Manometric Research Articles

Flow boiling of liquid nitrogen in a horizontal macro-tube at low pressure: Part Ⅱ – Heat transfer characteristics

Nitrogen is the most important cryogen in superconductivity. This study investigates the heat transfer characteristics of flow boiling in a horizontal macro-tube with an inner diameter of 10 mm, particularly focusing on flow boiling at negative gauge pressure. The experiments cover the following ranges: inlet pressure from −31.0 to 2.5 kPa, mass flux from 27.0 to 71.3 kg/(m2·s), and heat flux from 0 to 28.68 kW/m2. The effects of operating parameters on the heat transfer coefficient (HTC) are examined, and the HTC data are compared with the predicted value from four correlations. At the bottom wall, the HTC distribution exhibits a “two-peak” shape. The primary peak is dominated by nucleate boiling in bubbly, plug, and slug flow with low vapor quality, while the secondary peak is dominated by convective evaporation with higher vapor quality. These two regions are roughly divided by the vapor quality of 0.3 to 0.4. In stratified flow, the HTC at the top wall is generally lower than that at the bottom. The HTC increases as the pressure decreases, particularly in the convective evaporation region. This is attributed to the high liquid–vapor density ratio, extensive thermal conductivity, and substantial surface tension at lower pressure. The effect of heat flux or mass flux on the HTC at the bottom wall differs between the nucleate boiling and convective evaporation regions. Increasing the heat flux improves the HTC where nucleate boiling dominates, while increasing the mass flux significantly improves convective evaporation, especially at higher heat flux. All selected correlations overestimate the HTC at the top wall. The Shah correlation demonstrates the best prediction accuracy for the HTC at the bottom wall, both at near atmospheric pressure (Mean Relative Error, MRE = 21 %) and at negative pressure (MRE = 19 %).

Theoretical Hydrodynamic Modeling of the Fluidized Bed Photoreactor (FBP) Using Computational Fluid Dynamics (CFD): Fluidization Conditions for TiO2-CuO Immobilized on Beach Sand Granules

The flow regime is essential in the photoreactor’s performance in pollutant degradation in the aqueous medium, especially in fluidized systems. Therefore, this study is focused on determining the fluidization conditions of a granular catalyst based on TiO2-CuO nanoparticles (1 wt.% CuO) immobilized on beach sand granules using an FBP photoreactor. COMSOL Multiphysics 6.0 was employed for inlet velocities between 0.1 m/s and 1.0 m/s, mainly from the Reynolds averaged Navier–Stokes (RANS) turbulence model and the Stokes drag law. The results indicated that the average velocities in the annular section are much higher (4.11ut and 5.42ut) than the required particle terminal velocity. Moreover, the pressure contour lines revealed that these flow velocities do not represent excessive pressures in the concentric cylinders, with maximum gauge pressures of 740.52 Pa and 1310 Pa for inlet velocities Uo=0.75 and 1.0 m/s, respectively. Finally, it was determined that the Reynolds number adjusted (Repf) values lower than or equal to 1.37×10−3 allow high fluidization after 2 seconds. This information makes it possible to adapt and assemble the FBP equipment for future photocatalytic evaluation.

Island-based GNSS-IR network for tsunami detecting and warning

Deep-sea tsunami detection relies on Deep-ocean Assessment and Reporting of Tsunamis (DART), GNSS buoys, and cabled Ocean-Bottom Pressure (OBP) gauges, which are very expensive and difficult to maintain, and often suffer from vandalism or negligent damage. Here, we exploit the potential of establishing a less expensive and more robust island-based geodetic network for tsunami detecting, source reconstruction and warning. The network locates at the coastline of islands and uses a new technique: GNSS Interferometric Reflectometry (GNSS-IR). GNSS-IR retrieves sea levels from combination of the direct and reflected signals from the sea surface sent by satellites. To test the feasibility and efficiency of such a new geodetic network, we use the South China Sea region as an example, and compare its performance in reconciling the variable slip distribution on the Manila megathrust with the previously designed deep-sea monitoring system, i.e., DARTs and planned cable-based OBP gauges. We find that the newly designed GNSS-IR network could work equally well as the cabled OBP network in detecting tsunamis if the stations are built in strategically chosen locations. Combining GNSS-IR with a Kalman filter approach, we demonstrate that carefully situated coastal GNSS stations at global remote deep-ocean islands could function similarly to conventional tide gauges but with advantages of simultaneously measuring relative sea-level and land-height changes, meanwhile suffering lower risk from damaging sea-level events and potential vandalism.

