Design and optimization of fluid lubricated bearings operated with extreme working performances——a comprehensive review

Fluid lubricated bearings have been widely adopted as support components for high-end equipment in metrology,semiconductor devices,aviation,strategic defense,ultraprecision manufacturing,medical treatment,and power generation.In all these applications,the equipment must deliver extreme working performances such as ultraprecise movement,ultrahigh rotation speed,ultraheavy bearing loads,ultrahigh environmental temperatures,strong radiation resistance,and high vacuum operation,which have challenged the design and optimization of reliable fluid lubricated bearings.Breakthrough of any related bottlenecks will promote the development course of high-end equipment.To promote the advancement of high-end equipment,this paper reviews the design and optimization of fluid lubricated bearings operated at typical extreme working performances,targeting the realization of extreme working performances,current challenges and solutions,underlying deficiencies,and promising developmental directions.This paper can guide the selection of suitable fluid lubricated bearings and optimize their structures to meet their required working performances.

A Review on Technologies for the Use of CO2 as a Working Fluid in Refrigeration and Power Cycles

The use of carbon dioxide as a working fluid has been the subject of extensive studies in recent years, particularly in the field of refrigeration where it is at the heart of research to replace CFC and HCFC. Its thermodynamic properties make it a fluid of choice in the efficient use of energy at low and medium temperatures in engine cycles. However, the performance of transcritical CO2 cycles weakens under high temperature and pressure conditions, especially in refrigeration systems;On the other hand, this disadvantage becomes rather interesting in engine cycles where CO2 can be used as an alternative to the organic working fluid in small and medium-sized electrical systems for low quality or waste heat sources. In order to improve the performance of systems operating with CO2 in the field of refrigeration and electricity production, research has made it possible to develop several concepts, of which this article deals with a review of the state of the art, followed by analyzes in-depth and critical of the various developments to the most recent modifications in these fields. Detailed discussions on the performance and technical characteristics of the different evolutions are also highlighted as well as the factors affecting the overall performance of the systems studied. Finally, perspectives on the future development of the use of CO2 in these different cycles are presented.

CAD/CAE OF THE WORKING CHARACTERISTICS OF A NEW TYPE OF FLUID COUPLING SHOCK ABSORBER

For purpose of simulation of the working characteristics of a new type offluid coupling shock absorber for vibration protection of sensitive equipment, a physical model ispresented by analyzing the internal fluid dynamic phenomenon with respect to the coupling shockabsorber and implemented in MATLAB software package. Using the model it is possible to evaluate theimportance of different factors for design of the shock absorber. In the meantime, the key-modelmachine is designed for coupling dynamic test. Comparisons with experimental results confirm thevalidity of the model. So the CAD/CAE software has been developed in MATLAB for design andexperimental test of the new coupling shock absorber.

Effects of ORC Working Fluids on Combined Cycle Integrated with SOFC and ORC for Stationary Power Generation

The purpose of this study is to explore the effects of working fluid on conventional combined cycle integrated with pressurized solid oxide fuel cell (SOFC) and waste heat recovery organic Rankine cycle (ORC) for stationary utility power generation. The mathematical model of a natural gas fueled design configuration is developed in Matlab and Simulink and simulated with 14 working fluids. The effluent gases of SOFC undergo combustion in the combustion chamber and it is utilized in the gas turbine, steam turbine cycle and ORC. The model is compared with those found in literature and the parametric studies of temperature, flow rate, fuel utilization factor and exhaust gas on the system efficiency are examined. Results revealed that working fluids show a closely related behavior in efficiency at low pressure ratio and high flow fraction, fuel utilization, and temperature. R-123 was found to perform the best among 14 working fluids studied, yielding a system energy efficiency of 70% in the combined cycle integrated with SOFC and ORC.

Tribological Properties and Machining Performance of Vegetable Oil Based Metal Working Fluids—A Review

Lubricants are playing an important role in world industrial and economic development, mainly by reducing friction and wear in mechanical contacts. The outlook for eco-friendly MWFs for the next decade is 15% of global volume share. Due to ever increasing demand for environmentally acceptable products suitable for use as MWFs, vegetable oil-based MWFs are drawing the attention of researchers across the globe. Owing to the desirable properties of vegetable oils as cutting fluids, vegetable oil-based cutting fluids play an important role in conserving the environment by means of sustainability. This paper focuses on various vegetable oil being developed to promote biodegradable MWFs across the world. The performance of vegetable oils with respect to cutting and thrust force, tool wear, temperature, surface roughness in turning, drilling, milling and grinding a wide variety of materials are studied and reported. The review also throws light on the tribological behavior of vegetable oils that influence the lubricity in Metal working process. The review reveals that vegetable oils offer an alternative, eco-friendly and sustainable MFWs for the future of manufacturing.

