Flow Characteristics Of Porous Media

Porous media are closely related to our life and can be seen everywhere,such as soil,sand,wood,or bread,sponge,clothes,ceramics,etc.The study of porous media flow is of great significance in the field of chemical engineering,improving soil permeability and research and development of aviation materials.However,due to the strong randomness and anisotropy of pore structure in porous media,the study of internal flow in porous media is greatly troubled.This paper attempts to study the flow and heat transfer characteristics in porous media with various models.First of all,in terms of flow characteristics,the author deduced the resistance formula based on the single-sphere flow around the sphere as the model.However,the initial resistance formula is quite different from the experimental value and the traditional resistance formula,which indicates that flow around the sphere to explain the flow characteristics inside the porous medium is unreasonable and the disturbance between the spheres has a great influence..Therefore,the interference coefficient is proposed,and the influence of flow around the whole flow is analyzed through the analysis of the variation law.The revised formula is almost in agreement with the experimental data and the calculated values of the traditional formula.It is even closer to reality than Ergun equation in a certain range of Reynolds number.At the same time,when analyzing the modified resistance formula,it is found that the pressure drop inside the porous medium is different from the velocity under different Reynolds numbers.When the Reynolds number is less than 1,the pressure drop has a linear relationship with the velocity;The Reynolds number is between 1 and 50,and the pressure drop is linear with the speed of 1.1.;The Reynolds number is between 50 and 300;The pressure drop is in good agreement with the speed of 1.5;the Reynolds number is in the range of 300 to 1000,and the pressure drop is linear with the speed of 1.8;When the Reynolds number is greater than 1000,the pressure drop is linear with the square of the flow velocity.At this time,the pressure drop inside the porous medium is only related to the roughness.On the other hand,the pressure drop ofporous media is deduced based on the pipe flow model,but the deduced formula differs greatly from the Ergun equation.The reason is that the laminar flow state of the fluid in the pipe flow can be maintained to Reynolds number 2000,but from the deduced conclusion,when the Reynolds number is less than 1000,the flow state in the porous media has already taken place great changes.For this reason,the author revised the pipe flow relationship with Reynolds number less than 50.When Reynolds number is greater than 50,the pipe flow model can not describe the flow characteristics in porous media.However,according to the relationship between pressure drop and velocity in the formula of pipe flow model and the formula of flow around the porous media,there are several different resistance zones for similar pipe flow in porous media.The resistance zones in porous media are divided by analogy of pipe flow: Reynolds number less than 50 belongs to laminar flow zone;Reynolds number between 50 and 300 belongs to critical zone;Reynolds number between 300 and 1000 belongs to turbulent transition zone;Reynolds number greater than 1000 belongs to turbulent rough zone.From the point of view of zoning,the Reynolds number zoning in porous media is smaller than that in circular tube flow zoning,so the influence of viscous force in porous media is much larger than we imagined.In addition,the author uses the fractal method to deduce the resistance relation of the flow around the porous media model,and obtains the resistance relation suitable for the Reynolds number below 50.For a fractal relation with a Reynolds number greater than 50,although the pressure drop loss in the porous medium cannot be described,the fluid flow state at each Reynolds number can be described indirectly.