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A chilled ceiling panel using PCM is developed. Study has research on its thermal performance and analysis on heat transfer mechanism. Phase change process of PCM has three stages, solid Mushy and Liquid. Mathematic model is built for the... more
A chilled ceiling panel using PCM is developed. Study has research on its thermal performance and analysis on heat transfer mechanism. Phase change process of PCM has three stages, solid Mushy and Liquid. Mathematic model is built for the cool room and simulation is made to evaluate the thermal performance. Contact thermal resistance and conduction shape factor are taken into
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Jet impingement is effective at improving the heat transfer between air and a heated surface. Studies have shown that jet impingement can marginally improve the thermal efficiency of a glazed collector. However, little attention has been... more
Jet impingement is effective at improving the heat transfer between air and a heated surface. Studies have shown that jet impingement can marginally improve the thermal efficiency of a glazed collector. However, little attention has been placed on applying jet impingement to ...
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Designing a cost-effective phase change thermal storage system involves two challenging aspects: one is to select a suitable storage material and the other is to increase the heat transfer between the storage material and the heat... more
Designing a cost-effective phase change thermal storage system involves two challenging aspects: one is to select a suitable storage material and the other is to increase the heat transfer between the storage material and the heat transfer fluid as the performance of the system is limited by the poor thermal conductivity of the latent heat storage material. When used for
Research Interests: Engineering, Heat Transfer, Cost effectiveness, Phase Change, High Temperature, and 10 morePhase Change Material, Thermal Power Plant, Thermal Performance, Thermal Conductivity, Energy Storage, Thermal Energy Storage, Storage system, Latent Heat Thermal Energy Storage, Melting Temperature, and Heat Transfer Rate
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... Lakes SA 5095 - Mawson Lakes Adelaide, Australia 1 edward.halawa@unisa.edu.au, 2 frank.bruno@unisa.edu.au, 3 wasim.saman@unisa ... Monthly space heating (SH) loads were estimated using an Australian building energy rating software,... more
... Lakes SA 5095 - Mawson Lakes Adelaide, Australia 1 edward.halawa@unisa.edu.au, 2 frank.bruno@unisa.edu.au, 3 wasim.saman@unisa ... Monthly space heating (SH) loads were estimated using an Australian building energy rating software, AccuRate (Hearne website, 2006 ...
Abstract An engine driven high-pressure micro-compressor has been developed which employs a unique driving principle. Its advantages make it ideal for supplying high-pressure gaseous fuel to direct injection gas engines. Possible... more
Abstract An engine driven high-pressure micro-compressor has been developed which employs a unique driving principle. Its advantages make it ideal for supplying high-pressure gaseous fuel to direct injection gas engines. Possible arrangements of the compressor ...
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ABSTRACT Thermal energy storage allows improved dispatch-ability of power from a concentrated solar power plant and increases its annual capacity factor. The selection of an appropriate heat transfer fluid (HTF) is important for designing... more
ABSTRACT Thermal energy storage allows improved dispatch-ability of power from a concentrated solar power plant and increases its annual capacity factor. The selection of an appropriate heat transfer fluid (HTF) is important for designing a cost-effective thermal storage system and to improve the cycle efficiency of the power plant. The current state-of-the-art HTF for tower power plants is molten salts, which have the drawback of having low degradation temperature and high melting temperatures respectively. Alternative HTFs under investigation allow for a much larger range of operation, and can offer other cost and performance advantages. In this study, a comparison of six gaseous and liquid HTFs was carried out to determine their suitability for use in a high temperature thermal storage unit with flat slabs of phase change materials. The comparison is in terms of their thermo-physical properties, heat transfer characteristics between the flat plates and the total delivered electrical energy to the grid. Using a validated mathematical model of phase change material in thin slabs, the HTF outlet temperature, heat transfer rate and liquid fraction profiles were predicted when using different HTFs at a constant heat capacity rate for both charging and discharging processes. For the capacity rate considered, liquid sodium was identified as the best HTF, delivering the highest electrical energy to the grid, achieving 99.4% relative to the ideal case. Solar salt achieved a value of 93.6%, while the gaseous fluids of atmospheric air, air at 10 bar, s-CO2 at 100 bar and steam at 10 bar achieved between 87.9% and 91.3% of the ideal delivered electricity. Gaseous fluids have the advantage of being able to be used as the working fluid in the power block. This study shows that gaseous fluids are comparable to liquid HTFs in PCM storage facilities.
