Development Of A New Variable Flow Resistance Based On Temperature Change

Porous materials are used as pneumatic components in a wide range of industrial applications.Such porous materials contain thousands of interconnected irregular micro-pores that produce a large pressure drop(?P)between the upstream and downstream sides of the porous material when a fluid flows through it.The relationship between the pressure drop and flow rate(i.e.,?P-G characteristic)and the relationship between flow resistance(?)and flow rate(the y-G characteristic)are two very important basic characteristics because their applications mainly depend on the pressure drop-flow rate and flow resistance characteristics.One factor affecting them is temperature,whose variation changes the viscosity and density of the fluid.In this study,we experimentally and theoretically analyzed the effect of temperature on ?P-G and flow resistance characteristics of porous materials by heating them under constant electric heating power,as this has scarcely been addressed in previous studies.The resulting experimental AP-G and flow resistance curves shift upward relative to their counterparts at room temperature owing to the increase of fluid temperature,but remain within the adiabatic and room temperature curves.The temperature-effect ratio ? at constant heating power increases from 1.3 to 1.7 as the flow rate decreases from 21.53 × 10'5 kg/s to 5.80 × 10-5 kg/s,indicating that ?P-G and flow resistance characteristics and pumping power change significantly when a porous material is heated.Furthermore,temperature distributions were obtained numerically to gain deeper understanding of the temperature effect.The effects of heating power values,characteristic porous material coefficients,and average fluid density on ?P-G and flow resistance characteristics were also investigated.It is found that the greater the heating power,the larger are the values of ?P,? and ?;the smaller the value of permeability and porosity(K?),the larger is the effect of temperature change on AP and y;and the smaller the average density,the larger is the effect of temperature change on AP and y.However,? remains approximately the same despite the changes in K? and the average density.Lastly,we deduced the dimensionless equation of the porous material.We separated the density and friction terms of the equation by the logarithmic method,and based on the experiment data,we discussed the effect of the density and friction terms on the dimensionless pressure difference,?PT*.The discussions revealed that the relation of ?PT*and Re?is determined by the density ratio,?0/?T,and the viscosity ratio,?T/?0.The friction term In(?T/?01/Re?+1),which includes ?T/?0,is only determined by temperature;that is to say,the In(?T/?01/Re?+1)-Re? curves overlap as long as the temperature is the same,despite differences in pressure and the character parameters of the porous materials.The density term In(?0/?T)is determined by pressure and temperature.Therefore,changes of both pressure and temperature will lead to variation in the In(?0/?T)-Re? curves.As to the curve of In(?T+1)-Re?,it depends on the heating power and the ?(?)value.For the ?(?)and Re? value,the higher the heating power,the larger the value of In(?T+1).However,at the same heating power,the difference of ?(?)will cause the In(?T+1)-Re? curve to a shift along the horizontal axis(based on the ?T-G curve).Curves with a larger ?(?)value shift to the right,whereas curves with a smaller ?(?)value shift to the left.