Effect of Ultra-low Temperature on Carbonation Performance of SFRRC and Prediction Model

Through the rapid carbonation test of SFRRC with different fiber volume fractions at ultralow temperature,the influence of ultra-low temperature damage on the carbonation resistance of SFRRC was analyzed,which provides a theoretical basis for the application of SFRRC in ultra-low temperature engineering.The experimental results show that ultra-low temperatures can significantly weaken the carbonization resistance of SFRRC.When the temperature reaches 160℃,the carbonization depth increases by 67.66%compared with the normal state.The proper amount of steel fiber has an evident influence on the carbonation resistance of the material.However,when the addition amount exceeds the optimum content,the carbonation resistance of the material decreases.The grey prediction model established by constructing the original sequence can reasonably predict the carbonation resistance of SFRRC after ultra-low temperatures.

ExperimentonPerformanceofLow-TemperatureExhaustSteamReclamation

针对不同的喉嘴距、面积比，实验研究了不同的进水压力、进水温度和出水压力对低温乏汽回收利用装置性能的影响规律．发现在进水压力为0．14～O．50MPa、进水温度为23～60℃、出水压力为0．096-0．110MPa，以及4种喉嘴距、3种面积比的实验条件范围内，随着喉嘴距和面积比的增加，加热温升和流量比先增大后减小，得到最佳归一化喉嘴距L=4．50，以及最佳面积比m=6．25，使得加热温升和流量比最大．同时，加热温升和流量比均随着进水压力和进水温度的增加而减小，当出水压力升高时，装置性能变差，加热温升和流量比均减小．

Innovation for forming aluminum alloy thin shells at ultra-low temperature by the dual enhancement effect

Integral thin shells made of high strength aluminum alloys are urgently needed in new generation transportation equipment. There are challenges to overcoming the co-existing problems of wrinkling and splitting by the cold forming and hot forming processes. An innovative technology of ultra-low temperature forming has been invented for aluminum alloy thin shells by the new phenomenon of ‘dual enhancement effect’. That means plasticity and hardening are enhanced simultaneously at ultra-low temperatures. In this perspective, the dual enhancement effect is described, and the development, current state and prospects of this new forming method are introduced. This innovative method can provide a new approach for integral aluminum alloy components with large size, ultra-thin thickness, and high strength. An integral tank dome of rocket with 2 m in diameter was formed by using a blank sheet with the same thickness as the final component, breaking through the limit value of thickness-diameter ratio.

Anisotropic Rock Poroelasticity Evolution in Ultra-low Permeability Sandstones under Pore Pressure,Confining Pressure,and Temperature:Experiments with Biot's Coefficient

This study aimed to show anisotropic poroelasticity evolution in ultra-low permeability reservoirs under pore pressure,confining pressure,and temperature.Several groups of experiments examining Biot's coefficient under different conditions were carried out.Results showed that Biot's coefficient decreased with increased pore pressure,and the variation trend is linear,but the decreasing rate is variable between materials.Biot's coefficient increased with increased confining pressure;the variation trend is linear,but the increasing rate varies by material as well.Generally,Biot's coefficient remains stable with increased temperature.Lithology,clay mineral content,particle arrangement,and pore arrangement showed impacts on Biot's coefficient.For strong hydrophilic clay minerals,expansion in water could result in a strong surface adsorption reaction,which could result in an increased fluid bulk modulus and higher Biot's coefficient.For skeleton minerals with strong lipophilicity,such as quartz and feldspar,increased oil saturation will also result in an adsorption reaction,leading to increased fluid bulk modulus and a higher Biot's coefficient.The study's conclusions provide evidence of poroelasticity evolution of ultra-low permeability and help the enhancing oil recovery(EOR)process.

Retrofit of 350-MW Supercritical Boiler Based on the Analysis on Exhaust Gas Temperature

Since the first batch of 350-MW supercritical utility boilers was put into operation, the exhaust flue gas temperature of the boilers has always been higher than the designed value. The main reason is that the heat absorbed by the air heater is not sufficient. In Huaneng Dongfang Power Plant, the exhaust flue gas temperature is lowered through modifications to the economizer and the air heater. The experimental results reveal that every year, each boiler could save 3 850 tons of standard coal and reduce 85 tons of SO2 and 9 000 tons of CO2 respectively after retrofit.

