高速运行齿轮泵的吸油空化与抑制

为揭示齿轮泵高转速运行时的空化发展规律,对装载机用大功率双联齿轮泵的吸油特性展开研究。通过全流域仿真模拟及试验,分析了转速、吸油压力对双联齿轮泵空化现象及输出流量特性的影响。结果表明,双联齿轮泵发生明显吸油空化的临界转速为2400 r/min,当转速大于2400 r/min后,泵内的气体含量骤增,严重影响输出流量的连续性和稳定性;双联齿轮泵的临界吸油压力为0.19 MPa,继续增大吸油口压力会增大泵出口的流量脉动,与入口为0.1 MPa相比,吸油压力为0.19 MPa时齿轮副1和齿轮副2的气体体积分数分别降低0.059和0.067,有效流量分别增大7.96%和9.24%。通过增压装置增加泵的入口压力,对齿轮泵空化的抑制以及有效流量的提升有明显的改善作用,具有工程实际意义。

空化洗油机械溶胀对新疆准东西沟煤液化性能的影响

以空化洗油为溶剂,对新疆西沟自然溶胀煤样进行二次机械溶胀,考察机械溶胀对煤样加氢液化性能的影响。研究结果显示,煤样机械溶胀后,颗粒结构更为疏松,棱角变钝,体积平均粒径和真密度分别减小了60.52%和8.06%,比表面积和溶胀度分别增加了90.91%和25.18%;失重过程可分为110～330,330～550和550～1 000℃等3个阶段,但失重率分别增加了189.15%,28.22%和30%,总失重率增加了64.79%,质量变化速率分别增加了208.9%,24.62%和30.01%,在330～430℃温度段的热解活化能降低了4.5 k J/mol;脂碳率f_（al）由0.31降至0.22,芳香簇尺寸指数X_b由0.12增加至0.21;沥青质产率、油产率和转化率分别提高了40.78%,8.87%和8.44%,气产率减小了36.03%,氢耗量有所降低。

空化流动下液压锥阀所受推力的数值计算

为寻求一种较准确的方法来计算油空化流动下液压锥阀所受的推力,通过对Fluent软件中壁面函数、空化流动模型及模型参数的分析、选择和调整,经数值计算并与实验数据的对比结果表明:采用可缩比例壁面函数和Zwart-Gerber-Belamri空化模型,在空泡半径为1μm,蒸发和凝结校正系数分别为0.4和0.000 1时,空化流动下锥阀所受推力的数值计算结果与实验结果吻合良好.并用所述模型研究了锥阀锥角及阀座倒角长度对锥阀阀口空化的影响.结果表明:阀芯锥角越小,阀座倒角长度越小,阀口空化强度越弱.

Thermal oxidation of two aviation synthetic lubricant base oils

The thermal degradation of two synthetic lubricants base oils, poly-a-olefins （PAO） and di-esters （DE）, was investigated under oxidative pyrolysis condition and their properties were characterized in simulated ＂areo-engine＂ by comparing the thermal stability and identifying the products of thermal decomposition as a function of exposure temperature. The characterization of the products were performed by means of Fourier transform infrared spectrometry （FTIR）, gas chromatography/mass spectrometry （GC/MS） and viscosity experiments. The results show that PAO has the lower thermal stability, being degraded at 200℃ different from 300 ℃ for DE. Several by-products are identified during the thermal degradation of two lubricant base oils. The majority of PAO products consist of alkenes and olefins, while more oxygen-contained organic compounds are detected in DE samples based on GC/MS analysis. The related reaction mechanisms are discussed based on the experimental results.

Effect of cavitation bubble collapse on hydraulic oil temperature

Cavitation bubble collapse has a great influence on the temperature of hydraulic oil. Herein, cone-type throttle valve experiments are carried out to study the thermodynamic processes of cavitation. First, the processes of growth and collapse are analysed, and the relationships between the hydraulic oil temperature and bubble growth and collapse are deduced. The effect of temperature is then considered on the hydraulic oil viscosity and saturated vapour pressure. Additionally, an improved form of the Rayleigh–Plesset equation is developed. The effect of cavitation on the hydraulic oil temperature is experimentally studied and the effects of cavitation bubble collapse in the hydraulic system are summarised. Using the cone-type throttle valve as an example, a method to suppress cavitation is proposed.

