Abstract

Phase change materials (PCMs) are applied in heat storage units, as they are able to accumulate the energy in the form of the latent heat of fusion. Thus, they can be used in recovering the excess of heat from various industrial processes. Their main weakness is their low thermal conductivity coefficient, which strongly limits their usage. In this paper, the benefits of the application of metallic inserts in heat storage PCM-based units were elaborated. Two kinds of Al–Si spatial elements (foams and honeycomb structures) were produced with the use of means of the investment casting method. Key factors influencing the technological process were established. The surface’s roughness was measured in order to compare the obtained structures with their patterns in terms of the casting’s accuracy. The compressive strength of the samples was tested, and their fatigue resistance was considered. The thermal performance of manufactured inserts in the PCM (paraffin)-based accumulator, supported by the calculation of heat fluxes, was analyzed and adjusted. Finally, further optimization was conducted in terms of the volume ratio of the metal insert to the PCM. Metallic inserts were found to significantly affect the performance of the entire energy storage system, as their use results in reduced charging time, a longer heat release time, increased maximum temperature, and a significant reduction in the temperature gradient in the heat storage unit.

Highlights

  • Phase change materials (PCMs) are widely used in heat storage applications as they are able to accumulate a great amount of energy in the form of the latent heat of fusion gained during their phase transition

  • It can be concluded that PCM materials are good thermal capacitors, but poor thermal conductors

  • Both of the foam shape and honeycomb structures, were manufactured by the means of the investment casting method, which consists of the production of the model, molding, heat treatment of the mold, and the liquid metal alloy pouring under low pressure

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Summary

Introduction

Phase change materials (PCMs) are widely used in heat storage applications as they are able to accumulate a great amount of energy in the form of the latent heat of fusion gained during their phase transition This unique feature allows them to e.g., recover waste heat sources or absorb the excess of energy from various industrial processes. Among different ways to improve the heat transfer within PCM, the following so-called thermal conductivity enhancers can be distinguished: the addition of graphite fiber preforms, porous matrices, nanofillers (graphite, Cu, graphene), silica or alumina catalysts [1,2,3], PCM micro- or macro-encapsulation with organic or metal shells [4,5] or immersing highly thermally conductive complex metal structures within the PCM [6,7,8,9,10]. Tao et al, investigating the performance of metal foams/paraffin composite PCM, found out that reducing the Materials 2020, 13, 415; doi:10.3390/ma13020415 www.mdpi.com/journal/materials

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