GaAs-based fiber-optic pressure sensor

A new sensor developed for measurement of hydrostatic pressure up to at least 100 MPa at a standard range of ambient temperatures is described. The sensor exploits the displacement of the optical absorption edge occurring in semiconductors under the influence of hydrostatic stress as a result of pressure-induced energy shifting of conduction band extrema. The sensing element is composed of an intrinsically pure GaAs single crystal configured in the form of a microprism located at the sensor tip, and attached to two multimode (50/125 μm) optical fibers designed to deliver input light to the sensor and to output a pressure-modulated light signal to the outside of a pressure region. Characterization of the sensor has been performed for pressures up to 100 MPa and for temperatures ranging from 5 to 50°C. A procedure has been proposed involving the use of two sensors (active and compensating) to minimize temperature drift through appropriate signal processing     

The effects of pressure on the carbonization of pitch and pitch/carbon fibre composites

Three pitches which give carbons of varying optical texture have been carbonized singly and with different carbon fibres at pressures in the range 0.1 to 200 MPa. The effect of pressure on the carbonization system is to retard growth and coalescence of the growth units of mesophase, thus reducing the size of the optical texture of the resultant carbon. With increasing pressure botryoidal (spherical) structures are formed. On co-carbonization of pitches with carbon fibres the alignment of the basal planes of the matrix carbon parallel to the fibre length at the fibre/matrix interface is improved within a given pressure range. This range is dependent upon the parent pitch used and is experimentally determined. This effect is seen for all fibre types.     

A Liquid Density Standard Over Wide Ranges of Temperature and Pressure Based on Toluene

The density of liquid toluene has been measured over the temperature range −60 °C to 200 °C with pressures up to 35 MPa. A two-sinker hydrostatic-balance densimeter utilizing a magnetic suspension coupling provided an absolute determination of the density with low uncertainties. These data are the basis of NIST Standard Reference Material® 211d for liquid density over the temperature range −50 °C to 150 °C and pressure range 0.1 MPa to 30 MPa. A thorough uncertainty analysis is presented; this includes effects resulting from the experimental density determination, possible degradation of the sample due to time and exposure to high temperatures, dissolved air, uncertainties in the empirical density model, and the sample-to-sample variations in the SRM vials. Also considered is the effect of uncertainty in the temperature and pressure measurements. This SRM is intended for the calibration of industrial densimeters.     

Revised Standardized Equation for Hydrogen Gas Densities for Fuel Consumption Applications

An equation for the density of hydrogen gas has been developed that agrees with the current standard to within 0.01 % from 220 K to 1000 K with pressures up to 70 MPa, to within 0.01 % from 255 K to 1000 K with pressures to 120 MPa, and to within 0.1 % from 200 K to 1000 K up to 200 MPa. The equation is a truncated virial-type equation based on pressure and temperature dependent terms. The density uncertainty for this equation is the same as the current standard and is estimated to be 0.04 % (combined uncertainty with a coverage factor of 2) between 250 K and 450 K for all pressures, and 0.1 % for lower temperatures. Comparisons are presented with experimental data and with the full equation of state.     

Characteristics of a silicon pressure sensor in superfluid helium pressurized up to 1.5 MPa

It is known that a piezo-resistive pressure sensor, FPS-51B manufactured by Fujikura Ltd., is available for in situ pressure measurement in superfluid helium. The sensor covers a pressure range of zero to 103.4 kPa. The maximum rated pressure is 202.6 kPa at room temperature. The characteristics of the pressure sensor in a pressure range up to approximately 0.2 MPa were reported in detail for use in superfluid helium. We measured the pressure characteristics of this sensor up to 1.5 MPa to determine its availability to be used under much higher pressure. Measurements were taken using a cryostat, which can be pressurized up to 1.5 MPa at room temperature and superfluid helium temperatures. It was found that the sensor could be used in a superfluid helium environment at pressures up to 1.5 MPa, without any damage and with good reproducibility.     

Search for Anisotropic Effects of HCP Solid Helium on Optical Lines of Cesium Impurities

The anisotropic effect of a hcp ⁴He solid matrix on cesium atoms has been proposed as a tool to reveal the parity violating anapole moment of its nucleus. It should also result in splitting the D₂ optical excitation line in a way depending on the light polarization. An experimental investigation has been set up using oriented hcp helium crystals in which cesium metal grains are embedded. Atoms are created by laser sputtering from this grains. Optical absorption spectra of the D₂ line have been recorded in the temperature range of 1.0 to 1.4 K at liquid/solid coexistence pressure by monitoring the fluorescence on the D₂ line at 950 nm. No significant effect of the light polarization has been found, suggesting a statistically isotropic disordered solid environment for the cesium atoms.      

