External Pressure Measurements Research Articles

High-pressure fluorescence measurements using a diamond anvil cell (DAC)

A fluorescence detection system for high-pressure experiments was developed. The system pressurizes a diamond anvil cell (DAC) with a stepper motor and acquires impression images and external pressure measurements. Fluorescence images and spectra of the sample are collected by a separate module in the instrument. During experiments, the DAC does not need to be continuously removed and placed back in the instrument for further pressurizing or sample detection. All operations are performed under software control so that pressure inaccuracies caused by manual operations are mitigated. By automatic operation, the detection time at each pressure can be reduced to less than 1 min, which greatly reduces the time required. This instrument can replace several commonly used commercial instruments and is more convenient for high-pressure studies. It will become a powerful tool for in situ examination of samples under high pressure.

Reassessing ISO 9972 constraints: A mathematical analysis of errors in building airtightness tests due to steady wind and stack effect

Building airtightness significantly impacts its energy use estimation. The fan pressurization test, outlined in ISO 9972, is the most commonly used assessment method. A crucial component is the zero-flow pressure difference, influenced only by wind and stack effects. The ISO 9972 mandates that the absolute value of this pressure difference be less than 5 Pa and the minimum pressure station be either 10 Pa or five times the zero-flow pressure difference. The rationale behind these constraints is not evident, often excluding high-rise and buildings in wind-prone areas from standardized testing.This research examines these ISO 9972 requirements, aiming to clarify their basis and propose alternatives. Equations were developed to connect airflow estimation error with the ratio of the measured pressure station to zero-flow pressure difference. The external pressure measurement location during the test was found pivotal in determining airflow errors due to ISO constraints. While existing constraints limit airflow errors in many scenarios, enhancements are possible. If ISO 9972 conditions are unfeasible, always maintaining a 10 Pa buffer across façades can contain maximum airflow errors. This study suggests an alternative constraint with a similar error range (about 15 %) to current ones, enabling standardized testing in environments where existing ISO conditions are unattainable.

A Thirty-Month Seafloor Test of the A-0-A Method for Calibrating Pressure Gauges

Geodetic observations in the oceans are important for understanding plate tectonics, earthquake cycles and volcanic processes. One approach to seafloor geodesy is the use of seafloor pressure gauges to sense vertical changes in the elevation of the seafloor after correcting for variations in the weight of the overlying oceans and atmosphere. A challenge of using pressure gauges is the tendency for the sensors to drift. The A-0-A method is a new approach for correcting drift. A valve is used to periodically switch, for a short time, the measured pressure from the external ocean to the inside of the instrument housing at atmospheric pressure. The internal pressure reading is compared to an accurate barometer to measure the drift which is assumed to be the same at low and high pressures. We describe a 30-months test of the A-0-A method at 900 m depth on the MARS cabled observatory in Monterey Bay using an instrument that includes two A-0-A calibrated pressure gauges and a three-component accelerometer. Prior to the calibrations, the two pressure sensors drift by 6 and 2 hPa, respectively. After the calibrations, the offsets of the corrected pressure sensors are consistent with each other to within 0.2 hPa. The drift corrected detided external pressure measurements show a 0.5 hPa/yr trend of increasing pressures during the experiment. The measurements are corrected for instrument subsidence based on the changes in tilt measured by the accelerometer, but the trend may include a component of subsidence that did not affect tilt. However, the observed trend of increasing pressure, closely matches that calculated from satellite altimetry and repeat conductivity, temperature and depth casts at a nearby location, and increasing pressures are consistent with the trend expected for the El Niño Southern Oscillation. We infer that the A-0-A drift corrections are accurate to better than one part in 105 per year. Additional long-term tests and comparisons with oceanographic observations and other methods for drift correction will be required to understand if the accuracy the A-0-A drift corrections matches the observed one part in 106 per year consistency between the two pressure sensors.