Measurement and Prediction of Vapor Pressure for H20 ＋ CH3OH] C2H5OH ＋ [BMIM][DBP] Ternary Working Fluids

The ionic liquid, 1-butyl-3-methylimidazolium dibutylphosphate ([BMIM][DBP]) was prepared and the vapor pressures of three set of binary solutions H2O(1)/CH3OH(1)/C2H5OH(1) + [BMIM][DBP](2) were measured at different temperature and in the ILs mole fraction range from 0.1 to 0.6 with a static equilibrium apparatus. The measured vapor pressures were correlated with Non-Random Two Liquid (NRTL) activity coefficient model and the average relative deviations (ARD) between experimental and correlated vapor pressures for these binary solutions were 3.19%, 2.42% and 2.95%, respectively. Then, the vapor pressures of two set of ternary solutions H2O(1) + CH3OH(2)/C2H5OH(2) + [BMIM][DBP](3) were measured with an inclined boiling apparatus and further predicted with NRTL activity coefficient model based on the binary interaction parameters coming from fitting the vapor pressures of the binary solutions. The results indicated that the ternary solutions containing [BMIM][DBP] were shown a strong negative deviation from Raoult's Law when the mole fraction of [BMIM][DBP] was larger than 0.2, which meant that ternary solutions could absorb the refrigerant vapors at the same or below solution temperature. Meanwhile, the average relative deviations between experimental and predicted vapor pressures for ternary solutions were 2.92% and 3.06%, respectively. Consequently, the NRTL active coefficient model used for non-electrolyte solutions was still valid for predicting vapor-liquid equilibrium of binary or ternary solutions containing ILs.

Selection of organic Rankine cycle working fluid based on unit-heat-exchange-area net power

To improve energy conversion efficiency, optimization of the working fluids in organic Rankine cycles(ORCs) was explored in the range of low-temperature heat sources. The concept of unit-heat-exchange-area(UHEA) net power, embodying the cost/performance ratio of an ORC system, was proposed as a new indicator to judge the suitability of ORC working fluids on a given condition. The heat exchange area was computed by an improved evaporator model without fixing the minimum temperature difference between working fluid and hot fluid, and the flow pattern transition during heat exchange was also taken into account. The maximum UHEA net powers obtained show that dry organic fluids are more suitable for ORCs than wet organic fluids to recover low-temperature heat. The organic fluid 1-butene is recommended if the inlet temperature of hot fluid is 353.15-363.15 K or443.15-453.15 K, heptane is more suitable at 373.15-423.15 K, and R245 ca is a good option at 483.15-503.15 K.

Analysis on optimal working fluid flowrate and unstable power generation for miniaturized ORC systems

For efficient utilization of a limited geothermal resource in practical projects,the cycle parameters were comprehensively analyzed by combining with the heat transfer performance of the plate heat exchanger,with a variation of flowrate of R245 fa.The influence of working fluid flowrate on a 500 W ORC system was investigated.Adjusting the working fluid flowrate to an optimal value results in the most efficient heat transfer and hence the optimal heat transfer parameters of the plate heat exchanger can be determined.Therefore,for the ORC systems,optimal working fluid flowrate should be controlled.Using different temperature hot water as the heat source,it is found that the optimal flowrate increases by 6-10 L/h with 5 ℃ increment of hot water inlet temperature.During experiment,lower degree of superheat of the working fluid at the outlet the plate heat exchanger may lead to unstable power generation.It is considered that the plate heat exchanger has a compact construction which makes its bulk so small that liquid mixture causes the unstable power generation.To avoid this phenomenon,the flow area of plate heat exchanger should be larger than the designed one.Alternatively,installing a small shell and tube heat exchanger between the outlet of plate heat exchanger and the inlet of expander can be another solution.

