Date of Award

Spring 1988

Project Type

Dissertation

Program or Major

Engineering

Degree Name

Doctor of Philosophy

Abstract

Space missions in the near future will require power plants and cooling systems to operate in space. Such systems will often incorporate two-phase (vapor-liquid) heat transfer loops. Heat transfer processes such as boiling and condensation involve two-phase flow and are gravity dependent. Such unit operations would, therefore, be expected to behave differently in a micro-gravitational ("micro-g") environment. In this study, a unique approach to study the flow patterns of vapor-liquid flow on earth is presented. Simulation of a micro-g vapor-liquid flow on earth is accomplished by the use of two immiscible liquids of equal density. This equal density two-liquid system makes the buoyancy forces approach zero which is the case for real vapor-liquid flow in micro-g conditions. Water and properly selected oils are used in the experiments. In simulating micro-g vapor-liquid flow, the oil which is more viscous and more wettable liquid represents the "liquid" phase and water (less viscous and less wettable with respect to waxed tube surface) corresponds to the "vapor" phase.

The experiments are carried out in a horizontal pyrex glass tube (6.1 m long and 2.54 cm ID). Data are obtained for five different fluid systems to study the effect of viscosity ratio, interfacial tension, and wettability of two fluids on flow regime boundary lines. Comparison of the simulated versus actual micro-g vapor-liquid flow regime data indicates the validity of this simulation approach. The experimental results are also compared against Taitel-Dukler and Weisman et al. model predictions under micro-g conditions. A flow regime map for vapor-liquid flow in a micro-g environment is developed for usage in designing two-phase systems in space applications.

The effect of gravity on nucleate boiling is also considered. The static and dynamic forces acting on a growing vapor bubble on heating surface are evaluated and how their interaction causes the bubble to detach from the surface is presented. By using a force balance, the bubble departure radius is calculated and compared with experimental measurements from literature under micro-g conditions.

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