Clement Roy, Prasanna Venuvanalingam, James F. Klausner, Renwei Mei

Frontiers in Heat and Mass Transfer (FHMT) 11 - 1 (2018)

This article presents both an experimental and numerical study of both stationary and sliding bubbles in a horizontal duct with forced convection heat transfer. An experimental facility was fabricated using a fully transparent, electrically-heated test section in which the bubble dynamics and the thermal field on the heated wall can be acquired using high-speed cameras and Thermochromic Liquid Crystals (TLC). Experiments were conducted using the working fluid HFE 7000 for two different turbulent Reynolds numbers. The experimental temperature field in the span-wise direction is first compared to the numerically calculated temperature field of a bubble sliding near a wall and second to the temperature field calculated for a stationary bubble under the same flow and thermal conditions. In both cases the thermal field influence of the microlayer thickness, bubble shape, and the presence of multiple bubbles is investigated. An important outcome is that, unlike the sliding bubble case, the temperature field calculated in the stationary case is in agreement with the experimental results. The temperature field does not show any remarkable sensitivity to the micro-layer thickness or the bubble shape. It is concluded that the mechanism of heat transfer enhancement due to growing bubbles in forced convection is due to the flow perturbation induced by the bubble at the growth site or injection site rather than the thermal boundary layer disruption of the sliding bubbles.