Pressure Decay Test Research Articles

Long-Term Statistical Process Monitoring of an Ultrafiltration Water Treatment Process.

As water treatment technology has improved, the amount of available process data has substantially increased, making real-time, data-driven fault detection a reality. One shortcoming of the fault detection literature is that methods are usually evaluated by comparing their performance on hand-picked, short-term case studies, which yields no insight into long-term performance. In this work, we first evaluate multiple statistical and machine learning approaches for detrending process data. Then, we evaluate the performance of a PCA-based fault detection approach, applied to the detrended data, to monitor influent water quality, filtrate quality, and membrane fouling of an ultrafiltration membrane system for indirect potable reuse. Based on two short case studies, the adaptive lasso detrending method is selected, and the performance of the multivariate approach is evaluated over more than a year. The method is tested for different sets of three critical tuning parameters, and we find that for long-term, autonomous monitoring to be successful, these parameters should be carefully evaluated. However, in comparison with industry standards of simpler, univariate monitoring or daily pressure decay tests, multivariate monitoring produces substantial benefits in long-term testing.

Validation research of pressure decay test method for internal leakage detection of hydraulic cylinder

Leakage test is one of the acceptance tests to ensure hydraulic cylinder reliability. Under the consideration of economic and technical maturity conditions, the existing internal leakage detection methods may be difficult to achieve rapid screening. After research, the pressure decay test method is a common method of quickly testing hydraulic cylinders for internal leakage in the manufacturing industry. However, the validity of the pressure decay test method has not been theoretically verified, limiting the versatility of the method. This paper will theoretically validate the effectiveness of the pressure decay test method and provide important theoretical support for its use as a general rapid screening method for internal leakage, thereby improving the reliability and safety of hydraulic systems. Both simulation and experimental results show that there is a linear relationship between the pressure decay rate and the internal leakage rate. Especially for working pressures greater than 16 MPa, the pressure factor has an insignificant impact on the application of this method.

An optimization method for equivalent bulk permeability of gas shale matrix with crushed samples and re-recognition of the influence of pressure and particle size

The pressure decay (or gas expansion) test with crushed samples has been used to evaluate the matrix permeability of shale and other low-permeability rock for many years. However, there still exist uncertainties relating to particle size and equilibrium pressure. The existing late-stage curve fitting method has the advantage of easy calculation, but the assumption that gas enters particles with a single permeability value is not generally applicable for shale samples, and late-stage analysis may lead to underestimation. This study proposes an optimization method to determine the equivalent bulk permeability that ensures the smallest sum of squares of errors between the forward-predicted pressure decay curve and the measure one. Both the optimization and curve fitting method are applied to two shale samples from the Ordovician Wufeng Formation of two wells in the Sichuan Basin, China with improved apparatus and testing procedures. The optimization method is superior to the curve fitting method in the repeatability and regularity on the change of apparent permeability with pressure. A strong linear relationship between apparent permeability and coefficient of compressibility is established between 3 and 12 bars. The variation of permeability with particle size is more diverse than that is commonly understood and might be nonmonotonic, depending on the change of pore structure during crushing. Change of apparent permeability with pressure (non-Darcy feature) is proposed as a criterion of whether pore structure has changed significantly. It is suggested to measure the variation of permeability with pressure and particle size to obtain a more comprehensive understanding of matrix permeability and pore structure.

Determination of Concentration-Dependent Effective Diffusivity of Each Gas Component of a Binary Mixture in Porous Media Saturated with Heavy Oil under Reservoir Conditions

Summary One frequently used enhanced heavy oil recovery technique is gas injection, during which heavy oil viscosity is reduced due to diffusion of gaseous components and heavy oil swelling in porous media. Effective diffusivities of gas components are generally assumed to be constants, while no attempts have been made to determine both the concentration-dependent effective diffusivity in porous media saturated with heavy oil and the preferential contribution of each component in a binary/ternary gas mixture. In this study, a pragmatic and robust technique has been proposed to determine the concentration-dependent effective diffusivity of each gas component by reproducing the experimental measurements during pressure decay tests for CO2-C3H8-heavy oil systems in porous media. Experimentally, CO2 and C3H8 are utilized to diffuse into sandpacks fully saturated with heavy oil. Under a constant temperature within a thermostatic chamber, the pressures of the aforementioned gas(es)-heavy oil systems are consistently tracked and saved while gas samples are taken at the start and end of the diffusion tests for gas chromatography analyses. Theoretically, a mass transfer model is formulated to determine effective gas diffusivity in heavy oil as a concentration-dependent function by incorporating Fick’s second law and the modified Peng-Robinson equation of state (PR EOS). The concentration-dependent effective diffusivity for each gas component is ascertained when the measured pressure profiles and gas compositions are matched well to their correspondingly calculated values with minimum deviations. Compared to either a constant assumption or a linear concentration-dependent relation with respect to diffusivity, an exponential concentration-dependent relation leads to more accurately reproducing the measured pressure profiles. Compared with pure CO2, its effective diffusivity in a binary (i.e., CO2 and C3H8) gas system is found to be larger, indicating that C3H8 accelerates the CO2 mass transfer into heavy oil under the same circumstances. Furthermore, this study confirms that a larger tortuosity of a porous medium leads to a longer diffusion path with less contact between gas and liquid phases and that a lower concentration of a gaseous component yields a lower effective diffusivity.

