Heat transfer characteristics of cryogenic helium gas through a miniature tube with a large temperature difference

Heat transfer with a large temperature difference between the inlet and outlet flows is often encountered in many cryogenic systems. The heat transfer characteristics of cryogenic gas with temperature-dependent thermophysical properties (TDTP) are different from those in the ambient condition with constant thermophysical properties. In this paper, a combined experimental and numerical study has been conducted to determine the heat transfer characteristics of cryogenic helium gas with temperature-dependent thermophysical properties in a miniature tube. In order to validate the theoretical model, an experimental investigation was conducted. Utilizing the validated model with the FLUENT software, the temperature distribution and velocity profile in a miniature tube have been calculated, and a correlation predicting the temperature effect on the Nusselt number determined.     

根据振动信号诊断氦风机故障的方法研究

氦风机是10MW高温气冷实验堆(HTR-10)的一回路主风机,是大功率、高转速、多环节的旋转运动系统,有发生多种故障的可能,而其工作正常与否直接关系到反应堆的安全运行。通过在线分析氦风机运行时的振动信号,可以对氦风机的运行情况进行深入、彻底地评估,对可能的故障尽可能早地进行预防性诊断,从而保证氦风机能够正常和安全运行。本课题从氦风机本身结构和特点出发,研究提出并实现了分别在时域和频域上对氦风机的振动信号进行分析、进而对氦风机故障进行诊断的方法和框架。     

10MW高温堆气体透平方案初探

讨论了10MW高温气冷实验堆（HTR－10）气体透平总体方案设计中应考虑的主要因素。根据HTR－10及一期工程的特点,介绍了HTR－10可能的气体透平方案,初步探讨了直接循环和间接循环的特点。对一种可能的间接循环方案进行了总体设计方案的初步研究。该方案能够比较全面地研究氦气透平的特性,同时与HTR－10一期工程较容易衔接。     

1K～100K温区He-3低温热物性数据计算

由于量子效应的影响，低温下He-3的性质与He-4有很大差异，对于4K－20K气相He-3的性质可利用改进的Strobridge方程来计算，而在20K－100K温区，通过引入对比德布罗意波长作为第三参数来描述量子效应而建立的改进量子对比态模型可用于计算该温区He-3的性质，基于上述计算方法，采用计算机程序设计，建立了He-3低温热物性数据库，该数据库可以计算压力在10MPa以下，温度介于1K－100K之间He-3的pVT性质，焓、内能、熵，热导率和粘度，其计算精度基本可以满足工程需要。     

Structural study of CH3S self-assembled monolayers on Au(111)

We present preliminary results of an experimental investigation of ordered phases of CH₃S chemisorbed on Au(111). The self-assembled monolayer has been grown by dosing dimethyl disulfide in ultrahigh vacuum at different substrate temperatures between 200 K and 320 K and following different protocols. The monolayers have been characterized by means of low-energy He atom scattering with time-of-flight detection in a temperature range between 150 K and 300 K. The observed diffraction patterns show that the main periodicity is well-described by the (3 × 4) overlayer of the Au(111) lattice, coexisting with the (√3 × √3) periodicity, in agreement with previous results obtained by means of low-energy electron diffraction.     

Studies on the structural properties of SiO:H films prepared from (SiH4+CO2+He) plasma in RF-PECVD

A comprehensive report on the structural studies on SiO:H films prepared at high growth rate from He-diluted (SiH₄+CO₂) plasma has been presented and extraction of some intriguing ideas that deserve high relevance for the potential development of nano-crystalline hydrogenated silicon oxide (nc-SiO:H) films has been tried. Poly-hydrogenation has been found as inherent to increasing alloying of the network; however, the bonded H-content reduces linearly with the degree of oxygen incorporation, i.e., the solubility of H in the SiO:H network decreases as the O-content increases in the presence of He. This result happens to be opposite to the conventional H₂-diluted plasma condition and appears to be attractive as well. In addition, He-dilution contributes to a high growth rate of the material. Dynamic interaction of He* in the formation of activated oxygen atoms in the plasma and their efficient mobilization on the surface reaction process at the growing network induces abstraction of H from the SiH_n groups and the terminal H atoms are replaced by bridging O atoms to form the SiO:H network. Abstraction of H from the network being an essential criteria for developing nanocrystallinity and it being inherent to oxygenation in Si network when prepared from He-diluted (SiH₄+CO₂) plasma in PECVD, the process could provide an appropriate pathway for preparing nc-SiO:H structures for solar cells, from such plasma in suitable parametric conditions.     

Molecular dynamics simulations of collision cascades in FeCrHe

Radiation damage due to 1 and 5 keV collision cascades in Fe₉₀Cr₁₀ in the presence of 0.1%, 0.5% and 1.0% He defects, relevant for fusion reactor steels, has been studied using molecular dynamics simulations. We show that with 0.1% interstitial He the effect on the damage production in the FeCr matrix is minor, while with 1.0% He, the number of Frenkel pairs is significantly increased in comparison to pure FeCr. The positions of the He interstitials and clusters depend on the Cr atoms and the amount of He inside the cascade region is increased by about 30% due to the cascade. With substitutional He less damage is formed in the FeCr matrix due to cascades.