An apparatus to measure thermal conductivity of ceramic pebble beds under uniaxial compressive stress

Pebble beds have various applications in many industrial and research sectors. Lithium ceramic pebble beds have specific application in fusion reactors as one of the most promising candidates for tritium breeding material. During the operation of the fusion reactor, these pebble beds will have to sustain various thermal and mechanical stresses. Therefore, it is necessary to do thermal characterisation of these pebble beds under different stress conditions and generate sufficient data on their thermal properties, which is essential for designing breeder units of fusion reactors. In this work, an apparatus has been designed to evaluate the thermal conductivity of ceramic pebble beds under compressive stress. It can be mounted to any standard universal testing machine with the necessary adjustments. The apparatus is based on the transient hot-wire method, widely used to evaluate the thermal conductivity of porous materials. A platinum wire with a diameter of 0.5 mm was used as a hot-wire. Instead of utilising a thermocouple, the 4-wire approach was used to obtain the temperature. The transient temperature response of the hot-wire was obtained by applying a 7A constant current to it and monitoring the voltage drop along its 40 mm length. The thermal conductivity of the water gel was measured to assess the accuracy of the apparatus; the results showed a less than 1.5 % variation from the reference value. In this study, the thermal conductivity of Li2TiO3 pebbles was measured in an air and helium environment in different stress conditions. In an air environment, measurements were done at atmospheric pressure, whereas in a helium gas environment, they were performed at gauge pressures of 0.05 bar, 0.5 bar, and 1 bar. The measurements were conducted in two scenarios: (i) constant stress condition at 0, 3, and 6 MPa, and (ii) Cyclic loading-unloading of 0.037–3 MPa and 0.037–6 MPa. It was found that the pebble bed's thermal conductivity rose in tandem with increased compressive stress in both the helium and air environments. Pebble bed’s thermal conductivity was found to be higher in a helium gas environment than in air. The thermal conductivity of the pebble bed increased slightly with rising helium gas gauge pressure from 0.05 bar to 1 bar. This work provides a design to incorporate 4-wire temperature measurement in the hot-wire method for thermal conductivity measurement of compressed pebble beds. It also contributes to the thermal conductivity data of Li2TiO3 pebbles in cyclic stress conditions in helium and air environments.

Demonstration of a Transparent and Adhesive Sealing Top for Microfluidic Lab-Chip Applications.

A transparent and adhesive film-based enclosing and sealing method is here presented for out-of-cleanroom-based open-form microfluidic devices. The commercially available polyester flexible film known as Microseal 'B' is presented in this paper as a cover seal for open-form microfluidic devices. This film is adaptable to high working temperatures and is biocompatible. The quality of the sealing film was investigated by leak tests, fluorescence tests, and contact angle measurements. The investigations revealed its sealing strength, fluorescence detection compatibility, and surface wettability. It was found that the proposed sealing polyester film on the 3D-printed device could sustain a gauge pressure of 2.7 atm at a flow rate of 4 mL/min without any leaks. It also provided fluorescence detection compatibility and an intensity-to-background ratio in the range of 2.3 to 4.5 for particle sizes of 5 μm and 15 μm, respectively, which is comparable with the performances of other sealing materials. The film's hydrophobicity is comparable to other polymers used in microfluidics. This paper concludes by showcasing some applications of such transparent tops in classical microfluidic devices used for droplet generation and fluid mixing, in order to demonstrate the prospects of this fabrication technique in lab-on-a-chip devices.

