Date of Award

2014

Degree Type

Thesis

Department

Mechanical Engineering

First Advisor

Ibrahim, Mounir

Subject Headings

Fluid dynamics (Space environment), Liquids -- Effect of reduced gravity on, Computational fluid dynamics, Low temperature engineering, Heat -- Transmission, CFD Computational Fluid Dynamics model boiling pressure rise microgravity tank engineering modeling

Abstract

NASA's missions in space depend on the storage of cryogenic fluids for fuel and for life support. During long-term storage, heat can leak into the cryogenic fluid tanks. Heat leaks can cause evaporation of the liquid, which pressurizes the tank. However, when the tanks are in a microgravity environment, with reduced natural convection, heat leaks can also create superheated regions in the liquid. This may lead to boiling, resulting in much greater pressure rises than evaporation at the interface between the liquid and vapor phases. Models for predicting the pressure rise are needed to aid in developing methods to control the pressure rise, so that the safety of the storage tank is ensured for microgravity operations.In this work, a CFD model for predicting the pressure rise in a tank due to boiling has been developed and validated against experimental data. The tank was modeled as 2D axisymmetric. The Volume of Fluid (VOF) model in ANSYS Fluent version 15 was modified using a User Defined Function (UDF) to calculate mass transfer between the liquid and vapor phases. A kinetic based Schrage equation was used to calculate the mass flux for evaporation and condensation at the interface. The Schrage equation and the Lee model were compared for calculating the evaporation due to boiling that occurred in the bulk liquid. The results of this model were validated against microgravity data provided by the Tank Pressure Control Experiment, a tank pressurization and pressure control experiment performed aboard the Space Shuttle Mission STS-52 that experienced boiling. During this experiment, the tank pressure rose from about 43400 Pa to about 47200Pa, a difference of about 3800 Pa. The heater temperature rose from about 296K to about 303K, a difference of about 7K.The tank pressure predicted by the CFD model compared well with the experimental pressure data for self-pressurization and boiling in the tank. The validated CFD model uses the Schrage equation to calculate the mass transfer. Three different accommodati

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