Effects of wall temperature on the heat and mass transfer in microchannels using the DSMC method

Micro-electro-mechanical systems (MEMS) and nano-electro-mechanical systems (NEMS) have become the research focuses which attract a great deal of attention in recent years. The fluidic and thermal behaviors are usually different from those of the macro devices. In this paper, the heat and mass transfer characteristics of the rarefied nitrogen gas flows in microchannels are investigated using DSMC method. In order to study the effects of the wall temperature (T_w) on the mass flux and wall heat flux in the microchannels, the temperature of the incoming gas flow (T_infin) is set constant at 300 K, and the wall temperature varies from 200 K to 800 K. For all of the simulated cases, majority of wall heat flux stays within the channel entrance region and drops to nearly zero when it reaches the middle region of the channel. When T_w < T_infin, with the restriction of the pressure driven condition and continuity of pressure, the number density of the flow has to decrease along the flow direction eventually after a short increase at the entrance region. When T_w > T_infin, the number density of the flow drops rapidly near the inlet, and the temperature of the gas flow increases. As the T_w increases, the flow becomes more rarefied, the mass flux decreases, and the resistance at the entrance region increases. Furthermore, when T_w > T_infin, sudden jump in heat transfer flux and temperature are observed at the exit region of the channel.