Ten Years of Experience on the Effectiveness and Efficiency of the Cleanfield Device in Cardiothoracic Surgery

AbstractThe process of blood management and treatment from the surgical field to produce concentrated red blood cells (RBC) is crucial in the context of cardiothoracic surgery and in other branch of surgery. The role of autotransfusion reservoir is not well described in the literature in terms of superiority suction for hemolysis prevention. In this context, we presented a ten-year single-center retrospective analysis on suction, filtering, and blood collection from surgical field through the use of the Cleanfield Autotransfusion Reservoir (Eurosets SRL, Medolla, Italy) in terms of performance, effectiveness, and safety. From January 2013 to January 2023 were collected and analyzed the consecutive uses of Cleanfield Autotransfusion Reservoir in a single cardiothoracic surgery center Anthea Hospital Gvm Care & Research, Bari, Italy. For single procedure, the number of cleanfield disposable used, the relative maximum blood volume filtered and collected, the suction pressure from devices through vacuum meter and the electronic suction pressure measurements in the devices for suctions and the presence and the incidence of adverse events during the use (implosion, clot formation, inability to cell saver use, inability to suction during the use) were analyzed. 5202 Cleanfield disposable autotransfusion reservoir were analyzed for blood volume suction, filtering and collection on 5199 cardiac surgery procedures, the maximum blood volume filtered and collected was 1997 ± 123 ml, the mean suction pressure measured from the device with vacuum meter during suction use was 38 ± 3 mmHg, the mean suction pressure measured in the device during suction use was 38 ± 2 mmHg, no presence of adverse event was reported for implosion, clot formation, inability to cell saver use, and inability to suction during the use. In our retrospective report, the use of Cleanfield autotransfusion reservoir (Eurosets SRL, Medolla Italy) in cardiothoracic surgery context was safe and effective for blood volume suction, filtering, and collection.

Comparison between Microwave Radar Gauge and Pressure Gauge in Monitoring Sea Level Surface at Alexandria Naval Port

Comparison between Microwave Radar Gauge and Pressure Gauge in Monitoring Sea Level Surface at Alexandria Naval Port

Technological challenges in manufacturing of vacuum gauge thermionic cathode using thick-film technology

Abstract This paper focuses on the development of a technological challenges of manufacturing the planar ceramic vacuum sensor based on the principles of hot-cathode ionization in the Bayard-Alpert configuration. The goal is to simplify the technological process by utilizing planar platinum structures with gold electrical paths instead of 3-dimensional structures. Various methods were tested, including the use of carbon-based SVM (Sacrifice Volume Materials) materials, but without success. Wet-etching using potassium hydroxide on Al2O3 substrates showed promise results. The findings highlight the challenges and progress made in developing the thermo-emittercomponent of the vacuum sensor.

Real‐Time Water Levels Using GNSS‐IR: A Potential Tool for Flood Monitoring

AbstractGlobal Navigation Satellite System Interferometric Reflectometry (GNSS‐IR) using low‐cost antennas is a practical solution for monitoring water levels from rivers, lakes and seas that does not require submerging any instruments in water. Here we present a novel method for obtaining real‐time water levels using multiple low‐cost antennas that we validate by comparing with measurements from a co‐located pressure gauge at two sites with variable tides. Additionally, we use survey measurements to show that there is a site‐dependant mean bias in GNSS‐IR measurements up to a few centimeters, but this mean bias can be effectively removed by using a correction for the effect of tropospheric delay. We conclude that GNSS‐IR water level sensors could be a powerful tool for real‐time applications such as flood or storm surge monitoring and water resource management, as well as for improving the spatial coverage of sensors in remote regions.

Optimizing suction force in mechanical thrombectomy: Priming the aspiration tubing with air versus saline.

We sought to investigate how priming the tube between air versus air mixed with saline ex vivo influenced suction force. We examined how priming the tube influenced peak suction force and time to achieve peak suction force between both modalities. Using a Dwyer Instruments (Dwyer Instruments Inc., Michigan City, IN, USA), INC Digitial Pressure Gauge, we were able to connect a .072 inch aspiration catheter to a rotating hemostatic valve and to aspiration tubing. We recorded suction force measured in negative inches of Mercury (inHg) over 10 iterations between having the aspiration tube primed with air alone versus air mixed with saline. A test was used to compare results between both modalities. Priming the tube with air alone compared to air mixed with saline was found to have an increased average max suction force (-28.60 versus -28.20 in HG, p<0.01). We also identified a logarithmic curve of suction force across time in which time to maximal suction force was more prompt with air compared with air mixed with saline (13.8 seconds versus 21.60 seconds, p<0.01). Priming the tube with air compared to air mixed with saline suggests that not only is increased maximal suction force achieved, but also the time required to achieve maximal suction force is less. This data suggests against priming the aspiration tubing with saline and suggests that the first pass aspiration primed with air may have the greatest suction force.

