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The present study explores numerically the energy storage and energy regeneration during Melting and Solidification processes in Phase Change Materials (PCM) used in Latent Heat Thermal Energy Storage (LHTES) systems. Transient two-dimensional (2-D) conduction heat transfer equations with phase change have been solved utilizing the Explicit Finite Difference Method (FDM) and Grid Generation technique. A Fortran computer program was built to solve the problem. The study included four different Paraffin's. The effects of container geometrical shape, which included cylindrical and square sections of the same volume and heat transfer area, the container volume or mass of PCM, variation of mass flow rate of heat transfer fluid (HTF), and temperatures difference between PCM and HTF were all investigated. Results showed that the PCMs in a cylindrical container melt and solidify quicker than the square container. The increase in mass flow rate and/or temperature difference decreases the time required for complete phase change. Paraffin's solidify quicker than they melt and store more energy than they release.

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Abstract This paper presents the feasibility of utilizing thermal energy storage systems in reducing both the initial and running expenses of chiller systems in large mosques. The study focused on the great mosque in the city of Mosul as a model. Two load profiles are considered, the occasional and the normal profiles with three different partial storage control strategies. The conventional strategy is also considered for the purpose of comparisons. From the results, it can be concluded that, the amount of the shifted load from the on-peak period for the occasional profile is equal to 45.2%, 24%, and 39.1% for the three control cases respectively. Up to 74% reduction in the on-peak power consumption can be achieved with a total shifted power, (from the on-peak to the off-peak periods) of up to 47.2%, which will add significantly to the total cost reduction. For the normal profile, the amount of the shifted load from the on-peak period is equal to 9.8%. The peak power consumption is reduced by 33.1%, and about 10% of the consumed power is shifted to low price period.Key words: A/C systems, refrigeration systems, thermal energy storage

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In this paper, the unsteady state heat transfer through the thermal energy storage system is investigated numerically by using finite difference method in order to study the optimum thermaldesign of the latent heat thermal storage. The present analysis takes into account the heat transfer intwo dimensions for fluid, tube and the PCM. The conical shape of the PCM is examined here fordifferent diameters depending on the cone angle (ψ). The results of the present study are comparedwith other study to confirm the accuracy. Results of a numerical case study are presented anddiscussed. The results show that the decreasing the value of (ψ) will increase the hot and cold fluidseffectivenesses and the difference between the effectiveness (hot and parallel cold and counter cold)increased with decreased value of (ψ) in the negative range (ψ = -0.13 deg). The counter flow forthe cold fluid produce higher effectiveness than the parallel flow for the cold fluid especially for thenegative value of (ψ = - 0.13 - 0 deg).

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A theoretical study of storage thermal energy using capsulated cylinders filled with phase change material PCM is performed. These cylinders are arranged in-line in the direction of heat transfer fluid. The energy equations of fluid (water) and PCM capsules are solved numerically using finite volume method with heat capacity method for phase change of PCM. The effect of Reynolds number and the ratio of pitch to diameter of the cylinders on the temperature distribution and melt fraction are presented. The results show that the increment of both Reynolds number and the ratio of the pitch to diameter gives decrement in the final time of melting of PCM in the cylinders.

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In this work numerical and experimental investigation have been adopted to collect and store solar energy in exterior-wall cladding, Various improvements have been investigated inside and outside the duct to increase the efficiency of thermal heating. ANSYS software has been used to simulate current case. Results show that there is a good agreement between experimental and numerical results and this agreement increases as air velocity increases. The average percentage error for air inside duct at velocity of air 1 m/s, 3 m/s and 5 m/s is 8%, 16.5% and 5% respectively. Several vertical cooper cylinders with 12 mm diameter were added inside basin to increase the surface area. It has been found that the enhancement in temperature of air between this case and Smooth Duct, Smooth Cover base model for air velocity of 1,3and 5 m/s is 3, 4 and 11 % respectively. The effect of increasing surface area by using granular (corrugated) duct on the air temperature distribution along the duct. Have been also investigated the percentage enhancement in temperature of air between this case and previous base smooth duct case for velocities of 1, 3 and 5 m/s is 19.4, 28.6 and 16.5 % respectively. The enhancement in heat transfer when using both granular hollow sphere duct with vertical metal cylinders for air velocity of 1, 3 and 5 m/s is 27.5, 33 and 35.2 % respectively.

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This paper presents a theoretical analysis on packed bed thermal energy storage using phase change material (PCM) to improve the performance of solar organic Rankine cycle power generation system by extending its operational time demand to the night. The transient behavior of packed bed thermal energy storage using spherical capsules filled with paraffin wax as a storage unit has been studiednumerically by finite difference technique for charging and discharging process .The effects of different parameters such as inlet temperature, mass flow rate, bed porosity , diameter of capsule and turbine inlet temperature have shown to be dominant parameters in determining the effective thermal efficiency of the solar ORC. It is seen that, turbine inlet temperature is plays animportant role in the geometrical parameters of the packed bed.Comparison between theoretical results and experimental results of previous study for solar water heating system has been carried out where good agreement is noticed.

