Effects of cooling rate on thermal expansion of Cu_(49)Hf_(42)Al_9 metallic glass

Effects of cooling rate on thermal expansion of Cu49Hf42Al9 metallic glass were studied. Five types of amorphous samples with different sizes were prepared in order to get a broad range of cooling rates （from 102 to 107 K/s）. The average thermal expansion coefficients （αaver） of as-quenched samples range from 6.14×10-6 to 9.20×10-6 K-1. When the temperature is below the glass transformation temperature （Tg）, αaver of as-quenched samples has a negative correlation with cooling rate; the values of αaver of annealed and crystallized samples are closed to each other. The results indicate that the amount and motion of free volume play important roles in thermal expansion of metallic glasses.

Optimisation of Direct Expansion (DX) Cooling Coils Aiming to Building Energy Efficiency

Efficient Air Conditioning (A/C) system is the key to reducing energy consumption in building operation. In order to decrease the energy consumption in an A/C system, a method to calculate the optimal tube row number of a direct expansion (DX) cooling coil for minimizing the entropy generation in the DX cooling which functioned as evaporator in the A/C system was developed. The optimal tube row numbers were determined based on the entropy generation minimization (EGM) approach. Parametric studies were conducted to demonstrate the application of the analytical calculation method. Optimal tube row number for different air mass flow rates, inlet air temperatures and sensible cooling loads were investigated. It was found that the optimal tube row number of a DX cooling coil was in the range of 5 - 9 under normal operating conditions. The optimal tube row number was less when the mass flow rate and inlet air temperature were increased. The tube row number increased when the sensible cooling load was increased. The exergy loss when using a non-optimal and optimal tube row numbers was compared to show the advantage of using the optimal tube row number. The decrease of exery loss ranged from around 24% to 70%. Therefore the new analytical method developed in this paper offers a good practice guide for the design of DX cooling coils for energy conservation.

Experimental Investigation of the Cooling Capacity of Gaseous Carbon Dioxide in Free Jet Expansion for Use in Portable Air-Cooling Systems

This paper investigates the possibility of using the free expansion of gaseous CO2 in portable air-cooling systems. The cooling capacity of the gaseous CO2 free jet expansion was calculated using three different approaches and the results showed that the simplified calculations would give approximated cooling values with an 11.6% maximum error. The mass flow rate, upstream pressure and cooling capacity of the gaseous CO2 decreased with time. A maximum 48.5 watts of cooling was recorded at minute 4 and a minimum value of 10.4 watts at the end of the test. The drop in cooling capacity is due to the evaporation of the liquid CO2 inside the small cylinder which cools the two-phase CO2 mixture and causes a pressure drop (from 6 MPa to 2.97 MPa), which also affects the mass flow rate of gaseous CO2 exiting the orifice (from 0.56 g/s to 0.24 g/s). If this cooling technique is to be considered in portable compact-cooling systems, the mass, pressure and cooling capacity drop with time must be solved. One of the solutions could be to cover the cylinder with a heating coat to compensate for the heat absorbed by the evaporation of the liquid CO2.

Air/CO2 cooling garment: Description and benefits of use for subjects exposed to a hot and humid climate during physical activities

The severity of the hot and humid conditions to which miners are exposed increases as the depth of the work site increases.This can cause heat stress that can greatly affect the health and safety of workers.To resolve this,a cooling garment has been developed that uses an atmospheric discharge of liquid CO2 to create a cool microclimate with an average temperature of 12.5(±0.4)℃ beneath the garment.To evaluate the garment's cooling efficiency,19 male subjects participated in an experimental procedure.The two modes,cooling on and off,were compared.Significant physiological differences were found between the two modes after minute 27(p<0.05)until the end of the recovery phase for the heart rate(maximum difference of 10 beats per minute)and the internal body temperature(maximum difference of 0.33℃).It was found that the modes also affected the subjects'perceptions.The ON-mode was associated with better well-being and thermal comfort,and reduced humidity sensation.Perceptions of exertion were lower in the ON-mode condition from minute 2.The findings provide strong evidence of the ability of this cooling garment to reduce heat stress in hot and humid conditions similar to those encountered in deep mines.

