Abstract
This paper examines the influence of four different porous hosts (lightweight aggregates (LWA)) having different pore structure features, as hosts for phase change materials (PCM). The porosity and absorption capacity of the LWAs significantly influence the composite thermal conductivity. The incorporation of 5% of PCMs by total volume of the cementitious system reduces the composite thermal conductivity by ⩾10%. The fact that the inclusions (LWAs) in these composites are by themselves heterogeneous, and contain multiple components (solid phase, PCM, water, and air) necessitate careful application of predictive models. Multi-step Mori-Tanaka mean-field homogenization methods, either based on known microstructural arrangement in the composite, or property contrast between the constituents, are applied to predict the composite thermal conductivity. A microstructural contrast factor is used to account for both the thermal conductivities and the volume fractions of the phases with the highest property contrast. Smaller contrast factors result in improved agreement of the models with the experiments, thereby aiding in the selection of suitable predictive schemes for effective properties of such multi-phase composites.
Highlights
Phase change materials (PCMs) are combined sensible-and-latent thermal energy storage (TES)materials that can be used to store and release energy in the form of heat [1,2,3,4]
While several approaches have been considered to incorporate PCMs in cement-based materials, the most common variants include the addition of microencapsulated PCMs directly to the concrete [9,10,11], or impregnation of liquid PCMs into porous inclusions that can subsequently be added as aggregates in concrete [12,13,14,15,16,17]
The lightweight aggregates (LWA) mortars containing 5% of PCM showed thermal conductivities that are lower by 10% or more as compared to those of the plain LWA mortars, which can be attributed to the lower thermal conductivity of PCM as compared to that of water
Summary
Phase change materials (PCMs) are combined sensible-and-latent thermal energy storage (TES). While several approaches have been considered to incorporate PCMs in cement-based materials, the most common variants include the addition of microencapsulated PCMs directly to the concrete [9,10,11], or impregnation of liquid PCMs into porous inclusions that can subsequently be added as aggregates in concrete [12,13,14,15,16,17] In the latter case, PCM in liquid state is impregnated into the pores of lightweight aggregates (LWA). This paper characterizes four different types of LWAs with respect to their capacity to impregnate an organic paraffin-based PCM in their material structure, and influence the composite thermal properties. These porous inclusions are subsequently incorporated into cement mortars and their thermal conductivities measured using a guarded hot-plate method. The impact of phase property contrast in prediction is brought out
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