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One of the most suitable materials to be used in latent heat thermal energy storage system (LHTES) are Phase change materials, but a problem of slow melting and solidification processes made many researchers focusing on how to improve their thermal properties. This experimental work concerned with the enhancing of thermal conductivity of phase change material. The enhancing method was by the addition of copper Lessing rings in phase change material (paraffin wax). The effect of diameter for the used rings was studied by using two different diameters (0.5 cm and 1cm). Also, three volumetric percentages of rings addition (3%, 6% and 10%) were tested for each diameter. The discharging process was done with four velocities for each case. The obtained results indicated that the maximum volumetric percentage gave a diminished time for melting and maximized the heat transfer in both PCM and air sides as compare with the case of no rings, but the effect of these rings had lower effect on the solidification time. In case of 1 cm rings diameter minimum time for melting was obtained for both 3% and 6% volumetric percentages as compared with the same percentages in case of 0.5 cm diameter rings, while the latter with 10% volumetric percentage overcomes the 1 cm diameter rings for the same previous percentage. Also it can be seen that the minimum velocity (v=1m/s) gave the utmost outlet temperature and with the maximum one (v=3m/s), the minimum solidification time achieved.

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Polymer additives binder system provides many properties useful in thermal energy storage (TES) then developed the efficient energy storage materials and green strength bodies system.This paper studies the thermal energy storage property for polyvinyl alcohol (PVOH) / paraffin wax (WPw) blends. To enhance paraffin wax thermal conductivity, PVOH as a material which high conductivity was employed. A fixed weight of Paraffin wax was dispersed with PVOH heterogeneously at different additive weights ratios of PVOH/Pw (50/50, 67/33, 75/25, and 80/20) wt. ratio respectively. The composite material was prepared using wetted pressing method. Both base materials (polyvinyl alcohol and paraffin wax) were scanned using differential scanning calorimeter (DSC) under non-isothermal conditions, the result was analysed to determine the thermal transition temperature of PVOH and paraffin wax base material. The thermal decomposition of PVOH and waste paraffin wax proved that high transition temperature (TG) for PVOH reached 209ᴼc rather than wax of 60ᴼc respectively. This result shows that PVOH suppress the thermal stability of PVOH/waste paraffin wax composites. Afterward examines the thermal conductivity enhancement using Lee- disk techniques. Composite materials PVOH/paraffin wax have a high thermal conductivity which increases thermal conductivity of waste paraffin wax as a heat storage media and this allows to apply change in phase with wide range of temperatures, and the highest decreased ratio of phase-change heat is very low, compared to that of paraffin only. Therefore, PVOH, added to paraffin which has significant potential for enhancing the thermal storage characteristics of paraffin. A wax/PVOH system acts as strength body resistance to sever contact of both air and moisture then a moisture absorbance percent was achieved by use both Fourier transform infrared spectroscopy (FTIR) techniques and moisture solutions (100% H2O) for all pure and composite material system Pw/PVOH, the results shows high resistance to ambient conditions (air/ moisture) for composite system rather than pure materials (PVOH and Pw).

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The present work deals with an experimental investigation of charging and discharging processes in thermal storage system using a phase change material PCM. Paraffin wax was used as the PCM which is formed in spherical capsules and packed in a cylindrical packed column which acted as an energy storage system. Air was used as the heat transfer fluid HTF in thermal storage unit. The effect of flow rate and inlet temperature of HTF on the time of charging and discharging process were studied. The results showed that the faster storage of thermal energy can be made by high flow rate of heat transfer fluid HTF and high inlet temperature of heat transfer fluid. It was found that at 65°C HTF inlet temperature, the melting and solidification processes accelerated by 27.9% and 57.14% respectively, when the flow rate was increased from 9 to 24 L/s. Also, when the HTF inlet temperature changed from 65°C to 80°C, the time needed to complete melting process decreased by 38.8%.

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The reducing of heat gain through the outer walls of the buildings in summer will contribute in reducing the air conditioning costs. This is one of the best features of design requirements nowadays. To achieve this, the phase change materials (PCM) can be used as an embedded material in the walls to reduce heat transfer. The paraffin wax is one of the common materials used as a PCM in the building walls. The paraffin wax is used in this study with (20%) volume percentage in the external layer of the treated wall. In the present work, the treated wall (with embedded wax in the wall) and non-treated walls have been experimentally investigated. Two Iraqi wall models were employed to run the experiments, whereby these models were exposed to an external heat source using (1000 W) projector for each model. The temperatures were recorded at different locations in the walls during the charging and discharging periods. The results showed that the temperature of the internal surface for the treated wall was lower than that of the non-treated wall at the end of the discharging period (6 hr) where the temperature difference between the treated and non-treated walls was reached (1.6℃).

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