| The problem of flow and heat transfer of porous media has become widespread in nature and in many fields of production in our country.When the fluid flows in a porous medium,the increase in the contact area with the solid will lead to an increase in the heat exchange capacity,but inevitably result in a lack of fluid flow power.Therefore,in order to better explore the fluid flow and heat transfer process,it is a research focus to reduce the flow resistance while improving the heat transfer effect as much as possible.The research work for this article is mainly from the following aspects:First of all,for the polyacrylamide solution needed in this paper,thermal conductivity coefficient of the solution with different water quality,different temperature and different concentration was measured with a thermal conductivity meter.For the porous material and heating plate in the physical model,in order to reduce the error between the simulation and the experiment,the thermal conductivity of the brass ball and the copper plate was measured with a laser thermal conductivity meter.Secondly,the rheological properties of the PAM solution with different water quality,different mass concentration,temperature,and shear rate were measured with a rotary rheometer.Experimental results show: the apparent viscosity of the solution prepared with deionized water was higher than that of the solution prepared with tap water.When the temperature is too high,the solution will be degraded and other reflections will occur,which will affect the instrument’s detection results.The higher the concentration,the greater the dependence of the viscosity of the fluid on temperature,and the greater the apparent viscosity increase,especially in the 1.5 g/L to 2.0 g/L stage.Non-linear regression fits the measured data to the corresponding rheological parameters.Thirdly,using fluent,the flow and heat transfer of PAM solution in the porous media of six rows were studied.In terms of flow,for the same model,when the flow rate is relatively low,the higher the concentration is,the higher the pressure drop is.When the flow rate is high,the resistance reduction phenomenon occurs due to the shear thinning property of the PAM solution,the condition of the drop resistance phenomenon is u ≥ 0.05m/s,c≥1.5g/L.The arrangement of the copper spheres in the porous region and the properties of the solution are two important factors affecting the drag coefficient.The polyacrylamide solution in high concentration has a large number of molecules and the activity is relatively intense,it is easy to enter the non-Darcy state and the critical Reynolds number is smaller.The larger the contact area between the ball and the heating plate,the smaller the porosity at the side wall.At high flow rates,the effect of the side wall effect on the pressure drop cannot be ignored.In terms of heat transfer,the bottom and upper parts of the porous area are strongly disturbed by the influence of the boundary effect,but the bottom fluid receives less heat from the upper fluid,so no significant temperature gradient change will occur.Compared with the five-row model,the six-row body-center model has more pores,and the “ribbed effect” of the solid skeleton is more prominent,so that the enhanced heat transfer capability is more significant.The larger the contact area between the ball and the heating plate,the faster the ball will get heat from the heating plate,and the overall convection heat transfer coefficient will increase.Finally,fluent was used to simulate the heat transfer of PAM in porous media.As the heat flux increases and the flow rate decreases,the wall superheat increases and the local boiling heat transfer coefficient decreases.The location of the heating plate is better at the bottom than it is at the top.The smaller the particle diameter,the greater the local boiling heat transfer coefficient. |
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