Showing papers on "Pressure measurement published in 1993"

Introduction of fluid mechanics

Abstract: A fluid is a substance in which the constituent molecules are free to move relative to each other Conversely, in a solid, the relative positions of molecules remain essentially fixed under non-destructive conditions of temperature and pressure While these definitions classify matter into fluids and solids, the fluids subdivide further into liquid and gases

Optical in-fibre grating high pressure sensor

Abstract: A high pressure fibre optic sensor using an in-fibre grating has been constructed. The wavelength of peak reflection from an in-fibre grating is tracked as it is pressurised, and a wavelength shift of 0.22nm at 70MPa hydraulic pressure has been observed. This sensor is expected to be an attractive choice for ultrahigh-pressure monitoring.

A survey and new measurements of ice vapor pressure at temperatures between 170 and 250K

Abstract: New measurements of ice vapor pressures at temperatures between 170 and 250 K are presented and published vapor pressure data are summarized. An empirical vapor pressure equation was derived and allows prediction of vapor pressures between 170 k and the triple point of water with an accuracy of approximately 2 percent. Predictions obtained agree, within experimental uncertainty, with the most reliable equation derived from thermodynamic principles.

The variation of the specific heat ratio and the speed of sound in air with temperature, pressure, humidity, and CO2 concentration

Abstract: This paper describes a precise numerical calculation of the specific heat ratio and speed of sound in air as a function of temperature, pressure, humidity, and CO2 concentration. The above parameters are calculated utilizing classical thermodynamic relationships and a real gas equation of state over the temperature range 0 °C–30 °C. The shortcomings of previous determinations are also discussed. For both parameters, the coefficients of an interpolating equation are given, which are suitable for use in applications requiring high precision. The overall uncertainty in the specific heat ratio is estimated to be less than 320 ppm and the uncertainty in the speed of sound is similarly estimated to be less than 300 ppm.

Device for monitoring the air-pressure in pneumatic tyres fitted on vehicle wheels

Abstract: A device for monitoring the air pressure in pneumatic tires comprises a transmitting device fitted to each wheel of a vehicle and rotating with it, and a receiver which is built into the vehicle or accommodated in a separate housing. The transmitting device mounted in the wheel comprises a pressure gauge for measuring the tire pressure, a transmitter and a signal generator which generates an identification signal unique to each transmitter and transmitted before or after the pressure signal. The receiver processes received signals only when the identification signal received matches a reference identification signal stored in the receiver. This facilitates reliable operation of the monitoring device and prevents false alarms.

Apparatus and method for determining a plurality of hemodynamic variables from a single, chroniclaly implanted absolute pressure sensor

Abstract: A method and apparatus for monitoring and measuring the hemodynamic status of a patient's pulmonary pressure and right atrial pressure. The aforementioned is achieved by using an implanted absolute pressure sensor located in the right ventricle, coupled to an implantable monitoring device, which records pressure values in response to a combination of sensed electrical depolarizations of the atrium and ventricle and occurrence of first and second derivatives of the pressure signal having values less than zero.

Apparatus and method for measuring relative permeability and capillary pressure of porous rock

Abstract: A core sample of a porous rock from a subterranean reservoir is placed in a pressure cell holder. The sample is desaturated to first fluid irreducible desaturation with a second fluid through a porous plate preferentially wet to only the first fluid. The sample is then flooded with a plurality of first and second fluid ratios. Core pressure is measured along the core at various differential pressure plateau's during initial first fluid desaturation and again during fluid flooding with first and second fluids. A computed tomography (CT) scanning system provides images of the density distribution within the core sample during such flooding. Fluid saturation, determined from these CT images, and the pressure measurements are used to determine the relative permeability and capillary pressure responses of the fluids within the subterranean reservoir.

Aerodynamic applications of pressure sensitive paint

Abstract: A pressure measurement technique based on a photoluminescent coating is being developed and used for aerodynamic applications. Visible light excites probe molecules in the paint and their luminescence is related to the static pressure. Details of the illumination, luminescence detection, and data reduction for this technique are presented. These include key issues such as temperature effects, camera calibration, and model movement. Results from this technique in a variety of flowfields are given. Comparisons with pressures measured using standard wall taps show good agreement

Correlations between flow resistance and geometry in a model of the human nose.

