• Energy Research

Abstract An environmentally friendly phase change material (PCM) was successfully prepared by encapsulating natural soy wax into polyurethane (PU) nanofibers using coaxial electrospinning technique. The morphology and the structure of the wax/PU composites were characterized. Thermal behaviors as well as mechanical properties of the composites were also investigated. The results indicated that coaxial electrospinning produced uniform fiber morphology with a core–shell structure and a homogeneous wax distribution throughout the core of the fibers. The soy wax was successfully encapsulated into PU fibers without being miscible with PU fibers. Thermal analysis results show that the enthalpy increases as the wax content increases. The fibrous structures exhibited balanced thermal storage and released properties for thermo-regulating function. The thermal properties were unaltered after 100 heating–cooling cycles, demonstrating that the composite fibers had good thermal stability and reliability. Tensile tests also indicate that the presence of wax enhanced the modulus and lowered the tensile strain.

Abstract An environmentally friendly phase change material (PCM) was successfully prepared by encapsulating natural soy wax into polyurethane (PU) nanofibers using coaxial electrospinning technique. The morphology and the structure of the wax/PU composites were characterized. Thermal behaviors as well as mechanical properties of the composites were also investigated. The results indicated that coaxial electrospinning produced uniform fiber morphology with a core–shell structure and a homogeneous wax distribution throughout the core of the fibers. The soy wax was successfully encapsulated into PU fibers without being miscible with PU fibers. Thermal analysis results show that the enthalpy increases as the wax content increases. The fibrous structures exhibited balanced thermal storage and released properties for thermo-regulating function. The thermal properties were unaltered after 100 heating–cooling cycles, demonstrating that the composite fibers had good thermal stability and reliability. Tensile tests also indicate that the presence of wax enhanced the modulus and lowered the tensile strain.

Abstract The research of electric thermal storage (ETS) has attracted a lot of attention recently, which converts off-peak electrical energy into thermal energy and release it later at peak hours. In this study, new electric thermal storage composites are developed by employing paraffin wax as thermal storage media and carbon nanofiber (CNF) as conductive fillers. Electric heating and thermal energy release performances of the CNF/paraffin wax composites are experimentally investigated. Experimental results show that, when the composites are heated to about 70 °C, the developed electrically conductive CNF/paraffin wax composites present a thermal storage capacity of about 280 kJ/kg, which is five times of that of traditional thermal storage medium such as ceramic bricks (54 kJ/kg). The CNF/paraffin wax composites can also effectively store the thermal energy and release the thermal energy in later hours.

Abstract The research of electric thermal storage (ETS) has attracted a lot of attention recently, which converts off-peak electrical energy into thermal energy and release it later at peak hours. In this study, new electric thermal storage composites are developed by employing paraffin wax as thermal storage media and carbon nanofiber (CNF) as conductive fillers. Electric heating and thermal energy release performances of the CNF/paraffin wax composites are experimentally investigated. Experimental results show that, when the composites are heated to about 70 °C, the developed electrically conductive CNF/paraffin wax composites present a thermal storage capacity of about 280 kJ/kg, which is five times of that of traditional thermal storage medium such as ceramic bricks (54 kJ/kg). The CNF/paraffin wax composites can also effectively store the thermal energy and release the thermal energy in later hours.

Phase change materials (PCM) have been incorporated with cementitious construction materials to store thermal energy and control interior climate in buildings, which can reduce the energy consumption and improve thermal comfort. However, addition of PCM is found to decrease strength and thermal conductivity of the cement-based composite. Carbon nanotubes (CNT) are integrated into cementitious construction materials with microencapsulated PCM to improve their thermal-conductive and mechanical performances. Results of lab and outdoor tests show the modified cement mortar containing both PCM and CNT exhibits better heat insulation properties than plain cement mortar. A temperature difference up to 6.8 °C was observed between interiors of two same size scale-down building models (one made of plain cement mortar, the other one made of cement mortar with PCM and CNT). This indicates that the modified cement mortar can effectively enhance the thermal storage property of cement-based building materials.

Phase change materials (PCM) have been incorporated with cementitious construction materials to store thermal energy and control interior climate in buildings, which can reduce the energy consumption and improve thermal comfort. However, addition of PCM is found to decrease strength and thermal conductivity of the cement-based composite. Carbon nanotubes (CNT) are integrated into cementitious construction materials with microencapsulated PCM to improve their thermal-conductive and mechanical performances. Results of lab and outdoor tests show the modified cement mortar containing both PCM and CNT exhibits better heat insulation properties than plain cement mortar. A temperature difference up to 6.8 °C was observed between interiors of two same size scale-down building models (one made of plain cement mortar, the other one made of cement mortar with PCM and CNT). This indicates that the modified cement mortar can effectively enhance the thermal storage property of cement-based building materials.

In this study, thermal properties of carbon nanofiber (CNF) and carbon nanotube (CNT) filled phase change materials (soy wax and paraffin wax) were studied experimentally, aiming to improve their thermal conductivities. The composite phase change materials (PCMs) were prepared by the stirring of CNF or CNT in liquid wax at 60 °C, with CNF and CNT doping levels of 1, 2, 5, and 10 wt%. The experimental results show that the thermal conductivity of composite PCMs increases as CNF or CNT loading contents. Both CNF and CNT can improve the thermal conductivity of the composite, while CNF is shown to be more effective than CNT as the thermal conductive filler because of its better dispersion in the matrix.

In this study, thermal properties of carbon nanofiber (CNF) and carbon nanotube (CNT) filled phase change materials (soy wax and paraffin wax) were studied experimentally, aiming to improve their thermal conductivities. The composite phase change materials (PCMs) were prepared by the stirring of CNF or CNT in liquid wax at 60 °C, with CNF and CNT doping levels of 1, 2, 5, and 10 wt%. The experimental results show that the thermal conductivity of composite PCMs increases as CNF or CNT loading contents. Both CNF and CNT can improve the thermal conductivity of the composite, while CNF is shown to be more effective than CNT as the thermal conductive filler because of its better dispersion in the matrix.