• Energy Research

Abstract With the stupendous latent of microscale and nanoscale technologies in energy conversion and utilization, the design and analysis of porous dielectric materials with open cells have required a more accurate calculation of the radiative thermal conductivity. This work introduces a mathematical model to accurately calculate the radiative thermal conductivity of micro/nanoscale porous open cell structures. Due to the limitations of the existing radiative thermal conductivity models, a full-scale method based on the Rosseland diffusion equation is proposed. Combining this full-scale Rosseland diffusion equation and fractal thermal conduction methods, the predicted total thermal conductivity values were well matched with the experimental results for various microscale and nanoscale porous open cell dielectric materials, with less than 15% error. Besides, seven influential factors on the thermal conductivity including cell size, porosity, cellular pore shape, volume specific surface area, temperature, refractive index, and extinction index were extensively investigated. The results show that the thermal conductivity of porous open cell materials mainly decreased with an increase in extinction index and/or the porous structure's volume specific surface area but increased with increase in temperature. This certainly indicated the potential of the full-scale Rosseland diffusion method for use in the design of specific micro/nanoscale porous dielectric structures like polymer foam in the personal energy management device or the silica aerogel in radiative cooling system.

Abstract With the stupendous latent of microscale and nanoscale technologies in energy conversion and utilization, the design and analysis of porous dielectric materials with open cells have required a more accurate calculation of the radiative thermal conductivity. This work introduces a mathematical model to accurately calculate the radiative thermal conductivity of micro/nanoscale porous open cell structures. Due to the limitations of the existing radiative thermal conductivity models, a full-scale method based on the Rosseland diffusion equation is proposed. Combining this full-scale Rosseland diffusion equation and fractal thermal conduction methods, the predicted total thermal conductivity values were well matched with the experimental results for various microscale and nanoscale porous open cell dielectric materials, with less than 15% error. Besides, seven influential factors on the thermal conductivity including cell size, porosity, cellular pore shape, volume specific surface area, temperature, refractive index, and extinction index were extensively investigated. The results show that the thermal conductivity of porous open cell materials mainly decreased with an increase in extinction index and/or the porous structure's volume specific surface area but increased with increase in temperature. This certainly indicated the potential of the full-scale Rosseland diffusion method for use in the design of specific micro/nanoscale porous dielectric structures like polymer foam in the personal energy management device or the silica aerogel in radiative cooling system.

AbstractMolecular weight reduction of natural rubber (NR) with hydrogen peroxide (H2O2) oxidizing agent is limited in biphasic water-toluene systems that is attributed to mass transfer. In this work, CO2was applied to the (aqueous H2O2)-(toluene-NR) systems with the objective of improving reaction efficiency. Experiments were performed on the reaction system with CO2at 12 MPa and at reaction temperatures and times of 60°C–80°C and 1 h–10 h to evaluate the reaction kinetics. CO2could enhance the NR molecular weight reduction by lowering the activation energy (from 121 kJ·mol−1to 38 kJ·mol−1). The role of CO2in the reaction system seems to be the formation of oxidative peroxycarbonic acid intermediate and promotion of mass transport due to the reduction in the toluene-NR viscosity and interfacial tension. The epoxidized liquid NRs (M̅n=4.9×103g·mol−1) obtained from NR molecular weight reduction was further processed to prepare hydroxyl telechelic NR (M̅n=1.0×103g·mol−1) and biobased polyurethane.

AbstractMolecular weight reduction of natural rubber (NR) with hydrogen peroxide (H2O2) oxidizing agent is limited in biphasic water-toluene systems that is attributed to mass transfer. In this work, CO2was applied to the (aqueous H2O2)-(toluene-NR) systems with the objective of improving reaction efficiency. Experiments were performed on the reaction system with CO2at 12 MPa and at reaction temperatures and times of 60°C–80°C and 1 h–10 h to evaluate the reaction kinetics. CO2could enhance the NR molecular weight reduction by lowering the activation energy (from 121 kJ·mol−1to 38 kJ·mol−1). The role of CO2in the reaction system seems to be the formation of oxidative peroxycarbonic acid intermediate and promotion of mass transport due to the reduction in the toluene-NR viscosity and interfacial tension. The epoxidized liquid NRs (M̅n=4.9×103g·mol−1) obtained from NR molecular weight reduction was further processed to prepare hydroxyl telechelic NR (M̅n=1.0×103g·mol−1) and biobased polyurethane.