An experimental study of salt expansion in sodium saline soils under transient conditions

Salt expansion in sulfate saline soils that are widely distributed in northwestern China causes serious infrastructural damages under low-temperature conditions. However, the mechanism of salt expansion under low temperatures is not clear. In this study, we conducted a series of cooling experiments combined with salt crystallization to study this mechanism, and employed an ionic model to calculate the supersaturation ratio of the solution. During the experiments, the strength and the process of salt expansion were examined under different cooling rates and various crystal morphologies. The relationship between temperature and supersaturation ratio under transient conditions was also considered. Results indicate that the initial supersaturation ratio of a sodium sulfate solution is closely related to environmental conditions, and that this ratio decreases with slowing the cooling rates and stabilizing the crystal forms. Higher initial supersaturation ratios lead to an increased non-steady-state zone, resulting in less salt expansion. On the other hand, chloride ion content has a distinct influence on the crystallization supersaturation ratio of the sodium sulfate solution, and higher chloride ion content can inhibit salt expansion in sodium saline soils. These findings help explain salt expansion mechanisms in complex conditions such as seasonally frozen soils, and thus help search for improved methods of preventing salt expansion in sulfate saline soils.

Study and Strategy on Expansion of Steam Cracking Unit to 650 kt/a at Yanshan Petrochemical Company

After having expanded its capacity from 300 kt/a to 450 kt/a in 1994, the steam cracking unit of Yanshan Petrochemical Company was still experiencing such problems as low feedstock flexibility, high energy consumption and smaller production capacity as compared to other ethylene units constructed in the same time. In order to fully improve technical capability, reduce energy consumption, improve feedstock flexibility and increase production capacity of steam crackers, a lot of technical transform schemes on steam cracking were studied and compared with attention focused on the feasibility, safety, operability of the related revamp schemes, as well as the advanced nature and economical features. The transform scheme decided includes following projects. For the pyrolysis quench compression system, the pyrolysis gasoline fractionation tower is retrofitted on the site, quench water tower, pyrolysis gas compressor and steam turbine are replaced by new ones respectively. For the separation system a low pressure methane removal technology is adopted with the demethanizer tower replaced, coupled with the C 3 catalytic rectification/hydrogenation technology, while the high pressure depropanizer is replaced with addition of a propylene rectification tower. The fractionation flow sheet and equipment are adjusted with addition of a propylene compressor and compressor for binary mixture of methane ethylene cooling agents. The revamped complex has expanded the ethylene capacity to the target of 660 kt/a with the actual capacity reaching 710 kt/a, remarkably reduced the energy consumption, and is capable of using naphtha, light diesel fuel, heavy diesel fuel and the hydrocracked tail oil as the steam cracking feedstock. This project is the first to apply refrigeration by means of a mixed cooling agent and has succeeded in using C\-3 catalytic rectification/hydrogenation technology, which has given an impetus to the progress of steam cracking industry in the world.

System Design and Analysis of Hydrocarbon Scramjet with Regeneration Cooling and Expansion Cycle

A new expansion cycle scheme of the scramjet engine system including a hydrocarbon-fuel-based(kerosene)regenerative cooling system and supercritical/cracking kerosene-based turbo-pump was proposed in this paper.In this cycle scbeme,the supercritical/cracking kerosene with high pressure and high temperature is formed through the cooling channel.And then,in order to make better use of the high energy of the supercritical/cracking fuel,the supercritical/cracking kerosene fuel was used to drive the turbo-pump to obtain a high pressure of the cold kerosene fuel at the entrance of the cooling channel.In the end,the supercritical/cracking kerosene from the turbine exit is injected into the scramjet combustor.Such supercritical/cracking kerosene fuel can decrease the fuel-air mixing length and increase the combustion efficiency,due to the gas state and low molecular weight of the cracking fuel.In order to ignite the cold kerosene in the start-up stage,the ethylene-assisted ignition subsystem was applied.In the present paper,operating modes and characteristics of the expansion cycle system are first described.And then,the overall design of the system and the characterisitics of the start-up process are analyzed numerically to investigate effects of the system parameters on the scramjet start-up performance.The results show that the expansion cycle system proposed in this paper can work well under typical conditions.The research work in this paper can help to make a solid foundation for the research on the coupling characteristics between the dynamics and thermodynamics of the scramjet expansion cycle system.

Improvement of Hole-Expansion Property for Medium Carbon Steels by Ultra Fast Cooling After Hot Strip Rolling

The improvement of hole-expansion properties for medium carbon steels by ultra fast cooling （UFC） after hot strip rolling was investigated.It was found that finely dispersed spherical cementite could be formed after ultra fast cooling , coiling and annealing treatment.Tensile strength of the steel after annealing was measured to be about 440MPa.During hole-expansion test , cracks were observed in the edge region around the punched hole because necking or cracking took place when tangential elongation exceeded the forming limit.Cracks were mainly formed by the coalescence of micro-voids.Fine and homogeneous microstructure comprised of ferrite and spheroidized cementite could increase elongation values of the tested sheets by suppressing the combination of the adjacent micro-voids , resulting in the improved hole-expansion property.

