Microstructure-guided computational model for predicting effective thermal conductivity of cementitious composites filled with phase change particles

Abstract

Functional composite phase change materials (CPCMs) are particularly emphasized by integrating PCM particles in building materials for energy-saving applications, due to PCM's excellent temperature adjustment capacity. However, the inherent drawback of low thermal conductivity of PCM decreases its phase-changing efficiency. Finding highly-efficient heat transfer technique becomes quite necessary. This work utilizes small hollow steel balls (HSBs) to encapsulate paraffin to provide a simple and practical solution, not only ensuring sufficient protection to PCM core in alkaline environment but also enhancing heat transfer into PCM. Then the PCM-HSBs aggregates mix with cementitious matrix to fabricate CPCM. The composite thermal conductivity (CTC) is respectively determined by experiment, theory and computational microstructure model precisely representing random morphology of PCM-HSBs in matrix, and a good agreement is observed between them. Then the dependence of CTC on microstructure features is illustrated to identify their roles. Finally, the composite compressive strength (CCS) and failure mode is discussed briefly to establish comprehensive understanding of composite properties. The results show that CTC has a significant increase of 25.84%, while CCS decreases 12.7%, when 15.28% PCM-HSBs are used. The degradation of CCS is mainly attributed to the smooth surface of HSB, which can be roughened by abrasive blasting.

Keywords

• Composite latent heat storage system
• Thermal conductivity
• Cementitious material
• Phase change material
• Hollow steel balls