Ludger Josef Fischer

Glauber’s salt is a promising phase change material for thermal energy storage due to its high latent heat capacity of 234 J/g and melting point of 34 °C, making it well-suited for low-temperature heating applications. However, its practical use has been limited by phase separation and associated loss of performance during repeated thermal cycling. This study aimed to address this limitation through a novel stabilisation approach. The material was encapsulated within an emulsion matrix designed to physically constrain the salt and inhibit separation during melting and to form a phase change dispersion. The phase change dispersion was subjected to 100 controlled heating–cooling cycles whilst monitoring the latent heat capacity and phase transition plateaus. The phase change dispersion retained its thermal properties throughout testing, showing no measurable degradation in storage capacity nor shift in phase transition temperature. These results demonstrate that this encapsulation mechanism can effectively maintain the functional performance of Glauber’s salt under repeated thermal cycling. This approach may form the basis for more durable salt hydrate-based storage media and has potential relevance for applications in building heating, waste heat recovery and renewable energy integration. By improving stability, this method helps unlock the long-term operational viability of phase change materials.

Latent heat thermal energy storage (LHTES) based on phase change materials (PCMs) is receiving increasing interest since it offers high energy storage density while enabling the integration of variable renewable energies, hence boosting the transition towards a climate-neutral future. Despite the advantages that PCMs offer in providing a nearly isothermal solid–liquid phase transition, they still face some challenges that limit their deployment in real applications such as low thermal conductivity, phase separation, and supercooling, which affect charging and discharging rates. X-ray computed tomography (XCT) is a non-destructive imaging technique widely used in materials science for both qualitative and quantitative analysis of material microstructures and their evolution. Recent advances in laboratory-XCT instrumentation enabled short acquisition times on the order of tens of seconds which allows the investigation of dynamic processes in situ by time-lapse XCT measurements. These advances open new opportunities for revealing information on the morphology of solid–liquid PCMs. Despite the fact that XCT imaging has significant potential for energy research, its application in the field of PCMs is fairly new. A key enabler of applications of XCT to PCMs is the density difference between solid and liquid PCMs, which was found to be higher than 7% for all investigated PCMs. This enabled solid and liquid phases to be distinguished one from the other and properly quantified over time. The present work reviews the principles of laboratory-based XCT and the recent applications of XCT technology in the characterisation of PCMs, with emphasis on the study of the solid–liquid phase transition and validation of numerical PCM models by addressing the potentialities and challenges of XCT in PCM research.

Latent Heat Thermal Energy Storage (LHTES) based on phase change materials (PCM) is receiving increasing interest, since it offers high energy storage density while enabling the integration of variable renewable energies, hence boosting the transition towards a climate-neutral future. Despite the advantages that PCMs offer in providing a nearly isothermal solid–liquid phase transition, they still face some challenges that limit their deployment in real applications such as, low thermal conductivity, phase separation and supercooling, which affect charging and discharging rates. X-ray computed tomography (XCT) is a non-destructive imaging technique widely used in materials science for both qualitative and quantitative analysis of material microstructures and their evolution. Recent advances in laboratory-XCT instrumentation enabled short acquisition times on the order of tens of seconds which enable the investigation of dynamic processes in-situ by time-lapse XCT measurements. These advances open new opportunities for revealing information on the solid-liquid PCMs. Despite XCT imaging has significant potential for energy research, its application in the field of PCMs is fairly new. The present work reviews the principles of laboratory-based XCT and the recent applications of XCT technology in the characterisation of PCMs, with emphasis on the study of the solid-liquid phase transition and validation of numerical PCM models.

Thermal energy storage can be revolutionised by a groundbreaking stabilisation technique for Glauber’s salt, a material with great potential, yet plagued by instability. Known for its impressive latent heat capacity (234 J/g) and melting point of 34°C, Glauber’s salt is ideal for modern heating systems. However, its practical application has been stifled by severe phase separation during thermal cycling. Our innovative approach encapsulates the salt in a solid emulsion matrix, curbing decomposition and maintaining thermal properties across multiple thermal cycles (100). This breakthrough not only heralds a new era for Glauber’s salt in sustainable energy solutions but also sets precedence, extending these techniques to other salt hydrates. With this novel method, we unlock the full potential of salt hydrates, paving the way for more efficient and robust thermal energy storage systems.