Correlation of Performance, Exhaust Gas Temperature and Speed of a Spark Ignition Engine Using Kiva4

The objective of this study was to investigate performance characteristics of a spark ignition engine, particularly, the correlation between performance, exhaust gas temperature and speed, using Kiva4. Test data to validate kiva4 simulation results were conducted on a 3-cylinder, four-stroke Volkswagen (VW) Polo 6 TSI 1.2 gasoline engine. Three different tests were, therefore, carried out. In one set, variations in exhaust gas temperature were studied by varying the engine load, while keeping the engine speed constant. In another test, exhaust gas temperature variations were studied by keeping the engine at idling whilst varying the speeds. A third test involved studying variations in exhaust gas temperature under a constant load with variable engine speeds. To study variations in exhaust gas temperatures under test conditions, a basic grid/mesh generator, K3PREP, was employed to write an itape17 file comprising of a 45° asymmetrical mesh. This was based on the symmetry of the combustion chamber of the engine used in carrying out experimental tests. Simulations were therefore performed based on the input parameters established in the conducted tests. Simulations with the kiva4 code showed a significant predictability of the performance characteristics of the engine. This was evident in the appreciable agreement obtained in the simulation results when compared with the test data, under the considered test conditions. A percentage error, between experimental results and results from simulations with the kiva4 code of only between 2% to 3% was observed.

Novel Cascade Refrigeration Cycle for Cold Supply Chain of COVID-19 Vaccines at Ultra-Low Temperature -80°C Using Ethane (R170) Based Hydrocarbon Pair

Several media report highlight on that the pharmaceutical companies require ultra-low temperatures -80°C to transport and store its COVID-19 vaccines. This research presents the thermodynamic analysis on cascade refrigeration system (CRS) with several refrigerant pairs which are R32/R170, R123/R170, R134a/R170, R404A/R170, R407c/R170, R410/R170, and the hydrocarbon (HC) refrigerant pair Propane/Ethane, namely R290/R170. Besides, the results of R22/R170 pair, which is not recommended to be used due to phase out of R22 as per Montréal Protocol, are included as base case to compare the novel hydrocarbon pairs in CRS and the old trend of refrigerant pairs. Thermodynamic properties of all these pairs were investigated and compared under different intermediate temperature used in CRS heat exchanger, which thermally connected both the Low and High temperature cycles (LTC) and (HTC). By applying the first law of thermodynamics, the coefficients of performance (COPs) and the specific power consumptions (SPC) in kW/TR are presented and compared. In addition, by applying the second law of thermodynamics the exergetic efficiencies were estimated. The results reveal the promising opportunity of using the HC pair (R290/R170). The minimum SPC in kW/TR is recorded for the pair R123/R170. One the other hand, the highest exegetic efficiency values are observed to be 40%, 38%, and 35% for the pairs R123/R170, R290/R170, and R134/R170, respectively. This research concludes that the HC pair (R290/R170) is highly recommended for CRS applications either to transport the COVID-19 or store it in cold storage rooms in hospitals and clinics. All precautionary measures should be carefully applied in design and operation of HC pair (R290/R170) due to its flammability hazard.

Effects of tungsten on the oxidation resistance and high-temperature strength of 18CrNbTi ferritic stainless steel

18CrNbTi ferritic stainless steel is a low-cost material mainly used for the fabrication of manifolds, which usually work at temperatures below 950℃. With the development of engine technology, exhaust manifolds tend to work above 1 000 ℃ and this may be even higher in the future. For developing a new kind of steel to satisfy these requirements,the effects of tungsten （W）addition on the high-temperature strength and oxidation resistance of 18CrNbTi ferritic stainless steel are discussed in this study. The test results show that W enhances high-temperature strength at 1 000 ℃ and significantly improves oxidation resistance. However, W addition tends to degrade oxide layer adhesion,causing spalling during alternate hot and cold conditions.

High-temperature oxidation behavior of austenitic stainless steel Cr20Ni12Si2RE

Austenitic stainless steel Cr20 Ni12 Si2 RE was developed for use in hot-end components of automobile exhaust systems,especially in automobiles designed according to the China VI emission standard. The hightemperature oxidation kinetic curve of Cr20 Ni12 Si2 RE at 1 050 ℃ was obtained using the weighting method. The oxidation curves exhibit the parabolic law at 1 050 ℃; after 250 h of oxidation,the mass gain was 22 g/m^2. The morphology,structure,and composition of the oxide film were examined using scanning electron microscopy and Xray diffraction methods. A thin,stable,and dense spinel oxide film obtained after 250 h of oxidation at 1 050 ℃ was mainly composed of( Mn_(0.87)Fe_(0.13))( Mn_(0.13)Fe_(0.87)Cr) O_4 and Cr_2 O_3 with a silicon-containing oxide underneath. The addition of rare earth elements was found to restrict further diffusion of metallic atoms from the austenite toward the oxide film,and consequently,led to a low growth rate of the oxide film. The inner silicon-containing oxide was produced by the diffusion of oxygen atoms and enhanced the coherent strength of the oxide film.

