Studies of air-flow and temperature fields inside a passenger compartment for improving thermal comfort and saving energy. Part I: Test/numerical model and validation

It is important to analyze the temperature and air-flow field inside the passenger compartment to ameliorate the amenity and decrease energy consumption. This paper uses commercial software FLUENT to simulate 3-D temperature distributions and flow field in a compartment with or without passengers. Validated by the experimental data, the numerical model is used to investigate the influence of different factors on the thermal comfort and the energy consumption. In the first paper, the test conditions and the numerical models are described in details. The measured and predicted transient temperatures are compared and good agreement is obtained. In addition, the air temperature distribution in a steady test situation is also numerically predicted by both transient and steady model, and the agreements between the three sets of data are satisfactorily, showing the reliability of the models. In the companion part of the two papers the simulated effects of several operational conditions will be presented.     

Effect of surface modification on the performance of negative electrodes in Ni/MH batteries

The performance of a Nickel/Metal Hydride (Ni/MH) battery closely depends on the characteristics of the negative MH electrode. Exchange current density, high-rate dischargeability, discharge potential and apparent activation energy of a MH electrode are very important properties, among which the high-rate dischargeability and discharge potential of a MH electrode determine the specific energy and specific power of electric vehicles (EVs) when Ni/MH batteries are applied to EVs. Significant improvements in exchange current density, high-rate dischargeability and discharge potential of a MH electrode have been observed for a $\text{9.0}\text{wt}$% copper coated LaNi_4.7Al_0.3 MH electrode. The high-rate dischargeabilities were determined to be 88.4% for the LaNi_4.7Al_0.3 electrode and 99.4% for Cu-coated LaNi_4.7Al_0.3 electrode. The discharge potential for the Cu-coated LaNi_4.7Al_0.3 electrode is lower (i.e. more negative) than that for the LaNi_4.7Al_0.3 electrode, especially at a large discharge current density (i.e. $\text{200}\text{mA}\text{g}{}^{\mathrm{-1}}$). The discharge potentials of the Cu-coated LaNi_4.7Al_0.3 electrode are almost the same value (i.e. $\text{−0.930}\text{V}$ vs. Hg/Hgo) at both 20 and $\text{200}\text{mA}\text{g}{}^{\mathrm{-1}}$ discharge current densities. There is no significant difference between the two apparent activation energies for the electrode reactions for the electrodes with and without the microencapsulation of the MH powders at the same hydrogen concentration.     

预处理对金刚石薄膜质量及结合力的影响

目的改善硬质合金表面金刚石薄膜的结合力。方法采用热丝CVD法在硬质合金基体上制备金刚石薄膜,研究对比喷砂+一步法、喷砂+两步法、Al Cr N过渡层和传统两步法这四种预处理对金刚石薄膜质量及其结合性能的影响。对预处理后硬质合金基体表面的形貌和粗糙度进行分析,并通过扫描电子显微镜、X射线衍射、拉曼光谱及洛氏硬度计表征金刚石薄膜的形貌、结构及性能。结果喷砂有利于在基体表面获得均匀分布的凹坑,提高金刚石的形核密度及均匀性,尤其改善了金刚石颗粒的团聚现象。Al Cr N过渡层虽然表面粗糙度不高,但有大量的凸起颗粒,提供了极佳的形核点,也在一定程度上优于传统两步法的表面金刚石形核密度。在金刚石薄膜沉积参数不变的前提下,传统两步法预处理获得的涂层结合力为HF4级,喷砂结合一步法和两步法获得的结合力分别达到了HF3级和HF1级,但Al Cr N过渡层的结合力表现较差。结论 Al Cr N过渡层能阻挡Co的扩散,提高了金刚石的纯度,但金刚石膜的内应力较大,结合力差。喷砂和刻蚀复合预处理不仅能提高金刚石的结晶质量和纯度,金刚石薄膜的结合力也得到改善。     

Effects of viscous dissipation and fluid axial heat conduction on heat transfer for non-Newtonian fluids in ducts with uniform wall temperature: Part II. Annular ducts

The present paper, which is an extension of a previous study [O. Jambal, T. Shigechi, D. Ganbat, S. Momoki, Int. Commun. Heat Mass Transf. 32(9) (2005) 1165] on laminar heat transfer to non-Newtonian fluids in parallel plates and circular ducts, deals with concentric annular ducts subjected to a step change in wall temperature. A finite-difference scheme is applied to determine the velocity and temperature fields. Developing Nusselt numbers are graphically shown for various Brinkman numbers and Peclet numbers and the effects of viscous dissipation, fluid axial heat conduction, non-Newtonian behavior together with the radius ratio effect on heat transfer are discussed.