Abstract

Drag reduction is highly desired in various applications such as ships and underwater vehicles to reduce power consumption and minimize impact on environment. In recent years, the use of air/ gas lubrication to reduce hydrodynamic drag has been a topic of intense research interest. One possible method to create the lubricating layer is by utilizing Leidenfrost effect. In this study, The ability of Leidenfrost effect to reduce drag coefficient of a free-falling liquid droplet in an immiscible viscous liquid is experimentally examined. Liquid gallium was used to create the droplet and FC-72 was used as the continuous phase. In the experiments, the initial temperature of liquid gallium was varied in the range of 40°C to 170°C, while the temperature of FC-72 was kept constant at 50°C for all cases. High speed imaging system was used to record the motion of the free-falling droplet in FC-72. The fully-developed Leidenfrost regime was stabled at droplet temperature of 130°C indicated by the vapour layer stream moving upward on the droplet surface. A 57% drag reduction is observed for the 170°C droplet compared to the 40°C droplet. This research extends previous studies on the drag reduction efficiency of gas layers sustained on solid (rigid) spheres falling in liquid by the Leidenfrost effect. The understanding gained from this research will hopefully contribute to the current effort in developing and applying air/ gas lubrication based technologies for sustained drag reduction.

Bio

Sofwan is currently a PhD student in the School of Engineering of University of Edinburgh (at Institute for Multiscale and Thermofluids). He graduated with a bachelor’s degree in Mechanical and System Engineering from Kyoto Institute of Technology, Japan in 2007 and obtained his MSc degree in Mechanical Engineering from Universiti Sains Malaysia, Malaysia in 2013. He works as a lecturer in Universiti Malaysia Perlis in the School of Mechatronic Engineering.

His research explore the modes of drag reduction on surfaces interfacing with liquids with particular interest in using air/ gas as a lubrication layer.

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