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Investigation of Bubble Dynamics in Pure Liquids and Aqueous Surfactant / Polymer Solutions Under Adiabatic and Diabatic Conditions

Kalaikadal, Deepak Saagar

Abstract Details

2018, PhD, University of Cincinnati, Engineering and Applied Science: Mechanical Engineering.
The goal of this work is to gain a better understanding of the complex physics governing the growth of bubbles from orifices in liquid pools of pure liquids, and aqueous surfactant-and-polymer-solutions. The final phase of the bubble cycle - necking and pinch-off - was investigated initially. Understanding the nature of the governing forces yielded a correlation capable of predicting the neck-length at pinch-off, providing a closure criterion. The influence of orifice-size was then studied. Within the constant-bubble-volume region, the growth and departure of bubbles is completely governed by a balance between the capillary-forces and the buoyancy-forces. The resulting force-balance leads to a correlation to predict the bubble departure-size from any orifice. The influence of surface-tension on bubble-growth was further investigated in both pure liquids and aqueous-surfactant-solutions. The bubble-regime-map in aqueous-surfactant-solutions exhibited a characteristic `s’-shaped-curve, mimicking the relaxation-curve of the surfactant itself. Due to this, the slopes of the relaxation-curves were found to be excellent parameters for predicting the corresponding bubble-growth-curves. This was followed by a computational-study of thermo-capillary convection driven by the temperature and surface-tension gradients at the interface of a bubble subjected to a stratified thermal field. The effect of liquid-properties, wettability, bubble-size, channel-depth, and temperature-gradients on the strength of the thermo-capillary currents and the associated heat transfer enhancement at the bubble interface was studied. It was established that the Marangoni number, by itself, cannot capture the complexities of the transient capillary flow. The study on thermo-capillary convection was extended into a computational-study of bubble-induced thermo-diffuso-capillary convection in the presence of surfactants and a stratified thermal field. The complex interaction between the temperature-driven and concentration-driven capillary currents were observed and related to the enhancements in heat transfer near the bubble. The model was also used to simulate adiabatic bubble growth in surfactant-solutions. The interfacial variation of surface-tension, due to the presence of surfactants, is seen to change the shape and size of the growing bubble, as compared to water. However, it was established that the micro-convective capillary currents did not have a large role in determining the bubble departure-size. Liquid-viscosity was the last parameter of interest with respect to bubble growth in orifices. A critical criterion was established below which viscosity ceases to have influence on bubbles growing from orifices. Similarly, the existence of another regime, where surface-tension plays no role in the bubble-dynamics, was recognized. The clear demarcation of these two regimes resulted in a universal correlation for predicting the bubble departure-sizes under different growth conditions. Polymer-solutions impart a non-Newtonian, pseudo-plastic characteristic to the liquid. The influence of this shear-thinning behavior on bubble-growth was studied experimentally The effect of decreasing viscosity was clearly seen at high flow-rates by comparing the bubble-sizes with bubbles growing in water at corresponding flow-rates. Finally, the above results were applied to data available for nucleate-pool-boiling in aqueous-surfactant-solutions to propose a scaling parameter capable of estimating the heat-transfer enhancement. The enhancement in heat-transfer is shown to scale with the bubble departure-diameters, and the corresponding relaxation behavior of each surfactant-solutions.
Raj Manglik, Ph.D. (Committee Chair)
Je-Hyeong Bahk, Ph.D. (Committee Member)
Milind Jog, Ph.D. (Committee Member)
Murali Sundaram, Ph.D. (Committee Member)
305 p.

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Citations

  • Kalaikadal, D. S. (2018). Investigation of Bubble Dynamics in Pure Liquids and Aqueous Surfactant / Polymer Solutions Under Adiabatic and Diabatic Conditions [Doctoral dissertation, University of Cincinnati]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1525167893347615

    APA Style (7th edition)

  • Kalaikadal, Deepak Saagar. Investigation of Bubble Dynamics in Pure Liquids and Aqueous Surfactant / Polymer Solutions Under Adiabatic and Diabatic Conditions. 2018. University of Cincinnati, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=ucin1525167893347615.

    MLA Style (8th edition)

  • Kalaikadal, Deepak Saagar. "Investigation of Bubble Dynamics in Pure Liquids and Aqueous Surfactant / Polymer Solutions Under Adiabatic and Diabatic Conditions." Doctoral dissertation, University of Cincinnati, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1525167893347615

    Chicago Manual of Style (17th edition)