冷却通道对引射器红外辐射特性影响的研究

为降低燃气轮机排气系统中的引射器排气温度,从而减少排出燃气的红外辐射强度,本文提出了一种具有冷却通道的亚音速引射器结构,并提出了评价冷却通道引射器的综合系数。在原有的引射器喷嘴内增加冷却通道,使冷气直接与主流中心位置的高温气体掺混,破坏排气包覆性分布,达到提高主流温度均匀性、降低中心温度的目的。本文运用数值模拟的方法,研究引射器内冷却通道数量、冷却通道进深和排气通道的排布对引射器内阻力特性、换热特性、出口温度分布特性的综合影响。研究结果表明:单排冷却通道排布时,通道数量与换热特性成正比,与阻力损失成反比;双排冷却通道排布时,阻力损失降低。双排12通道引射器可有效降低出流总温,均匀主流温度,综合系数最高。

电控放气阀涡轮增压器在柴油机上的试验研究

在一台满足国六b阶段排放标准的柴油机上,开展电控放气阀涡轮增压器对发动机性能、排放影响的试验研究。试验验证表明:发动机匹配电控放气阀涡轮增压器在发动机中高转速工况对油耗有一定改善,在中低负荷工况能降低油耗、提高排气温度。通过电控放气阀开度特性优化并确定最优的控制参数,在WHTC循环SCR催化器平均温度从226℃提升到246℃,冷态WHTC循环NOx排放降低25%,冷热加权NOx排放降低8.6%。

EGR技术对生物柴油混合燃料发动机性能的影响研究

为缓解柴油掺烧生物柴油导致的NO_(x)排放过高问题,将4190ZLC船用中速柴油机作为试验台架,通过AVL_FIRE软件建立燃烧室模型,并验证该模型准确性。设置生物柴油掺混比0~40%等4组变量,EGR率0~12.5%等4组变量,进行柴油机燃烧、性能和排放分析。结果表明,掺烧适量生物柴油能够降低柴油机缸内温度,降低Soot排放,但同时会导致NO_(x)排放明显升高;EGR的引入能够实现低温燃烧,显著降低NO_(x)排放,但EGR率过高会增加Soot排放。生物柴油掺混比B40、EGR率12.5%组合NO排放比原机降低47.7%,Soot排放质量分数比原机降低98.13%。本文结果将为柴油掺混生物柴油燃烧并结合EGR技术提供一定的研究方向。

造纸机干燥部排风系统节能优化设计研究

为实现针对造纸机干燥部排风系统的节能优化,降低造纸企业的生产经营成本,收集了某造纸企业提供的干燥部信息管理系统数据并建立了服务于排风系统节能优化的弹性网络模型。通过该模型对干燥部排风系统内各个排风机的排风温湿度进行预测,发现弹性网络模型对排风机排风温湿度的预测效果显著优于支持向量回归模型。因此,基于弹性网络的节能优化模型应用于110 g/m^(2)红杉纸、90 g/m^(2)挂面箱板纸、120 g/m^(2)挂面箱板纸等3条产品线的排风系统参数调节工作中。根据生产应用结果发现,3条纸张产品生产线经过参数调节后的吨绝干纸干燥成本依次下降了0.72%、0.68%、1.07%,体现出了较为理想的节能优化效果。

基于冲击的涡扇发动机退化建模与下发预测

为解决多性能参数模型无法描述不同起飞推力下发动机性能退化的问题,利用单性能参数结合极端冲击模型描述起飞时发动机全功率运转对热端部件的热冲击影响,利用线性退化模型描述发动机自然退化过程,建立发动机性能可靠度退化模型。利用V2500发动机全寿命EGTM数据,结合最大似然估计给出性能可靠度表达式与模型参数,最后利用机队中同型V2500发动机非完整EGTM数据验证模型,预测下发时间,结果表明此模型预测下发时间和实际下发时间的误差小于3%,证明了模型的有效性。

某核电厂电气仪控房间火灾排烟温度分析

对某核电厂电气厂房的2个电气仪控房间进行了火灾排烟温度模拟分析。模拟计算了排烟系统不同时刻启动时,这2个防火空间室内空气温度的变化情况。结果表明:排烟系统启动后房间空气温度迅速降低,然后逐渐升高,最后随着火灾热释放速率的降低而逐渐降低;对于手动启动的排烟系统,需及时启动才能有效排除火灾中的烟气;需合理设置排烟防火阀,以保护排烟风机等。