Energy input in emulsion manufacturing comprises thermal and mechanical energy, with thermal energy being predominant. In terms of raw material selection, there is a widely accepted belief that natural formulations are more “eco-friendly” than their standard (not natural) counterparts. The aim of this study was to compare the energy consumption and subsequent carbon footprint resulting from the production of two main emulsion types, each represented by its standard and natural variant and made by using different manufacturing processes (hot, hot-cold and cold). This resulted in six samples of oil-in-water (O/W) and water-in-oil (W/O) emulsion types, respectively. Scale-down calculations were used to establish the required homogenisation time and speed of the laboratory homogeniser, necessary to achieve the same shear rates as the chosen industrial vessel. The resulting emulsions were characterised using rheological and textural analysis. The six emulsions within each emulsion type have exhibited sufficiently similar characteristics for the purpose of carbon footprint comparisons. Calculations were conducted to quantify the energy input of hot and hot-cold procedures, followed by cradle-to-gate life cycle analysis (LCA). Energy calculations demonstrated that the hot-cold manufacturing process saved approximately 82% (for O/W) and 86% (for W/O) of thermal energy in comparison to the hot process. LCA has shown that the effects of using natural instead of standard ingredients were negative, i.e., it led to a higher carbon footprint. However, it was dwarfed by the effect of the energy used, specifically thermal energy during manufacturing. This strongly indicates that the most efficient way for companies to reduce their carbon footprint is to use the hot-cold emulsification process.

Nuclear fusion is the gateway to a whole new paradigm of energy and is a strong candidate for the decarbonization of electricity generation on a global scale. With recent developments in high-temperature super-conducting magnets, the race is on to develop sub-systems which will support a commercially viable fusion reactor for use as a thermal power plant. The fusion of lighter elements creates an enormous amount of heat which must be transferred away from the reactor core. These intense conditions require novel approaches to efficiently transfer very high heat loads into useable thermal energy without compromising the structural integrity of the reactor core and the surrounding components. This report outlines the concept of a fundamental approach to solve the heat transfer problem as proposed by Commonwealth Fusion System’s design for a fusion reactor. A literature review was conducted for other applications that could serve as inspirations, as well as material properties and machining methods for the proposed power exhaust system. A dive into the theoretical thermodynamic and fluid dynamic characteristics of plate heat exchangers and finned surfaces was conducted from a fundamental perspective. A laminar flow regime was studied for the purpose of setting the floor for energy needed to pump coolant while simultaneously representing the least favorable heat transfer regime between a solid surface and a fluid. The results served as a basis for dimensioning and executing numerical simulations as a means for a first look into a solution of this heat transfer problem. The results were compared with the theoretical conclusions and judged based on constraints of the system. Recommendations were made for the continued development of a corresponding system.

Geothermal energy storage provides opportunities to store renewable energy underground during summer for utilization in winter. Vertically oriented systems have been the standard when employing boreholes as the means to charge and discharge the underground. Horizontally oriented borehole storage systems provide an application range with specific advantages over vertically oriented systems. They are not limited to the surface requirements needed for installation with vertical systems and have the potential to limit storage losses. Horizontal systems can be incorporated into the built environment and utilize underground storage sites below existing infrastructure. An experimental study examines configurations using a mix of renewable energy (photovoltaic panels) and grid energy to charge a storage system during summer for use during winter. A comparison of five different borehole configurations at three different loading temperatures was composed using an experimentally validated numerical model. The horizontal systems studied and analyzed in this work showed improved performance with scale and charging temperature. This paper supports further exploration into specific use cases for horizontal borehole thermal energy storage systems and suggests applications which would take advantage of better performance at scale.

This study investigates a measurement method of thermal diffusivity for samples with arbitrary geometries and unknown material properties. The aim is to curve fit the thermal diffusivity with the use of a numerical simulation and transient temperature measurement inside the object of interest. This approach is designed to assess bulk material properties of an object that has a composite material structure such as underground soil. The method creates the boundary conditions necessary to apply analytical theory found in the literature. It was found that measurements best correlated with theory and simulation at positions between the center and surface of an object.

Phase change dispersions are useful for isothermal cooling applications. As a result of the phase changes that occur in PCDs, they are expected to have greater storage capacities than those of single-phase heat transfer fluids. However, for appropriate heat exchanger dimensions and geometries for use in phase change dispersions, knowledge about the convective heat transfer coefficients of phase change dispersions is necessary. A test unit for measuring the local heat transfer coefficients and Nusselt numbers of PCDs was created. The boundary condition of constant heat flux was chosen for testing, and the experimental heat transfer coefficients and Nusselt numbers for the investigated phase change dispersion were established. Different experimental parameters, such as the electrical wall heat input, Reynolds number, and mass flow rate, were varied during testing, and the results were compared to those of water tests. It was found that, due to the tendency of low-temperature increases in phase change dispersions, the driving temperature difference is greater than that of water. In addition, larger heat storage capacities were obtained for phase change dispersions than for water. Through this experimentation, it was acknowledged that future investigation into the optimised operating conditions must be performed.