Gradients-based measurements to understand the boiling characteristics of dichloromethane for thermal management applications

The present work investigates the dynamical characteristics of single vapor bubble during saturated nucleate boiling of dichloromethane (DCM), one of the high volatile fluids. Boiling experiments have been performed for four heat flux conditions (25, 35, 50, and 65 kW/m²) under atmospheric pressure. Thin-film interferometry and high-speed rainbow schlieren deflectometry were employed in tandem to simultaneously capture the dynamics of microlayer and/or dry-patch and vapor bubbles. A detailed analysis of the temporal evolution of the equivalent diameter of DCM bubbles reveals distinct phases: inertia-controlled growth, a transitional regime, and diffusion-controlled expansion. Furthermore, the temporal evolution of various forces, such as buoyancy, contact pressure, surface tension, and growth forces are examined during the ebullition cycle. Unlike traditional force balance analyses, the spatio-temporally resolved whole-field experimental data is used for delineating the forces involved from bubble inception to departure time (t_d). Notably, in contrast to the conventional working fluids, for instance water, DCM displays a distinct bubble formation mechanism that is devoid of any microlayer, despite its high wettability with indium-tin-oxide coated glass. As the heat flux increases, there is a corresponding linear increase in bubble departure frequency, with no significant rise in growth time. The force balance analysis during the ebullition cycle of the vapor bubble of the considered high volatile fluid reveals that until 0.8t_d, the prevailing downward force promotes bubble growth while inhibiting departure. However, beyond 0.8t_d, the upward force takes precedence, counteracting the downward force and enables the bubble's departure from the nucleating surface.