Cylindrical single-wall and double-wall structures with or without internal water subjected to underwater shock loading

A series of experimental studies were conducted for cylindrical structures subjected to underwater shock loading to understand their dynamic responses and failure characteristics. All tests were performed inside an anechoic water tank. The submerged test cylinders were freely suspended, and an underwater shock loading was generated by the Compressed Air Shock Pipe Underwater Release (CASPUR) system. Cylinders were made of two different materials. The first group of cylinders was fabricated from carbon fiber and resin using the filament winding technique. The winding angles were ± 45° resulting in the same properties along axial and hoop directions. The second group of cylinders was constructed using a 3-D printer with polylactic acid (PLA) material. The 3-D printed cylinders had an orthotropic material property with different values in the axial and hoop directions. Both single-wall and double-wall cylindrical structures were tested. The latter consisted of two concentric cylinders of different diameters with uniform spacing between them. In addition, within the single-wall cylinders and the annuli of double-wall cylinders, the water fill was varied at 0%, 50%, or 100%. Pressure and strain gages were used to measure the shock pressure and deformation of the cylinders. The number of cylinders such as single-wall or double-wall and the internal water resulted in significant effects on the measured dynamic response (i.e., strain gage response) as well as the failure loading and failure characteristics including major failure locations. Internal water reduced the strain on the cylinders and made them withstand greater shock loading for both single-wall and double-wall cylinders.

Cold atom technology applied to ultra-high vacuum (UHV) measurements

Accurate measurements in ultrahigh vacuum (UHV) are increasingly critical for scientific research and industrial applications. Here, we report an experimental study of UHV measurements performed on a 7Li cold atom vacuum measurement setup. The setup enables cold atom vacuum measurements in the magneto-optical and magnetic traps (CAVM-MOT and CAVM-MT), respectively. The precision of the vacuum measurements in both traps was effectively improved after optimisation of the excited-state fraction data processing for CAVM-MOT and the initial loading control method for CAVM-MT. A comparison of the measurement methods was carried out in combination with an ionisation gauge, revealing the good linearity and accuracy of the CAVM. We believe that CAVM in the two potential traps have their own application situations and development directions, respectively.

The Procedure for Measuring Fuel Pressure on an Injection Motorbike Uses a Pressure Gauge

This study aimed to design and test a fuel pump pressure tester for injection motors to measure fuel pressure and determine whether the fuel pump is working properly. The qualitative method was used in the design process, which included creating design concepts, observation, and data processing. A literature review was conducted to strengthen the research results. The functional test in the final process showed that the tool could work well and provide information in measuring fuel pressure from the fuel pump. The implication of this study is that the fuel pump pressure tester can be used to prevent engine failure and improve engine performance. Highlight: Qualitative method used in the design process Literature review conducted to strengthen research results Functional test showed tool can measure fuel pressure accurately Keywords: fuel pump pressure tester, injection motors, fuel pressure, engine failure, engine performance.

Characterization of a NEG cartridge under high pressure conditions

The development of advanced sintered pumping elements based on the ZAO® alloy, characterized by a high affinity towards hydrogen and its isotopes, make Non Evaporable Getter (NEG) pumps particularly appealing for applications in fusion research, which typically deal with large fluxes of these gaseous species. NEG getters show high pumping speeds and capacity, excellent reliability with ability to withstand a high number of loading and unloading cycles without showing any type of failure, ease of integration within a complex system (such as a fusion reactor) because of their high specific properties and the simplicity of the mechanism that regulates its operation. These properties make NEG technology particularly suitable for the development of compact, efficient and easily scalable solutions, which are also very safe, since the release of absorbed hydrogen is prevented in the case of power outage or subsystem failures, as it can occur only by providing an adequate amount of heat to the getter material. This paper reports the results of an experimental campaign conducted on a new type of NEG pump, aimed to obtaining an accurate characterization in response to different operating conditions. Hydrogen pumping speed was investigated in a range of pressures of particular interest for the activities of the Divertor Tokamak Test facility (between 0.1 and 10 Pa). The influence of nitrogen absorption and getter material operating temperature on the pumping performances of the NEG pump were also examined. Finally, numerical simulations have been performed to estimate the nominal pumping speed of the NEG pump, that is, the one acting at the absorbing surface, stripped of the effects of the conductance of the paths from the pump NEG to the pressure gauges.

