Analysis Of Oscillation Flow Characteristics In A Circular Tube Filled With Porous Media

As the global energy and environmental protection situation becomes more and more severe,Stirling engines and refrigerators have received increasing attention due to their wide adaptability to various energy sources and excellent environmental characteristics.The regenerator is a key component in the Stirling machine.Its performance directly affects the efficiency and performance of the Stirling machine.The regenerator is the combination of porous media and oscillating flow.Therefore,it is very important to study it.In this paper,the oscillating flow characteristics in a tube fully filled with porous medium,in a tube partially filled with porous medium and in a tube filled with double-layer porous medium were studied.The flow characteristics in a tube fully filled with porous medium,in a tube partially filled with porous medium and in a tube filled with double-layer porous medium are analytically investigated.Reciprocating oscillating flow is driven by a sinusoidally varying pressure gradient and Hydrodynamically fully developed conditions is assumed in the tube.The Darcy-Brinkman model and modified Fanning friction coefficient are utilized to describe the fluid flow.In the study of the tube fully filled with porous medium,the analytically solution for velocity fields are derived.Further,using the obtained analytically solution of velocity and modified Fanning friction coefficient,the instantaneous friction coefficient,the cycle-averaged friction coefficient and the phase angle difference between the cross-sectional mean velocity and the wall shearing stress are derived.On these foundation,the influences of Darcy number and the dimensionless oscillation frequency on the velocity fields are analyzed.Meanwhile,the influences of Darcy number,the dimensionless oscillation frequency,the dimensionless oscillation amplitude and the porosity of porous medium on friction coefficient of the tube fully filled with porous medium are analyzed.The results indicate that porous media can effectively reduce the "speed loop" effect and the friction coefficient.In the study of the tube partially filled with porous medium,the analytical solutions of velocity field and friction coefficient are obtained by using velocity continuity and stress jumping interface condition.The analytical solutions of velocity field is validated by compared with the tube fully filled with porous medium in extreme situation.The influence of the stress jumping coefficient on the velocity fields in the tube partially filled with porous medium is discussed.And the influences of the stress jumping coefficient on the friction coefficient are analyzed.The study shows that the friction coefficient increases with the increase of the Darcy number,decreases with the increase of the dimensionless filling ratio of free fluid region,and increases with the increase of the stress jumping coefficient.In the study of the tube filled with double-layer porous medium,the analytical solutions of velocity field and friction coefficient are obtained by using velocity continuity and stress continuity interface condition.The influences of Darcy number,the dimensionless oscillation frequency,the dimensionless oscillation amplitude and four filling methods of porous medium on the velocity fields and friction coefficient of the tube filled with double-layer porous medium are analyzed.The results show that the influence of four filling methods on the friction coefficient is quite different under different dimensionless oscillation frequencies...