Effect of Wall Proximity and Shape on Bubble Enhanced Heat Transfer from a Vertical Heated Surface

Abstract

<div class="section abstract"><div class="htmlview paragraph">Numerical simulation has been performed to study the heat transfer enhancement from the vertical heated wall surfaces with the help of rising bubbles due to the buoyancy force. The effect of wall proximity and bubble shapes are investigated for three wall shapes such as plane wall, wavy wall and triangular wall. Numerical solution is obtained by solving both the thermos-fluid governing equations and the Volume of Fluid (VOF) advection equation along with the Piecewise-Linear Interface Construction (PLIC) algorithm available in ANSYS-Fluent, an FVM based commercial CFD code. The results observed in the three types of wall geometries were showing the heat transfer differently for the 3 mm bubble. For the plane wall from the rise of the bubble to 0.3 seconds the temperature gradient is 10 K whereas for the curved and triangular wavy walls these gradients are 9.6 K and 17.23 K respectively. and after 0.6 seconds, this gradient is almost the same for all the wall shapes. In the latter two cases, the heat transfer by the effect of the wall was changing because of the alternating widening and narrowing channel. The research also discusses the varying distance of the injection of the bubble from the heated wall viz. 6 mm, 12 mm, 8 mm, 14 mm. It is observed that in addition to the well-known wake enhanced heat transfer by rising bubble, the contribution in the heat transfer enhancement by the wall modification from plane surface to wavy/triangular surfaces is substantial. It is also found that, as expected, this enhancement is significantly decreased as the wall proximity is increased.</div></div>