Surface temperature changes of building materials affect the calculation of heat flow and thus the energy use in heating and cooling. The surface heat transfer coefficient , limiting the heat flow between material sur...Surface temperature changes of building materials affect the calculation of heat flow and thus the energy use in heating and cooling. The surface heat transfer coefficient , limiting the heat flow between material surface and ambient air is normally taken as a constant. In this study we propose a time-dependent function . We estimate from unidirectional heat flow experiments with transient and steady-state conditions. Using temperature measurements and the conservation of energy at the surface including convective and irradiative boundary conditions, the value of was obtained both using Finite Difference and Taylor Polynomials methods. Numerical solutions of temperature distribution as function of time were improved with the obtained -functions compared to with constant . There were no clear difference between on different materials, and the final values observed were in the order of magnitude expected from the literature.展开更多
We have developed and studied a novel high-strength glass-ionomer cement system composed of poly(acrylic acid) with different molecular architectures. These poly(acrylic acid) polymers were synthesized via ATRP techni...We have developed and studied a novel high-strength glass-ionomer cement system composed of poly(acrylic acid) with different molecular architectures. These poly(acrylic acid) polymers were synthesized via ATRP technique. The effects of arm number and branching on reaction kinetics, viscosity, and mechanical strengths of the formed polymers and cements were evaluated. The results showed that unlike the star-shaped polymer synthesis both hyperbranched and star-hyperbranched polymers syntheses proceed slowly at the early stage but accelerate at the later stage. The higher the arm number and initiator concentration are, the faster the ATRP reaction was. It was also found that the higher the arm number and branching that the polymer had, the lower the viscosity of the polymer aqueous solution is and the lower the mechanical strengths of the formed cement are. The mechanical strengths of three synthesized polymers-composed experimental cements were very similar to each other but much higher than those of Fuji II LC. The experimental cements were 31% - 53% in CS, 37% - 55% in compressive modulus, 80% - 126% in DTS, 76% - 94% in FS, 4% - 21% in FT and 53% - 96% in KHN higher than Fuji II LC. For wear test, the experimental cements were only 5.4% - 13% of abrasive and 6.4% - 12% of attritional wear depths of Fuji II LC in each wear cycle. The one-month aging study also showed that all the experimental cements increased their CS continuously during 30 days, unlike Fuji II LC.展开更多
文摘Surface temperature changes of building materials affect the calculation of heat flow and thus the energy use in heating and cooling. The surface heat transfer coefficient , limiting the heat flow between material surface and ambient air is normally taken as a constant. In this study we propose a time-dependent function . We estimate from unidirectional heat flow experiments with transient and steady-state conditions. Using temperature measurements and the conservation of energy at the surface including convective and irradiative boundary conditions, the value of was obtained both using Finite Difference and Taylor Polynomials methods. Numerical solutions of temperature distribution as function of time were improved with the obtained -functions compared to with constant . There were no clear difference between on different materials, and the final values observed were in the order of magnitude expected from the literature.
文摘We have developed and studied a novel high-strength glass-ionomer cement system composed of poly(acrylic acid) with different molecular architectures. These poly(acrylic acid) polymers were synthesized via ATRP technique. The effects of arm number and branching on reaction kinetics, viscosity, and mechanical strengths of the formed polymers and cements were evaluated. The results showed that unlike the star-shaped polymer synthesis both hyperbranched and star-hyperbranched polymers syntheses proceed slowly at the early stage but accelerate at the later stage. The higher the arm number and initiator concentration are, the faster the ATRP reaction was. It was also found that the higher the arm number and branching that the polymer had, the lower the viscosity of the polymer aqueous solution is and the lower the mechanical strengths of the formed cement are. The mechanical strengths of three synthesized polymers-composed experimental cements were very similar to each other but much higher than those of Fuji II LC. The experimental cements were 31% - 53% in CS, 37% - 55% in compressive modulus, 80% - 126% in DTS, 76% - 94% in FS, 4% - 21% in FT and 53% - 96% in KHN higher than Fuji II LC. For wear test, the experimental cements were only 5.4% - 13% of abrasive and 6.4% - 12% of attritional wear depths of Fuji II LC in each wear cycle. The one-month aging study also showed that all the experimental cements increased their CS continuously during 30 days, unlike Fuji II LC.
