双联叶片泵叶片早期磨损原因分析研究

双联叶片泵的早期磨损现象在SF31904型矿用自卸车上非常严重,为了探究其原因本文从油液污染和磨损两方面对其进行分析,通过对取样油液的化验,发现油液污染非常严重,油液中存在大量的硅和钙的化合物等高硬度的摩擦材料,油液的固体污染等级为NAS163812级,在标准中是最高污染等级,再通过叶片的磨损对比、对照实验及理论分析和推理得知其磨损量和磨损系数都较同等条件下的干净油液大了很多,而叶片的运行寿命则短了很多,这说明污染已成为影响叶片寿命的主要原因。     

Pool boiling heat transfer of carbon dioxide on a horizontal tube

Carbon dioxide is again becoming an important refrigerant. While the thermophysical properties are well known there is a lack of data on its heat transfer characteristics.

In this study, heat transfer coefficients for nucleate boiling of carbon dioxide are determined using a standard apparatus for the investigation of pool boiling based on a set-up from Karlsruhe [D. Gorenflo, J. Goetz, K. Bier. Vorschlag für eine Standard-Apparatur zur Messung des Wärmeübergangs beim Blasensieden. Wärme-und Stoffübertragung 16 (1982), 69–78; J. Goetz, Entwicklung und Erprobung einer Normapparatur zur Messung des Wärmeübergangs beim Blasensieden. Dissertation Universität Karlsruhe (1980).] and built at our institute. Electrically heated horizontal cylinders with an outer diameter of 16 mm and a length of 100 mm are used as heating elements. Measurements with constant heat flux are performed for different wall materials and surface roughnesses. The heat transfer is investigated within the pressure range of 0.53≤ p ≤1.43 MPa (0.072≤ p/p_c ≤0.190) and a temperature range of −56≤ t ≤−30 °C, respectively. Heat fluxes of up to 80,000 W m⁻² are applied.

The influences of wall material and roughness on the heat transfer coefficient are evaluated separately. The obtained coefficients are compared to generally accepted correlations and to experimental results of other authors, who used similar configurations with copper tubes and carbon dioxide. These are the only previous experimental data, which could be found. Results for copper, stainless steel and aluminium as wall materials are presented.     

Thermal Properties Measurement of Micro-electromechanical System Sensors by Digital Moire Method

Abstract:  The thermal properties of a micro-electromechanical system sensor were analysed by a novel digital moiré method. A double-layer micro-cantilever sensor (60  μ m long, 10  μ m width and 2  μ m thick) was prepared by focused ion beam milling. A grating with frequency of 5000 lines mm⁻¹ was etched on the cantilever. The sensor was placed into a scanning electron microscope system with a high temperature device. The observation and recording of the thermal deformation of the grating were realised in real-time as the temperature rose from room temperature to 300 °C at intervals of 50 °C. Digital moiré was generated by interference of the deformed grating and a digital virtual grating. The thermal properties including strain distribution of the sensor and the linear expansion coefficient of polysilicon were accurately measured by the phase-shifted moiré patterns.     

Heat transfer coefficient measurements for mixed gas working fluids at cryogenic temperatures

The use of mixed gas working fluids has become common in Joule-Thomson type cryocoolers for a variety of applications. However, there is very little data or theory currently available regarding the heat transfer coefficient associated with these multi-component, multi-phase mixtures at cryogenic temperatures. This paper describes an experimental test facility and procedure that has been used to make careful measurements of the horizontal, flow boiling heat transfer coefficient for several hydrocarbon mixtures that are nominally optimal for small, Joule-Thomson cryocoolers in the 80 K to 120 K operating range. Data are presented over a range of temperatures from 100 K to room temperature and for several pressures and mass flow rates. The results indicate that quality and mass flux are the most important parameters governing the heat transfer coefficient among those that were varied. The experiment is verified by carrying out tests using single-phase, pure nitrogen gas and comparing the results with the Dittus-Boelter equation. The experimental uncertainty of the measurements is estimated from 1st principles; additionally, the repeatability of the experimental measurements was investigated by replicating tests at a nominal set of operating conditions and composition on separate days. The measurements presented here are intended to aid in the design of small, mixed-gas Joule-Thomson cryocoolers.     

采用热敏电阻器研制风速传感器的设计

介绍了采用负温度系数热敏电阻器为检测元件的风速传感器的测量原理;阐述了风速/电压转换理论、风速测量电路;分析了测量误差。实验测试结果表明:这种风速传感器的各项性能指标均达到设计要求。     

城市污水生物除磷脱氮系统剩余污泥量的计算

剩余污泥量的计算是活性污泥法工艺设计的关键，而活性污泥法是同时生物除磷脱氮的主体工艺形式，因此，准确计算生物除磷脱氮系统的剩余污泥量十分必要。结合昆明市污水处理厂的运行实际。分析比较了传统计算法、污泥龄法和数学模型法在计算城市污水生物除磷脱氮系统剩余污泥量时的准确性，建议现阶段采用污泥龄法进行计算，提出修正系数K(0．75-1)与具体工艺形式有关，并给出K的几个建议值，同时指出数学模型法（ASM2）应是发展方向．     

平面波垂直入射浸渍吸收剂蜂窝的反射特性

提出一个数值方法,计算当平面波垂直于蜂窝板入射时浸渍吸收剂的蜂窝的反射系数。在引入蜂窝壁表面阻抗后,借助于周期格林函数对无限大蜂窝表面建立了电场积分方程,用矩量法求解未知的表面电流。在8~12 GHz频段内,得到的不同蜂窝高度、不同吸收剂和不同浸渍厚度的数值结果表明,所提出的方法是高效的,可用于蜂窝制备和吸波结构的工作中。     

两种摩擦力滑移隔震结构地震响应的研究

对选用的两种摩擦力(库仑摩擦力、指数函数摩擦力)分别编程计算单质点的地震响应，运用newmark方法推导了库仑摩擦力下单质点地震响应的计算公式。对计算结果进行分析，得出质量比、摩擦系数对隔震效果的影响，并给出在文章假定的结构参数下，滑移面摩擦系数的取值范围。     

两点应变测量法和岩石力--凿深特性的实验研究

岩石的力—凿深特性是冲击钻进波动力学研究的一个重要边界条件和基本参量,利用两点测量法对岩石的动态凿入特性进行实验研究,并考虑了钻头端部变截面和凿入速度对力—凿深特性的影响,运用最小二乘法的曲面拟合,得出了更为精确的凿入系数和粘度系数值,并在实验的基础上综合得到粘弹性类型岩石,即泰山花岗岩力 凿深特性的一般模式.