Real-Time Measurements Improve Managed-Pressure Operations in HP/HT North Sea Well

This article, written by JPT Technology Editor Judy Feder, contains highlights of paper SPE 195767, “Using Real-Time Downhole and Along-String Measurements During Drilling and Cementing Operations To Improve Managed-Pressure Operations in a Complex High-Pressure/High-Temperature North Sea Well,” by Tom Brian, Total, and Andy Hawthorn and Duncan Groves, Baker Hughes, prepared for the 2019 SPE Offshore Europe Conference and Exhibition held in Aberdeen, 3–6 September. The paper has not been peer reviewed. This paper describes how new technology was implemented and deployed through a downhole acoustic network through a sequence of runs in complex North Sea wells under managed-pressure conditions. The authors demonstrate how measurements and real-time solutions evolved over the course of the wells to exceed the originally perceived value of top-of-fluid under severe losses. As a result of this deployment and the lessons learned, the acoustic telemetry network will now be used on upcoming, equally challenging wells, and its range of operations will be expanded to include drilling, tripping, and liner-cementing operations. Introduction Several mature fields in the North Sea experience significant challenges relating to high pressures and temperatures, accompanied by the infill drilling challenge of very narrow margins between pore and fracture pressures. To navigate these narrow mud-weight windows, understanding the bottomhole pressure (BHP) is critical. However, in instances of fractured formations above the target zones, severe losses can be encountered during drilling and cementing operations, often leading to the inability to maintain a full mud column at all times and even threatening the ability to reach total depth (TD). To address these issues, the operator investigated an acoustic telemetry system that could provide internal and external pressure measurements, along with other downhole measurements, independently of traditional mud-pulse telemetry in the drilling assembly, to provide real-time distributed pressure data essential to understanding the downhole conditions regardless of circulation, even under severe losses or during tripping and cementing operations. Network Operation The downhole measurement and acoustic telemetry network was deployed on several wells through multiple hole sizes for loss management, liner running, and cementing operations. The initial primary purpose was to monitor the top of the mud at all times, even in significant loss situations. The network consisted of inline tools that picked up and handled like drillpipe. A surface sensor was deployed and attached to the quill of the top drive. This surface receiver then transmitted through a wireless network to a decoding laptop in a safe area. Once there, the data were integrated with other downhole data from the traditional measurement-while-drilling string and with surface data from the rig floor and sensor measurements from the managed-pressure-drilling (MPD) equipment. This process is described more fully in the complete paper. As real-time data were acquired, it became apparent that the data could also be used in real time to help quantify actual downhole pressures. New calculations were designed for simpler visualization of equivalent circulating densities (ECDs) at the shoe, bit, and weak zones in the well at depths beyond the acoustic tools themselves. These data were used to manage the BHP within a 300-psi mud-weight window to enable the well to be delivered ultimately to planned TD.

Internal and external pressure and its non-Gaussian characteristics of long-span thin-walled domes

Understanding the characteristics of internal and external pressures on structures is important for structural design. This paper has experimentally observed internal and external pressures on long-span domes and investigated their non-Gaussian characteristics. Wind tunnel tests on internal and external pressure measurements for a single dome and two neighboring domes were performed. The distribution, non-Gaussian characteristics, and non-Gaussian peak factor of the internal and external wind pressure on the single dome were analyzed. After the results were validated, the distribution, non-Gaussian characteristics, and non-Gaussian peak factor of the internal and external wind pressure on the two neighboring domes under different wind attack angles (interference effect) were discussed. The results show that the characteristics of internal pressures on the single dome and the two neighboring domes are different from that of external pressures, and both the internal and external pressure show remarkable non-Gaussian characteristics. According to these characteristics, positive and negative areas of the internal and external pressure on the domes were defined, and the non-Gaussian peak factors were determined. This study has not only advanced our understanding on characteristics of internal and external pressure on long-span domes, but determined non-Gaussian peak factors that are used for structural design.