A calorimeter for μW level optical power transfer standard

A calorimeter which can measure microwatt-level optical power has been developed for an optical power transfer standard. It can measure the optical power of a light beam and can be used with optical fiber simply by attaching an adapter. This calorimeter sensor uses a compensative absorber to reduce the influence of pressure fluctuation and temperature variation in the measurement room and an ultra-low-noise preamplifier. With this calorimeter, the standard deviation of the measured value is in the range of 0.02-0.4% in 20-mW to 10-μW optical power measurements. An error evaluation for an optical power level of 10 μW yielded a two-sigma (two standard deviation) total uncertainty of 0.9%     

Solid-liquid phase equilibria of benzene + 2-methyl-2-propanol system under high pressures

Solid-liquid phase equilibria of the benzene + 2-methyl-2-propanol system have been investigated at temperatures from 278 to 323 K and pressures up to 300 MPa using a high-pressure optical vessel. The uncertainties of the measurements of temperature, pressure and composition are within ±0.1 K, ±0.5 MPa, and ±0.001 mole fraction, respectively. The freezing pressure at a constant composition increases monotonously with pressure. The eutectic point shifts to a higher temperature and benzene-rich composition with increasing pressure. In order to describe the pressure-temperature-composition relation of high-pressure solid-liquid phase equilibria, a new simple equation has been proposed as follows:

Solid-liquid phase equilibria of benzene + cyclohexane system under high pressures

Solid-liquid phase equilibria of the benzene + cyclohexane system have been investigated experimentally at temperatures from 278 to 323 K and pressures up to 500 MPa using a newly designed optical vessel. The uncertainties of the measurements of temperature, pressure, and composition are within ±0.1 K, ±0.5 MPa, and ±0.001 mole fraction, respectively. The solid-liquid equilibrium pressure at a constant composition increases almost linearly with increasin temperature. The eutectic point shifts to a higher temperature and to a benzenerich composition with increasing pressure. This trend is found to agree with the direction predicted by the van Laar equation. The solid-liquid coexistence curves can be expressed by the Wilson equation with a mean deviation of 0.007 and a maximum deviation of 0.029 in mole fraction.     

Effect of pressure on the solid-liquid phase equilibria of (carbon tetrachloride + p-xylene) and (carbon tetrachloride+benzene) systems

Solid-liquid phase equilibria of the carbon tetrachloride + p-xylene and the carbon tetrachloride+benzene systems have been investigated at temperatures from 278 to 323 K and pressures up to 500 MPa using a high-pressure optical vessel. The uncertainties in the measurements of temperature, pressure, and composition are within ±0.1 K, ±0.5 MPa, and ±0.001 mole fraction, respectively. In the former system, which has an intermolecular compound with a congruent melting point, the freezing temperature at a constant composition increases monotonously with increasing pressure. The two eutectic points of this system shift to higher temperatures and richer compositions of the compound with increasing pressure. In the latter system, which has two intermolecular compounds with incongruent melting points, the one compound disappears under the present experimental conditions and the incongruent melting point of the other compound changes to the congruent melting point under high pressures. The solid-liquid coexistence curves of these systems can be correlated satisfactorily by the equation previously proposed.     

Volumetric properties under pressure for 1,2-dichlorofluoroethane (R141), 1-fluoro-1,1,2-trichloroethane (R131a), and 1,2-dichloro-1,1-difluoroethane (R132b)

The effect of pressure on the volume of R141, R131, and R132b is reported as volume ratios (the volume under pressure relative to its value at atmospheric pressure) at six temperatures covering the range 278.15 to 338.13 K and pressures up to 380 MPa for R141 and R131a. For R132b the same temperature range has been used, but above its normal boiling point experimental arrangements have limited maximum pressures to below 300 MPa, with some loss of accuracy. Densities have been measured at atmospheric pressure for each liquid. The experimental data have been used to calculate isothermal compressibilities, thermal expansivities, and internal pressures: the change in isobaric heat capacity from its value at atmospheric pressure has also been estimated. The volume ratios for all three compounds can be represented by a version of the Tait equation based on previously reported data for 1,2-dicloroethane and 1,1,2-trichloroethane with the inclusion of allowances for the substitution in the former of chlorine or fluorine for the hydrogens on one of the carbons.     

Diffusion of Aroma Compounds into Packaging Films under High Pressure

Diffusion of the aroma compounds p-cymene and acetophenone into three different packaging films was studied at 500 MPa for kinetic measurement, and in the range of 0.1–450 MPa for measurement of the diffusion rate as a function of pressure. Absorption of aroma compounds was lower in pressurized than in nonpressurized polymeric films. PET/A1/LDPE was impermeable to either substance; absorption was limited to the LDPE lining inside. Distribution of aroma compounds to solution and films depended on their polarity; acetophenone virtually did not diffuse into the films. Measurements of the diffusion rate as a function of pressure has shown a diffusion barrier in the range of 100–200 MPa for the films investigated. The assumption that this is due to transition into the glassy state has been supported by studies of diffusion as a function of temperature.     

