液氧密度标准计量装置的研制

研制的液氧密度标准计量装置主要由液氧容器、专用恒温器、测控系统、质量测量系统、PC机组成.分析和评定了温度测量不准确度,考核了液氧密度计量装置的性能.液氧密度标准计量装置在温度90～100 K、压力0.1～0.6 MPa条件下,其扩展不确定度(K=3)沸点条件下不大于0.3kg/m3,沸点之外不大于0.5 kg/m3.     

定容法正压漏孔校准装置

研制出定容法正压漏孔校准装置。采用满量程分别为133 Pa(差压式)、1.33×105Pa(绝压式)的两台高精度电容薄膜真空计测量压力变化,通过全金属密封结构减小定容室漏放气对测量结果的影响;采用高精度半导体双级恒温系统获得了296±0.02 K的恒温效果,减小温度对漏孔漏率的影响;通过三个不同的标准体积作为定容室,拓宽装置的校准范围。研究结果证实,研制的校准装置仅采用定容法实现了3×10-1~4×10-8Pa·m3/s的校准范围,合成标准不确定度为1.2%~3.2%。     

高精度液位计自动检测系统研制

为快速准确开展液位计计量检测,研制了量程为0～2500mm的新型液位计检测系统。该系统的硬件基于绝对编码器作为标准器,包括高精度直线运动单元、温度传感器、倾角传感器、溢流口等,其配套检测软件则是基于图形化编程软件Lab VIEW开发的,实现了非侧装液位计的自动快速准确计量检测。对该系统的液位测量不确定度评定方法进行了研究,分析了测量不确定度的来源。实测表明,溢流后单次液位高度测量的重复性小于0.1mm。在测量范围内,该液位计检测系统的液位测量不确定度为0.3mm(k=2),可以检测准确度等级不高于0.1级、量程为600～2500mm的液位计。     

宽温压力可变标准湿度发生器的研制

采用双温双压法原理研制了一套宽温度范围、测试室压力可变的标准湿度发生器。它能够测量发生温度范围为-50～90 ℃、相对压力范围为-50～0 kPa、扩展不确定度为0.3%RH～0.8%RH（k=2）的5%RH～96%RH全量程相对湿度。其测试室尺寸为150 mm×400 mm,样气流量为5～30 L/Min。通过设计高精度饱和器压力和流量自动调节装置,采用工控机与PLC相结合的操作控制方式,实现了全自动运行。冷镜式精密露点仪和重量法湿度计的实际测试结果均验证了其不确定度。     

谈《对〈精密压力表的测量不确定度〉一文的不同理解》的建议

<正>《中国计量》2013年第1期刊出了《对〈精密压力表的测量不确定度〉一文的不同理解》,其中提出"对标准不确定度分量的分析计算中以一只量程为(0~2.5)MPa、准确度等级为0.4级的精密压力表为分析对象,以量程为(0.1~6)MPa、准确度为0.05级的活塞式压力表为标准器进行分析计算。认为该例存在标准器选用错误。该例中标准器的允许误差绝对值为(6-0.1)×0.05%=0.00295MPa……"     

对《精密压力表的测量不确定度》一文的不同理解

《中国计量》2009年第8期刊出的《精密压力表的测量不确定度》一文,对标准不确定度分量的分析计算中以一只量程为(0~2.5)MPa、准确度等级为0.4级的精密压力表为分析对象,以量程为(0.1~6)MPa、准确度为0.05级的活塞式压力表为标准器进行分析计算。笔者认为该例存在标准器选用错误。该例中标准器的允许误差绝对值为     

二等活塞压力计标准装置测量结果不确定度评定

一、概述1.评定依据JJG49-1999《弹簧管式精密压力表和真空表》检定规程、JJF1059-1999《测量不确定度评定与表示》。2.环境条件温度为(20±3)℃,相对湿度不大于85%,标准大气压,恒温2h以上。3.测量标准标准器为二等活塞式压力计,允许示值误差为±0.05%。4.被测对象0.4级弹簧管式精密压力表,量程为(0～10)MPa。     