A silicon rectangular micro-orifice for gas flow measurement at moderate Reynolds numbers: design, fabrication and flow analyses

This work describes a micro-flowmeter for moderate flow rates of gases based on a differential pressure measurement. The micro-flowmeters consist of a microfabricated silicon–glass rectangular micro-orifice plate, with external pressure measurement. We experimentally evaluate the effects of geometrics parameters, Reynolds number and compressibility on the discharge coefficient. The paper examines a series of 13 rectangular micro-orifice sizes, with orifice hydraulic diameters ranging from 115 to 362 µm. The behavior of the discharge coefficient is presented for orifice Reynolds numbers ranging from 200 to 18000. Agreement is shown between the experimental and numerical results of the discharge coefficient. The micro-flowmeters measure moderate flow of air ranging from 1 to 106 mg/s. This demonstration implements a design method of micro-flowmeters that can be used in a broad range of microfluidic applications, such as microreactors and power MEMS.

Experimental Analysis of Thermal Runaway in 18650 Cylindrical Li-Ion Cells Using an Accelerating Rate Calorimeter

In this work commercial 18650 lithium ion cells with LiCoO2 and LiMn2O4 cathodes were exposed to external heating in an Accelerating Rate Calorimeter (es-ARC, THT Company) in order to investigate the thermal behavior under abuse conditions. During the experiments the temperature and the internal pressure changes of the cells were measured in the ARC. Furthermore, external pressure changes were measured in order to detect venting of the cells. Before the measurement the cells were fully charged and the so-called Heat-Wait-Seek method was applied. This procedure starts by heating the sample in small incremental steps. At the end of each step the calorimeter “waits” if the battery is generating heat that can be measured by a temperature rise (so called "seek" step). When self-heating of the cell is detected, the ARC switches to the adiabatic mode in which the temperature of the calorimeter follows instantaneously the surface temperature of the cell, i.e. the cell cannot exchange heat with the surroundings anymore. This procedure is repeated until a thermal runaway occurs. For the external pressure measurements, the cell was placed in a gas-tight cylindrical compartment inside the calorimeter chamber. This compartment was equipped with an outlet where a pressure line is connected with a pressure sensor. In contrast to the external pressure measurement for internal pressure measurements this pressure line was directly inserted into the cell. Therefore, a suitable place had to be found by using images from X-Ray Tomography. In a second experiment a current profile was applied to the cell with maximal C-rate and cycled until a thermal runaway occurs. During these experiments again the internal and external pressure was measured as well as the cell temperature. In addition the heat capacity was measured to calculate the heat of reaction. From the results of the thermal runaway experiments, three stages (low rate reactions stage, medium rate reactions stage and high rate reactions stage) have been observed. Both pressure and temperature change indicated different stages of exothermic reactions, which would produce gases or/and heat. The onset temperature of thermal runaway was estimated according to temperature and pressure changes in the measurements. Moreover, the different activation energies for the exothermic reactions could be derived from Arrhenius plots. Finally, the experimental data were compared with the results of numerical simulations based on an electrochemical-thermal model which was extended with additional source terms in order to describe the exothermic reactions inside the cell during thermal runaway. The experimentally determined activation energies have been used as input parameters for these simulations. It could be shown that the above mentioned reactions stages can also be found in the simulations.

On the dynamics and kinematics of two‐fluid‐phase flow in porous media

AbstractA model formulated in terms of both conservation and kinematic equations for phases and interfaces in two‐fluid‐phase flow in a porous medium system is summarized. Macroscale kinematic equations are derived as extensions of averaging theorems and do not rely on conservation principles. Models based on both conservation and kinematic equations can describe multiphase flow with varying fidelity. When only phase‐based equations are considered, a model similar in form to the traditional model for two‐fluid‐phase flow results. When interface conservation and kinematic equations are also included, a novel formulation results that naturally includes evolution equations that express dynamic changes in fluid saturations, pressures, the capillary pressure, and the fluid‐fluid interfacial area density in a two‐fluid‐system. This dynamic equation set is unique to this work, and the importance of the modeled physics is shown through both microfluidic experiments and high‐resolution lattice Boltzmann simulations. The validation work shows that the relaxation of interface distribution and shape toward an equilibrium state is a slow process relative to the time scale typically allowed for a system to approach an apparent equilibrium state based upon observations of fluid saturations and external pressure measurements. Consequently, most pressure‐saturation data intended to denote an equilibrium state are likely a sampling from a dynamic system undergoing changes of interfacial curvatures that are not typically monitored. The results confirm the importance of kinematic analysis in combination with conservation equations for faithful modeling of system physics.