A study on the effect of process parameters on the joint strength and leak tightness in electromagnetically assisted adhesive Cu-SS tube-to-tube joining through statistical analysis

This work studies an improved hybrid joining technique combining electromagnetic forming and adhesive joining to create a leak-tight Cu-SS tube-to-tube joint named as electromagnetically assisted adhesive joining (EAAJ). An experimental investigation is performed considering three discharge energy (3.9 kJ, 4.4 kJ and 5.0 kJ), four adhesive application lengths (20 mm, 15 mm, 10 mm and 5 mm), three adhesives (Loctite 638, Loctite 567, and Loctite SI 596) and four curing times (24 h, 48 h, 96 h and 120 h) ad process parameters. The mechanical properties of the joints are investigated using testing techniques like pull-out, compression, and micro-hardness tests. An increase in joint strength is observed with the decrease in adhesive application length and increase in curing time. Maximum joint strength, 90% of the base copper tube strength, is obtained in the case of Loctite 638, with 5 mm of adhesive application length, 5.0 kJ of discharge energy and 96 h of curing time. Furthermore, a three-way analysis (3-way ANOVA) of variance technique is implemented to calculate the contribution of the three factors (discharge energy, adhesive application length, type of adhesives) on the joint strength. A cohesive and adhesive failure mode combination leading to sliding failure mode is observed as a joint failure mechanism during pull-out and compression testing. A leak testing setup has been developed to investigate the joint's leak tightness by an air pressure decay test. An increment in leak tightness by 1000 times is observed in 638 EAAJ samples compared to samples joined without adhesives. A 3-way ANOVA analysis is also performed to calculate the contribution of different factors on leak tightness of the joint. Micro-hardness is observed to be increased near the joint interface compared to the base metal. Deformation analysis has highlighted the impact of field shaper slit causing a non-uniformity in radial deformation in the circumferential direction and leading to non-uniform circumferential accumulation of adhesive.

Sensitivity of physical membrane damage detection on low pressure membranes of commercialized specification

In this study, a pressure decay test (PDT) was applied to microfiltration (MF) and ultrafiltration (UF) membranes that were in use for more than 7 years at a wastewater treatment plant. Laboratory-scale hollow-fiber membrane modules were made from treatment plant used membranes having areas of 0.18 and 0.027 m2 for MF and UF membranes, respectively. Filtration was performed on a feed solution containing organic, inorganic and turbidity elements as foulants for 1 h followed by clean-in-place (CIP) with 1 N HCl and 3000 mg L−1 NaOCl solutions for 3 h and continued for 6 CIP cycles. Membrane characteristics were analyzed by using Fourier-transform infrared analysis, scanning electron microscopy and atomic force microscopy. Changes in mechanical strength were estimated with a universal testing machine and integrity was evaluated by comparing the upper control limit (UCL) of the pressure decay rate (PDR) with the experimental PDR of these membranes. Results showed that UCLs of both membranes were less than the actual decay rate, confirming the compromising of 4 log removal value (LRV) removal in both membranes in a Ptest of 100–160 kPa, with a maximum of 3.78 LRV at the end of the experiments at a 100 kPa Ptest. Membrane characterization revealed the loss of hydrophilicity and strength due to the oxidation and dehydrofluorination of the membranes, particularly in MF membranes. Scratches on membrane structures due to complex foulants and exposure to CIP chemicals are the most likely causes of integrity loss associated with membrane operation in a treatment plant.

