الفهرس 
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Abstract
This thesis reports the results of an experiment study on the heat transfer during freezing (charging) and melting (discharging) of water inside a spherical capsule of the type often found in the beds of thermal (ice) storage systems used for the building air conditioning systems.
A suitable test rig is established, to enable conducting the charging and discharging experiments.
Spherical capsules of different diameters and materials are tested.
80%of each capsule inner volume is filled with water as a phase change material (PCM).
The aqueos solution of 35-wt% ethylene glycol is used as the heat transfer fluid (HTF).
Effects of the size and material of the spherical capsule, the volume flow rate and temperature of the heat transfer fluid (HTF) on the time for complete charging/discharging, the solidified/melted mass fraction, the charging/discharging rate, the energy stored/regain, and the energy recovery ratio (ERR)are he major studied parameters.
The experimental results show that :
_ The time for completed charging is decreased by using metallic capsules, smaller capsule sizes, lower HTF
volume flow rates and lower HTF temperatures.
- The percentage of the energy stored is increased by using metallic capsules, smaller capsule sizes, higher
HTF volume rates and lower HTF temperatures.
-The time for complete discharging is increased by using nonmetallic capsules, bigger capsule sizes,
lower THF temperatures and lower volume flow rates.
-The thermal conductivity of the capsule material has a relatively small effect on the time for complete discharging, solidified mass fraction, melted mass fraction and the energy recovery ratio.
-Although shorter time is consumed for the charging process using the metallic capsules, significant longer time is takenfor the discharging process when using the non-metallic capsules, wich lead to select the later type to
enhance the thermal energy storage system.