Instability and breakup of cavitation bubbles within diesel drops

A modified mathematical model is used to study the effects of various forces on the stability of cavitation bubbles within a diesel droplet. The principal finding of the work is that viscous forces of fluids stabilize the cavitation bubble, while inertial force destabilizes the cavitation bubble. The droplet viscosity plays a dominant role on the stability of cavitation bubbles compared with that of air and bubble. Bubble–droplet radius ratio is a key factor to control the bubble stability, especially in the high radius ratio range. Internal hydrodynamic and surface tension forces are found to stabilize the cavitation bubble, while bubble stability has little relationship with the external hydrodynamic force. Inertia makes bubble breakup easily, however, the breakup time is only slightly changed when bubble growth speed reaches a certain value(50 m·s-1). In contrast, viscous force makes bubble hard to break. With the increasing initial bubble–droplet radius ratio, the bubble growth rate increases, the bubble breakup radius decreases, and the bubble breakup time becomes shorter.

Commercial Test of Two Diesel Demulsifiers

PetroChina Lanzhou Petrochemical Company conducted commercial tests for application of two types of diesel demulsifiers, the HPL-2 and GX-02 demulsifiers, in order to solve the emulsion problem arising from caustic washing of straight-run diesel fraction obtained from atmospheric and vacuum distillation unit at the Lanzhou refinery. After addition of each demulsifier into the diesel fraction the oil content in caustic residue was apparently decreased, and discharge of waste caustic was reduced, resulting in the elimination of emulsification and a significant increase of economic benefits. When 70 ppm of the HPL-2 demulsifier was added to diesel fraction, the oil content in waste caustic exiting the second-stage caustic wash settling tank was reduced to 2.45% from 7.90 %, whereas this value was reduced to 2.81% from 5.96% with addition of the GX-02 demulsifier.

Process Optimization of Vacuum Fried Rice-Straw Mushroom （Volvariella Volvacea） Stem Chip Making

The study was aimed to obtain the optimum conditions for vacuum frying and predicting the moisture lost during rice straw mushrooms stem chip production. The raw materials were obtained from the local farmer around the campus. A completely randomized factorial experimental design and Duncan＇s multiple range tests were used to achieve the objectives. Three temperatures, i.e. 80, 90 and 100 ℃ and five frying time, i.e. 3, 6, 9, and 15 minutes with a 2 mm slice thickness were studied to determine the optimum condition and predict the moisture decrease. Results showed that the vacuum frying time in general affects the chips color and oil uptake significantly （p 〈 0.01） and correlated with the moisture decrease. The chips moisture content decline significantly after vacuum frying at 90 ℃ and 100 ℃ for 3 minutes. While for the 80 ℃ vacuum frying, the significant decrease of moisture occurred due to the increase of vacuum frying time from 3 to 6 minutes （p 〈 0.01）. The optimum conditions for a 2 mm slice thickness chips making are vacuum frying at 100 ℃ for 3 minutes. The chips moisture lost followed generally a two-stage of falling rate pattern during vacuum frying, and each could be well predicted by an exponential equation （R2 = 0.99）.

Carbon Monoxide Exposure during Cooking in Households： A Case of Dares Salaam City, Tanzania

Exposure to CO （carbon monoxide） during cooking in households using LPG （liquefied petroleum gas）, natural gas and charcoal as fuels has been conducted. The study aimed at assessing the indoor air quality in order to address potential hazards associated with CO. Carbon monoxide concentrations and flame temperature were measured at an interval of 1 min for 1 h using CO and thermometer data loggers respectively. While the CO concentration from LPG and natural gas were found below 26 ppm for 1 h, as recommended by WHO （World Health Organization） standards, the average CO concentration from charcoal exceeded the standard limit. In addition closing the kitchen door during cooking increased the CO concentration from 26-295 ppm to 92-597 ppm. According to WHO, the observed CO concentrations from charcoal stove highlights questionable life support atmosphere. It can therefore be suggested that switching to LPG or natural gas from charcoal will reduce CO exposure to persons during cooking.

The Spatial Optimization of Eastern China's Crude Oil Pipeline Network upon Cost Minimum

Eastern China＇s crude oil pipeline network is of the largest scale and freight volume in China.Here,we analyze 37 oil pipelines and one railway（38 oil flow channels）,20 oil fields with output of over a million tons of crude oil,and 32 refineries each of which refine over a million tons of crude oil.We construct a supply and demand balance sheet of oil sources and sinks by considering the transportation cost variance of variant pipeline diameters to determine the spatial optimization of Eastern China＇s pipeline network.In 2009,the optimal cost of this network was 34.5% lower than the total actual cost,suggesting that oil flow is overall inefficient and there is huge potential to improve flow efficiency.Within Eastern China,the oil flow of the Northeast network was relatively better than others,but the flow in Northern China is inefficient because all pipelines are underload or noload,and there were similar conditions in the Huanghuai region.We assumed no difference in pipeline transport speed,compared to rail or road transportation,thus transportation distance,rather than time,is the main influential factor under the definite transporting cost of variant pipeline diameters.