See-saw motion of thermal boundary layer under vibrations: An implication of forced piston effect

The phenomenon of piston effect is well known in supercritical fluids wherein the thermal homogenization of the bulk occurs on a very short time scale due to pressure change caused by expansion or contraction of the fluid in the thermal boundary layer. In this article, we highlight an interesting phenomenon wherein by the application of external forces (vibration) normal to the temperature gradient, see-saw motion of the thermal boundary layer is observed in weightlessness conditions. This is attributed to the thermomechanical coupling caused by the temperature change due to external forces. We term this change in the temperature field due to external forces as forced piston effect (FPE). A detailed investigation of this intriguing behavior shows that the see-saw motion is attributed to the variation of the relative thickness of the thermal boundary layer, defined on the basis of relative local bulk temperature, along the direction of vibration. This change in the temperature field, which is observed to b...