Experimental study of the gravity influence on the periodic thermocapillary convection around a bubble

International Journal of Heat and Mass Transfer

2013

Thermal Marangoni convection about a 1 mm radius hemispherical air bubble attached to a heated wall immersed in a silicone oil layer of constant depth of 5 mm was numerically investigated. Tests were performed for a range of Marangoni numbers (145≤Ma≤915) with varying levels of gravitational acceleration between zero gravity and earth gravity in order to quantify the rates of heat transfer. For the zero gravity condition, a thermocapillary-driven vortex develops around the bubble extending the entire height of the channel. This flow structure causes a jet-like flow of heated liquid to emanate from the bubble tip which impinged on the cold wall. With the addition of gravity, a counter rotating secondary buoyancydriven vortex forms which reduces the size of the thermocapillary vortex and disrupts the jet flow from the bubble tip. The wall heat flux profiles indicate that under zero gravity, the peak heat fluxes increase monotonically with Ma with an area of influence that increases asymptotically with Ma. Likewise, under gravity conditions the peak heat flux also increases with Ma and for low Ma is higher than that of 0-g. However, the area of influence is considerably smaller and not sensitive to Ma or the level of gravity. Experimental validation of selected terrestrial gravity numerical results was obtained using particle image velocimetry (PIV) for low to moderate Marangoni numbers. For all experiments, steadystate Marangoni convection was observed. The experimental flow patterns showed good agreement with the numerical solutions.

Section: Validation Of Numerical and Experimental Approachsupporting

confidence: 64%

Heat transfer near an isolated hemispherical gas bubble: The combined influence of thermocapillarity and buoyancy

International Journal of Heat and Mass Transfer

2013

“…In this study, the bubble radius was selected as the characteristic length, and the definition of the Marangoni number was chosen to include the depth of the liquid layer. This form of the dimensionless number is consistent with that of [6,7,20,24,25]. The Marangoni number for this 210 study is fixed at 915.…”

Section: Methodsmentioning

confidence: 50%

“…The liquid jet, in flowing away from the bubble, causes the temperature contours to project outward, transporting hot fluid into the cooler bulk, and toward the cold surface. This type of flow pattern has been seen in various experiments [6,7,20,25]. By applying the same streamline range and grayscale to each 340 plot, it is evident that with increased gravitational acceleration, and therefore increased buoyancy, the thermocapillary effect becomes increasingly confined to a region closer to the bubble.…”

Section: Methodsmentioning

confidence: 71%

See 1 more Smart Citation

The Influence of the Magnitude of Gravitational Acceleration on Marangoni Convection About an Isolated Bubble under a Heated Wall

Heat Transfer Engineering

2009

“…Reynard et al [10] experimentally studied the influence of gravity level on the periodic thermocapillary convection around a bubble. Using shadowgraphy to visual the flow field, experiments were conducted in reduced and increased gravity conditions.…”

Section: Introductionmentioning

confidence: 99%

Convective heat transfer due to thermal Marangoni flow about two bubbles on a heated wall

International Journal of Thermal Sciences

2014

Three dimensional simulations of thermal Marangoni convection about two bubbles situated on a heated wall immersed in a liquid silicone oil layer have been performed to gain some insight into the thermal and flow interactions between them. The distance between the two bubbles' centres was varied between three and twenty five bubble radii to analyse the influence of the inter-bubble spacing on the flow and temperature fields and the impact upon local wall heat transfer. For zero gravity conditions, it was determined that the local wall heat flux was greatest for the smallest separation of three bubble radii, but that the increase in heat transfer over the whole domain was greatest for a separation of ten bubble radii. When the effects of gravity were included in the model, the behaviour was observed to change between the cases. At large separations between the bubbles, increasing the gravity level was found to decrease the local wall heat flux, which was consistent with two-dimensional work. At small separations however, the increase in gravity led to an increase in the local wall heat flux, which was caused by a buoyancy-driven flow formed by the interaction of secondary vortices.