Differential capillary viscometer for measurement of non-Newtonian fluids

Here we demonstrate a novel differential microfluidic device for the determination of the rate dependence of the shear viscosity of complex fluids. The device design is simple, robust and does not require internal or external pressure measurements, making the method open for miniaturisation and incorporation into lab-on-a chip applications and online monitoring purposes in process control. The working principle is tested in several possible geometries with different shear thinning model fluids with power-law exponents n ranging from 0 < n < 1.

Response of Hemispherical, Air‐Supported Structures to Wind

This paper examines the response of hemispherical, air‐supported structures to turbulent wind, both theoretically and experimentally. Wind‐tunnel tests were conducted on an aeroelastic model of a hemispherical, air‐supported structure to investigate the wind‐induced response and the internal pressure fluctuations for different gradient wind speeds, exposures, enclosure volumes, and mean internal pressures. Also, a semi‐analytical approach, which depends on external pressure measurements and static deflections, is established for predicting the wind‐induced response of air‐supported structures. To verify this methodology, a rigid hemispherical model was wind‐tunnel tested to measure the external pressures, and static deflections were calculated using the finite element method. The response predicted using the semi‐analytical approach agrees well with the experimental data. The experiments resulted in a number of observations: The mean membrane deflections in strong wind are very large, compared with conventional structures, and mostly outward except on the windward side. The dynamic response is broad band in character, does not feature any resonance amplification, and is much smaller than the mean response. The roof response is very sensitive to the variations in the mean internal pressure. A marked increase of the response occurs when the internal pressure is reduced.

Internal and external pressure measurements in reshaped breakwaters

A series of hydraulic model tests was carried out to investigate the mechanisms by which reshaped breakwaters, that is breakwaters in which the initial profile is adjusted into a more stable profile as a result of wave action, gain their stability. This type of structure has been used frequently in the past decade, particularly in areas where a good supply of rock is available, and has been shown for these circumstances to have better stability characteristics and a much lower cost than conventional multi-layered designs. The breakwater models were instrumented with miniature stainless-steel diaphragm pressure transducers placed along the outer slope of the structure and along the core/filter interface. The motion of the phreatic surface within the internal porous matrix was determined using a set of specially designed capacitance gauges. A substantial reduction in the magnitude of the internal and external pressure fields was found for the reshaped structure compared with a conventional structure. The wave height at which the initiation of armour stone movement occurred was 60% higher for the reshaped structure than for a conventional breakwater armoured with two layers of the same size stone placed on a 1 : 2 slope.

The solar wind interaction with Venus: Pioneer Venus observations of bow shock location and structure

Pioneer Venus observations are used in conducting a study of the location and structure of the Venus bow shock. The trace of the shock in the solar wind aberrated terminator plane is nearly circular at an altitude of 1.38RVindependent of interplanetary magnetic field orientation with an extrapolated subsolar height of 0.38RV. Gas dynamic relations and scaling of the terrestrial analogue are used to determine the effective impenetrable obstacle altitude from the mean shock surface with the conclusion that it lies beneath the observed height of the ionopause. The short‐term variability in shock position is similar to that found at the earth, while over the long‐term bow shock, altitude varies by up to ∼35% in phase with the solar cycle owing to causes other than changing solar wind Mach number. In contrast to ionopause position, which is shown to be well determined by external pressure measurements, bow shock altitude is found to be only weakly dependent upon ionopause height and solar wind dynamic pressure. These results are interpreted in terms of interactions with exospheric neutrals and/or lack of complete deflection of the incident solar wind by currents induced in the ionosphere modifying the flow about Venus from that associated with a tangential discontinuity obstacle of nearly constant radius. The downstream bow shock is smaller in diameter than that of terrestrial case despite the larger Mach cone angle at 0.72 AU most probably due to the smaller relative size of the Venus magnetotail. A brief survey of shock structure with Pioneer Venus instrumentation shows general agreement as to the time and location of the shock crossings with a transition layer thickness of the order of the ion inertial length scale. The observed variation in bow shock structure and the foreshock with upstream parameters was similar to that seen at the earth.