Experimental Study On Gas Flow In Micro-channels

In this paper, the characteristic of gas flow and heat in small or micro-channel is researched by experimental and numerical simulation methods in adiabatic condition. The channels are changed by depth/width,length,hydraulic diameter,relative roughness,kinds of gas and cross section. The experimental systems for rectangle and round micro-channels are set up.In laminar flow, characteristic of gas flow in all rectangle channels (except L/D= 38 of the micro-channel) are good agreement with the macro-theoretical, and numerical simulation results match that conclusion.The Re number of laminar to turbulent in all rectangle channels are almost about 1000, a few are about 500-600(in larger relative roughness channel), that fact is not fit for macro-theory. In turbulent flow, it's found that the friction constant grows up when the depth/width decreases or relative roughness increases. The formula of constant friction with length/diameter,relative roughness depth/width and Re number is set up in rectangle channels.During numerical research, it's found that friction constant decreases when the diameter of channels decreases without the roughness effect in laminar flow. The pressure loss in rectangle micro-channels is a linear trend when the Re number is small. As the velocity of fluid increases, the flow resistance increases significantly in smaller ratio of LID channels. Rarefaction effect will reduce the resistance of flow if the hydraulic diameter decreases.Third, the study of heat transfer and flow characteristics of the different gases (He, N2) in the hydraulic diameter of 0.255mm micro-tube is completed. As the relative roughness and the entrance effect decreases, the rarefaction effect and compressibility on the flow and heat transfer increase; rarefaction effect can reduce the friction constant, compressibility can increase friction constant; transition Re number occurs at around 2000-3000. It's found flow characteristics of He is lower than theoretical prediction in micro-tubes (both in laminar flow or turbulent region). However, the flow characteristic of N2 agrees with theoretical prediction. Rarefaction effect has contributed to the lower friction constant. Friction constant changes little when shapes of cross section (whether is rectangular or round) is altered. The Friction constant value should be decided by rarefaction effect,compressibility,entrance effect,cross section and the rough effects.Finally, without external heat source, analysis of heat is finished. It's found when the channels'relative roughness,depth/width,length increases or the diameter of channels decreases, the temperature discrepancy between inlet and outlet increases. The numerical simulation results also verify this.