针对Na_(2)O-CaO-SiO_(2)(NCS)多孔微晶玻璃内部气孔大小不同、分布不均问题,提出通过添加固态Si颗粒调控NCS多孔微晶玻璃孔结构。通过扫描电子显微镜(SEM)、图像处理软件Image pro plus 6.0、DSC等分析手段研究固态Si颗粒对NCS多孔微...针对Na_(2)O-CaO-SiO_(2)(NCS)多孔微晶玻璃内部气孔大小不同、分布不均问题,提出通过添加固态Si颗粒调控NCS多孔微晶玻璃孔结构。通过扫描电子显微镜(SEM)、图像处理软件Image pro plus 6.0、DSC等分析手段研究固态Si颗粒对NCS多孔微晶玻璃内部热场、液相的影响,以及Si颗粒调控NCS多孔微晶玻璃气泡成核机制。结果表明,通过加入固态Si颗粒可以使NCS多孔微晶玻璃基础配合料内部热扩散速率提高23.5%,NCS多孔微晶玻璃内部液相产生温度降低60℃,液相产生速率增大7~8倍;在固态Si颗粒周围先产生液相,液相中的气泡分子在固态Si颗粒表面非均相成核,随着配合料温度的升高,无固态Si颗粒位置处产生新的液相,液相中气泡分子扩散至固态Si颗粒表面促进原始气泡长大或者在新液相中均相成核。展开更多
Nucleation of gaseous hydrogen bubbles is the initial stage of GASAR process. Through the theoretical analysis, it has been identified that heterogeneous nucleation of bubbles as caps on the solid surfaces of impuriti...Nucleation of gaseous hydrogen bubbles is the initial stage of GASAR process. Through the theoretical analysis, it has been identified that heterogeneous nucleation of bubbles as caps on the solid surfaces of impurities is impossible and only the heterogeneous nucleation in pits and cracks in impurities is the most feasible way in the GASAR process. The results also show that the probability of bubble nucleation progressively decreases from Al, Cu and Ni to Fe molten metal, which is the result of the increasing adhesion work of liquid metal on alumina.展开更多
Multiple size group （MUSIG） model combined with a threedimensional twofluid model were em ployed to predict subcooled boiling flow of liquid nitrogen in a vertical upward tube. Based on the mechanism of boiling heat...Multiple size group （MUSIG） model combined with a threedimensional twofluid model were em ployed to predict subcooled boiling flow of liquid nitrogen in a vertical upward tube. Based on the mechanism of boiling heat transfer, some important bubble model parameters were amended to be applicable to the modeling of liquid nitrogen. The distribution of different discrete bubble classes was demonstrated numerically and the distribu tion patterns of void fraction in the wallheated tube were analyzed. It was found that the average void fraction in creases nonlinearly along the axial direction with wall heat flux and it decreases with inlet mass flow rate and sub cooled temperature. The local void fraction exhibited a Ushape distribution in the radial direction. The partition of the wall heat flux along the tube was obtained. The results showed that heat flux consumed on evaporation is the leading part of surface heat transfer at the rear region of subcooled boiling. The turning point in the pressure drop curve reflects the instability of bubbly flow. Good agreement was achieved on the local heat transfer coefficient aalnst experimental measurements, which demonstrated the accuracy of the numerical model.展开更多
文摘针对Na_(2)O-CaO-SiO_(2)(NCS)多孔微晶玻璃内部气孔大小不同、分布不均问题,提出通过添加固态Si颗粒调控NCS多孔微晶玻璃孔结构。通过扫描电子显微镜(SEM)、图像处理软件Image pro plus 6.0、DSC等分析手段研究固态Si颗粒对NCS多孔微晶玻璃内部热场、液相的影响,以及Si颗粒调控NCS多孔微晶玻璃气泡成核机制。结果表明,通过加入固态Si颗粒可以使NCS多孔微晶玻璃基础配合料内部热扩散速率提高23.5%,NCS多孔微晶玻璃内部液相产生温度降低60℃,液相产生速率增大7~8倍;在固态Si颗粒周围先产生液相,液相中的气泡分子在固态Si颗粒表面非均相成核,随着配合料温度的升高,无固态Si颗粒位置处产生新的液相,液相中气泡分子扩散至固态Si颗粒表面促进原始气泡长大或者在新液相中均相成核。
文摘Nucleation of gaseous hydrogen bubbles is the initial stage of GASAR process. Through the theoretical analysis, it has been identified that heterogeneous nucleation of bubbles as caps on the solid surfaces of impurities is impossible and only the heterogeneous nucleation in pits and cracks in impurities is the most feasible way in the GASAR process. The results also show that the probability of bubble nucleation progressively decreases from Al, Cu and Ni to Fe molten metal, which is the result of the increasing adhesion work of liquid metal on alumina.
基金Supported by the National Natural Science Foundation of China （51106119, 81100707）, the Fundamental Research Funds for the Central University of China, Doctoral Fund of Ministry of Education （20110201120052） and the National Science and Technology Sur0orting Item （2012BAA08B03）.
文摘Multiple size group （MUSIG） model combined with a threedimensional twofluid model were em ployed to predict subcooled boiling flow of liquid nitrogen in a vertical upward tube. Based on the mechanism of boiling heat transfer, some important bubble model parameters were amended to be applicable to the modeling of liquid nitrogen. The distribution of different discrete bubble classes was demonstrated numerically and the distribu tion patterns of void fraction in the wallheated tube were analyzed. It was found that the average void fraction in creases nonlinearly along the axial direction with wall heat flux and it decreases with inlet mass flow rate and sub cooled temperature. The local void fraction exhibited a Ushape distribution in the radial direction. The partition of the wall heat flux along the tube was obtained. The results showed that heat flux consumed on evaporation is the leading part of surface heat transfer at the rear region of subcooled boiling. The turning point in the pressure drop curve reflects the instability of bubbly flow. Good agreement was achieved on the local heat transfer coefficient aalnst experimental measurements, which demonstrated the accuracy of the numerical model.