Abstract: The relationship between the pressure losses within the nasal airways and nasal geometry were studied in a 3:1 scale model. The geometry of the model was based on magnetic resonance images of the skull of a healthy male subject. Pressure measurements, flow visualization, and hot-wire anemometry studies were performed at flow rates that, in vivo, corresponded to flows of between 0.05 and 1.50 l/s. The influence of nasal congestion and the collapse of the external nares were examined by using modeling clay to simulate local constrictions in the cross section. A dimensionless analysis of the pressure losses within three sections of the airway revealed the influence of various anatomic dimensions on nasal resistance. The region of the exterior nose behaves as a contraction-expansion nozzle in which the pressure losses are a function of the smallest cross-sectional area. Losses in the interior nose resemble those associated with channel flow. The nasopharynx is modeled as a sharp bend in a circular duct. Good correspondence was found between the predicted and actual pressure losses in the model under conditions that stimulated local obstructions and congestion.

Deviatoric stress in a quasi-hydrostatic diamond anvil cell: Effect on the volume-based pressure calibration

Abstract: The deviatoric stress in gold as a function of pressure and temperature, in a diamond anvil cell with neon as the pressure medium, is measured based on gold diffraction peaks. We find that the deviatoric stress becomes detectable at a pressure of about 15 GPa and reaches 0.62 GPa by 30 GPa. Upon heating, the deviatoric stress decreases rapidly and disappears at a temperature of about 650 K. The effect of deviatoric stress on the unit cell volume measurement and further on the volume-based pressure calibration is directly proportional to K/μ of the measured material, and it is also related to the anisotropy, as well as the sign of the deviatoric stress and the orientation of the x-ray diffraction. We find that the measured unit cell volume of gold is very sensitive to the deviatoric stress due to a high value of K/μ. Although the observed deviatoric stress may be insignificant for most samples, it causes a significant systematic error on the pressure calibration based on the unit cell volume of gold.

Surface pressure field mapping using luminescent coatings

Abstract: In recent experiments we demonstrated the feasibility of using the oxygen dependence of luminescent molecules for surface pressure measurement in aerodynamic testing. This technique is based on the observation that for many luminescent molecules the light emitted increases as the oxygen partial pressure, and thus the air pressure, the molecules see decreases. In practice the surface to be observed is coated with an oxygen permeable polymer containing a luminescent molecule and illuminated with ultraviolet radiation. The airflow induced surface pressure field is seen as a luminescence intensity distribution which can be measured using quantitative video techniques. Computer processing converts the video data into a map of the surface pressure field. The experiments consisted of evaluating a trial luminescent coating in measuring the static surface pressure field over a two-dimensional NACA-0012 section model airfoil for Mach numbers ranging from 0.3 and 0.66. Comparison of the luminescent coating derived pressures were made to those obtained from conventional pressure taps. The method along with the experiment and its results will be described.

Continuous ultrasonic devulcanization of vulcanized elastomers

Abstract: This invention relates to a continuous ultrasonic method and apparatus for breaking the carbon-sulfur (C-S), sulfur-sulfur (S-S), and if desired, carbon-carbon (C-C) bonds in a vulcanized elastomer. It is well known that vulcanized elastomers having a three-dimensional chemical network, cannot flow under the effect of heat and/or pressure. This creates a huge problem in the recycling of used tires and other elastomeric products. Through the application of certain levels of ultrasonic amplitudes in the presence of pressure and optionally heat, the three-dimensional network of vulcanized elastomer can be broken down. As a most desirable consequence, ultrasonically treated cured rubber becomes soft, thereby enabling this material to be reprocessed and shaped in a manner similar to that employed with uncured elastomers. The apparatus relates to the ultrasonic reactor (20) (e.g. an extruder). The reactor (20) is connected to an ultrasonic die assembly (10); the die assembly (10) consists of a transducer portion (12), which includes a power converter (14) and booster (13), connected to a horn portion (15), the assembly being supported by mounting bracket (18), and being attached to the reactor (20) through an adaptor portion (19). The reactor (20) includes a barrel (22), fed through hopper (24), the screw (26) within the barrel portion being driven by a drive (25), energized by a motor (28) (not shown). The horn portion (15) includes a die portion (16) through which the devulcanized elastomer being extruded is forced at a pressure shown by a pressure gauge (21). The ultrasonic generator (10) of the ultrasonic die of the invention, movably attached by mounting bracket (18) through adaptor legs (19) to a reactor (20). The reactor (20) is surrounded by a heating jacket (42). Vulcanized material is fed into die (16) through reactor bore exit (36) of exit bore diameter (dr) and into die inlet bore (38) of diameter (di). The vulcanized material is moved under pressure toward die exit bore (37) and leaves through die inlet bore (38).

