Wicking Flow In Porous Media

Capillary flow in the porous media has received a lot of attention and widely used in many areas,such as oil recovery,irrigation in agriculture,heat pipes,microfluidic pumping.In IC industry,the feature size of electronic devices continues to decrease,chip integration,package density and operating frequency continue to increase,so that the heat flux density of the chip rises rapidly and heat pipes have been widely used for heat removal.The modern heatpipe technology often uses highly porous materials such as metal foam to increase the heat removal rate and the behavior of wicking flow in such materials has attracted a lot of attention in recent years.In spite of the numerous models to describe the wicking flow behavior in different porous materials,these models are all for low porosity materials,such as land seepage and rock fissure flow.For high porosity open-cell materials,there has been no specific model to satisfactorily describe the wicking flow behavior.The aim of this study is to investigate the microflows in a porous metal with open cell pore structures.This thesis will report the research findings on the wicking behavior of microfluid in treated copper foams.Capillary properties such as pore radius,contact angles,thickness are critical in defining the wicking performance.The surface of the used copper foams were treated to obtain nano-structures,which turned the surface to be super hydrophilic with a near zero contact angle.This significantly increased the wicking capacity.The wicking experiment was set up with a CCD camera,a height controller,a water bath with deionized water and an image analysis system.The camera was used to optically capture the wicking process.Different types of porous materials with different pore sizes(50?m,90PPI),different thicknesses(1mm,0.5mm,0.2mm),different porosity(66%~95%),different widths(3mm,2mm,1.5mm)were studied.The wicking height as a function of time was measured to quantify the wicking capability of the porous materials.Theoretical studies were also carried out to explain the wicking in porous materials.