现场真空校准装置性能研究

研制了一台校准范围为10~(-5)~10~5Pa的现场真空校准装置。将不同种类单一成分的校准气体引入装置上游室,通过几何尺寸为微米量级激光小孔的衰减,建立校准用标准压力p_(std)。上游室压力变化范围为1~10~3Pa,相应地,校准室内对应的标准压力范围10~(-5)~10~(-2)Pa(N2),测量不确定度为2.4%。另外,该装置可采用与标准真空计直接比较进行动态或静态校准,其极限真空度为10~(-6)Pa量级。对装置暴露大气后的抽气性能、静态压升及其主要计量特性进行了实验研究。实验结果表明,该装置外形尺寸以及质量分别为475 mm×420 mm×800 mm、37.8 kg,校准范围为1.9×10~(-5)~1.0×10~5Pa,相对合成标准不确定度为2.8%~0.40%。     

金属膨胀式真空计量标准

介绍了新研制的金属膨胀式真空计量标准及其起始压力和体积比的测量方法，讨论了实际气体特性、温度变化和气体吸附等干扰效应，分析了标准装置的不确定度（1σ）。该标准的校准范围为105～10-4Pa，校准电容薄膜规和磁悬浮转子规时不确定度为0．01％～1．0％。     

真空计在线校准系统的研制

为了解决真空计在线校准的问题,研制出一种真空计在线校准系统。真空计在线校准系统通过优化设计、材料及工艺处理已解决宽量程校准的问题。通过对在线校准技术的研究,采用比较法校准方法,以三台高精度的薄膜真空计和一台高精度电离真空计作为参考标准,解决了校准条件与使用条件基本一致性问题,可以减小量值传递过程产生的不确定度,保证测量的准确性和可靠性。真空计在线校准系统可实现(10~5～10~(-5))Pa范围内的真空计的在线计量,相对扩展不确定度不大于13%。     

热真空低温环境实验台研制

为满足低温实验的环境要求,建设了液氮温度级别(80 K)的热真空冷阱低温环境实验台,可进行低温实验中压力与压差、温度与温差、流量与热负荷的测量.该实验台采用附加液氮冷阱的真空多层绝热结构,冷阱温度最低可达80 K,无负载时冷箱真空度可达0.000 03 Pa;在采用外循环工质时,测试压力范围为0-1 MPa、压差范围为...     

A Small-Volume Apparatus for the Measurement of Phase Equilibria

An apparatus has been designed and constructed for the measurement of vapor-liquid equilibrium properties. The main components of the apparatus consist of an equilibrium cell and a vapor circulation pump. The cell and all of the system valves are housed inside a temperature controlled, insulated aluminum block. The temperature range of the apparatus is 260 K to 380 K to pressures of 6 MPa. The uncertainty of the temperature measurement is 0.03 K, and the uncertainty in the pressure measurement is 9.8 × 10⁻⁴ MPa. An automated data acquisition system is used to measure temperature and pressure at equilibrium. The apparatus has been performance tested by measuring the vapor pressures of propane, butane, and a standard mixture of propane + butane.     

Thermophysical Properties of Gaseous HBr and BCl3 from Speed-of-Sound Measurements

The speed of sound in gaseous hydrogen bromide (HBr) and boron trichloride (BCl₃) was measured using a highly precise acoustic resonance technique. The HBr speed-of-sound measurements span the temperature range 230 to 440 K and the pressure range from 0.05 to 1.5 MPa. The BCl₃ speed-of-sound measurements span the temperature range 290 to 460 K and the pressure range from 0.05 MPa to 0.40 MPa. The pressure range in each fluid was limited to 80% of the sample vapor pressure at each temperature. The speed-of-sound data have a relative standard uncertainty of 0.01%. The data were analyzed to obtain the ideal-gas heat capacities as a function of temperature with a relative standard uncertainty of 0.1%. The heat capacities agree with those calculated from spectroscopic data within their combined uncertainties. The speeds of sound were fitted with the virial equation of state to obtain the temperature-dependent density virial coefficients. Two virial coefficient models were employed, one based on the hard-core square-well intermolecular potential model and the second based on the hard-core Lennard–Jones intermolecular potential model. The resulting virial equations of state reproduced the speed-of-sound measurements to 0.01% and can be expected to calculate vapor densities with a relative standard uncertainty of 0.1%. Transport properties calculated from the hard-core Lennard–Jones potential model should have a relative standard uncertainty of 10% or less.     

