COOLING IN CONSTANT WALL TEMPERATURE MICROCHANNELS WITH THERMAL CREEP EFFECTS

摘要

Fluid flow and heat transfer in the entrance region of rectangular microchannels of various aspect ratios, 0.2 ≤ a~* ≤ 1, are numerically investigated in the slip flow regime, 10~（-3) ≤ Kn ≤ 10~(-1) , with particular attention to the thermal creep effects. Uniform inlet velocity and temperature profiles arc prescribed in a microchannel with constant wall temperature. The gas inlet temperature is prescribed higher than the wall temperature in order to study the thermal creep effects in a fluid cooling process. To avoid unrealistically large axial temperature gradients due to the prescribed uniform inlet temperature and upstream conduction associated with low Reynolds number flows encountered in microchannels, an adiabatic section is added to the inlet of the channel, which resembles an adiabatic reservoir. A control volume technique is employed to solve the Navier-Stokes and energy equations which are accompanied with appropriate velocity-slip and temperature-jump boundary conditions at walls. Despite the constant wall temperature, axial and peripheral temperature gradients form in the gas layer adjacent to the wall due to temperature-jump. The simultaneous effects of velocity-slip, temperature-jump and thermal creep on the flow and thermal patterns along with the key flow parameters arc examined in detail for a wide range of cross sectional aspect ratios, and Knudsen and Reynolds numbers (0.1 ≤ Re ≤ 5). Present results indicate that thermal creep effects influence the flow field and the temperature distribution significantly in the early section of the channel.