Dynamics of bubble growth under a heated substrate

This paper investigates the growth dynamics of a vapor-gas bubble pressed against a heating plate by the buoyancy force. The shadow method was used to capture images, which were then automatically processed to calculate the size of the bubble. As expected, the bubble dynamics significantly depends on the heating power. It was found that the ratio of bubble diameter to bubble height increases as it grows.

Modeling Unsteady Bénard-Marangoni Instabilities in Drying Volatile Droplets on a Heated Substrate

We study unsteady internal flows in a sessile droplet of capillary size evaporating in constant contact line mode on a heated substrate. Three-dimensional simulations of internal flows in evaporating droplets of ethanol and silicone oil have been carried out. For describing the Marangoni flows we find it necessary to account for the diffusion of vapor in air, the thermal conduction in all three phases and thermal radiation. The equations have been solved numerically by finite element method using ANSYS Fluent. As a result of the simulations, the nonstationary behavior of Bénard-Marangoni (BM) instabilities is obtained. At the first stage, a flower structure of BM cells near the triple line emerge. For smaller contact angles, the cells grow in size and occupy the central region of the droplet surface. Being closely connected with recent experimental and theoretical studies, the results obtained help to analyze and resolve the associated issues.

Evolution of Designs for Constructal Cooling of a Square Plate Using Water, Ionic Liquid, and Nano-Enhanced Ionic Liquids

In this paper, we investigate the design-evolution of an embedded pipe based on the constructal theory to obtain the best design that cools a square plate subjected to a constant heat flux boundary condition. The water, ionic liquids (ILs), and nano-enhanced ionic liquids (NEILs, i.e., [C4mim][NTf2] + Al2O3 and [C4mpyrr][NTf2] + Al2O3) have been used as the coolants. Several designs (Case 1 to Case 11) have been tested to quantify the non-dimensional temperature of the heated substrate by implementing the finite volume method of ansys fluent. The three-dimensional continuity, momentum, and energy equations have been solved iteratively in the fluid region by incorporating SIMPLE algorithm with appropriate boundary conditions; while the conduction equation is solved in the solid region. Among all the considered designs, it has been found that Case 3 provides a better cooling effect for the heated substrate. For all of the considered configurations/designs, it is also found that the non-dimensional temperature decreases with the length of the morphing pipe. NEILs exhibit a better cooling effect of the substrate when compared with the ILs and water. The present numerical methodology is also validated with the previous literature.

Study of transient condensation occurring during the starting of the evaporation of a droplet deposited on a heated substrate

The evaporation of a drop deposited on a heated substrate is a complex process, which combines several phenomena such as the Marangoni effect, mass and thermal transfers, etc. We developed, in this paper, a mathematical model and a numerical simulation code used to carry out an in-depth study about the evaporation of a drop deposited on a heated substrate surrounded by air. This numerical study was supported by experimental work. The numerical findings obtained showed the existence of a condensation phenomenon for certain configurations. At the beginning of the experiment, the evaporation started at the triple point. However, a local region of the interface remained relatively cold. In this region, the concentration gradient (Cv, Csat) directed from the liquid-gas interface to the air resulted in condensation of water steam. Although this phenomenon is temporary and visible only at the start of evaporation process, its study makes it possible to better understand and optimize the evaporation kinetics.