Effect of heat transfer through the release pipe on simulations of cryogenic hydrogen jet fires and hazard distances

Jet flames originated by cryo-compressed ignited hydrogen releases can cause life-threatening conditions in their surroundings. Validated models are needed to accurately predict thermal hazards from a jet fire. Numerical simulations of cryogenic hydrogen flow in the release pipe are performed to assess the effect of heat transfer through the pipe walls on jet parameters. Notional nozzle exit diameter is calculated based on the simulated real nozzle parameters and used in CFD simulations as a boundary condition to model jet fires. The CFD model was previously validated against experiments with vertical cryogenic hydrogen jet fires with release pressures up to 0.5 MPa (abs), release diameter 1.25 mm and temperatures as low as 50 K. This study validates the CFD model in a wider domain of experimental release conditions - horizontal cryogenic jets at exhaust pipe temperature 80 K, pressure up to 2 MPa ab and release diameters up to 4 mm. Simulation results are compared against such experimentally measured parameters as hydrogen mass flow rate, flame length and radiative heat flux at different locations from the jet fire. The CFD model reproduces experiments with reasonable for engineering applications accuracy. Jet fire hazard distances established using three different criteria - temperature, thermal radiation and thermal dose - are compared and discussed based on CFD simulation results.     

Quantum effect of cooling down the environment temperature of mesoscopic LC circuit

We examine the quantum effect of cooling down the environment temperature of mesoscopic LC circuit, and find that the ground state of the circuit is no longer in the thermo vacuum state, but in a negative binomial state. We calculate energy of the circuit in this new state, which increases with the cooling of the environment.     

Vacuum impregnation of chitosan‐based edible coating in minimally processed pumpkin

The goal of this research was to evaluate the use of vacuum impregnation (VI) and soaking techniques (ST) in the application of edible coatings of chitosan and chitosan + lauric acid to minimally processed pumpkins (MPP). The vacuum impregnation method led to greater component incorporation (5.9% and 1.75%, respectively) in the pumpkins when compared to soaking and consequently the formation of more uniform, thicker coatings (25.6 and 22.3 μm, respectively). However, VI caused greater changes in pH, acidity, colour and firmness. Relating to water content and carotenoid content, noncoated pumpkins presented greater losses during the storage period, regardless of impregnation method. The pumpkins with edible coatings, regardless of method, presented lower numbers of psychrotrophic micro‐organisms and coliforms during the storage period. Therefore, soaking was considered the best method for the application of chitosan‐based edible coatings to minimally processed pumpkins, as it led to smaller changes in the properties of the product.     

软土地基的真空预压+水载法处理施工技术

结合横琴国际商务中心(二期)项目中的软土地基处理实践,介绍了真空预压+水载法施工技术。从真空预压加速固结、设置水泥土搅拌桩形成密封墙等方面出发,对关键工艺进行了阐述。真空预压+水载法施工技术实施后,项目取得了良好的社会效益和经济效益,可供相关工程参考。     

Research and development of liquid hydrogen (LH2) temperature monitoring system for marine applications

Monitoring the temperature in liquid hydrogen (LH₂) storage tanks on ships is important for the safety of maritime navigation. In addition, accurate temperature measurement is also required for commercial transactions. Temperature and pressure define the density of liquid hydrogen, which is directly linked to trading interests. In this study, we developed and tested a liquid hydrogen temperature monitoring system that uses platinum resistance sensors with a nominal electrical resistance of approximately 1000 Ω at room temperature, PT-1000, for marine applications. The temperature measurements were carried out using a newly developed temperature monitoring system under different pressure conditions. The measured values are compared with a calibrated reference PT-1000 resistance thermometer. We confirm a measurement accuracy of ±50 mK in a pressure range of 0.1 MPa–0.5 MPa.     

