodynamics parameters and flow structures for two models are also investigated.Other aerodynamics parameters include the time-averaged drag coefficient(CD),the time-averaged lift coefficient(CL),the fluctuating lift coefficient(CLf)and the Strouhal number(St).The simulation results show that the maximum heat transfer ratio((?)/A*)for Model A is 0.217 and the optimum spacing occurs at g*= 0.6.While for Model B,the maximum heat transfer ratio is 0.235 and the optimum spacing ratio occurs at g*=0.5.The flow situation changes with the increase of g*and five flow patterns(Pattern A,B,C,D,E)are classified based on different flow situations.For each tube,the Nusselt numbers and other aerodynamics parameters approach to the corresponding parameters of single tube at large spacing ratio.Instantaneous vorticity contours,time-averaged temperature contours,time-averaged velocity contours,time-averaged streamlines and the local time-averaged Nusselt number graphs help us to further understand the effects of spacing ratio on the heat transfer and flow structure.