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... Due to the simple construction and high ratio of surface area to volume of the flat container, this geometry has been investigated numerically and experimentally ( [Ismail and Gon??alves, 1999] , [Simard and Lacroix, 2003] , [Zalba et... more
... Due to the simple construction and high ratio of surface area to volume of the flat container, this geometry has been investigated numerically and experimentally ( [Ismail and Gon??alves, 1999] , [Simard and Lacroix, 2003] , [Zalba et al., 2004] , [Halawa et al., 2010] , [Halawa and ...
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ABSTRACT This paper investigates the dynamic thermal behavior of phase change material (PCM) melting in a rectangular enclosure at various inclination angles. Lauric acid as a PCM with high Prandtl number (Pr ≈ 100) is used. The enclosure... more
ABSTRACT This paper investigates the dynamic thermal behavior of phase change material (PCM) melting in a rectangular enclosure at various inclination angles. Lauric acid as a PCM with high Prandtl number (Pr ≈ 100) is used. The enclosure is heated isothermally from one side while the other walls are thermally insulated. Experiments were performed with hot wall temperatures of 55, 60 and 70 °C (3.6×108⩽Ra⩽8.3×108)(3.6×108⩽Ra⩽8.3×108) for different inclination angles of 0°, 45° and 90°. Image processing of melt photographs along with recorded temperatures were used to calculate the melt fractions, Nusselt numbers and the local interfacial heat transfer rates at the solid–liquid interface. Qualitative time-dependent natural convection flow structures were deduced indirectly from the instantaneous shape of the solid–liquid interface which were confirmed by quantitative data from temperature measurements. The results reveal that the enclosure inclination has a significant effect on the formation of natural convection currents and consequently on the heat transfer rate and melting time of the PCM. As the inclination angle is decreased from 90° to 0°, the convection currents in the enclosure increases and chaotic flow structures appear. When melting commences in the horizontally inclined enclosure, the solid–liquid interface line becomes wavy which implies the formation of Benard convection cells in the liquid PCM. For the same hot wall temperatures, a decrease in inclination angle leads to a considerable enhancement in energy transport from the hot wall of the enclosure to the PCM. It is found that the heat transfer enhancement ratio for the horizontal enclosure is more than two times higher than that of the vertical enclosure.
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ABSTRACT An experimental validation for a computational fluid dynamics (CFD) and an effectiveness-number of transfer units (ε-NTU) model for tubes in a large phase change material (PCM) tank has been conducted. The inlet and outlet heat... more
ABSTRACT An experimental validation for a computational fluid dynamics (CFD) and an effectiveness-number of transfer units (ε-NTU) model for tubes in a large phase change material (PCM) tank has been conducted. The inlet and outlet heat transfer fluid (HTF) temperatures as well as twelve temperature locations in the PCM tank were compared with the CFD results. The average effectiveness of the phase change process of each experimental point was also compared with results from the CFD as well as the ε-NTU models. From this study, it was concluded that the CFD model and the ε-NTU model developed can accurately predict the behaviour of the thermal storage system during the freezing process. There are however, discrepancies in the melting process due to the exclusion of the effect of natural convection in the models. Using the experimental results, an effective thermal conductivity has been determined to account for buoyancy for various distances of tubes. The paper gives details of the CFD model of the phase change thermal storage system, and presents results from the CFD model, experiments and ε-NTU model.
