Ecological, health and environmental concerns are driving the need for bio-resourced foams for the building industry. In this paper, we examine foams made from polylactic acid (PLA) and micro cellulose fibrils (MCF). To ensure no volatile organic compounds in the foam, supercritical CO2 (sc-CO2) physical foaming of melt mixed systems was conducted. Mechanical and thermal conductivity properties were determined and applied to a net zero energy model house. The results showed that MCF had a concentration dependent impact on the foams. First structurally, the presence of MCF led to an initial increase followed by a decrease of open porosity, higher bulk density, lower expansion ratios and cell size. Differential Scanning Calorimetry and Scanning Electron Microscopy revealed that MCF decreased the glass transition of PLA allowing for a decrease in cell wall thickness when MCF was added. The mechanical performance initially increased with MCF and then decreased. This trend was mimicked by thermal insulation which initially improved. Biodegradation tests showed that the presence of cellulose in PLA improved the compostability of the foams. A maximum comparative mineralization of 95% was obtained for the PLA foam with 3 wt.% MCF when expressed as a fractional percentage of the pure cellulose reference. Energy simulations run on a model house showed that relative to an insulation of polyurethane, the bio-resourced foams led to no more than a 12% increase in heating and cooling. The energy efficiency of the foams was best at low MCF fractions.
A latent heat thermal energy storage (LHTES) system that operates at high temperature was analyzed for applications to supercritical CO 2 (s-CO 2 ) power cycles for a concentrated solar power (CSP) plant. Because the operation temperature of the s-CO 2 power cycles is high (650-700°C), sodium chloride (NaCl), with a melting point of 800°C, was selected as the phase-change material (PCM) for energy storage. Due to the low thermal conductivity of salt materials (usually <1 W/m K), use of graphite foam was chosen to improve the overall thermal conductivity of the graphite foam-PCM combination. Three-dimensional (3-D) heat transfer simulations were conducted for the envisioned full-scale LHTES system. The anisotropic thermal conductivities of graphite foam were considered in the simulations. The thermal performance and the exergy efficiency were investigated for the full-scale LHTES system to study the improvements due to the graphite foam. The results show that this material improves the heat transfer performance in the LHTES system and, therefore, significantly reduces the total number of the heat transfer fluid (HTF) pipes needed in the storage system by a factor of 12 compared to a PCM-only system. Furthermore, the graphite foam helps to increase the exergy efficiency of the LHTES system considerably. The system parameter (i.e. HTF inlet temperature, flow velocity) effects on the thermal performance and exergy efficiency of the graphite foam-PCM LHTES system were analyzed in the paper. Moreover, the graphite foam-NaCl system matches the temperature requirements of the s-CO 2 power cycles for the CSP plant.
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