Planar Measurement Technique for Compressible Flows Using Laser-Induced Iodine Fluorescence

Abstract: A unified laser-induced fluorescence technique for conducting planar measurements of temperature, pressure and velocity in nonreacting, highly compressible flows has been developed, validated and demonstrated. Planar fluorescence from iodine, seeded into air, was induced by an argon-ion laser and collected using a liquid-nitrogen cooled CCD camera. In the measurement technique, temperature is determined from the fluorescence induced with the laser operated broad band. Pressure and velocity are determined from the shape and position of the fluorescence excitation spectrum which is measured with the laser operated narrow band. The measurement approach described herein provides a means of obtaining accurate, spatially-complete maps of the primary flow field parameters in a wide variety of cold supersonic and transonic flows.

A square-diaphragm piezoresistive pressure sensor with a rectangular central boss for low-pressure ranges

Abstract: Describes the theory and experimental data for a piezoresistive low-pressure sensor featuring a variety of advantages. The objective of this development was a sensor with high sensitivity, high overload range, and good linearity. In comparison to familiar sensor types, the sensor developed for the pressure range of 10 kPa exhibits an excellent sensitivity of 35 mV/V FSO (full scale output) and nonlinearity >

Optical pressure/density measuring means

Abstract: An apparatus and method for rapidly and accurately determining the pressure of a fluid medium in either a static or dynamic state. The pressure is determined by making a measurement of the velocity of a light beam that is directed through the fluid medium along a pathway that enables an integrated pressure measurement to be made along the pathway, rather than making such a measurement only at a single point in the medium. A HeNe laser is configured to emit a beam of two frequencies separated by about 2 MHz. One of these beam frequencies is directed through the fluid medium and is reflected back through the medium to a non-linear diode detector. The other beam frequency is passed directly to a diode detector without traversing said medium. The diode detector is operated to determine the frequency shift or beat frequency between the two beam frequencies. Any variation in the frequency of said reflected beam that is caused by a change in its velocity as it is passed through the fluid medium causes a change in the beat frequency. This beat frequency change is then converted to an output signal value corresponding to the pressure of the medium. The measurement instrument apparatus is remotely positioned relative to the medium being measured, thus the apparatus is immune from electro-magnetic interference and can operate in conditions of high radiation, corrosion and extraordinarily high temperature.

Method and apparatus for measuring pressure with fiber optics

Abstract: A method and apparatus are provided for measuring pressure in a combustion chamber of an internal combustion engine is provided with a non-intrusive, metal-embedded fiber optic pressure sensor. A Fabry-Perot Interferometer is arranged in a terminated, single mode fiber to function as a pressure gauge. The fiber Fabry-Perot Interferometer (FFPI) is embedded in a metal part which is disposed in the cylinder head of the engine. The metal part and FFPI experience a longitudinal compression in response to the pressure in the chamber. In another aspect of the invention, a non-intrusive fiber containing the FFPI is embedded in a hole drilled or otherwise provided in the metal housing of a spark plug. The spark plug is threaded into the cylinder head of an internal combustion engine and is directly exposed to the combustion chamber pressure. Consequently, the spark plug housing and FFPI experience a longitudinal strain in response to the pressure in the chamber.

Low cost versatile pressure transducer

Abstract: A versatile low cost capacitive type of electrical pressure transducer includes a sensor module providing an output signal indicative of fluid pressure effective thereon, and an elongate cylindrical housing receiving the module and providing for communication thereto of a first fluid pressure (which may have a high pressure level), and of a second fluid pressure (which may range from a vacuum through atmospheric pressure to a pressure level of a few hundred pounds). Consequently the transducer may operate as a gauge pressure sensor or as a differential pressure sensor. Alternatively, other types of sensor modules may also be employed in housings of the same or substantially the same design to fulfill other types of pressure measurement tasks. The commonality of component parts of the various sensors contributes to a reduces cost. Also, the components of the housing are economical to manufacture and assemble, and provide for testing and calibration of the sensors at an intermediate step of manufacture. Thus, further cost savings are realized. The housing provides for electrical shielding of the sensor module from electromagnetic and radio frequency interference, as well as filtering power surges and higher frequency noise. Accuracy and service life of the transducers are thus improved. A connector portion of the housing is secured by a tubular portion thereof by means of low cost rolling operations, and also provides a second source of support to the sensor module in resisting displacement in the housing caused by high fluid pressures. As a result an inexpensive pressure transducer is realized which is applicable to measurement of rather high fluid pressures.

Uncertainty Estimates for Pressure Sensitive Paint Measurements

Abstract: A recently introduced surface pressure measurement technique for aerodynamic applications uses pressure sensitive luminescent coatings. The primary measurable is luminescent light intensity, but the determination of pressure also requires the measurement of other variables, such as a reference light intensity and surface temperatures. Each of the primary measurables is associated with an error that contributes to the uncertainty of the pressure computed from all inputs. This paper investigates these contributions to the resultant uncertainty, both in fundamental terms and in terms of commonly used wind tunnel parameters. The uncertainty is sharply dependent on both freestream and local flow conditions, such that a simple global characterization of error magnitude does not seem to be practical. Spatial surface temperature variations and temperature differences between reference and run conditions may significantly affect the results.

