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To accelerate the charging and discharging of molten salt thermal storage and to enhance heat transfer, the authors of this paper propose a novel idea of using direct contact heat exchange. Under this proposal, a gaseous fluid from the solar field is directly injected into the molten salt system without any heat exchanger. In direct contact heat exchange, efficient energy exchange takes place within a smaller volume, which contributes an order of magnitude increase in heat transfer. Relative to liquid metals, whose thermal conductivity varies from low 10 W/m.K to 180W/m.K, the thermal conductivity of molten nitrate salts is fairly low i.e. 0.55W/m.K to 0.654W/m.K The low thermal conductivity of molten salts in liquid, mushy and solid phase limits their charging, discharging efficiency and makes the heat transfer process an energy and engineering resource-intensive process. The proposed direct contact heat exchange will eliminate the use of electric blanket heating of molten salt tank and pipe and address the issue related to molten salt freezing in the tank, pipes, pumps or the solar field. The authors of this research paper are investigating an innovative concept in which a non-reactive gaseous heat transfer fluid from solar field is directly injected into the molten carbonate to melt and remelt and to enhance the heat transfer. During the cooling cycle, the liquid to solid phase change process will take place; the gaseous fluid cooling will enforce a porous solidification of the molten salts. This porous phase change phenomenon is of critical importance and is beneficial during the remelting of the molten salts. In the current research, the role of forced convection, liquid and vapour phase drops and the role of mass transfer due to evaporative losses are investigated. In addition, the issues related to the freezing and melting of phase change material by forced convection are also addressed. Modelling and analysis results of heat transfer due to forced convection are presented. The results of low and medium temperature testing, their analysis, some preliminary modelling and simulation work is presented in this research paper. The role of low vapour pressure, thermal stability, surface tension, the density of the molten salt and areas of critical importance are analyzed. Analysis of experimental results is presented to determine the energy exchange the exchange effectiveness and heat transfer coefficients.

To accelerate the charging and discharging of molten salt thermal storage and to enhance heat transfer, the authors of this paper propose a novel idea of using direct contact heat exchange. Under this proposal, a gaseous fluid from the solar field is directly injected into the molten salt system without any heat exchanger. In direct contact heat exchange, efficient energy exchange takes place within a smaller volume, which contributes an order of magnitude increase in heat transfer. Relative to liquid metals, whose thermal conductivity varies from low 10 W/m.K to 180W/m.K, the thermal conductivity of molten nitrate salts is fairly low i.e. 0.55W/m.K to 0.654W/m.K The low thermal conductivity of molten salts in liquid, mushy and solid phase limits their charging, discharging efficiency and makes the heat transfer process an energy and engineering resource-intensive process. The proposed direct contact heat exchange will eliminate the use of electric blanket heating of molten salt tank and pipe and address the issue related to molten salt freezing in the tank, pipes, pumps or the solar field. The authors of this research paper are investigating an innovative concept in which a non-reactive gaseous heat transfer fluid from solar field is directly injected into the molten carbonate to melt and remelt and to enhance the heat transfer. During the cooling cycle, the liquid to solid phase change process will take place; the gaseous fluid cooling will enforce a porous solidification of the molten salts. This porous phase change phenomenon is of critical importance and is beneficial during the remelting of the molten salts. In the current research, the role of forced convection, liquid and vapour phase drops and the role of mass transfer due to evaporative losses are investigated. In addition, the issues related to the freezing and melting of phase change material by forced convection are also addressed. Modelling and analysis results of heat transfer due to forced convection are presented. The results of low and medium temperature testing, their analysis, some preliminary modelling and simulation work is presented in this research paper. The role of low vapour pressure, thermal stability, surface tension, the density of the molten salt and areas of critical importance are analyzed. Analysis of experimental results is presented to determine the energy exchange the exchange effectiveness and heat transfer coefficients.

Abstract Achieving energy savings with domestic off peak air conditioning using phase change materials (PCMs) has always proved a challenge. Although the energy efficiency ratio of an air conditioner is higher during the night, this improvement often does not offset the exergy loss experienced when using thermal storage. Simulations have been conducted using the effectiveness-number of transfer units (ɛ-NTU) representation of a PCM system to determine the instantaneous heat transfer when coupled to an inverter chiller cooling system. Results show that although 85% of the energy consumption for cooling could be shifted to the off-peak period with an ice based system, the energy demand increased by 7.6%. The investigation demonstrated that by using a PCM with a melting point of 4 °C, it is possible to achieve an energy saving for cooling. A savings of around 13.5% can be achieved using a PCM with a melting point of 10 °C. Energy usage was increased with a more efficient PCM storage system. This unexpected result was due to which period the storage system was charged. A more efficient storage system charged quicker during the warmer part of the evening. Therefore energy minimisation requires optimal charging during the coldest part of the night.