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ABSTRACT An investigation into characterising and optimising the useful latent energy that can be stored within a tube-in-tank phase change thermal energy storage system has been conducted, with particular reference to off peak thermal... more
ABSTRACT An investigation into characterising and optimising the useful latent energy that can be stored within a tube-in-tank phase change thermal energy storage system has been conducted, with particular reference to off peak thermal storage applications for cooling buildings. This process involved determining the actual useful energy that can be stored within a phase change material (PCM) storage system coupled to a low energy night time cooling system using a cooling tower. The useful energy that can be stored within the PCM was determined using a validated effectivess-NTU model. The energy storage effectiveness of the PCM system was determined, which directly indicates how much of the PCM was useful. This storage effectiveness was optimised delivering a storage effectiveness of 68% and 75%. This parameter can be directly compared to sensible storage systems and it was found that tube-in-tank systems can store more than 18 times more useful energy than sensible storage systems per unit volume.
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AbstractPCMs have always been viewed as a suitable candidate for off peak thermal storage, particularly for refrigeration systems, due to the high latent energy densities of these materials. However, due to the need to have them... more
AbstractPCMs have always been viewed as a suitable candidate for off peak thermal storage, particularly for refrigeration systems, due to the high latent energy densities of these materials. However, due to the need to have them encapsulated within a container this ...
Phase Change Material (PCM) is considered as a good Thermal Energy Storage (TES) material as it can provide much higher energy storage densities compared to conventional sensible thermal storage materials. An extensive literature review... more
Phase Change Material (PCM) is considered as a good Thermal Energy Storage (TES) material as it can provide much higher energy storage densities compared to conventional sensible thermal storage materials. An extensive literature review has been ...
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A one-dimensional liquid-based model for a flat slab phase change thermal storage unit was developed. The model allows for varying wall temperatures along the direction of flow and integrates a convective boundary layer using a previously... more
A one-dimensional liquid-based model for a flat slab phase change thermal storage unit was developed. The model allows for varying wall temperatures along the direction of flow and integrates a convective boundary layer using a previously developed algorithm, which is ...
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ABSTRACT Considerable research has been conducted on heat transfer enhancement of phase change materials (PCMs) in thermal energy storage systems. Heat transfer enhancement techniques such as the use of conductors like graphite, carbon... more
ABSTRACT Considerable research has been conducted on heat transfer enhancement of phase change materials (PCMs) in thermal energy storage systems. Heat transfer enhancement techniques such as the use of conductors like graphite, carbon fibre and carbon brushes have been proven to be effective. Shell and tube heat exchangers which utilise many tubes in the PCM have also shown to have good heat transfer performance. Fins embedded on tubes are also effective and very popular due to its simplicity. In this paper, a new concept of a heat transfer enhancement technique for a tube-in-tank phase change thermal energy storage system has been investigated, dynamic melting. This technique is used to improve the heat transfer during the melting process. It was found from experiments that dynamic melting was more effective than those without dynamic melting. The time taken to complete the phase change process was also found to be shorter when dynamic melting was utilised. It can be concluded from experiments that dynamic melting is an effective technique for enhancing heat transfer.
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ABSTRACT An experimental validation for a computational fluid dynamics (CFD) model for tubes coiled in a phase change thermal energy storage system has been conducted. Using the validated CFD model, three CFD models have been developed.... more
ABSTRACT An experimental validation for a computational fluid dynamics (CFD) model for tubes coiled in a phase change thermal energy storage system has been conducted. Using the validated CFD model, three CFD models have been developed. The first model was developed having pins embedded on a tube with heat transfer fluid (HTF) flowing in it, with PCM surrounding the tube. Different configurations of pins on the tube have been analysed. The second model developed is similar to the first model; however, fins were embedded instead of pins. Different configurations of fins on the tube were also investigated. The last model developed was a plain copper tube surrounded by PCM with HTF flowing in it. This model was used as a benchmark for comparison for the first two models. The models were analysed for the freezing process. From this study, it was concluded that fins on the tube is better than pins on the tube. The paper gives details of the CFD models and presents the results obtained from simulations carried out using these models.