Effect Of Porous Fins On Convective Heat Transfer Performance In Enclosed Cavity With Periodic Temperature Boundary Heat Source

The natural convection heat transfer phenomenon in the closed cavity with different types of temperature boundary heat sources is widely used in various industrial production practices involving thermal processes such as sealed chassis heat dissipation,building insulation,and transformer cooling.It has been found that the method of enhancing or suppressing the flow and heat transfer in the closed cavity by installing porous fins on the side wall of the cavity to change the structure and development trend of the wall boundary layer is simple and applicable.In recent years,relevant literature research has found that the research on the influence law of built-in fins and the optimization of their geometric parameters and spatial positioning dimensions is still insufficient and comprehensive.Nowadays,the technology of high power density micro sealed electronic equipment is developing rapidly,the problem of high heat flux of heating elements and integrated circuit systems in the equipment needs to be solved urgently.The working efficiency and service life of electronic components are closely related to it.Therefore,it is particularly important to study the natural convection characteristics and heat transfer efficiency in the limited closed space.In this paper,ANSYS FLUENT 2020 R2 software was used to numerically analyze the influence of 6 dimensionless single parameters of porous fins(fin installation height S_a,fin installation height differenceΔS_ab,fin length L_a,fin length ratio A,fin inclination angleθ,fin thickness B)on the natural convection heat transfer performance in the closed cavity with fixed temperature boundary heat source and sinusoidal periodic temperature boundary heat source,and the interaction effect of porous fin parameters and multi-parameter combination optimization were studied by Design-Expert10.0 software.In order to provide theoretical reference for improving the convective heat transfer effect of heating components in the limited closed space of industrial system.The main contents of the study are as follows:（1）The symmetrical arrangement of double porous fins on the cold wall of the closed cavity with fixed temperature boundary heat source affects the convective heat transfer in the cavity.The influence of 6 kinds of fin single parameter changes on the convective heat transfer level in the cavity was analyzed.The results show that different single-parameter porous fins enhance the heat transfer efficiency of the heat source surface,and there are differences in the law of increase and decrease and the range of increase.Among them,the fin length L_ahas the most significant effect,and the fin length ratio A has the least effect.The single-parameter conditions that maximizes the average Nu number on the heat source surface are L_a=0.05,S_a=0.6,θ=120°,ΔS_ab=0.05,B=0.016,A=0.625,which are 10.66%,7.88%,7.30%,7.40%,6.71%,6.27%higher than without fins condition;（2）On the basis of the influence law of single parameter,the influence of the interaction of 6 kinds of double porous fins parameters on the convective heat transfer efficiency of the heat source surface with fixed temperature boundary was analyzed by response surface optimization.The significance of the interaction of two parameters is as follows:fin installation height S_aand length L_a>fin length L_aand inclination angleθ>fin installation height S_aand inclination angleθ>fin installation height S_aand length ratio A>fin installation height S_aand thickness B>fin installation height S_aand height differenceΔS_ab.The optimal combination of fin parameters predicted by the response surface is:S_a=0.35,L_a=0.061,ΔS_ab=0.250,A=0.500,B=0.016,θ=42.960°.At this time,the average Nu number on the surface of the heat source is 6.69,which is 15.4%higher than the finless cavity;（3）Based on the optimal fin parameters combination of the closed cavity with fixed temperature boundary heat source,the comprehensive effects of Rayleigh number Ra,wall emissivityξ,Darcy number Da and porosityεon the convective heat transfer in the cavity were studied respectively.It is found that the Rayleigh number Ra and the wall emissivityξ,the Darcy number Da and the porosityεhave synergistic effect on the improvement of the convective heat transfer level in the cavity.Among them,the combined effect of Rayleigh number Ra and wall emissivityξis more significant than that of Darcy number Da and porosityε;（4）The double porous fins are symmetrically arranged on the cold wall of the closed cavity with sinusoidal periodic temperature boundary heat source to change the convective heat transfer level in the cavity.The influence of 6 kinds of fin single parameter changes on the convective heat transfer performance in the cavity was analyzed.The results show that the temperature field and flow field structure in the cavity exhibit a periodic fluctuation distribution.The instantaneous average Nu number on the surface of the heat source is affected by single parameter of the fins,and fluctuates according to a sinusoidal law with differences.The time-average Nu number of the heat source surface under different single-parameter porous fins is improved.Among them,the fin length L_ahas the most significant effect on the heat transfer level of the heat source surface,and the fin installation thickness B has the least effect.The single-parameter conditions that maximizes the time-average Nu number on the surface of the heat source are L_a=0.3,S_a=0.35,θ=30°,ΔS_ab=0.25,A=1,B=0.008,which are 8.30%,8.39%,6.64%,7.33%,7.44%,6.45%higher than without fins condition;（5）Based on the influence of single parameter of porous fins on the convective heat transfer in the closed cavity with sinusoidal periodic temperature boundary heat source,the influence of the interaction of 6 kinds of double porous fins parameters on the convective heat transfer efficiency of the surface of sinusoidal periodic heat source was analyzed by response surface optimization.The significance of the interaction of two parameters is as follows:fin installation height S_aand fin length L_a>fin length L_aand fin inclination angleθ>fin installation height S_aand fin length ratio A>fin length L_aand fin height differenceΔS_ab>fin installation height S_aand fin inclination angleθ>fin length L_aand fin length ratio A.The regression equation predicts that the optimal fin parameter combination is S_a=0.351,L_a=0.300,ΔS_ab=0.237,A=0.999,B=0.004,θ=34.794°.At this time,the maximum time-average Nu number on the heat source surface is 11.63,which is 13.00%higher than the finless cavity;（6）Based on the optimal fin parameters combination of the closed cavity with sinusoidal periodic temperature boundary heat source,the influence of dimensionless amplitude a and dimensionless periodτ_pon the convective heat transfer level in the cavity was studied.It is found that the increase of dimensionless amplitude a increases the temperature fluctuation amplitude in the cavity and improves the convective heat transfer level in the cavity.When a=1,the convective heat transfer in the cavity is the most intense,and the average Nu number on the surface of the heat source reaches the maximum of 12.2,which is 18.52%higher than without fins working condition.The dimensionless periodτ_phas a relatively weak effect on the convective heat transfer efficiency in the cavity by affecting the frequency of temperature fluctuation in the cavity.The time-averaged Nu number on the heat source surface is negatively correlated with the dimensionless periodτ_p.Whenτ_p=0.1,the maximum time-averaged Nu number on the heat source surface is 11.6,which is 12.73%higher than the finless condition.