Abstract Achieving energy savings with domestic off peak air conditioning using phase change materials (PCMs) has always proved a challenge. Although the energy efficiency ratio of an air conditioner is higher during the night, this improvement often does not offset the exergy loss experienced when using thermal storage. Simulations have been conducted using the effectiveness-number of transfer units (ɛ-NTU) representation of a PCM system to determine the instantaneous heat transfer when coupled to an inverter chiller cooling system. Results show that although 85% of the energy consumption for cooling could be shifted to the off-peak period with an ice based system, the energy demand increased by 7.6%. The investigation demonstrated that by using a PCM with a melting point of 4 °C, it is possible to achieve an energy saving for cooling. A savings of around 13.5% can be achieved using a PCM with a melting point of 10 °C. Energy usage was increased with a more efficient PCM storage system. This unexpected result was due to which period the storage system was charged. A more efficient storage system charged quicker during the warmer part of the evening. Therefore energy minimisation requires optimal charging during the coldest part of the night.

Abstract An innovative refrigeration system incorporating phase change material (PCM) is proposed to maintain refrigerated trucks at the desired thermal conditions. The advantage of using PCM to maintain low temperatures is that a conventional refrigeration system does not have to be located on-board the vehicle. In addition, the system consumes less energy and produces much lower local greenhouse gas (GHG) emissions. The phase change thermal storage unit (PCTSU) is charged by a refrigeration unit located off the vehicle when stationary. The PCM is discharged and provides cooling when in service. A new PCM with a lower cost than currently available PCMs was developed, suitable for maintaining the refrigerated truck at a temperature of −18 °C. The PCM has a melting temperature of −26.7 °C and a latent heat of 154.4 kJ kg−1. A prototype system was constructed and test results proved that the proposed refrigeration system is feasible for mobile transport. An analysis shows that delivery of refrigerated products can be made with a PCM system having a weight comparable to that of an on board conventional refrigeration system with less than half of the energy cost.

Abstract An innovative refrigeration system incorporating phase change material (PCM) is proposed to maintain refrigerated trucks at the desired thermal conditions. The advantage of using PCM to maintain low temperatures is that a conventional refrigeration system does not have to be located on-board the vehicle. In addition, the system consumes less energy and produces much lower local greenhouse gas (GHG) emissions. The phase change thermal storage unit (PCTSU) is charged by a refrigeration unit located off the vehicle when stationary. The PCM is discharged and provides cooling when in service. A new PCM with a lower cost than currently available PCMs was developed, suitable for maintaining the refrigerated truck at a temperature of −18 °C. The PCM has a melting temperature of −26.7 °C and a latent heat of 154.4 kJ kg−1. A prototype system was constructed and test results proved that the proposed refrigeration system is feasible for mobile transport. An analysis shows that delivery of refrigerated products can be made with a PCM system having a weight comparable to that of an on board conventional refrigeration system with less than half of the energy cost.

Mathematical representations of the encapsulated phase change material (PCM) within thermal energy storage (TES) models are investigated. Applying the Effectiveness - Number of Transfer Unit (ɛ-NTU) method, the performances of these TES are presented in terms of the effectiveness considering the impact of different variable parameters. The mathematical formulations summarized can be used for future research work with the suggestion to maximize the heat transfer within the storage. Thus the optimisation on the configuration of the encapsulation can be done through a parametric analysis.

Mathematical representations of the encapsulated phase change material (PCM) within thermal energy storage (TES) models are investigated. Applying the Effectiveness - Number of Transfer Unit (ɛ-NTU) method, the performances of these TES are presented in terms of the effectiveness considering the impact of different variable parameters. The mathematical formulations summarized can be used for future research work with the suggestion to maximize the heat transfer within the storage. Thus the optimisation on the configuration of the encapsulation can be done through a parametric analysis.

The proliferation of non-scheduled generation from renewable electrical energy sources such concentrated solar power (CSP) presents a need for enabling scheduled generation by incorporating energy storage; either via directly coupled Thermal Energy Storage (TES) or Electrical Storage Systems (ESS) distributed within the electrical network or grid. The challenges for 100% renewable energy generation are: to minimise capitalisation cost and to maximise energy dispatch capacity. The aims of this review article are twofold: to review storage technologies and to survey the most appropriate optimisation techniques to determine optimal operation and size of storage of a system to operate in the Australian National Energy Market (NEM). Storage technologies are reviewed to establish indicative characterisations of energy density, conversion efficiency, charge/discharge rates and costings. A partitioning of optimisation techniques based on methods most appropriate for various time scales is performed: from “whole of year”, seasonal, monthly, weekly and daily averaging to those best suited matching the NEM bid timing of five minute dispatch bidding, averaged on the half hour as the trading settlement spot price. Finally, a selection of the most promising research directions and methods to determine the optimal operation and sizing of storage for renewables in the grid is presented.