Study On Coupling Heat Transfer Characteristics Of Inner-tube Filled With Porous Medium In Double Pipe Heat Exchanger

Based on the important position of the tube heat exchanger in the industrial field and the current situation that the heat transfer efficiency needs to be improved,improving and improving the heat transfer performance of the heat exchanger will produce huge economic benefits.The coupling heat transfer characteristics of the inner tube filled with porous medium in the double-pipe heat exchanger has been investigated.Assuming that there is no heat exchange on the outer wall of the outer tube,the Darcy-Brinkman model and the local heat balance model are used for the flow and heat exchange in the porous medium to analyze the influence of the filled porous medium and axial heat conduction on the heat exchange performance of the double-pipe heat exchanger.In this work,the coupled heat transfer characteristics of the inner tube filled with porous medium in the concurrent flow and countercurrent flow tube heat exchangers of the fully developed section were analyzed.Assuming that the flow and heat transfer in the inner tube and the annular channel of the double-pipe heat exchanger have been fully developed,a new method is used to solve the Nusselt number in the inner tube and the annular channel on the basis of ignoring the axial heat conduction.The size of the heat exchanger,the heat capacity ratio,the ratio of the effective thermal conductivity of the porous medium to the thermal conductivity of the inner tube wall,the ratio of the effective thermal conductivity of the porous medium to the thermal conductivity of the fluid in the annular channel,the porosity of the porous medium,and the Darcy number to the inner tube are analyzed.Neutralize the influence of the fluid heat transfer performance in the annular channel.The results show that whether it is downstream or countercurrent,the tube filled with porous media can effectively enhance the heat transfer.The Nusselt number in the inner tube depends on both the flow and heat transfer in the inner tube and the annular channel,and so does the Nusselt number in the annular channel.Then,considering the influence of the inlet section and axial heat conduction,the coupling heat transfer of the inner tube filled with porous medium countercurrent flow casing heat exchanger was numerically studied.The calculation fluid dynamics software calculates the temperature field and velocity field in the double-pipe heat exchanger,and analyzes the effects of heat capacity ratio,inner tube wall thermal conductivity,porous media thermal conductivity,porosity and Darcy number on the heat transfer coefficient.And compared with the results of ignoring the axial heat conduction,analyze the influence of the axial heat conduction on the heat transfer performance.The results show that the local Nusselt number in the inlet and fully developed section of the inner tube is affected by the flow and heat transfer in the inner tube and the annular channel,and the local Nusselt number in the inlet and fully developed section of the annular channel is also affected by the flow and heat transfer in both downstream and countercurrent tube heat exchangers.The existence of axial heat conduction will affect the variation trend of local Nusselt number from inlet to outlet,and ignoring the axial heat conduction will make the fluid heat transfer faster and reach the fully developed stage.The study shows that the coupling heat transfer characteristics of the tube filled with porous media can provide a basis for improving the heat transfer efficiency of the tube heat exchanger and researching the new compact heat exchanger,which has a certain research and application value.