Use of cryogenic machining to improve the adhesion of sphene bioceramic coatings on titanium substrates for dental and orthopaedic applications

Rods of commercially pure titanium were machined using standard oil-based emulsion and cryogenic cooling, and were then coated with sphene (CaTiSiO₅) bioceramic by spray coating using an automatic airbrush. The sphene bioceramic was synthesized in-situ starting from a suspension of polysiloxane that used as SiO₂ precursor, CaCO₃ and TiO₂ nanoparticles. The suspension was deposited on the machined substrates, which were heat treated up to 950?°C in order to promote the formation of sphene ceramic. The produced coated prototypes were characterized to evaluate the effect of the machining conditions on surface roughness and microstructure of the substrate, and thereby their effect on coating adhesion. Nanoindentation tests were employed to determine the hardness and elastic modulus of the coating through its thickness. Results showed that the reduced amount of defects on the surface of the cryo-machined substrates, contributed to increase the hardness, elastic modulus and adhesion strength of the coating-substrate interfaces compared to standard machined samples, therefore improving adhesion of the coating to the underlying substrate.     

The combined effect of cryogenic and boronising treatments on the wear behaviour and microstructure of DIN 1.2344 steel

In this study, the effects of cryogenic and boronising treatments on the wear behaviour and microstructure of 1.2344 steel were evaluated. X-ray diffraction analysis and scanning electron microscopy were used to investigate the microstructure, percentage of the retained austenite, and the carbides' morphology. In addition, a micro-hardness test and pin-on-disk wear method were utilised to assess the samples’ wear resistance. The results showed that the use of a cryogenic treatment improved hardness and wear resistance by 25% and 39%, respectively, compared with a quenching - tempering heat treatment. In addition, cryogenic and boronising treatments improved hardness and wear resistance by 228% and 75%, respectively, compared with a quenching - tempering heat treatment. The improvement in the properties of cryogenically treated and boronised-cryogenised samples in comparison with the quenched-tempered ones is due to the transformation of retained austenite to martensite, precipitation of fine carbides, and better carbide distribution. Also, the formation of the Fe₂B phase affected the properties of the boronised-cryogenised samples. Moreover, examining the wear levels revealed that the dominant wear mechanism is adhesive and tribochemical wear.     

Effects of Environments on the Noise of Atomic Force Microscopy Cantilevers

环境对原子力显微镜悬臂噪声的影响

句宏宇 张松 崔树勋

（西南交通大学 生命科学与工程学院 材料先进技术教育部重点实验室，四川 成都 610031）

创新点说明：

1）发现了原子力显微镜（AFM）在高真空环境中具有非常小的噪声；

2）发现了AFM在液体环境中的噪声与液体粘度和悬臂运动速率之间的关系。

研究目的：

得到AFM的噪声和使用环境、悬臂种类以及仪器参数设置之间的关系，找出减小AFM噪声的有效方法。

研究方法：

模拟基于AFM的单分子力谱实验过程，通过计算AFM在高真空、大气和不同粘度液体环境中不同运动速率下力信号数值的标准差（即噪声大小），分析AFM噪声的影响因素。

研究结果：

1）V形悬臂在高真空环境中具有非常小的噪声，在大气环境中噪声有微小增大，在液体环境中噪声显著增大；

2）AFM具有较低的系统噪声，且系统噪声大小和悬臂到基底的距离相关；

3）随着悬臂运动速率的增加，V形悬臂在不同粘度液体环境中的噪声表现出相似的增大趋势。且液体黏度越大，噪声随速率增大的趋势越显著；

4）相同环境中矩形悬臂的噪声小于V形悬臂的噪声。

结论：

1）高真空环境中AFM具有较小的噪声和较高的分辨率，是进行单分子力谱实验的理想环境；

2） 在液体环境中为了获得较高的信噪比，应尽可能地减小悬臂的运动速率和液体粘度。

关键词：原子力显微镜；悬臂；噪声；高真空；粘度

     

高能量离子束诊断质谱仪的研制及性能表征

本研究开发了一台应用于高能量离子束诊断的直线式飞行时间质谱仪，实现了其与高能真空弧放电离子源的联用。该仪器加速电压30 kV，飞行腔有效飞行距离1.5 m，通过短脉冲离子门精确截取，ICCD高速相机优化聚焦，仪器分辨率优于90 FWHM，对放电过程中产生的等离子体可实现不同时间的离子成分分析。将该方法用于真空弧放电离子源放电过程中离子成分的检测，放电2 μs时，电离成分以气态离子C⁺、O⁺、C²⁺、O²⁺为主；放电6 μs后，除气体成分外，还可以检测到Fe⁺、Cu⁺及其同位素金属离子峰。该仪器能够给出离子源放电产生离子的种类、价态以及相对含量等信息，可实现整个放电过程产生离子成分信息的准确诊断。