EFFECTS OF COMPRESSIBILITY AND RAREFACTION ON GASEOUS FLOWS IN MICROCHANNELS

A two-dimensional flow and heat transfer model is used to study gas co mpressibility and rarefaction in microchannels assuming a slip flow re gime. The compressible forms of momentum and energy equations are solv ed with slip velocity and temperature jump boundary conditions in a pa rallel plate channel for both uniform wad temperature and uniform wall heat flux boundary conditions. The numerical methodology is based on the control volume finite difference scheme. To verify the model, the mass flow rate was compared with the experimental results of helium th rough a microchannel. Also, the normalized friction coefficient was co mpared with the experiments for nitrogen and helium flow in a microcha nnel. Finally, the axial pressure distribution was compared with the e xperimental results for nitrogen flow in a microchannel. The computati ons were performed for a Hide range of Kn(in), Re, dimensionless dista nce from the entrance, and for the wall parameters q and T*, to study the effects elf rarefaction and compressibility. It was found that Nu sselt number and friction coefficient were substantially reduced for s lip flows compared with the continuum flows. The velocity and temperat ure distributions were flattened compared with continuum flows, and th e axial variation of pressure became nonlinear. It was shown that the effect of compressibility was important for higher Re and that the eff ect of rare faction was significant for lower Re.