الفهرس 
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Abstract
Thermal energy storage systems (TES) based on the latent heat storage energy have great importance in practical applications to develop economical and efficient storage system with high performance during charging/discharging processes. Therefore, present work
aims to improve the heat exchange between the stored medium of paraffin wax as a phase change material (PCM) and water as a heat transfer fluid (HTF) that indicates the duration
time and amount of energy stored/regained during charging/discharging processes.
Experimental test rig simulating the thermal energy storage (TES) system has been designed and fabricated. An insulated stainless-steel tank with 33-liter storage capacity has
been used as a TES tank which contained the test section. The test section composed of three stainless steel discs punctuated by twenty-one copper tubes with 5/8-inch diameter
which are packed with paraffin wax and ZnO NCPCM. Nanoparticles of ZnO at different concentrations by weight of 0.10 wt.%, 0.15 wt.%, 0.30 wt.%, and 0.70 wt.% have been prepared to produce nanocomposite PCM to augment the thermal performance of base
PCM. The thermal performance of TES was investigated using the instantaneous temperature variation of TES with and without nanoparticle, energy absorbed/regained,
Energy Recovery Ratio, and Enhancement ratio during charging/discharging processes. Experiments have been done at constant operating conditions for both charging and discharging processes. The HTF is allowed to inter the TES tank during charging process
at 70˚C and at 24 ˚C discharging process. Both of charging and discharging processes are
carried out at five different volume flow rates that are 4, 6, 8, 9, 10 LPM. The results demonstrate that using PCM with small concentration (0.10 wt.%) at high flow
rate (8 LPM) or with NCPCM at concentration (0.15 wt.%) and low flow rate (4 LPM) are recommended for efficient energy use. Results showed that as the volume flow rate of HTF
increases from 4 to 9 LPM, the duration time required to store the thermal energy decreases
but at 10 LPM the duration time rise. Also, the duration time required for melting decreases as the ZnO concentration particle increases except at 0.70 wt.% concentration where the melting time is higher than low concentration at low and high HTF volume flow rate (4 LPM and 10 LPM). On the other hand, reduction in charging time of about 56.7 % for the
NCPCM at a nanoparticle concentration of 0.30 wt.% at 6 LPM. The
concentration at 0.30 wt.% and 6 LPM HTF flow rate is suitable for practical engineering for minimum energy cost and high thermal performance of energy storage system. The total duration time for complete charging process of pure PW decreases by 65.6 % of original time when the HTF volume flow rate increases from 4 LPM to 9 LPM.