A simple differential thermal analysis technique for determining the pressure dependence of solid-liquid and solid-solid transition temperatures

A simple differential thermal analysis technique for determining solid-liquid and solid-solid transition temperatures as functions of pressure is described. The important feature of the technique is the use of a thin-walled ptfe tube both to contain the sample and to transmit pressure to it. The method has been tested at temperatures in the range 200–310 K at pressures of up to 350 MPa. Transition temperatures as functions of pressure are reported for benzene, carbon tetrachloride, and acetonitrile and compared with literature data.     

Fluorescence spectrum of 2-trifluoromethyl-1,1,1,2,4,4,5,5,5-nonafluoro-3-pentanone

A perfluorinated ketone, 2-trifluoromethyl-1,1,1,2,4,4,5,5,5-nonafluoro-3-pentanone, has been investigated to determine several physical and spectroscopic properties. It was found to exhibit fluorescence similar to that of acetone, emitting over the 360-550 nm range with a peak near 420 nm when excited at 355 nm. This compound's emission is nearly unaffected over a wide range of temperature and pressure in an argon bath gas. Its fluorescence efficiency was found to be three times higher than that of acetone. Combined with low reactivity and thermal stability up to 500 degrees C, this makes the material an excellent tracer for spectroscopic measurement techniques.     

石英纤维/聚酰亚胺复合材料的制备与性能

采用DSC、TG、FTIR和流变仪对KH-370聚酰亚胺树脂的化学反应特性和流变性能进行了表征。以QWB200石英纤维为增强体,采用热压成型工艺制备了QWB200/KH-370复合材料。研究了加压温度、压力大小、固化温度等不同工艺参数对QWB200/KH-370复合材料力学性能的影响,在此基础上确定了复合材料的成型工艺制度。考察了QWB200/KH-370复合材料400℃高温下的力学强度及宽频范围内的介电性能。结果表明,制备QWB200/KH-370复合材料的最佳工艺参数为:加压温度290~310℃,压力范围3.0~4.0 MPa,固化温度380℃。所得QWB200/KH-370复合材料具有良好的力学性能,400℃下力学强度保持率高于58%,表现出良好的耐热性能;而且在1~18 GHz的宽频范围内具有稳定的介电常数和介电损耗。      

Compressibility and sound velocity measurements on N2 up to 1 GPa

A gas expansion technique has been used to determine the pVT properties of N₂ up to 1 GPa at 298.15 K, with an accuracy of 0.08% in density, 1 mK in temperature, and 0.05%+0.2 MPa in pressure. The sound velocity has been measured by a phase-comparison pulse-echo technique between 123 and 298 K at intervals of 25 K and at pressures up to 1 GPa, with an accuracy of better than 0.02% in sound velocity, 10 mK in temperature, and 0.05%+0.2 MPa in pressure. An equation of state is presented that correlates the density data over the wide pressure range of 36–1000 MPa with maximum deviations between the calculated and the experimental densities of less than 0.05%.     

Compressibilities of ternary mixtures C1-nC16-CO2 under pressure from ultrasonic measurements of sound speed

Speed of sound measurements have been performed on three mixtures of the ternary system methane + carbon dioxide + normal hexadecane. The systems have been investigated from 12 to 70 MPa in the temperature range from 313 to 393 K. Furthermore, these measurements have allowed the evaluation of the isothermal and the isentropic compressibilities up to 70 MPa from low pressure (<40-MPa) density data.     

The thermal conductivity of 1-chloro-1,1-difluoroethane (HCFC-142b)

The thermal conductivity of 1-chloro-1,1-difluoroethane (HCFC-142b) has been measured in the temperature range 290 to 504 K and pressures up to 20 MPa with a concentric-cylinder apparatus operating in a steady-state mode. These temperature and pressure ranges cover all fluid states. The estimated accuracy of the method is about 2%. The density dependence of the thermal conductivity has been studied in the liquid region.     

Measurements of the viscosity of liquid R22, R124, and R125 in the temperature range 273–333 K at pressures up to 17 MPa

Viscosity masurements of refrigerants R22, R124, and R125 in the liquid phase have been performed in the temperature range 273–333 K and at pressures up to about 17 MPa. A vibrating-wire instrument has been employed. The overall uncertainty of the experimental values is estimated to be ±0.5%. The experimental data have been represented by polynomial functions of temperature and pressure for the purposes of interpolation.     

高精度单浮子磁悬浮密度测量系统研制

研制了一套高精度的流体压力-密度-温度(p,ρ,T)测量系统,其适用温度、压力和密度范围分别为90—290 K,0—3 MPa,0—2 000 kg/m3。该系统基于阿基米德原理,采用单浮子磁选耦合力传递方法,实现密度的高精度测量。该系统的温度、压力测量标准不确定度分别为5 mK、250 Pa(1.5 MPa量程)/390 Pa(3 MPa量程),密度测量最大相对标准不确定度为0.1%。用新研制的密度测量系统,对190—276 K温度区间和0—3 MPa压力区间的甲烷气体密度进行了测量,实验结果与REFPROP密度值有较好的一致性,验证了该系统的可靠性。