Regular Article

Experimental investigation of drag coefficient of free-falling deformable liquid gallium droplet^★

¹ Institute for Multiscale Thermofluids, School of Engineering, University of Edinburgh, Faraday Building, King's Buildings, EH9 3DW, UK
² School of Mechatronic Engineering, Universiti Malaysia Perlis (UniMAP), Kampus Pauh Putra, 02600 Arau, Perlis, Malaysia

^* e-mail: ksefiane@ed.ac.uk

Received: 19 September 2018
Received in final form: 30 October 2018
Accepted: 31 October 2018
Published online: 28 November 2018

Abstract

In this article, the effect of shape and deformation on the drag coefficient of a free-falling liquid gallium droplet in water in a terminal state is investigated experimentally. The temperature of the dispersed and continuous liquid was varied in order to examine the effect on the liquid–metal droplets. The falling droplets were imaged using a high-speed camera, and a simple model was developed to predict drag coefficient over a Reynolds number range of 10³ < Re < 10⁴. The drag coefficients of the deformed liquid gallium droplets were found to be larger than that associated with a solid sphere and the associated Weber number was below 4.5. It was found that the shape of all droplets in our experiment were oblate spheroid. A correlation has been established to predict the aspect ratio of a liquid gallium droplet moving in quiescent water. The deformation is highly dependent on interfacial surface tension and inertial force, while the viscosity ratio and pressure distribution have negligible effect.