不同尾气热管理策略对当量天然气发动机WHTC循环排放的影响

国六天然气发动机采用等当量燃烧结合外部冷却EGR及TWC的排放控制技术路线,TWC的转化效率是保证发动机排放达标的重要因素,而催化器的入口温度是决定TWC转化效率高低的最重要影响参数之一。然而,在冷起动阶段及排气管路温降较大的情况下,存在TWC入口尾气温度难以满足发动机及整车排放高效转化需求的问题。针对该问题,在一台4.5 L排量的发动机和一辆搭载该发动机的城市环卫车上探究不同尾气热管理策略对发动机WHTC循环排放及整车作业循环排放的影响。研究结果表明:采用起动快速温升的尾气热管理策略,能有效提高冷起动阶段发动机尾气温度,WHTC循环的TWC入口温度达到300℃所需时间缩短了300 s,显著降低了NO_(x),CH 4和CO循环排放,降幅分别达到38.5%,38.5%和5.8%;采取在TWC上增加金属载体前级方案的尾气控制策略,WHTC循环的NO_(x),CH 4和CO循环排放分别降低了62.2%,42.8%和15.7%;采用对整车排气尾管包裹的尾气热管理策略,在整车作业循环工况下,TWC入口温度相比采用普通石棉包裹的方案提高了近200℃,使得NO_(x)瞬时排放值30 s平均值的最大值降低了60.9%,能更好地满足北京第六阶段的排放法规要求。

考虑实际路况下排气温度的重型柴油车NO_(x)排放模型

选择性催化还原技术(SCR)是降低重型柴油车氮氧化物(NO_(x))排放的常用技术之一,且SCR系统内的NO_(x)转化率与尾气温度密切相关。然而,现有的NO_(x)排放测算模型主要考虑车辆行驶工况,缺少与排气温度的关联分析,从而增加了NO_(x)排放测算结果的不确定性,对排放清单的建立和减排政策的评估提出了挑战。本研究基于车辆实际运行工况和实测排放数据,建立NO_(x)排放速率库和NO_(x)排放率模型。随后,建立基于机动车比功率(VSP)和热损失系数的尾气温度模型。在此基础上,根据SCR系统中的化学反应原理,建立基于尾气温度的NO_(x)排放模型。最后,利用建立的NO_(x)模型和MOVES模型(移动源排放测算模型)分别估算NO_(x)排放量,并与实际排放情况进行比较分析。结果表明,本研究所提出的考虑实际路况下尾气温度的NO_(x)排放模型可以有效提高NO_(x)排放测算的准确性,在3辆重型柴油公交车上的NO_(x)测算相对误差分别为9.1%、3.9%和3.3%。相较于MOVES模型,相对误差分别降低了24.0、13.1和16.3个百分点。对不同运行工况下的NO_(x)排放特性分析表明,重型柴油货车的平均NO_(x)转化率比柴油公交车高39.2个百分点。

米勒循环对重型柴油机燃烧和排放的影响

基于某重型高压共轨柴油机开展了米勒循环在外特性工况点、排放控制工况点和最低燃油消耗率工况点对发动机性能、燃烧和排放的影响研究.米勒循环依靠进气门晚关来实现,其中进气门关闭时刻分别推迟了30°、50°和70°CA.结果表明:重型柴油机应用米勒循环能够在实现较低缸内压力峰值下,较低燃油消耗率的目标,相同缸内压力峰值下燃油消耗率能够降低约1 g/(kW·h);大的进气门晚关角度能够实现在相同燃油消耗率下,排气温度提升20℃以上,可作为发动机排气热管理的储备技术.大的进气门晚关角度在外特性高转速段会造成功率损失,因而必须与高效增压器配合使用才能保证全局功率不损失,同时降低燃油消耗率,提升排气温度.

铝熔炼炉排烟罩捕集性能分析及优化数值模拟

铝加工厂房熔炼工艺中高温烟尘散发强度大、浓度高,对建筑室内外环境和人员健康危害大。为提高铝熔炼炉局部排烟罩捕集效率,本文研究了排烟罩捕集效率与量纲一排风量(排烟罩排风量/烟尘散发量)的关系;基于消涡原理及气流卷吸特性,提出了排烟罩捕集性能优化方法。研究表明,当量纲一排风量小于3.2时,增大排风量会显著提升排烟罩的捕集效率,为风量经济区。排烟罩几何特征优化后,在风量经济区内烟尘逃逸率降低了20%左右,系统排风量降低了6.1%~44.1%。