Evaluation of bovine carbonic anhydrase for promoting CO2 capture via reaction with KOH and high-salinity reject brine

In this study, we investigate the preliminary effect of bovine carbonic anhydrase (BCA) catalyst on CO2 capture via a reaction with potassium hydroxide (KOH) and reject brine under different operational conditions. Experiments were performed at a constant gauge pressure of 2 bar, with a CO2 inlet concentration of 10% and a CO2 flow rate of 776 mL/min. First, the impact of the BCA catalyst on CO2 capture in the absence of the alkaline material (KOH) was studied. Results showed that using 3-mg/L BCA increases the CO2 capture by 181% compared with the case without BCA. Second, the effect of BCA on CO2 uptake and ions reduction was examined in the presence of KOH. At a KOH concentration of 10-g/L, BCA concentration of 50-mg/L, and temperature of 40℃, a CO2 uptake value of 0.08 g CO2/g KOH was obtained. In comparison, adding 30-g/L KOH and 50-mg/L BCA increased the CO2 uptake by 737.5% (0.67 g CO2/g KOH). Furthermore, the sodium (Na+) reduction percentage reached a maximum of 40.8% at KOH and BCA concentrations of 30 g/L and 50 mg/L, respectively. However, increasing the BCA concentration to 100 mg/L negatively impacted CO2 capture and ion removal, indicating that the BCA concentration could be better optimized to achieve maximum efficiency. Additionally, when the BCA concentration was increased from 50 to 100 mg/L, the reaction rate remained nearly constant at 0.0047 mol/L·min.

Investigation on the pressure drop characteristics of ITER thermal shield cooling pipes

This paper presents the experimental results of the pressure drop through the cooling pipes of the ITER Thermal Shield (TS) panels. High pressure and room temperature nitrogen gas is selected for the experiment, which is equivalent operating condition with the 80 K helium gas from fluid mechanics point of view. Flow rate is set by a mass flow controller and pressure difference between the inlet and the outlet of the cooling pipe is measured by a differential pressure gauge. The experimental set-up is open loop type, which is connected to high pressure gas bottle. Flexible corrugated pipes are used to connect the TS cooling pipes with the measurement system line. The effect of the corrugated pipe is evaluated separately and excluded from the measurement results of the TS pipes. Test results of several TS panels are shown in this paper and are compared with the calculation using existing friction factor correlation and local loss coefficient of the pipe bends. The limitation of the calculation is discussed considering the hydrodynamic developing flow in the pipe routing.

Effect of twisting of intravitreal injections on ocular bio-mechanics: a novel insight to ocular surgery.

Although intravitreal (IVT) injections provide several advantages in treating posterior segment eye diseases, several associated challenges remain. The current study uses the finite element method (FEM) to highlight the effect of IVT needle rotation along the insertion axis on the reaction forces and deformation inside the eye. A comparison of the reaction forces at the eye's key locations has been made with and without rotation. In addition, a sensitivity analysis of various parameters, such as the needle's angular speed, insertion location, angle, gauge, shape, and intraocular pressure (IOP), has been carried out to delineate the individual parameter's effect on reaction forces during rotation. Results demonstrate that twisting the needle significantly reduces the reaction forces at the penetration location and throughout the needle travel length, resulting in quicker penetration. Moreover, ocular biomechanics are influenced by needle insertion location, angle, shape, size, and IOP. The reaction forces incurred by the patient may be reduced by using a bevel needle of the higher gauge when inserted close to the normal of the local scleral surface toward the orra serrata within the Pars Plana region. Results obtained from the current study can deepen the understanding of the twisting needle's interaction with the ocular tissue.

Experimental Study of Failures of the Rigid Spinal Posterior Fixation System Under Compressive Load Conditions: A Cadaver Study.

