Experimental Measurement of the Electric Forces Acting on a Growing Gas Bubble in Quasi-Static Conditions

Abstract

This work was aimed at measuring the resulting electric forces acting on a gas bubble growing quasistatically, with gas supplied to it through a circular orifice, and to compare them with their theoretical counterparts. An experimental apparatus has been set up, consisting essentially of an orifice drilled in a flat stainless steel plate submerged in the test fluid (FC-72). A dedicated gas injection system allowed creating slowly growing or even static bubbles of any desired volume, up to the detachment volume. An electric field could be imposed by means of a washer-shaped electrode laid parallel to the surface and centered on the orifice. The apparatus could be operated with the orifice both in upward and in downward direction to investigate the favorable or adverse role of the buoyancy force. Data were acquired via a highresolution video camera, equipped with a microscopic lens, and were digitized and processed via dedicated software, implemented in Matlab. The resulting forces acting on the bubbles were derived from bubble shape and size. The data in the absence of electric field were compared with their theoretical counterpart to validate the method and the image processing technique and showed an excellent agreement. In a second phase, data with electric field were acquired. The resulting electric force was evaluated from the force balance, as the opposite of the sum of all the other forces acting on the bubble. The values of measured electric forces showed excellent agreement with the theoretical evaluations.

Bubble departure and sliding in high-pressure flow boiling of water

“…Their findings suggest that plausible magnitudes for all the external forces and resulting bubble acceleration can only be precisely quantified if the bubble shape is accurately known at all times. Several studies demonstrated that these conclusions also apply to quasi-static injection of bubbles through orifices (Duhar & Colin 2006; Di Marco, Giannini & Saccone 2015; Lebon, Sebilleau & Colin 2018). One major source of uncertainty comes from contact line surface tension forces.…”

The role of the electric field in the departure of vapor bubbles in microgravity

“…4 to compute the electric force is that the Maxwell stress tensor only depends on the local value of the electric field, and it does not require determining charge density distributions or dealing with discontinuities at the liquid-vapor interface. This facilitates the evaluation of the electric force, that in practice is performed by numerically solving the electrostatic problem in the fluid domain and then using the values of the electric field at the liquid-vapor interface in the liquid side [26,30]. In this work, we aim to investigate the integral momentum balance of the vapor bubble based on high-speed video measurements only.…”

“…To partially fill this knowledge gap, we investigated the effect of electric field on the dynamics of bubble growth in microgravity conditions by means of an integral momentum balance (IMB) analysis. A similar approach has been adopted by Di Marco et al in [26,30]. Recently, Garivalis and Di Marco [31] reformulated the integral force balance in a different form, where however the determination of the electric force required an "a priori" numerical solution of the laws of electrostatics in the dielectric fluid.…”

The not-so-subtle flaws of the force balance approach to predict the departure of bubbles in boiling heat transfer

“…see Refs. [24][25][26]) have revealed that the resultant of the "classical" forces (for negligible growth forces) prior to detachment is practically null. This observation suggests that the issue could be in the description of the external forces, and in particular the growth force, rather than due to the absence of an additional London-Van der Waals reaction force.…”