基于裂变矩阵的谐波计算及其在气冷微堆功率监测中的应用

气冷微堆受限于堆芯体积及堆内高温高辐照运行环境,仅能布置少量堆外探测器用于功率监测。采用基于裂变矩阵产生高阶谐波的谐波展开法进行堆芯功率重构。通过反应堆蒙特卡罗程序RMC统计裂变矩阵,使用瑞利商迭代法求解特征向量,构造高阶谐波库;将堆芯三维功率分布用高阶谐波展开,结合探测器响应矩阵,实现三维功率在线监测。进一步研究了温度、燃耗、控制棒棒位对功率重构精度的影响,结果表明:温度、燃耗变化的工况下,气冷微堆节块平均功率的重构值与蒙特卡罗模拟参考值之间的均方根相对误差小于3%,最大相对误差小于5%;控制棒棒位变化对重构精度的影响较大,通过采用临近棒位的谐波组进行功率重构,均方根相对误差小于3%。验证结果为气冷微堆在线监测系统的后续研发提供参考。

花岗岩侵位后的热应力时空演化及其影响因素

花岗岩与岩浆热液型矿床、油气成藏等有密切的成因关系。高温岩浆侵位到较冷的围岩中会形成岩浆热场和热应力,但热应力的大小和其影响范围尚缺乏系统研究。随着岩浆热耗散、与周围地层达到热平衡后,热应力会逐渐消失,因而数值模拟是定量研究岩浆热应力的常见方法之一。以往模拟岩浆热应力时往往采用岩石在常温下的线性热膨胀系数,但这与高温下岩石线性热膨胀系数存在较大差距。文章利用FLAC3D软件模拟花岗质岩浆侵位至上地壳范围内引起的热应力。求解物理方程包括热传导方程与线性热弹性本构方程,其中热场可通过温度差和线性热膨胀系数改变应力场,但应力场的变化不影响热场(即热场与应力场的单向耦合)。通过一系列数值模拟实验考察围岩岩性(花岗岩或碳酸盐岩)、杨氏模量、热学参数和岩浆侵位深度如何影响岩浆在上覆围岩产生的热应力。数值实验结果表明:岩石热传导系数通过传热快慢影响热应力的变化;围岩的杨氏模量越大,热应力也越大;由于花岗岩的平均杨氏模量大于碳酸盐岩,所以围岩为花岗岩时产生的热应力要高于碳酸盐岩;围岩无论是花岗岩还是碳酸盐岩,其在高温条件下的线性热膨胀系数比常温时高约1个数量级,产生的热应力最高可达100 MPa。花岗岩浆侵位后,围岩温度逐渐升高,对应的热应力不断增大;随着与岩浆房距离的增大,热应力不断减小,影响范围为岩浆房上方2 km以内;侵位深度浅的岩浆房冷却较快,其产生的热应力更有利于上覆围岩裂隙的形成和扩展。综合数值模拟结果可知,岩浆侵位所产生的热应力可影响岩体2 km内的应力场,这一局部存在且短瞬的热应力促使围岩破裂,为热液流体成矿提供运移通道或容矿空间。

基于在线监控数据分析的水冷壁膨胀特性

锅炉水冷壁的膨胀状态影响火电机组的稳定和安全运行。基于在线监控数据对某超超临界机组锅炉的膨胀特性进行评价。基于最小二乘法对正常运行阶段锅炉测点膨胀位移数据进行拟合,通过膨胀位移波动率展现正常运行阶段中测点膨胀情况。结果表明,锅炉启动阶段、停炉阶段膨胀量均随时间急剧变化,而正常运行阶段膨胀监控值则围绕热态膨胀设计值波动。冷灰斗处测点Z轴方向位移平均拟合值较热态设计值减小24.73 mm,这可能源于锅炉水冷壁通过屈服或变形,吸收了部分膨胀。同一标高不同测点水平方向膨胀情况存在差异。5号测点Y轴位移波动率δ基本分布在±5%内,而6号测点仅有33.05%的监控膨胀值波动率分布在±5%内,这可能源于燃烧动力场分布不均匀。因此,水冷壁膨胀监控分析能够有效反映锅炉设备状态。

The “Dead Universe” Theory: Natural Separation of Galaxies Driven by the Remnants of a Supermassive Dead Universe

This article explores the dead universe theory as a novel interpretation for the origin and evolution of the universe, suggesting that our cosmos may have originated from the remnants of a preceding universe. This perspective challenges the conventional Big Bang theory, particularly concerning dark matter, the expansion of the universe, and the interpretation of phenomena such as gravitational waves.

