Effect Of Porous Fin On Heat Transfer Characteristics Of Natural Convection In Closed Cavity With Different Flow Modes

Natural convection in a closed chamber with side heating is widely used in industrial production,such as heat dissipation in electronic equipment,solar collectors,and energy-efficient design of buildings.The setting of vortex generators on the heat transfer surface is an effective measure to enhance heat transfer,and the study of fins on the hot wall surface inside the side heating cavity is based on this aspect and has become a hot topic in the field of closed cavity research.Literature research reveals that domestic and foreign scholars have achieved many results in the experimental research and numerical simulation of natural convection in the heating cavity with built-in fin side,but there is a lack of research on the influence of porous fin parameters and fin physical properties on the heat transfer characteristics in the cavity under different flow regimes.Therefore,based on the research objective of the effect of porous fins on the natural convection heat transfer characteristics in different flow regimes in the side heating cavity,this paper numerically analyzes the effect of porous fin parameters(porous fin length l,installation position s,installation angleθ)and fin physical properties(effective thermal conductivity Ke and Darcy Da of porous fins)on the fluid flow in different flow regimes in the cavity by using Ansys-Fluent 21 R1 software.The mechanism of fluid flow and heat transfer in different flow regimes in the cavity.The coupling effect between the parameters of the porous fins is considered,and the response surface method is introduced to study the interaction effect of the fin parameters on the heat transfer characteristics in the cavity and the effect of wall radiation on the flow and heat transfer in the cavity is also studied.The main research works are as follows:(1)A single porous fin is arranged on the hot wall surface inside the side-heated closed cavity,and the influence law of the porous fin parameters on the heat transfer characteristics inside the cavity under laminar flow condition is investigated.The results show that the heat transfer in the cavity is enhanced as the Rayleigh number increases,regardless of the changes in the length,installation position and installation angle of the porous fins.The average Nu of the hot wall surface increases with the fin length for porous fin lengths between 0 and 0.2 H,while the hot wall surface average Nu is weakly influenced by the fin length for fin lengths between 0.2 H and 0.5 H.The heat transfer thermal effect in the cavity is better when the porous fins are installed near the bottom of the cavity.The heat transfer effect in the cavity is better when the installation angle of the porous fin is 90°.When Ra=10~5,the porous fin parameters that make the maximum hot wall surface average Nu in the cavity are:l=0.35 H,s=0.375 H,andθ=90°,respectively,which increases the hot wall surface average Nu by33.3%compared to the finless condition.(2)The effect of fin parameters on the heat transfer characteristics in the cavity is analyzed by the response surface method considering the coupling effect of the multi-hole fin parameters.The results show that when Ra=10~5,the response surface method analysis finds that the interaction between the installation position of the porous fin and the installation angle has the most significant effect on the convective heat transfer in the cavity,the interaction between the length of the porous fin and the installation angle is the second,and the interaction between the length of the porous fin and the installation position has the least effect on the convective heat transfer in the cavity;the response surface model equation predicts that the combination of the porous fin parameters with the optimal effect on the convective heat transfer in the cavity is:l=0.44 H,s=0.34 H,andθ=101.72°.At this time,the hot wall surface average Nu is increased by 34.4%compared with the no-fin structure.(3)Based on the optimal combination of porous fin parameters obtained by the response surface method,the effect of the physical properties of porous fins on the heat transfer characteristics in the cavity was investigated.The results show that:when Ra=10~5,the effective thermal conductivity of the porous fin increases with the increase of the effective thermal conductivity of the porous fin,and the convective heat transfer in the cavity is enhanced with the increase of the effective thermal conductivity of the porous fin.The difference in the strengthening effect of increasing the effective thermal conductivity on the intracavity convective heat transfer is increasing with a larger Darcy number and the synergistic effect of the porous fin Darcy number and the effective thermal conductivity on the improvement of the intracavity convective heat transfer.(4)The effect of the parameters and physical properties of the porous fins on the natural convection heat transfer characteristics of the turbulent flow in the closed cavity is numerically studied by arranging single porous fins on the hot wall surface of the closed cavity heated by the built-in heat source side,and based on this,the effect of the coupling between the fin parameters on the heat transfer characteristics of the cavity is analyzed by applying the response surface method.And based on this,the influence of the coupling effect between the fin parameters on the heat transfer characteristics in the cavity is analyzed by the response surface method,and the results show that:The single parameters of the porous fins that make the largest hot wall surface average Nu in the cavity are:l=0.053 H,s=0.375 H,andθ=90°,which increases the hot wall surface average Nu by 37.73%compared with no-fin structure.The response surface model equation predicts the optimal combination of porous fin parameters for convective heat transfer:l=0.053 H,s=0.373 H,andθ=93.21°.At this time,the hot wall surface average Nu achieves a maximum value of 73.65,which is 38.72%higher compared with the no-fin structure.The effect of the physical properties of porous fins on the heat transfer from the hot wall surface and the heat source surface is not synchronous,with the increase of fin Darcy number and effective thermal conductivity,the hot wall surface average Nu increases while the heat source surface average Nu decreases.(5)The effect of wall radiation on fluid flow and heat transfer in different flow regimes inside the hot wall arrangement porous fin side heating cavity was numerically studied.The results show that when considering the radiation effect,the hot wall surface average Nu in the cavity increases and increases with the increase of the wall emissivity;when the wall emissivity is 0.3,0.6,0.9,the increase of the hot wall surface average Nu in the cavity under the laminar flow regime is 19.27%,42.14%,70.14%,respectively.The improvement rates of intracavity hot wall surface average Nu in turbulent flow state are 36.64%,87.97%,146.22%,respectively,and the improvement rate of intracavity hot wall surface average Nu in turbulent flow state is significant compared with laminar flow;in intracavity turbulent flow state,the wall emissivity has a significant effect on the intracavity temperature field and flow field,with the increase of wall emissivity,the fluid temperature difference between the upper and lower walls of the cavity decreases and the isotherms become sparse;the flow lines near the wall surface As the wall emissivity increases,the fluid temperature difference between the upper and lower walls of the cavity decreases,the isotherms become sparse;the flow lines near the wall become denser,the number of vortices in the center of the cavity increases,the fluid flow velocity becomes larger,and the disturbance between flow layers is enhanced.