First Advisor

Raúl Bayoán Cal

Term of Graduation

Summer 2024

Date of Publication

7-10-2024

Document Type

Dissertation

Degree Name

Doctor of Philosophy (Ph.D.) in Mechanical Engineering

Department

Mechanical and Materials Engineering

Language

English

Physical Description

1 online resource (xii, 85 pages)

Abstract

Understanding the life cycle of droplets, from generation to capture, for example, is critical to understanding environments from the air-sea interface to the indoor environment of the International Space Station. Investigations have been performed in this work to provide insight into three droplet phenomena, each ubiquitous in both terrestrial and microgravity settings, through a lens of capillary flow. Each investigation attempts to disentangle the effects of gravity from the effects of surface tension. A drop tower test campaign is performed for each of the three investigations. Models are developed and simulations are performed to rationalize the observations. Each investigation is outlined below.

The first investigation considers a droplet impacting a fiber array. Droplets interacting with fiber arrays is common in nature, textiles, microelectromechanical devices, and fog harvesting. The phenomena of droplet impact on an equidistant array of fibers is experimentally studied. Drop tower tests are performed to characterize the droplet dynamics in the absence of the effects of gravity which could deform fibers and bias equilibrium configurations. Results show that contact line dissipation is largely responsible for arresting the droplet. Additionally, the penetration length is affected by fiber flexibility. A model is developed predicting the droplet penetration dynamics which shows good agreement with experiments.

The second investigation considers the jump of a droplet from a particle bed. Drop Tower experiments have been performed investigating droplet jump from a particle bed across a wide range of fluid viscosities. The presence of a particle layer is shown to affect contact line dissipation of the jumping droplet. Additionally, the study has identified the impact of the Ohnesorge number (Oh) on droplet morphology. The investigation has yielded results that not only validate a modified version of the spring-mass-damper model proposed by Jha et al. but also extend its applicability to previously unexplored initial conditions. In particular, the model predicts droplet jump time and velocity. Moreover, the presence of particle layers has been found to effectively eliminate contact line dissipation without introducing substantial additional forms of dissipation. Experiments have been conducted at the Dryden Drop Tower facility at Portland State University.

Lastly, the collapse of an air jet blown cavity and subsequent generation of a jet and jet droplets is investigated both experimentally and numerically. It is shown that surface tension forces alone are sufficient to generate a liquid jet from the cavity collapse. The dependence of the properties of the resulting liquid jet and jet droplets on the initial cavity geometry are discussed. Axisymmetric simulations of the Navier-Stokes equations for a simplified geometry are performed to look more closely at the evolution of the cavity geometry.

Rights

In Copyright. URI: http://rightsstatements.org/vocab/InC/1.0/ This Item is protected by copyright and/or related rights. You are free to use this Item in any way that is permitted by the copyright and related rights legislation that applies to your use. For other uses you need to obtain permission from the rights-holder(s).

Comments

Financial support for this work has been provided in part by a NASA Space Technology Research Fellowship (NSTRF) under grant 80NSSC19K1191.

Persistent Identifier

https://archives.pdx.edu/ds/psu/42530

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