• boiling
• bubble dynamics
• bubble growth
• force balance
• integral momentum balance
• microlayer

Predicting the departure diameter of vapor bubbles growing on a heated surface is key to the development of mechanistic boiling heat transfer models, e.g., heat flux partitioning models, used for the design and the safety analysis of two-phase heat transfer systems such as nuclear reactors. This task is typically achieved with force balance models that aim at capturing the departure through a mechanistic description of the forces acting on a growing bubble. However, despite the efforts of the thermal science community, the accuracy and even the physical basis of these models are still questionable. A crucial limiting factor is the lack of ad-hoc experimental data, since most databases only report operating conditions and values of the bubble diameter at the detachment. There is a need for more detailed investigations, characterizing all the parameters that may affect the bubble growth. Importantly, there is a need to quantify experimentally all the forces acting on a bubble, including those associated with hydrodynamic effects. In this work, we present a fundamental study of bubble growth and departure in carefully controlled horizontal pool boiling conditions. The contribution is twofold. First, we propose an analytic breakdown of the forces acting on a growing vapor bubble in such a way that each force can be measured experimentally, separating hydrodynamic from hydrostatic effects, without any tuning parameter or modeling assumption. Second, we perform an experiment featuring high-speed video and infrared diagnostics to capture the growth of the bubble, through the bubble profile, and the dynamic of the bubble contact line, analyzing the time-dependent temperature and heat flux distribution at the bubble footprint.