A water-TiO2nanofluid with a weight fraction of 5% and an average particle size of 75 nm is used to investigate the effect of TiO2 nanoparticles on the crystallization and melting behaviors of deionized water by using...A water-TiO2nanofluid with a weight fraction of 5% and an average particle size of 75 nm is used to investigate the effect of TiO2 nanoparticles on the crystallization and melting behaviors of deionized water by using differential scanning calorimetry（DSC）at four different cooling rates,3,5,7,9 ℃/min.The DSC experimental results show that the water-TiO2 nanofluid has a lower supercooling degree and a faster crystallization rate than the deionized water.With the increase in the cooling rate,the influence of the TiO2 nanoparticles on the supercooling degree of the deionized water becomes greater,but on the crystallization rate it turns lower.During the melting process,compared with the deionized water,the water-TiO2 nanofluid has a lower melting temperature,a less latent heat and a higher melting rate.展开更多
During last 45 years, two groups of the experimental data on critical heat flux were obtained in bare tubes, covering the pressures from atmosphere to near-critical point. One group of the data were obtained in the in...During last 45 years, two groups of the experimental data on critical heat flux were obtained in bare tubes, covering the pressures from atmosphere to near-critical point. One group of the data were obtained in the inner diameter of 2.32, 5.16, 8.05, 10.0 and 16.0 mm, respectively, with the ranges of pressure of 0.1-1.92 MPa, velocity of 1.47-23.3 m/s, local subcooling of 3.7-108.7 ℃ and heat flux of up to 38.3 MW/m2. Another group of the data were obtained in the inner diameter of 4.62, 7.98 and 10.89 mm, respectively, with the ranges of pressure of 1.7-20.6 MPa, mass flux of 454-4,055 kg/（m2.s） and inlet subcooling of 53-361 ℃. The results showed complicated effects of the pressure, mass flux, subcooling and diameter on the critical heat flux. They were formulated by two empirical correlations. A mechanistic model on the limit of heat transfer capability from the bubbly layer to the subcooled core was also proposed for all the results.展开更多
When a liquid is supercooled,its structural equilibration timeτeqincreases sharply approaching the glass transition temperature Tg,below which it is kinetically arrested in the out of equilibrium glassy state.Upon an...When a liquid is supercooled,its structural equilibration timeτeqincreases sharply approaching the glass transition temperature Tg,below which it is kinetically arrested in the out of equilibrium glassy state.Upon annealing below Tg,such glassy state relaxes toward the equilibrium state.There is growing evidence that such relaxation process is quite complex,influenced by the complexity of the potential energy landscape.Here we report the observation of a hierarchical aging pathway in the process of the glass-to-supercooled liquid transition in various molecular glass forming systems.Differential scanning calorimetry reveals that the glassy state upon annealing below Tgfirstly enters a transient metastable supercooled liquid state with slightly higher enthalpies than that of the equilibrium supercooled liquid state when extrapolated to below Tg.This observation is also confirmed by structural measurements via Raman scattering.The dynamics of the transient metastable-to-stable supercooled liquid transition exhibits characteristics of thermodynamic transition at spinodal temperature Tspslightly above Tg,leading to anomalous behaviors such as the appearance of a transition-like behavior in the plot of fragility measurements.These observations imply that the free energy landscape of the supercooled liquid develops complexity with qualitative changes approaching Tgand could have strong influence on the process of the glass transition.展开更多
基金The National Natural Science Foundation of China(No.50876022)
文摘A water-TiO2nanofluid with a weight fraction of 5% and an average particle size of 75 nm is used to investigate the effect of TiO2 nanoparticles on the crystallization and melting behaviors of deionized water by using differential scanning calorimetry（DSC）at four different cooling rates,3,5,7,9 ℃/min.The DSC experimental results show that the water-TiO2 nanofluid has a lower supercooling degree and a faster crystallization rate than the deionized water.With the increase in the cooling rate,the influence of the TiO2 nanoparticles on the supercooling degree of the deionized water becomes greater,but on the crystallization rate it turns lower.During the melting process,compared with the deionized water,the water-TiO2 nanofluid has a lower melting temperature,a less latent heat and a higher melting rate.
文摘During last 45 years, two groups of the experimental data on critical heat flux were obtained in bare tubes, covering the pressures from atmosphere to near-critical point. One group of the data were obtained in the inner diameter of 2.32, 5.16, 8.05, 10.0 and 16.0 mm, respectively, with the ranges of pressure of 0.1-1.92 MPa, velocity of 1.47-23.3 m/s, local subcooling of 3.7-108.7 ℃ and heat flux of up to 38.3 MW/m2. Another group of the data were obtained in the inner diameter of 4.62, 7.98 and 10.89 mm, respectively, with the ranges of pressure of 1.7-20.6 MPa, mass flux of 454-4,055 kg/（m2.s） and inlet subcooling of 53-361 ℃. The results showed complicated effects of the pressure, mass flux, subcooling and diameter on the critical heat flux. They were formulated by two empirical correlations. A mechanistic model on the limit of heat transfer capability from the bubbly layer to the subcooled core was also proposed for all the results.
基金supported by the National Basic Research Program of China (2015CB856801)
文摘When a liquid is supercooled,its structural equilibration timeτeqincreases sharply approaching the glass transition temperature Tg,below which it is kinetically arrested in the out of equilibrium glassy state.Upon annealing below Tg,such glassy state relaxes toward the equilibrium state.There is growing evidence that such relaxation process is quite complex,influenced by the complexity of the potential energy landscape.Here we report the observation of a hierarchical aging pathway in the process of the glass-to-supercooled liquid transition in various molecular glass forming systems.Differential scanning calorimetry reveals that the glassy state upon annealing below Tgfirstly enters a transient metastable supercooled liquid state with slightly higher enthalpies than that of the equilibrium supercooled liquid state when extrapolated to below Tg.This observation is also confirmed by structural measurements via Raman scattering.The dynamics of the transient metastable-to-stable supercooled liquid transition exhibits characteristics of thermodynamic transition at spinodal temperature Tspslightly above Tg,leading to anomalous behaviors such as the appearance of a transition-like behavior in the plot of fragility measurements.These observations imply that the free energy landscape of the supercooled liquid develops complexity with qualitative changes approaching Tgand could have strong influence on the process of the glass transition.
