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Dr. Hany Al-Sawy Abdel-Rahman :: Theses : |
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| Title | An Experimental and Parametric Study on Freezing and Melting of Water Inside Spherical Capsules used in Thermal Energy Storage (TES) Systems |
| Type | MSc |
| Supervisors | R. A. Abdelaziz, M.H. Sakr, R. I. ElGhnam, |
| Year | 2010 |
| Abstract | This thesis reports the results of an experimental 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 aqueous solution of 35-wt% ethylene glycol is used 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 the major studied parameters. The experimental results show that: • The time for complete charging is decreased by using metallic capsules, smaller capsule sizes, lower HTF temperatures and higher HTF volume flow rates. • The solidified mass fraction is increased by employing metallic capsules, using smaller capsule sizes, higher 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 HTF temperatures and lower volume flow rates. • The melted mass fraction and the percentage of the energy regained are increased by employing metallic capsules, using smaller capsule sizes, higher HTF volume flow rates and higher HTF temperatures. • The energy recovery ratio is becoming better, when using metallic capsules, increasing the capsule size and reducing the HTF volume flow rates. • The thermal conductivity of the capsule material has a relatively small effect on the time for complete charging, 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 taken for the discharging process when using the non-metallic capsules, which lead to select the later type to enhance the thermal energy storage system. • It is economical to use nonmetallic capsules (cheap and easy to fabricate), as the change in time for complete charging and discharging as well as ERR is small. • The gained results of the present research are confident as reasonable agreement is noticed when compared with the results of one of the literature. |
| Keywords | Freezing and melting; Spherical capsules; Thermal energy storage |
| University | Benha University |
| Country | Cairo |
| Full Paper | - |
| Title | Heat Transfer Enhancement During Pool Boiling Using Micro-Structured Surfaces and Surfactants |
| Type | PhD |
| Supervisors | R. M. Abdel Aziz, R. Y. Sakr, A. A. Abellattif, |
| Year | 2014 |
| Abstract | The main objective of the present study is to investigate the effect of adding definite amounts of different surfactants to boiling distilled water on the nucleate pool boiling heat transfer performance using micro-structured heated tubes. Effects of wall heat flux, surface roughness, type of surfactant and its concentration in aqueous surfactant solutions (boiling fluids) on the nucleate boiling heat transfer coefficient are the major studied parameters. The tested surfactants are Sodium Dodecyl Sulfate (SDS) as anionic and Cetyl Trimethyl Ammonium Bromide (CTAB) as cationic. Six tested horizontal copper tubes are used; one is smooth, while the other tubes are roughened using sandblasting with different surface roughness parameters. A pool boiling test rig is designed and constructed to carry out heat transfer experiments. The effects of both of surfactants concentration and surface roughness on the heat transfer performance during pool boiling are studied. The experimental investigations showed that the addition of definite amounts of aqueous anionic and cationic surfactants (SDS and CTAB) to the water improves its physical and thermal properties and in turn improves the heat transfer coefficient in percentages reaching to 257 % for CTAB and 302 % for SDS using the most rough surface. A detailed analysis of the experimental data showed good enhancement in the heat transfer coefficient for all test concentrations of SDS and CTAB using the six test tube surfaces with different percentages. The size distribution functions N(r) for the size of the stable vapor bubbles in the active nucleation sites are deduced for the six test tubes using different test concentrations of aqueous surfactant solutions. Attention is directed to correlate the experimental results of the wall heat flux, surface roughness and aqueous surfactant solution concentration; to get a helpful tool for predicting the enhancement of the heat transfer coefficient during nucleate pool boiling. Reasonable agreement is found between the present experimental data and the available published data. |
| Keywords | Pool Boiling; Surfactants; Surface Roughness |
| University | Benha University |
| Country | Cairo |
| Full Paper | - |
