New models that describe gas flow behaviour inmicrotubes are presented. To avoid time- consuming calculationsin solving the integral equation which is obtained from themicroscopic point of view, the high-order slip-flow boundarycondition is utilized to correct the gas flow in such a micron orsubmicron spacing. The proposed model can be applied toarbitrary Knudsen number conditions under the assumption thatthe bulk flow velocity is megligible compared with the sonicvelocity of the gas. The analytical solution of the pressuredistribution for the first-order slip-flow model is obtained. Theresults show that the first-order slip-flow model is in goodagreement with this model. The nonlinear pressure distribution isdue to gas compressibility. The dominant mechanism influencingthe nonlinear pressure distribution comes from the rarefaction ofgas and the inlet pressure. The rarefaction effect increases thepressure drop at the inlet region of the channel and decreases thepressure drop at the exit region of the channel. The decrease ofinverse Knudsen number changes the pressure distribution fromconcave to almost linear and increases the mass flow.
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