Nonequilibrium gaseous heat transfer in pressure-driven plane Poiseuille flow.

Nonequilibrium heat and mass transfer in a pressure-driven plane Poiseuille flow is investigated using the direct simulation Monte Carlo method from the early slip to the free molecular regime. Our investigations reveal several nonintuitive, nonequilibrium thermal flow patterns, including expansion cooling near the walls, a nonconstant pressure profile, and counter-gradient heat transfer along the channel center-line. A bimodal trend in the tangential heat flux is found in the slip and the early transition regime. In the upper transition and free molecular regime, the net heat flow in the entire channel is largely unidirectional and in the opposite direction of mass flow. However, in the slip and the early transition regime, a two-way heat flow is observed in the channel as the normal heat flux profile plays a key role in determining the net gaseous heat flow direction. Moreover, the heat flow rate profile exhibits a maximum value at an intermediate value of Knudsen number. The effects of incomplete surface accommodation on nonequilibrium heat flow are also investigated in this work. It is shown that for very low values of the accommodation coefficient, the gaseous heat flow direction is reversed and is consistently in the direction of mass flow.