Heat Transfer Characteristics of Work Fluid Including Phase Change Material That Flow into Heating Surface from Narrow Path

Use of the low temperature (less than 100°C) energy contributes to effective use of heat resources. The cost recovery by power generation is difficult by using an existing system (the binary cycle or the thermoelectric conversion element), because the initial investment is large. The final purpose of this research is development of the low temperature difference drive engine supposing use in a hot-springs resort as a power source for electric power generation. In order that a traveler may look at and delight a motion of an engine, it is made to drive at low-speed number of rotations. An engine cycle of this study is aimed at the development of Stirling cycle engine which can maintain high efficiency in small size. This kind of engine has simple structure;it brings low cost, and it is easy to perform maintenance. However, it is difficult to obtain enough output by this type of engine, because of its low temperature difference. This paper deals with the heat transfer characteristic that the working fluid including a phase change material flows into the heating surface from the narrow path. In order to increase the amount of the heat transmission, Diethylether is added to the working fluid. Diethylether is selected as a phase change material (PCM) that has the boiling point which exists between the heat source of high temperature and low temperature. The parameters of the experiment are additive amount of PCM, rotational speed of the displacer piston and temperature of heat transfer surface. It is shown that it is possible to make exchange of heat amount increase by adding phase change material. The result of this research shows the optimal condition of the difference in temperature in heat processing, number of revolutions, and addition concentration of PCM.

MY WORK IN THE FIELD OF FLUID MECHANICS

I graduated from the National Peiyang University (now called Tianjin University) in 1950, majoring in hydraulic engineering. Starting from 1952, my teaching work was basically in mechanics.My first academic probe was in cybernetics, resulting in the publication of the first Chinese paper concerning optimal control. After 1963, I worked on the theory of hydrodynamic stability. My explorative thrust is at the eigenvalues of the Orr Sommerfeld Equation,a non-self adjoint problem in

基于过程解耦和工质物性的有机朗肯循环性能分析

通过对有机朗肯循环工作过程的拆分解耦,利用工质物性中的临界温度、偏心因子结合循环参数推导其热力学性能表征式,进而建立循环的热力学模型,并借助该模型分析循环参数对循环热力学性能评价指标的影响规律。研究结果显示:当蒸发温度升高时,循环热效率会增大,但其净输出功和效率先增大,然后再降低;当冷凝温度升高时,循环的热效率、净输出功和效率都会下降;当过热度升高时,循环的净输出功和效率随过之降低,而循环的热效率随之增大。基于工质物性引入雅各布数,循环的净输出功和热效率随雅各布数的增大分别呈现出增大和减小的趋势,而临界温度越高热效率随之升高。

天然气井井筒解堵工作液的研究进展

通过文献调研,分析了各种井筒解堵工作液的解堵机理,综述了各类型常用井筒解堵工作液的应用进展及优缺点;介绍了有机解堵工作液、有机缓释微乳酸解堵工作液、复合型解堵工作液等新型解堵工作液的研究进展;分析了解堵工作液在制备与实际应用过程中存在的问题,并提出了未来解堵工作液的发展趋势。

自复叠制冷技术研究进展

自复叠制冷技术在低温领域的应用十分广泛。本文首先介绍了自复叠制冷技术的原理,并与单级压缩、多级压缩及复叠制冷技术进行比较,指出了自复叠制冷技术具有结构简单、制冷温区宽的优势。从自复叠制冷系统的循环特性、混合工质的选择和配比优化、系统流程优化三方面,对当前自复叠制冷技术的研究进行分析总结。最后,展望该技术的发展前景,为拓宽该技术的应用提供参考。

微小型压缩空气储能系统用涡旋压缩机流动特性研究

以空气为工质,基于计算流体动力学方法,对无油空气涡旋压缩机在变工况运行条件下进行了三维非稳态数值模拟。研究发现:动静涡旋齿之间存在的径向间隙,会使得压缩机工作腔内温度、流速和压力的分布不规律;增大转速,不但可以增加涡旋压缩机的质量流量,而且还可以减小切向泄漏量,进而提高压缩机的工作效率;排气压力过大,会降低涡旋压缩机的基本输出性能;在低转速下,过高的排气压力会使得压缩机排气口出现“净回流”现象。

