A foamed cement blocks with paraffin/expanded graphite composite phase change solar thermal absorption material

Abstract

When solar radiation reaches its peak value during the midday, buildings' external walls absorb the highest amount of heats and result in dramatic spikes in cooling load and energy consumption. To flatten the energy peak, promote energy efficiency, and preserve thermal comfort, this study developed a novel foamed thermal insulation cement block with extraordinary heat storage capacity. To prepare the proposed foamed cement block, a paraffin/expanded graphite composite phase change heat storage material with a phase transition temperature of 41.9 °C and an enthalpy value of 207.8 J/g was used to load paraffin into expanded graphite in a water bath at 44 °C. After mixing the paraffin/expanded graphite composite phase change material (PCM) with cement, foams were added, stirred and poured into the mold to make a novel foaming cement thermal insulation block. Due to its porous structure, the foamed cement has lightweight as well as high heat preservation capacity. To investigate the characteristics of the proposed material, this investigated its physical structure, thermal conductivity, and heat energy storage performance when the material mass fractions of PCM are 10%, 15%, 20%, 25% and 30%, and regular (pure) cement blocks. The experimental results show that there is no chemical reaction during material preparation. In addition, composite materials’ PCM mass fraction and their thermal storage capacity increase simultaneously. The comprehensive analysis shows that foamed cement blocks with 30% PCM contents have the best thermal energy storage performance and can maintain the lowest average indoor temperature. Therefore, the proposed foamed cement blocks can be applied to building outer surfaces and sandwiched middle enclosures to develop energy efficiency insulation walls.