Date of Award

2002

Level of Access Assigned by Author

Open-Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Mechanical Engineering

Advisor

Justin H. Poland

Second Committee Member

Richard Sayles, Jr.

Third Committee Member

John J. Hwalek

Abstract

The object of this thesis is to develop a numerical model that simulates the transient behavior of a coaxial, thermal energy storage system consisting of a phase changing material ( P O interacting with a two-phase fluid. The purpose of this model would be to have a useful design tool that could be applied when sizing and building iceon- coil, cooling systems (ice-banks). The numerical model is an explicit finite volume approximation applied to the enthalpy method. It solves a two-dimensional, axisymrnetric, heat conduction problem with conjugate forced convection at its inner boundary. Natural convection is neglected in the PCM. The conjugate boundary is modeled with existing, empirical correlations for heat transfer coefficient during evaporation/condensation of a two-phase fluid. Pressure drop is also modeled with existing correlations. The model is validated analytically for small times by comparing it to Paterson's one-dimensional, solidification of a line heat sink in an infinite medium. A test apparatus was built also, to validate the model experimentally. Mean and average deviation between numerical and experimental results fall within 9% and 6%, respectively. Parametric studies are performed to determine relevant characteristics of a themla1 energy storage unit. Results indicate that axial conduction in the PCM cannot be neglected when interacting with high Reynolds number, two-phase flows. It is shown that it is more efficient to increase the volume of PCM by adding length rather than thickness. The effects of Reynolds number on two-phase, local Nusselt number are investigated. The results of adding sensible heat to the PCM are examined by looking at the effects of Stefan number on wall temperature and on Biot number. The behavior of pressure drop, during evaporation and condensation, is discussed. The results of applying this numerical approach indicate some important criteria to determining the optimal design of a thermal energy storage system.

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