Student:	Mithat AKGÜN
Supervisor:	Assoc. Prof. Dr. Orhan AYDIN
Department:	Mechanical Engineering
Institution:	Graduate School of Natural and Applied Sciences
University:	Karadeniz Technical University, Turkey

Title of the Thesis:	An Experimental Study on Optimization of the Storage Geometry in Latent Heat Storage Systems Using Paraffin
Level:	Ph.D.
Acceptance Date:	22/5/2006
Number of Pages:	385
Registration Number:	di541

Summary:

The discrepancy between energy supply or availability and demand can be overcome

by the implementation of a proper energy storage system. There are three main methods for

storing the thermal energy: sensible, latent and thermo chemical. The latent heat storage

employing phase change material (PCM) is the most effective way due to its advantages of

high energy storage density and its isothermal operating characteristics during melting and

solidification processes.

Heat transfer in a storage device during charging/discharging should be enhanced for a

better performance. This can be realized in two ways: active and passive. The active method

requires usage of extra energy while the passive one does not. In this study, a passive

enhancement technique has been applied, which is based on the modification of the storage

geometry, in order to intensify the natural convection currents inside the PCM, decrease the

charge/discharge time and increase the efficiency of the storage container. A novel

modification on a tube-in-shell type storage geometry is suggested. In the proposed geometry,

the outer surface of the storage container, i.e. the shell, is inclined in order to respond the

melting and solidification characteristics observed earlier. Three kinds of pure paraffin have

been used. At first, the thermo physical properties of the paraffins used are determined

through the differential scanning calorimeter (DSC). Five different inclination angles of the

shell have been tested: 0°, 5°, 10°, 15°, and 20°. In addition, different positions of the storage

container have also been examined: vertical, horizontal, and tilted to the horizontal axis with

angles of 30° and 60°. At different geometrical configurations, for each paraffin type, the

effects of the inlet temperature and the mass flow rate of the heat transfer fluid (here, water)

on the melting/solidification behavior have been examined. In order to assess the validity of

the experimental results, an uncertainty analysis has been conducted. Finally, a

thermodynamic analysis has been performed in order to determine the optimum storage

geometry and the working conditions.

Keywords: Thermal energy storage, experimental, PCM, paraffin, melting, solidification,

tube-in-shell geometry, thermodynamic analysis.