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Thermally induced motion, collision and mixing of levitated droplets
Title
Thermally induced motion, collision and mixing of levitated droplets.
Creator
Davanlou, Ashkan, Kumar, Ranganathan, Cho, Hyoung Jin, Deng, Weiwei, Mansy, Hansen, Shivamoggi, Bhimsen, University of Central Florida
Abstract / Description
This dissertation investigates the motion of a levitated droplet experimentally and analytically against the Marangoni flow in an immiscible outer fluid at higher speeds than is possible currently. Based on our earlier experiments, when a droplet is released from a height of 1.5 (-) 4 times its diameter from the liquid surface, it can overcome the impact and stay levitated at the liquid-air interface due to the existence of an air gap between the droplet and the liquid film. In order to...
Show moreThis dissertation investigates the motion of a levitated droplet experimentally and analytically against the Marangoni flow in an immiscible outer fluid at higher speeds than is possible currently. Based on our earlier experiments, when a droplet is released from a height of 1.5 (-) 4 times its diameter from the liquid surface, it can overcome the impact and stay levitated at the liquid-air interface due to the existence of an air gap between the droplet and the liquid film. In order to explain this behavior of droplet traveling against the counter-current motion, we propose a simple approach: first, the Marangoni convection inside the thin film is considered without the droplet floating on the surface. By using a level-set method and solving the Navier-Stokes equation, the free surface velocity and deformation are calculated. Then, these quantities are used to solve for droplet velocity and drag coefficient simultaneously using a force balance. In order to compare the simulation results, experiments with levitated water droplets on an immiscible carrier liquid, FC-43, were conducted for various temperature gradients, and droplet velocities were measured at different locations using high-speed imaging. The experimental results are in good agreement with the developed theoretical model. For a Reynolds number range of 2-32, it is shown that the drag coefficients are up to 66% higher than those for the fully immersed sphere at the same Reynolds numbers. A correlation is proposed to calculate the drag coefficient of levitated droplets for various temperature drops across the channel.For the first time, it is shown that it is possible to realize the natural coalescence of droplets through Marangoni effect without any external stimulation, and deliver the coalesced droplet to a certain destination through the use of surface tension gradients. The effects of the various shapes and sizes upon collision are studied. Regions of coalescence and stretching separation of colliding droplets are delineated based on Weber number and impact number. The existence of the transition line between coalescence and stretching separation in this passive mode of transport is similar to what was observed in the literature for forced coalescence at significantly higher Weber numbers. It is also found that a thermocapillary environment improves the mixing process. In order to illustrate and quantify the mixing phenomenon, the dispensed droplets were made of potassium hydroxide and phenolphthalein which is used as a pH indicator. The experiments show the possibility to reach mixing rates as high as 74% within 120 ms. This study offers new insight to thermo-coalescence and demonstrates how natural coalescence could be used to transport, mix and collect biochemical assays more efficiently. The results of this research can be engineered to enhance the performance of self-cleaning surfaces and micro-total analysis systems ((&)#181;TAS), where sample transport, filtration, chemical reactions, separation and detection are of great interest.
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Date Issued
2015
Identifier
CFE0006213, ucf:51106
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0006213
Biomechanical Models of Human Upper and Tracheal Airway Functionality
Title
Biomechanical Models of Human Upper and Tracheal Airway Functionality.
Creator
Kuruppumullage, Don Nadun, Ilegbusi, Olusegun, Kassab, Alain, Moslehy, Faissal, Santhanam, Anand, Mansy, Hansen, Hoffman Ruddy, Bari, University of Central Florida
Abstract / Description
The respiratory tract, in other words, the airway, is the primary airflow path for several physiological activities such as coughing, breathing, and sneezing. Diseases can impact airway functionality through various means including cancer of the head and neck, Neurological disorders such as Parkinson's disease, and sleep disorders and all of which are considered in this study. In this dissertation, numerical modeling techniques were used to simulate three distinct airway diseases: a weak...
Show moreThe respiratory tract, in other words, the airway, is the primary airflow path for several physiological activities such as coughing, breathing, and sneezing. Diseases can impact airway functionality through various means including cancer of the head and neck, Neurological disorders such as Parkinson's disease, and sleep disorders and all of which are considered in this study. In this dissertation, numerical modeling techniques were used to simulate three distinct airway diseases: a weak cough leading to aspiration, upper airway patency in obstructive sleep apnea, and tongue cancer in swallow disorders. The work described in this dissertation, therefore, divided into three biomechanical models, of which fluid and particulate dynamics model of cough is the first. Cough is an airway protective mechanism, which results from a coordinated series of respiratory, laryngeal, and pharyngeal muscle activity. Patients with diminished upper airway protection often exhibit cough impairment resulting in aspiration pneumonia. Computational Fluid Dynamics (CFD) technique was used to simulate airflow and penetrant behavior in the airway geometry reconstructed from Computed Tomography (CT) images acquired from participants. The second study describes Obstructive Sleep Apnea (OSA) and the effects of dilator muscular activation on the human retro-lingual airway in OSA. Computations were performed for the inspiration stage of the breathing cycle, utilizing a fluid-structure interaction (FSI) method to couple structural deformation with airflow dynamics. The spatiotemporal deformation of the structures surrounding the airway wall was predicted and found to be in general agreement with observed changes in luminal opening and the distribution of airflow from upright to supine posture. The third study describes the effects of cancer of the tongue base on tongue motion during swallow. A three-dimensional biomechanical model was developed and used to calculate the spatiotemporal deformation of the tongue under a sequence of movements which simulate the oral stage of swallow.
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Date Issued
2018
Identifier
CFE0007034, ucf:51986
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0007034

Pages