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Topic

Ambient Air Pressure Effects on Droplet Descent and Dry Surface Impact Dynamics

Department of Mechanical Engineering

Date & location

• Tuesday, June 11, 2024

• 12:00 P.M.

• Engineering Office Wing

• Room 230

Reviewers

Supervisory Committee

• Dr. Peter Oshkai, Department of Mechanical Engineering, ·¬ÇÑÉçÇø (Supervisor)

• Dr. Mohsen Akbari, Department of Mechanical Engineering, UVic (Member)

External Examiner

• Dr. Alexandre Brolo, Department of Chemistry, ·¬ÇÑÉçÇø 

Chair of Oral Examination

• Dr. Caetano Dorea, Department of Civil Engineering, UVic

   

Abstract

Droplet impact and the affect of ambient pressure on the droplet impact dynamics are of interest in many applications. These include applications in the industrial, biomedical, environmental and academic fields. When a droplet descends, prior to impact, the ambient pressure, air density and drag forces affect how the droplet behaves in this multi-phase flow. It has been shown that, by reducing ambient pressure, droplet splash can be removed completely [1]. The aim of this study is to perform experiments to further the understanding of that multi-phase flow and gain clarity on how ambient pressure may influence the droplet shape and in-turn, potentially influence the onset of prompt splash upon droplet impact on a dry surface. Instead of reducing ambient pressure to remove splash, this study attempts to increase ambient pressure to induce splash and investigate and compare the droplet dynamics in the pressurized and non-pressurized scenarios using high speed imaging. Conventionally, studies have investigated the droplet upon impact, mostly ignoring the droplet’s descent dynamics prior to contacting the dry surface [1] [2] [3] [4]. This study focuses on those pre-impact droplet dynamics by investigating how droplet shapes differ between the pressurized and non-pressurized scenarios. By imaging the droplet descent in a pressurized chamber, a significant difference in the droplet aspect ratio (width to-height) could be witnessed in the pressurized scenario, compared to the non-pressurized one. The average aspect ratio for droplets descending in an environment with 4atm pressure tended to be greater than 1, deforming droplets to an oblate or elliptical shape. Under standard 1atm pressure, however, droplets under the same velocity conditions tended towards an aspect ratio of 1 (or a spherical shape). Additionally, the amplitude of droplet aspect ratio changes (from oblate to prolate) was higher in the 4atm condition, compared to the 1atm one. As such, it was concluded that when ambient pressure is increased to the point where prompt splash is witnessed, droplet aspect ratio is affected. This may be something to consider when developing a full understanding of the dynamics that affect droplet splash on impact with a dry surface.