基于人工神经网络的工质基础物性预测

烃类及卤代烃是制冷及余热发电等热力学循环系统潜在的理想工质,但其数量繁多且多数物性参数未知,建立准确的物性预测模型对新型工质的开发至关重要。从多个公开数据库中收集了2500多种烃类及卤代烃分子(含C,H,F,Cl)的基础物性参数,包括正常沸点(T_(b))、临界温度(T_(c))、临界压力(p_(c))、偏心因子(ω),构建了一个工质物性数据库;进一步,通过改进基团贡献-人工神经网络(GC-ANN)的方法,模型的输入参数除基团频率外,还加入相对分子质量、T_(b)、约化维纳指数,建立了预测烃类及卤代烃分子T_(b),T_(c),p_(c),ω的神经网络模型,所开发模型的预测误差小于传统的GC-ANN的误差。

空载湿式离合器临界碰摩转速影响机理分析

定义空载湿式离合器摩擦片/钢片的周期无量纲轴向位移范围λ,根据其值确定湿式离合器的临界碰摩转速。通过分析润滑油温度、供油流量、摩擦副间隙与特征量λ变化趋势的关系,得到工况参数对湿式离合器临界碰摩转速的影响规律。从力学角度出发,分析流场刚度和阻尼的变化规律,探寻摩擦片/钢片三自由度运动的影响因素,在此基础上提出流场临界刚度和临界阻尼的概念,揭示湿式离合器工况参数对其临界碰摩转速的影响机理,并进行了试验验证。研究结果表明:润滑油温度升高或摩擦副间隙增大会导致流场中的交叉刚度系数和交叉阻尼系数变大,湿式离合器的临界碰摩转速降低;供油流量增大会导致流场中的交叉刚度系数和交叉阻尼系数减小,湿式离合器的临界碰摩转速升高。

高性能密胺降滤失剂的研究

用多聚甲醛与三聚氰胺合成了密胺树脂,对经黏土改性后的丙烯酰胺类聚合物进行包覆,制备了一种抗温抗盐的钻井液降滤失剂。采用单因素实验对样品的加量及耐温耐盐性能进行了评价,实验结果表明,2号样品的性能最佳。在盐浓度为8%的钻井液中,加量为1.5%时,经100℃老化后,2号样品的加量比对照样品减少3%,滤失率为77.7%,性能更优良。

基于工况特征的高速插齿机静压主轴润滑特性研究

针对高速插齿机静压主轴在实际工况特征下存在润滑特性不明晰的问题,以摩擦学和流体力学理论为基础,采用有限元仿真法建立不同受载状态下的静压主轴流体仿真模型及流固耦合模型,基于实际工况特征探究不同工况参数下静压主轴的润滑特性变化规律。结果表明,油膜承载力、主轴轴套变形量及黏性阻力随径向增大而增加,而油膜刚度则是随径向载荷增大先减小后增加。轴套最大变形位置随径向载荷增大而不同。在相同径向载荷下,主轴冲程速度对油膜承载力基本无影响而黏性阻力随冲程速度增大而增加。增大供油压力可显著提高静压主轴承载性能但轴套最大变形量也有明显增大,同时会改变油液流动方向进而加剧油膜黏性剪切应力集中现象,最终使得应力集中区域油膜破裂出现润滑失效现象。

液化天然气冷能回收系统的设计与优化分析

液化天然气(LNG)在气化过程中释放的冷能通常未被有效利用。提出了制冷与发电相结合的LNG冷能回收系统,可以有效地回收LNG冷能。该系统的结构包括两级有机朗肯循环(ORC)、空调(AC)和直接膨胀循环(DEC)。利用HYSYS软件,对系统性能进行了模拟分析,采用遗传算法(GA)对系统中四元混合工质(甲烷、乙烷、丙烷和异丁烷)配比、蒸发压力、冷凝压力和一级膨胀压力进行了优化,随后对优化方案进行了经济性评价。结果表明,两级ORC最佳的四元混合工质配比(质量分数)前级为28.9%、57.3%、5.5%和8.3%,后级为0.4%、20.3%、56.4%和22.9%。优化方案中,系统的净输出功率可达218.28 kW,LNG冷能利用率、热效率和㶲效率分别为54.69%、20.89%和41.18%。系统具有良好的经济可行性,经济收益可达160.30×10^(4) CNY,设备的总投资成本为1215.91×10^(4) CNY,平均能源成本为0.63 CNY/(kW·h),预计7.59 a内可收回投资成本。