The influence of convection on heat transfer in liquid tin

Heat flow through liquid tin has been measured with convective flow present in the melt. The results indicate that heat flow in the melt is enhanced by a factor of 9.6 due to this fluid flow, as compared to heat flow through a stagnant melt. The enhancement factor was found to be essentially constant at temperature differences greater than 4 °C across the melt. This is shown to be due to a constant fluid flow rate at higher temperature differences. It is noted that the thermal flow through a convective melt can be strongly limited by the thermal resistance of the container walls along the heat flow path.     

新型螺旋翅片管对流换热系数的研究

采用数值计算的方法，自行设计螺旋翅片管温度场计算软件，并利用其计算结果讨论了管内壁和外壁对流换热系数的变化规律，及管内外热阻的匹配问题。数值计算结果表明，管内换热系数随温度的升高而升高，管内空气和管外烟气的流速分别显著影响管内管外换热系数。翅片管的外形尺寸同样影响到螺旋翅片管的温度分布。     

1400F轧机工作辊与冷却液之间换热特性的最优值

为了提高分段冷却在板形控制中的作用,对1400F铝带箔轧机工作辊与冷却液之间对流换热特性进行了模拟研究,采用正交实验方法获得了一组最优的冷却参数,并进行了模拟验证.结果表明,影响冷却效率重要性的因素依次是冷却液粘度、喷射速度、冷却液温度和喷射角度.     

旋流叶片传热管内湍流强化传热数值模拟

基于管内核心流强化传热原理,在管内核心流布置旋流器以实现强化传热.建立了强化管内流体流动与传热的数学模型,结果表明:在强化传热管内布置旋流器可以显著强化湍流换热,而且其流动阻力增加幅度不大.当旋流器距圆管人口200mm,Re数为6000时,强化传热管的PEC值可达1.7.     

Adiabatic electron transfer: comparison of modified theory with experiment

The radical cations of properly designed bishydrazines allow comparison of observed and calculated electron transfer rate constants. These compounds have rate constants small enough to be measured by dynamic electron spin resonance spectroscopy and show charge transfer bands corresponding to vertical excitation from the energy well for the charge occurring upon one hydrazine unit to that for the electron-transferred species. Analysis of the data for all six compounds studied indicates that the shape of the adiabatic surface on which electron transfer occurs can be obtained from the charge transfer band accurately enough to successfully predict the electron transfer rate constant and that explicit tunneling corrections are not required for these compounds.     

Regenerative heat transfer in rotary kilns

A mathematical model has been developed to determine the temperature distribution in the wall of a rotary kiln. The model, which incorporates a detailed formulation of the radiative and convective heat-transfer coefficients in a kiln, has been employed to examine the effect of different kiln variables on both the regenerative and the overall heat transfer to the solids. The variables include rotational speed, pct loading, temperature of gas and solids, emissivity of wall and solids, convective heattransfer coefficients at the exposed and covered wall, and thermal diffusivity of the wall. The model shows that the regenerative heat flow is most important in the cold end of a rotary kiln, but that generally the temperature distribution and heat flows are largely independent of these variables. Owing to this insensitivity it has been possible to simplify the model with the aid of a resistive analog. Calculations are presented indicating that both the shell loss and total heat flow to the bed may be estimated to within 5 pct using this simplified model.     

Radiative heat transfer in rotary kilns

Radiative heat transfer between a nongray freeboard gas and the interior surfaces of a rotary kiln has been studied by evaluating the fundamental radiative exchange integrals using numerical methods. Direct gas-to-surface exchange, reflection of the gas radiation by the kiln wall, and kiln wall-to-solids exchange have been considered. Graphical representations of the results have been developed which facilitate the determination of the gas mean beamlength and the total heat flux to the wall and to the solids. These charts can be used to account for both kiln size and solids fill ratio as well as composition and temperature of the gas. Calculations using these charts and an equimolar CO₂−H₂O mixture at 1110 K indicate that gas-to-surface exchange is a very localized phenomenon. Radiation to a surface element from gas more than half a kiln diameter away is quite small and, as a result, even large axial gas temperature gradients have a negligible effect on total heat flux. Results are also presented which show that the radiant energy either reflected or emitted by a surface element is limited to regions less than 0.75 kiln diameters away. The radiative exchange integrals have been used, together with a modified reflection method, to develop a model for the net heat flux to the solids and to the kiln wall from a nongray gas. This model is compared to a simple resistive network/gray-gas model and it is shown that substantial errors may be incurred by the use of the simple models.     

Contribution to the metal-mold interfacial heat transfer

Formerly with the SVUSS Bechovice, Prague 9     

Microstructural Aspects of Adiabatic Shear Failure in Annealed Ti6Al4V

This work reports a comprehensive examination of the microstructural evolution in Ti6Al4V subjected to high-strain-rate deformation. The sequence of microstructural rearrangements leading to adiabatic shear banding is presented. A detailed microstructural comparison between two types of specimens, one that failed by adiabatic shear and the other that was strained to half its failure strain, is carried out. The main observation is that for this material, the microstructure of the two types of specimens is qualitatively identical, indicating that from approximately half the failure strain until adiabatic shear failure, no additional micromechanism is observed to develop and operate. Overall, the microstructure undergoes a significant refinement with the increasing strain until the formation of dynamically recrystallized grains. It is therefore suggested that the evolution of the volume fraction of recrystallized grains should be characterized from its early onset until final failure by adiabatic shear banding.     

敞开式SF6断路器弹簧操作机构的缺陷整改

敞开式SF6断路器岗其结构简单，操作能耗小、安装容易等特点被广泛采用。应用结果表明：SF6断路器关键部件如内动锄头导向环用材不当，二次控制回路设计不合理，为设备重大缺陷，应引起重视。