Experimental Investigation of Thermal Discharge Performance of a Metallic Latent Thermal Energy Storage System

Abstract

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...

Conjugate heat transfer analysis of the transient thermal discharge of a metallic latent heat storage system

“…Figure 1 shows the schematic representation of the prototype design and experimental setup. More details about the prototype and the experimental investigation are reported elsewhere [9]. The storage is based on the aluminum silicon alloy AlSi12 and a box-shaped graphite container design.…”

“…However, there is a need for a better understanding of the physics and thermal behavior involved, in particular for the heat extraction process. First extensive experimental measurements of the thermal discharge characteristics of a lab-scale prototype configuration using mPCM as storage material was performed by Nees et al, thus showing the functionality and performance [8,9]. For a deeper analysis IOP Publishing doi:10.1088/1742-6596/2766/1/012212 2 of the transient discharge, this paper presents a three-dimensional computational fluid dynamics (CFD) model of the previous experimentally investigated prototype for the first time.…”