Recommended Practice for the Calibration of Mass Spectrometers

Abstract: This Recommended Practice addresses issues involved in the use of partial pressure analyzers (PPAs) for quantitative analysis and describes recommended apparatus and procedures for determining resolution and sensitivity of a PPA so that the instrument can be used quantitatively for partial pressure, partial flow and gas composition analysis. This updates previous material in the AVS Standard 2.3-1972 (tentative) by including reference to current pressure transfer standards and computer controlled PPAs. This document presents an introduction to PPAs and how they work, definitions pertinent to the use of PPAs, equipment needed for calibration, instrument setup prior to calibration and the measurement of sensitivity and linearity by various methods. Four methods of calibration of a PPA are described as follows: (1) the direct comparison of the PPA output with a transfer standard pressure gauge, (2) the indirect comparison of PPA readings with readings of a transfer standard pressure gauge separated by a flow restriction (pressure divider method), (3) comparison of the PPA output response to known gas flow rates. The first three methods may be carried out on a test stand of suitable design or in situ. The fourth method requires that the pumping speed during calibration be the same as the pumping speed during use, and normally implies that the PPA is calibrated in situ. Discussion on gas interactions, sources of nonlinearity, stability of sensitivity and quality assurance methods is given.

Blood extraction flow control calibration system and method

Abstract: A method and system for calibrating and controlling the withdrawal of a fluid, such as blood, from a fluid source, such as a blood vessel, includes a fluid pump (26), a pressure sensor (24), a flow rate sensor, and a microprocessor based flow control subsystem. The flow control subsystem optimizes the flow rate by sensing zero flow rate pressure within the subject, making a plurality of periodic flow path pressure measurements and extrapolating a calibration flow rate curve (110). A control curve (130) is generated by utilizing the zero-flow rate pressure point (100), the slope of the calibration curve (110), and an empirically predetermined pressure offset value (150). The blood pump (26) is then operated at a maximum speed that is limited by the flow control curve (130) to maximize flow without occlusion or collapse of the blood vessel during blood withdrawal. The method and system of the invention is particularly applicable to automated apheresis system.

Coiled tubing system used for the evaluation of stimulation candidate wells

Abstract: The present invention is an improved apparatus and method for measuring downhole flowing and shut-in pressures to determine the condition of the reservoir and the potential of the well as a stimulation candidate. The tool string of the present invention is a novel combination of existing equipment that allows an electronic pressure gauge and shut-in tool to be run into the hole with coiled tubing. The present invention, in most cases, solves the potential problem of having to shut in or kill a flowing well prior to and after performing pressure testing, preventing lost production or potential well damage due to the killing operation. In addition, the present invention provides accuracy over current coiled tubing systems by reducing the effects of wellbore storage on pressure build-up testing.

Pressure measurements on a pitching airfoil in a water channel

Abstract: Measurements of unsteady pressures over a symmetric NACA 0015 airfoil performing pitching maneuvers are reported. The tests were performed in an open-surface water channel specially constructed for this purpose. The design of the apparatus allowed the pressure measurements to be made to a very high degree of spatial and temperal resolution. Reynolds numbers in the range of 5.2×10 4 to 2.2×10 5 were studied. Although the results qualitatively agreed with earlier studies performed at similar Reynolds numbers, the magnitudes of pressure and aerodynamic forces measured were observed to be much larger than those measured in earlier pitchup studies

Improved calibtration curve for the Sm2+:BaFCl pressure sensor

Abstract: The pressure sensor proposed by Shen, Gregorian & Holzapfel [High Press. Res. (1991), 7, 73–75], based on the pressure-dependent shift of the luminescence line due to the 5D0−7F0 electronic transition of Sm2+ in a matrix of BaFCl, has been tested in a diamond-anvil cell and calibrated against the R1−R2 doublet shift of ruby and the known NaCl equation of state, in the pressure range between 0.0001 and 4.3 GPa. The parabolic dependence of the shift from the pressure can be approximated by the equation Δ(nm) = 1.46P − 0.047P2, where the shift, Δ, is in nm and the pressure, P, in GPa. The estimated error in the pressure measurements is 5%. The Sm2+: BaFCl luminescence sensor can be advantageously used in the low to moderate pressure range (0.0001–5 GPa or more).