Background Many studies have been conducted on the biomechanics of the spine to elucidate the fixation properties of spinal fusion surgery and the causes of instrumentation failure. Among these studies, there are some studies on load sharing in the spine and measurement using strain gauges and pressure gauges, but there is a lack of research on axial compressive loads. Methods Axial compressive load tests were performed on human cadaveric injured lumbar vertebrae fixed with pedicle screws (PS). Both the strain generated in the PS rod and the intradiscal pressure were measured. Subsequently, the stress generated in the PS rod and the load sharing of the spine and instrumentation were calculated. Results Even when only compressive load is applied, bending stress of more than 10 times the compression stress was generated in the rod, and the stress tended to concentrate on one rod. Rod deformation becomes kyphotic, in contrast to the lordotic deformation behavior of the lumbar spine. The stress shielding rate was approximately 40%, less than half. Conclusions This study obtained basic data useful for constructing and verifying numerical simulations that are effective for predicting and elucidating the causes of dislodgement and failure of spinal implants.

Highly‐Sensitive, Tri‐Modal Luminescent Manometer Utilizing Band‐Shift, Ratiometric and Lifetime‐Based Sensing Parameters

AbstractIn addressing the broad spectrum of applications for optical pressure sensors, their predominant drawback lies in their limited sensitivity to pressure fluctuations. To overcome these constraints, this study introduces a luminescent manometer harnessing the emission properties of Cr3+ ions in Li3Sc2(PO4)3, operational in three distinct reading modes: spectral shift, ratiometric, and lifetime‐based. Notably, the conducted research establishes this luminescent manometer as the most sensitive reported to date in both spectra shift (λ/dp = 23.9 nm/GPa) and lifetime‐based (SR = 93.56%/GPa) modes. A departure from conventional lifetime‐based luminescent pressure gauges, Li3Sc2(PO4)3:Cr3+ exhibits a prolongation of lifetime of the 4T2 state correlated with increasing pressure. The advantages extend beyond sensitivity, encompassing a three‐fold surge in emission intensity with pressure escalation from ambient to 3 GPa, coupled with minimal susceptibility to temperature‐induced fluctuations. Unquestionably, Li3Sc2(PO4)3:Cr3+ showcases remarkable manometric performance, validating its significant application potential in diverse scenarios within the realm of optical pressure sensors.

Dynamic Simulation Platform Aids Deep Transient Tests, Well-Control Safety

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 215454, “Enhancing Well-Control Safety With Dynamic Well-Control Cloud Solutions: Case Studies of Successful Deep Transient Tests in Southeast Asia,” by M. Ashraf Abu Talib, SPE, M. Shahril Ahmad Kassim, and Izral Izarruddin Marzuki, SPE, Petronas, et al. The paper has not been peer reviewed. _ The complete paper addresses challenges related to well control and highlights the successful implementation of deep transient tests (DTT) in an offshore well performed with the help of a dynamic well-control simulation platform. The paper aims to provide insights into the prejob simulation process, which ensured a safer operation from a well-control perspective. Additionally, a comparison between simulated and actual sensor measurements during the DTT operation is presented. DTT DTT is a formation-testing (FT) method that allows pressure transient tests that reach deeper into the formation compared with conventional interval pressure transient tests (IPTT). DTT enables the testing of formations with higher permeability, greater thickness, and lower viscosity and real-time measurement of crucial parameters. During a DTT, formation fluid is pumped from the reservoir; upon stopping the pump, the formation pressure begins to recover as fluid further from the wellbore replaces the extracted fluid. By analyzing the resulting pressure transient, properties such as formation permeability, permeability anisotropy, and other characteristics can be determined. DTT allows for a better understanding of reservoir characteristics and rock heterogeneity. When properly designed and executed, DTT can reveal potential baffles and boundaries within the radius of investigation. A further advantage of DTT over drillstem tests (DST) is its minimal fluid flow, which allows for the attainment of objectives while contributing to the United Nations sustainable development goals. In DTT operations, the FT tool is connected to the drillpipe through a circulating sub and a slip joint. The circulating sub plays a critical role in DTT operations because it enables the continuous mixing of pumped formation fluid with circulated mud and facilitates its transportation to the surface (Fig. 1). Typically, a constant circulation rate ranging from 100 to 250 gal/min is maintained. During circulation, the annular preventer is closed and the mud/hydrocarbon mixture is directed through the choke line to the mud/gas separator (MGS) once it reaches the surface. No formation fluids are flared during DTT operations. Instead, the circulated oil is retained in the mud and only small amounts of gas are vented. By use of a slip joint, the FT remains anchored to the borehole wall. A high-resolution pressure gauge is used to capture and interpret even minor pressure fluctuations during the pressure transient buildup.