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.

Measurement and Prediction of Vapor Pressure for H20 ＋ CHaOH] C2HsOH ＋ [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.

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.

Evaluation of working fluids for organic Rankine cycles using group-contribution methods and second-law-based models

The group-contribution (GC) methods suffer from a limitation concerning to the prediction of process-related indexes, e.g., thermal efficiency. Recently developed analytical models for thermal efficiency of organic Rankine cycles (ORCs) provide a possibility of overcoming the limitation of the GC methods because these models formulate thermal efficiency as functions of key thermal properties. Using these analytical relations together with GC methods, more than 60 organic fluids are screened for medium-low temperature ORCs. The results indicate that the GC methods can estimate thermal properties with acceptable accuracy (mean relative errors are 4.45%-11.50%);the precision, however, is low because the relative errors can vary from less than 0.1% to 45.0%. By contrast, the GC-based estimation of thermal efficiency has better accuracy and precision. The relative errors in thermal efficiency have an arithmetic mean of about 2.9% and fall within the range of 0-24.0%. These findings suggest that the analytical equations provide not only a direct way of estimating thermal efficiency but an accurate and precise approach to evaluating working fluids and guiding computer-aided molecular design of new fluids for ORCs using GC methods.

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.

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.

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.

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.

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

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。

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。

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。

基于砂浆流变性能的自密实混凝土制备方法研究

通过测定机制砂掺量、胶砂比和粉煤灰掺量因素下砂浆剪切应力随着剪切速率的变化规律,根据宾汉姆流体模型线性拟合,结果得到的屈服应力和塑性黏度指导砂浆组分优化,并基于砂浆-粗骨料两相悬浮原理制备自密实混凝土(SCC)。试验结果表明:混合使用超细砂与机制砂、增大胶砂比及掺入粉煤灰都可以有效地改善砂浆流变性,制备强度等级为C50的SCC时,机制砂用量为40%、胶砂比为1.0、粉煤灰掺量为30%的砂浆具有较小的屈服应力和适宜的塑性黏度,其对粗骨料的动力传输能力及包裹性也最佳,制备的SCC表现出优良的工作性能。

基于水动力空化的微通道设备研究进展

针对微通道设备中的水动力空化现象,从限流元件的几何形状及尺寸、工作流体和通道粗糙度3个方面分析了其影响规律.限流元件的常见形状主要有微孔、微文丘里、微隔膜和微柱,不同几何形状的限流元件具有不同的空化流动特性;限流元件自身的尺寸参数以及尺寸缩小引起的尺度效应都对空化流型起着重要作用.常用的工作流体包含去离子水、乙醇、磷酸盐缓冲盐水(PBS)、制冷剂(R-123)、聚乙烯醇(PVA)微泡(MBs)悬浮液、全氟戊烷(PFC5)悬浮液、二氧化钛(TiO_(2))纳米颗粒悬浮液、多元液体混合物等;与水相比,其余工作流体均不同程度地提高了空化强度.粗糙度的引入主要体现于通道的表面粗糙元件和侧壁粗糙元件,其空化强度相较于光滑表面得到明显提高.微通道水动力空化设备主要应用于能量收集、液相剥离和生物医学领域.基于近年来国内外对微尺度水动力空化的研究现状,设想了微通道设备中的水动力空化现象的潜在研究方向及应用趋势.

叠合式有机朗肯循环的热力学分析

针对有机朗肯循环(ORC)中传热过程对循环性能的影响,该文提出一种既相似但又区别于混合工质,各工质独立运行的叠合式有机朗肯循环(AORC)。AORC中,各工质进行串/并联的叠合换热,可形成类似于非共沸混合工质的温度滑移。由于各工质独立运行,使得叠合工质的温度滑移量可进行调节,以减小与外界热/冷源的传热温差,提高传热匹配性以及循环性能。以两种工质叠合的AORC为例进行循环性能分析,并与常规ORC进行对比。结果表明,AORC并不是各工质基本ORC的简单线性叠加,而是一种优化叠加。相比常规ORC,AORC的净输出功率最大可提升34.48%。但当热源温度高于高温工质的热源转折温度时,AORC趋近于高温工质的基本ORC。

深层地热能丛式多分支U型井采热技术及传热算法

深层地热能是一种分布广、资源量大具有发展前景的可再生新能源,当前的主要开采方法有增强型地热系统(EGS)、环绕式井筒换热系统(AGS)、断层带流体循环开采和同轴套管开采法,但存在采热功率不稳定、地震风险高和采热效率低等难题。针对当前深层地热开采技术面临的瓶颈问题,本文以开采过程只有能量交换而没有物质交换为原则,以深层干热岩地热规模化可持续稳定开发为目标,提出了深层地热能丛式多分支U型井采热方法(UMW-DGS)及关键技术,在此基础上建立了井筒轴对称热传导模型,以青海共和盆地恰卜恰深部干热岩储层为背景,提出了高温高压岩石热导率测试新方法,计算了在定井径条件下井周温度场和采热功率的时空演化规律,分析了温度差、热导率和井径等3个敏感因素对采热功率的影响。此外,针对UMW-DGS定解问题,研发了基于有限体积法(FVM)的三维热流固耦合数值算法,研究了UMW-DGS单水平井段换热效率和在不同泵注量条件下温度场时空演化。通过分析不同流量的有效换热量、换热时长和功率发现:泵注流量的增加会导致有效换热能量和有效换热时长的降低,并且使有效换热功率先增加后减少。研究结果表明,深层地热能开发需要在平衡换热温度和功率的条件下设计注入排量,从而得到最优的换热效果。

串联双级蒸发有机朗肯循环系统的多目标优化及工质优选

为了探究串联双级蒸发有机朗肯循环系统在特定工况下的最佳混合工质,选取了3组不同特性的混合工质,即R21/R113、R1234ze/R141b和R227ea/R245fa,引入热力学性能指标、经济指标和环境指标,利用非支配排序遗传算法进行多目标优化.通过求解Pareto边界,采用3种决策方法对每组工质流体进行最优解的选择,根据偏移量选取最优决策方法.结果表明:在热源温度为150℃、冷源温度为15℃的工况下,混合工质R1234ze/R141b最优解的[火用]效率相对较高,平准化度电成本(levelized cost of energy, LCOE)和当量二氧化碳排放量(equivalent carbon emission, ECE)相对也较低,热源温度也适配,为该工况下较为合适的混合工质.