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Renewables should become more continuously available, reliable and cost-efficient to manage the challenges caused by the energy transition. Thus, analytic and numerical investigations for the layout of a pilot plant of a concept called Fluidisation-Based Particle Thermal Energy Storage (FP-TES)—a highly flexible, short- to long-term fluidised bed regenerative heat storage utilising a pressure gradient for hot powder transport, and thus enabling minimal losses, high energy densities, compact construction and countercurrent heat exchange—are presented in this article. Such devices in decentralised set-up—being included in energy- and especially heat-intensive industries, storing latent or sensible heat or power-to-heat to minimise losses and compensate fluctuations—can help to achieve the above-stated goals. Part I of this article is focused on geometrical and fluidic design via numerical investigations utilising Computational Particle Fluid Dynamics (CPFD). In the process a controlled transient simulation method called co-simulation of FP-TES is developed forming the basis for test bench design and execution of further co-simulation. Within this process an advanced design of rotational symmetric hoppers with additional baffles in the heat exchanger (HEX) and internal pipes to stabilise the particle mass flow is developed. Moreover, a contribution bulk heat conductivity is presented to demonstrate low thermal losses and limited needs for thermal insulation by taking into account the thermal insulation of the outer layer of the hopper. [ABSTRACT FROM AUTHOR]

This work examines a high temperature latent heat storage system, which could find use in future concentrated solar power and other combined heat and power plants. In contrast to lab-based fully charged or totally discharged states, partial load states will be the principal operation states in real-world applications. Hence, a closer look on the partial load states and the effective power rates are worthwhile for a successful implementation of this storage type. A vertical finned shell and tube heat exchanger pipe with a combination of transversal and longitudinal fins is applied. Sodium nitrate with a melting temperature of 306 ° C is used as phase change material and thermal oil serves as heat transfer fluid. Temperatures in the storage and the heat transfer fluid as well as the mass flow are measured for data analysis. The state of charge formulation is based on an enthalpy distribution function, where the latent heat of fusion is spread over a specific temperature range. The data show consistently high power rates for all partial load cycles at any state of charge. The mean power rate for charging is 6.78 kW with an 95.45 % confidence interval of ± 1.14 kW for all cycles. The discharging power rate is −5.72 kW with a 95.45 % confidence interval of ± 1.36 kW for all cycles. The lowest power rate is measured for the full cycle at the end of charging/discharging. It is caused by a narrow volume, which is not penetrated by fins, near the perimeter of the cylindrical heat exchanger. The state of charge formulation correlates with the storage capacity and enables state of charge based cycling. With the energy balance of the storage, the data validity is proven and further storage parameters are determined. The energy density is as high as 110 kW h m−3 and a power rate of 2.28 kW m−1 for the finned tube is confirmed. These values are highly promising for further development and application of latent heat storage systems. • Novel analysis of the partial cycle behavior of a high temperature latent heat storage. • The state of charge of a latent heat storage is defined. • Steady and high power rates for all partial and full cycles with the applied fin geometry. • Energy balance of a latent heat storage. [ABSTRACT FROM AUTHOR]

Versatile and economically competitive thermal energy storages are necessary to fulfill the widely differing requirements for storages applied in renewable energy systems, process heat, district heating, power generation and domestic heating. We present the concept of a hybrid sensible-latent heat storage based on an adapted commercial shell-and-tube heat exchanger. The phase change material (PCM) is encapsulated within the tubes and thermal oil serves as sensible heat storage as well as the heat transfer medium. We designed and built a prototype using high density polyethylene (HDPE) as PCM and characterized the storage on a dedicated test rig at AIT. Energy capacities and power profiles are presented for different mass flows and (dis)charging temperatures. Two physical models were developed and implemented using the Modelica language. Dymola was used to simulate the behavior of the prototype storage. Very good agreement was achieved between simulation and experiment. Using the models, we studied the heat transfer within the storage in detail, which enabled us to present how to adapt the storage geometry and PCM properties to cover a broad range of applications. We discuss storage costs and calculate material costs per stored kilowatt-hour for different PCM-thermal oil volume ratios as a function of the tube outer diameter. Finally, we highlight the main advantages and design freedoms of our concept and describe concrete application scenarios in district heating and process heat. [ABSTRACT FROM AUTHOR]