Bubble spreading during the boiling crisis: modelling and experimenting in microgravity

TL;DR

This paper models and experimentally investigates the boiling crisis, focusing on vapor recoil effects that cause bubble spreading and film formation, especially under microgravity conditions, to better understand heat transfer failures.

Contribution

It introduces a physical model based on vapor recoil to explain bubble spreading during the boiling crisis, supported by experiments in microgravity environments.

Findings

Vapor recoil causes bubble spreading and dry spot growth.

Microgravity preserves convex bubble shapes for observation.

Simulations confirm the vapor recoil effect in boiling crisis.

Abstract

Boiling is a very efficient way to transfer heat from a heater to the liquid carrier. We discuss the boiling crisis, a transition between two regimes of boiling: nucleate and film boiling. The boiling crisis results in a sharp decrease in the heat transfer rate, which can cause a major accident in industrial heat exchangers. In this communication, we present a physical model of the boiling crisis based on the vapor recoil effect. Under the action of the vapor recoil the gas bubbles begin to spread over the heater thus forming a germ for the vapor film. The vapor recoil force not only causes its spreading, it also creates a strong adhesion to the heater that prevents the bubble departure, thus favoring the further spreading. Near the liquid-gas critical point, the bubble growth is very slow and allows the kinetics of the bubble spreading to be observed. Since the surface tension is very small in this regime, only microgravity conditions can preserve a convex bubble shape. In the experiments both in the Mir space station and in the magnetic levitation facility, we directly observed an increase of the apparent contact angle and spreading of the dry spot under the bubble. Numerical simulations of the thermally controlled bubble growth show this vapor recoil effect too thus confirming our model of the boiling crisis.