Thanks to their high energy density and thermal conductivity, metallic Phase Change Materials (mPCM) have shown great potential to improve the performance of thermal energy storage systems. However, the commercial application of mPCM is still limited due to their corrosion behavior with conventional container materials. This work first addresses on a fundamental level, whether carbon‐based composite‐ceramics are suitable for corrosion critical components in a thermal storage system. The compatibility between the mPCM AlSi12 and the Liquid Silicon Infiltration (LSI)‐based carbon fiber reinforced silicon carbide (C/C‐SiC) composite is then investigated via contact angle measurements, microstructure analysis, and mechanical testing after exposure. The results reveal that the C/C‐SiC composite maintains its mechanical properties and microstructure after exposure in the strongly corrosive mPCM. Based on these results, efforts were made to design and manufacture a container out of C/C‐SiC for the housing of mPCM in vehicle application. The stability of the component filled with mPCM was proven nondestructively via computer tomography (CT). Successful thermal input‐ and output as well as thermal storage ability were demonstrated using a system calorimeter under conditions similar to the application. The investigated C/C‐SiC composite has significant application potential as a structural material for thermal energy storage systems with mPCM.
Battery-powered electric buses currently face the challenges of high cost and limited range, especially in winter conditions, where interior heating is required. To face both challenges, the use of thermal energy storage based on metallic phase change materials for interior heating, also called thermal high-performance storage, is considered. By replacing the battery capacity through such an energy storage system, which is potentially lighter, smaller, and cheaper than the batteries used in buses, an overall reduction in cost and an increase of range in winter conditions could be reached. Since the use of thermal high-performance storage as a heating system in a battery-powered electric bus is a new approach, the requirements for such a system first need to be known to be able to proceed with further steps. To find these requirements, a review of the relevant state of the art of battery-powered electric buses, with a focus on heating systems, was done. Other relevant aspects were vehicle types, electric architecture, battery systems, and charging strategies. With the help of this review, requirements for thermal high-performance storage as a heating system for a battery-powered electric bus were produced. Categories for these requirements were the thermal capacity and performance, long-term stability, mass and volume, cost, electric connection, thermal connection, efficiency, maintenance, safety, adjustment, and ecology.
Latent thermal storage in metals can overcome many issues related to the temporal or spatial intermittency of heat resources, particularly in the provision of heat in electric vehicles. Alloys that are energy dense and thermally conductive are most attractive for thermal storage applications. The eutectic alloy, Al-25% Cu-6% Si (wt%) has been identified as an optimal metallic phase change material melting in the temperature range 508 C to 548 C. Through differential scanning calorimetry, light flash analysis and long-term reaction experiments, the thermal and compatibility characteristics of this alloy are experimentally determined. Graphite and alumina are observed as compatible housing materials for the alloy after 2 weeks at 550 C. Reaction depth and products at the interface with iron and stainless steel are identified with energy-dispersive Xray spectroscopy and electron backscatter diffraction analysis. A volumetric energy density of 0.7764 ± 0.0178 kWh/L was calculated for an operating range of 160 C to 660 C from the measured properties, suggesting the material is an excellent candidate for thermal storage in electric vehicles.
Metallic latent thermal energy storage systems are a promising technology for efficient storage of heat with a small foot print in volume and weight. Metallic phase change materials (mPCMs) are characterized by high energy densities and thermal conductivities [1,2], which allow for fast thermal charging and discharging. These attributes make this kind of storage system attractive for mobile applications. High heat supply rates are required for battery electric vehicles under cold ambient conditions. In opposite to fuel cell or combustion driven engines, battery electric engines reject only little waste heat available for heating purposes. However, the usage of the battery for resistive heating or operation of a heat pump goes along with a reduction in range, which can be more than 50% at cold temperatures [3]. Therefore, a metallic latent thermal energy storage is a possible approach to solve this problem [4] and is currently considered in particular of interest for applications in battery electric buses.Kraft et al. presented a first experimental demonstrator utilizing mPCM as storage material for vehicle applications, realizing the thermal output by forced convection of air [4]. Lanz et al. proposed a heat transport system for a similar storage concept, implementing the evaporation and condensation of a working fluid in a closed cycle [5]. A recent study by the authors discussed the general impact of a wide operating temperature range on heat transport system design for a mPCM thermal storage unit in mobile applications [6]. Despite the potential of metallic latent thermal energy storage systems, extensive experimental data of the thermal discharge performance of a real prototype configuration is missing.Therefore, this study describes a small-scale prototype of a novel mPCM storage concept, that was built-up and experimentally investigated for the first time. The focus of the presented work lies on the characterization of the thermal discharge performance and the heat extraction system. The design is based on the mPCM AlSi12 as storage material. Caused by the strong corrosive behaviour of this specific material, it is stored in a box-shaped graphite container. The storage container bears on a steel plate, which contains several electrical heaters for charging heat. Integrated fluid channels serve as heat transfer structure for discharging heat. The fluid channels are connected to an air fan in order to achieve a forced convection thermal discharge with ambient air as heat transfer fluid. The test bench accommodates several thermocouples and the possibility to measure the fluid pressure drop and mass flow. Experiments were conducted for full thermal discharge cycles in an operating temperature range from 650 °C down to 100 °C by variations in air fan power or rather mass flow rates.The results show that the heat output increases with a rise in storage temperature and air mass flow. Around the phase change temperature of 577 °C, an interesting physical phenomenon is observed. In liquid state of the mPCM, the hea...
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