The effect of thermal creep in an enclosure under variable gravity conditions

A thermophoretic phenomenon, known as "thermal creep," has recently become the focus of several studies in flow analysis under microgravity conditions. Thermal creep drives a slip flow from lower to higher temperature regimes over a wall nonuniform temperature. It is suggested that in microgravity environment where the effect of buoyancy is reduced, the effect of thermal creep may become important and even critical in the kinematics and heat transfer of enclosed fluids.

This study presents a numerical analysis of a vapor movement inside a rectangular enclosure under a variable gravity condition and in the presence of thermal creep. Three different thermal boundary conditions are considered; a linear wall temperature along sidewalls, a nonlinear wall temperature along sidewalls, and a linear wall temperature along sidewalls in conjunction with heating from below. The results are obtained by solving the governing equations for velocity and temperature fields. A control volume formulation and SIMPLER algorithm are used in the numerical investigation of the problem.

It is found that under microgravity conditions, thermal creep induced by a nonisothermal wall would significantly alter the behavior of flow, but heat transfer remains dominated by conduction. As the gravity (buoyancy) effects increase, the resulting flow patterns are observed to be more complicated than pure buoyancy-induced flow. At certain critical values of gravity vector, the buoyancy effects and thermal creep are observed to achieve parity. Under these conditions, the flow is unstable and convective heat transfer become important. For large values of gravity, the effect of thermal creep is observed to be limited to the layers near the walls with nonuniform temperatures.

In general, the results indicate that thermal creep can be very important under microgravity condition and its effects should be included in applications in which the movement of a gas over a surface with nonuniform temperature is of interest.