Isochoricp-ϱ-T measurements on Difluoromethane (R32) from 142 to 396 K and pentafluoroethane (R125) from 178 to 398 K at pressures to 35 MPa

Thep--T-relationships were measured for difluoromethane (R32) and pentafluoroethane (R125) by an isochoric method with gravimetric determinations of the amount of substance. Temperatures ranged from 142 to 396 K for R32 and from 178 to 398 K for R125, while pressures were up to 35 MPa. Measurements were conducted on compressed liquid samples. Determinations of vapor pressures were made for each substance. I have used vapor pressure data and thep--T data to estimate saturated liquid densities by extrapolating each isochore to the vapor pressure, and determining the temperature and density at the intersection. Publishedp--T data are in good agreement with this study. For thep T apparatus. the uncertainty of the temperature is ±0.03 K. and for pressure it is ±0.01%, atp > 3 MPa and ±0.05% atp < 3 MPa. The principal source of uncertainty is the cell volume (28.5193 cm³ at 0 K and 0 M Pa), which has a standard uncertainty of ±0.003 cm³. When all components of experimental uncertainty are considered. the expanded uncertainty (at the two-sigma level) of the density measurements is estimated to be 0.05%.     

Thermodynamic properties of the R-415A refrigerant in the vapor phase and on the condensation line

The speed of sound in the R-415A refrigerant vapor and its density and pressure on the condensation line were measured by the ultrasonic interferometer and constant-volume piezometer methods within a range of temperatures from 293 to 373 K and pressures from 0.04 to 0.5–2.45 MPa. The temperature, pressure, density and speed of sound measurement errors were ±20 mK, ±4 kPa, and ±(0.1–0.2)%, respectively. The temperature dependence of the ideal-gas heat capacity was calculated on the basis of the obtained data. The obtained results were compared with the properties calculated by the REFPROP software.     

Density of Methylcyclohexane at Temperatures up to 600 K and Pressures up to 200 MPa

Using a bellows variable volumometer, precise density data were measured for methylcyclohexane, which is expected to be a chemical hydride for transportation and storage of hydrogen. For further development of an accurate equation of state, measurements were taken in the temperature and pressure ranges 410 K to 600 K and 10 MPa to 200 MPa, respectively. The uncertainties (\(k=2\)) were less than 3.5 mK for the temperature measurements, 0.080 MPa for the pressure measurements, and 0.11% for the density measurements. In the region above 100 MPa and 450 K, the uncertainty for the density measurement increased from 0.11% to 0.22%. The data obtained in this study were systematically compared with available experimental data and theoretical values derived from the available equation of state. This comparison indicated that the model needs to be improved.     

Experimental Investigation of the Density of Liquid Lithium Hydride at High Temperatures

The density of molten lithium hydride is measured by the dilatometric method in the temperature range from 970 to 1260 K. Lithium hydride is obtained directly in an ampoule by hydrogenation of lithium at a temperature of the order of 920 K and a constant hydrogen pressure of 1 MPa. The purity of lithium and hydrogen used is 99.96 mass % and 99.999 vol %, respectively. The confidence error of the experiments does not exceed 2%. The measurement results are compared with the available literature data, and the reasons for discrepancy are analyzed.     

Thermodynamic Properties of Gases from Speed-of-Sound Measurements

A procedure for deriving thermodynamic properties of gases from speed of sound is presented. It is based on numerical integration of ordinary differential equations (ODEs) (rather than partial differential equations—PDEs) connecting speed of sound with other thermodynamic properties in the T-p domain. The procedure enables more powerful methods of higher-order approximation to ODEs to be used (e.g., Runge-Kutta) and requires only Dirichlet initial conditions. It was tested on gaseous argon in the temperature range from 250 to 450 K and in the pressure range from 0.2 to 12 MPa, and also on gaseous methane in the temperature range from 275 to 375 K and in the pressure range from 0.4 to 10 MPa. The density and isobaric heat capacity of argon were derived with absolute average deviations of 0.007% and 0.03%, respectively. The density and isobaric heat capacity of methane were derived with absolute average deviations of 0.006% and 0.09%, respectively.     

Density and speed of sound of R-406A refrigerant in the vapor phase

The speed of sound and the density of the gaseous R-406A refrigerant within the temperature range 293–373 K and at the pressures from 0.05 MPa up to 0.6–2.3 MPa were investigated by means of an ultrasound interferometer and a constant volume piezometer. The measurement errors for the temperature, the pressure, and the speed of sound were ±20 mK, ±4 kPa, and ±(0.1–0.3)%, respectively. The approximation dependences of the investigated properties of the R-406A vapor are obtained and their errors are estimated. The obtained results are compared with the calculations using the REFPROP software.