水冷直膨式空调机组与水冷多联机组合系统在地铁车站的应用分析

以实际工程为例,提出了一种新的地铁空调设计方案,用水冷直膨式空调机组与水冷多联机系统取代冷水机组。与传统空调系统在初投资、运行能耗等方面进行了对比分析。结果表明,水冷直膨式空调机组与水冷多联机组合系统相比于传统系统,初投资增加约42.5%,节能率约为27.9%。

700 MPa级热轧高扩孔钢组织性能研究

以一种低碳+铌钛微合金试验钢为对象,通过研究轧制过程中不同冷却速度对高扩孔钢组织和性能的影响,开发出了700 MPa级热轧高扩孔钢,并研究和分析了扩孔试验后产生的裂纹情况。结果表明:当终轧温度870℃,卷取温度500℃,冷却速度30℃/s时,金相组织为铁素体和贝氏体,其中当铁素体体积分数约占60%时,抗拉强度达到719 MPa,扩孔率为81%,综合性能最好,满足用户使用要求。扩孔试验表明,当试验钢以微孔聚集制度形成裂纹及扩展时,缩小两相之间硬度差是降低裂纹扩展的有效手段。

一种高速高效PVC-U管材生产工艺

介绍了一种高速高效的PVC-U管材生产工艺。通过优化和改进加热单元、扩口系统及相应的冷却系统等相关技术,开发了PVC-U管材关键生产技术的工艺和设备,解决了工艺开发和设计过程中影响管材生产速度和性能的难题,实现了PVC-U管材高速、高效、连续、稳定生产的目的。

提高膨胀机制冷的液态产品产量

通过技术创新、设备升级、运营流程优化及管理与组织创新等综合措施,中海油某终端成功应对了提高液态产品产量的挑战。优化后的膨胀机制冷应用使液态产品产量显著提升,不仅提高了公司经济效益和市场竞争力,同时在环保和安全保障方面取得显著进展。这一系列改进措施满足了天然气行业高效生产需求,展现了企业积极履行社会责任的决心,推动了整个行业向可持续、绿色的发展方向迈进。

磷石膏基自产气膨胀浆体防灭火性能研究

为防治煤矿顶煤和上分层遗煤自燃等高位火源灾害,以工业固废物磷石膏为基料,加入碳酸氢钠和聚丙烯酰胺等成分,制备出一种自产气膨胀浆体。首先,应用热重(TG)分析仪研究浆体在不同升温速率下的热稳定性;然后,采用自行搭建的隔热性能测试系统测试浆体的隔热性;最后,通过灭火试验研究浆体的灭火降温性能。结果表明:磷石膏基自产气膨胀浆体在160℃以下时存在35%~46%的质量损失,当温度大于160℃时,浆体的质量分数不再发生改变;浆体堆积厚度达到30 mm时,有效隔热时间超过139 min,可实现对煤自燃危险区域较好的覆盖;浆体通过在煤堆裂隙中膨胀扩散,自下而上完全包裹碎煤,隔绝氧气,具有良好的降温灭火性能,注浆36 min后,各点位温度已全部降低至50℃以下,未出现复燃现象。

空分设备国产化技术改造总结

马钢气体公司全套35000 m^(3)/h空分设备均自国外引进,因膨胀机、工艺液氧泵、粗氩循环泵原设计因素,精馏系统制冷量不足,工艺液氧泵、粗氩循环泵无法自动调节负荷。通过对膨胀机、工艺液氧泵、粗氩循环泵实施国产化技术改造,增加精馏系统制冷量,使工艺液氧泵、粗氩循环泵能够自动调节其出口压力。文章叙述了膨胀机、工艺液氧泵、粗氩循环泵运行存在的问题和技术改造的具体方法。

电炉炼钢软水密闭循环冷却水系统的组成及技术改进

软水密闭循环冷却水系统已广泛应用于高炉、电炉炼钢等工艺中。结合50 t特殊合金冶炼水处理工程实例对电炉炼钢软水密闭循环冷却水系统进行论述,详细介绍了该工程实例中系统的设计参数、设备选型及设计技术改进之处,并分析了该系统的应用前景。

高压直流输电换流阀冷却系统氮气稳压方式电磁阀隐患治理方法

某换流站阀冷系统膨胀罐排气电磁阀故障导致一系列报警。介绍了阀冷系统的主要结构,并结合此次故障案例进行分析,得出阀冷系统目前氮气稳压控制方式中电磁阀的隐患,并提出相应的隐患治理方法建议。