C. Edwards

Development of an automated phase behaviour measurement system for lean hydrocarbon fluid mixtures, using re-entrant rf/microwave resonant cavities

Abstract A re-entrant resonator has been developed and tested, specifically tailored for automated phase boundary measurements in the natural gas fluids of the north west shelf of Western Australia. The resonator is based on a constant volume, rf re-entrant resonant cavity capable of detecting phase boundaries in binary mixtures [1] . Our resonator is capable of isothermal and isobaric measurements in addition to isochoric measurements. The vacuum characteristics of the resonator have been studied using extensive models, and measured in experiments with helium. The resonator was then employed to study phase transitions in pure carbon dioxide and a binary mixture of propane and carbon dioxide. The suitability of the resonator for dew point detection in lean hydrocarbon mixtures was also tested. The results indicate that microwave resonators are not just limited to phase boundary measurements, rather they can measure phase volumes and potentially determine the compositions of the two-phases. However, further development is needed to achieve a system in which accurate measurements can be made for gas condensate type fluids.

Laboratory tests of a mobile superconducting gravity gradiometer

Abstract We describe a gravity gradiometer designed to measure off-diagonal components of the earths gravity gradient tensor, and intended for airborne geophysical exploration. The instrument consists of an orthogonal pair of mass quadrupoles pivoted about a common vertical axis. Each quadrupole is a rectangular bar of niobium having square cross section and with integrally machined flexural micro-pivots. Superconducting niobium pancake coils form the basis of the SQUID based transducers and provide supplementary magnetic springs to enable matching of mechanical parameters.

Dew Point, Liquid Volume, and Dielectric Constant Measurements in a Vapor Mixture of Methane + Propane Using a Microwave Apparatus

An apparatus based on a microwave resonant cavity has been used to measure dew points and liquid volume fractions in a zC3H8+(1−z)CH4 mixture with z=0.250±0.001 mole fraction. The microwave cavity is optimized for the measurement of small liquid volume fractions in lean natural gases. Argon and carbon dioxide were used to calibrate the resonator for dielectric constant and liquid volume measurements in mixtures. Estimated uncertainties are 1×10−4 for dielectric constants and (0.05 K, 0.05 MPa) for dew points. The novel use of multiple cavity modes, each sensitive to different liquid volume regimes, substantially improves the reliability of liquid volume measurements. Liquid volume fractions can be resolved to better than 0.01%. Densities inferred from (P,T,ε) measurements agree within 0.6% of equation of state (EOS) densities with an estimated uncertainty of 0.1%. Liquid volume fractions measured with the microwave apparatus compare well with values determined using a conventional PVT cell. Fourteen dew points were measured at ten different temperatures. From these data, the mixture cricondentherm is estimated to be (293.45±0.05) K, which is 0.15 K higher than the value predicted using the Peng–Robinson equation of state.

Performance of a superconducting gravity gradiometer

Abstract We report the laboratory operation of an rf SQUID-based superconducting gravity gradiometer designed to measure from an aircraft, off-diagonal components of the earths gravity gradient tensor. A detailed numerical model of the multi-mode electromechanical system shows excellent agreement with the experimental observations. We have demonstrated a common mode rejection ratio to linear accelerations of 180dB, as well as 60dB of active thermal compensation below 0.01Hz. Short term measurements show the instrument to be SQUID noise limited at 0.5Eo¨/√Hz in a frequency band from 50mHz to 1Hz. After correcting for the remaining effects of thermal fluctuations and flux creep the noise below 50mHz has a 1/f characteristic which is also dominated by the SQUID.

A prototype superconducting gravity gradiometer

We report the successful laboratory test of a single-axis gradiometer designed to measure a diagonal component of the earths gravitational gradient tensor. It Consists of a pair of accelerometers mounted with their sensitive axes vertical and in line. The difference in displacement of the accelerometers is proportional to the component of the tensor gradient and is sensed via the modulated inductance of a superconducting coil coupled by a superconducting transformer into an RF biased SHE SQUID with energy sensitivity 4 × 10-29J/Hz. Rejection of in-line common mode accelerations is achieved by trimming the natural resonant frequency of each accelerometer: the restoring force acting on an accelerometer test mass is partly magnetic and can be trimmed by adjusting the persistent currents in a pair of force coils. A common mode rejection ratio exceeding 95 dB has been achieved in the presence of linear accelerations \sim 10^{-3} ms-2, and a laboratory generated gradient of 30 Eo rms has been detected with a signal to noise ratio of about 100. The dependence of this signal on the distance between source and detector has the expected Newtonian form. Under quiet conditions the background noise level of the instrument is at present 3 Eo/ \sqrt{Hz} . ( 1 Eo = 10-9s-2.) This is close to the practical limit achievable for such a single axis configuration: a three axis instrument for geophysical application is under development.

A high-resolution superconducting pressure gauge for studies of critical phenomena in quantum fluids

Abstract We are developing a pressure gauge based on a superconducting transducer for measuring pressures up to 30 bar with a fractional resolution of 10 −11 . It is intended that this instrument will enable pressure control better than 10 −10 bar. We report the current performance of a second-generation prototype pressure transducer being developed at the University of Western Australia.

An application of diffusion bonding in the construction of a miniature pressure vessel

Abstract The diffusion bonding technique has been used to meet an exacting specification calling for the flux-free sealing of a shallow, disc-shaped pressure shell (0.022 × 1.020 in. dia) whose components parts were machined as two separate pieces. The joint involved the simultaneous edgewise bonding of many annular bulkheads 0.005 in. wide and, in the same operation, the fabrication of a pressure valve by sandwiching a thin flexible diaphragm between the valve features machined in each half of the vessel. Relative drift of the valve parts and buckling of the thin outer shell ( 0.005 in.) of the container during bonding were prevented by careful design of the compression jig. Destructive testing of a trial joint and pressure testing (up to 100 atms) of the finished vessel indicate that the strength of the multiple bond is of the order of that of the parent titanium.