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

Abstract

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 be caused by FPE in vibration, is shown to depend on the compressibility (and thus proximity to the critical point), the imposed acceleration and the cell size. It is also found that see-saw motion persists in the presence of gravity and thus is described ubiquitous in nature for all conditions. A plot illustrating the maximum change in the temperature as a function of these parameters is further proposed.

Vibration-induced thermal instabilities in supercritical fluids in the absence of gravity

“…Thetis, which has already been described and validated for a number of benchmark cases for incompressible fluids [26,27] and compressible fluids [24,[28][29][30]. The fluxes in the equations are discretized using second order centred difference scheme.…”

On the long-time transient formation of sink zones in near-critical fluids. A theoretical perspective

“…1996; Accary et al. 2005 a , b ) and simultaneous thermal quench and vibration (Amiroudine & Beysens 2008; Zappoli, Beysens & Garrabos 2016; Sharma, Erriguible & Amiroudine 2017 a , b ). A striking phenomenon, wherein the temperature of the SCF in the bulk drops below the imposed boundary temperature upon simultaneous thermal quench and vibration in zero-gravity conditions, was previously investigated numerically (Sharma, Erriguible & Amiroudine 2017 a ).…”

“…This subsequently affects the overall temperature profile thereby leading to the formation of sink zones. The explanation for the one-dimensional case can be judiciously extended to explain the sink-zone appearance in the two-dimensional numerical simulations of Sharma, Erriguible & Amiroudine (2017 a , b ). Furthermore, the appearance of sink zones is found to depend on several factors such as proximity to the critical point and acceleration.…”

“…The temperature in their case was found to rise above the wall temperature near the corners. Very recently, Sharma, Erriguible & Amiroudine (2017 a , b ) analysed numerically the behaviour of a SCF under the combined effect of thermal perturbation and mechanical vibration. They considered a square cell (size h = 7 mm) with solid walls filled with supercritical H 2 .…”

“…The inset in figure 2 highlights the sink zone corresponding to .

Figure 2.The contour plots for , δT = 10 mK, f = 20 Hz and A = 5 mm at time t = 7 s. Reprinted figure from: Sharma, Erriguible & Amiroudine (2017 a , b ) with permission obtained from APS (2020).

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