Monitoring of the Operating Membrane Condition Using PZT Based EMI of External Steel Pipe

Membrane systems are increasingly being used for treating water, wastewater, and reused water. However, membrane damage can decrease removal efficiency and hinder downstream applicability. Thus, the operating conditions of the membrane should be monitored. This study monitored the operating conditions of the membrane using lead zirconate titanate (PZT)-based electro-mechanical impedance (EMI) measurements in an external air pipe. Pilot-scale tests were performed to verify the performance of the proposed method. A pressure decay test (PDT) was performed using a PZT-attached air pipe, in which the pressure was measured using PZT, and a pressure gauge was employed to measure the reference pressure. The EMI signals changed according to the variations in the pressure inside the steel air pipe. To index the signal variation, the amplitude of the major peak was extracted and compared with the reference pressure. The amplitude of the major peak was inversely proportional to the pressure change. The pressure estimation equation was derived using a linear regression between the amplitudes of the major peak and the reference pressures. According to the results, the proposed monitoring system that utilizes the EMI of an external steel pipe is a potential solution to improve the sensitivity and speed of the PDT.

Determination of individual concentration-dependent diffusivity of binary gas-mixtures in reservoir-fluid systems

Diffusion is one of the main mass transfer principles associated with a gas injection process, e.g., vapor extraction (VAPEX) and cyclic solvent injection (CSI), to reduce the viscosity of heavy oil by dissolution of light gas(es). A few efforts have been made to estimate the diffusivity of each gas component of a binary gas-mixture in heavy oil as a constant, but no attempts have been made to determine individual diffusivity of each gas component in the binary gas-mixture as concentration-dependent. In this study, the concentration-dependent diffusivities of CO2 and C3H8 in a CO2/C3H8 mixture, which preferentially diffuses in a Lloydminster heavy oil, are evaluated implicitly as a power function of gas concentration, pressure, and temperature through the oil viscosity. The coefficient and exponent of such a power function for each gas are determined once the deviations between the measured and calculated values for oil swelling factors and composition of each gas dissolved in heavy oil at the completion of a dynamic volume analysis (DVA) test are minimized by applying the 1D time-dependent finite element method (FEM). Compared with the constant diffusivities for the same test, considering concentration-dependency of the dissolved gases reproduces the experimentally measured oil swelling factors and compositions at the end of the test with a significantly enhanced accuracy. Then, such obtained concentration-dependent diffusivities are extended to reproduce the experimentally measured swelling factors of a pressure-decay test performed with another CO2/C3H8 gas-mixture and the same heavy oil. From such an evaluation, it can be inferred that the coefficient and exponent of the diffusivity correlation associated with a binary gas-mixture are functions of pressure, temperature, feed gas composition, and test duration, respectively. This is because the coefficient and exponent for one gas component may be affected by the presence of the other as the latter alters the composition of heavy oil in which the former diffuses.

Testing Low-Melting-Point Alloy Plug in Model Brine-Filled Wells

Summary Low-melting-point bismuth- (Bi-) based alloys have recently been proposed for plug-and-abandonment (P&A). Previous experiments have shown the feasibility of BiSn [58-wt% Bi and 42-wt% tin (Sn)] and BiAg [97.5-wt% Bi and 2.5-wt% silver (Ag)] alloy plugs in moderate temperature wells, both across shales and across the shale/sandstone sequence. These were validated in linear and cylindrical wellbore cavity geometries for various differential setting pressures for alloy over air. Until now, all of the experiments for setting alloy plugs have been conducted with air as the wetting fluid. Given the lack of adhesion between minerals and alloy, our concept for providing bond strength and integrity has hinged on providing a bicontinuous structure through alloy penetration into the pore network. For shales, with a positive setting pressure, anchors on the surface, in lieu of pores, have proven to be adequate. With results obtained under excess alloy pressure, we have quantified the effect of setting pressure on the alloy/shale bond quality. With brine as the wetting fluid, imposing an excess pressure on the alloy has not been demonstrated previously. This paper is the continuation of our previously published papers (Zhang et al. 2020, 2021), and our objective here is not only to show the possibility of forming a plug under brine but also to quantify the plug’s quality with and without an excess alloy pressure. We first describe an apparatus that controls alloy and brine pressures independently through a semipermeable piston assembly and demonstrate forming alloy plugs in a brine-filled borehole cavity. Based on pressure decay tests across the plug, we demonstrate that wellbore integrity is possible only with a positive alloy pressure over that of brine.

Design and development of hermetic storage bin for de-hulled Kodo millet

Hermetic storage is sealed airtight non-chemical based storage system used to preserve the quality of grain, protect from pests, insects, and minimizes the storage losses. A hermetic storage bin was designed with a capacity 200 kg for de-hulled kodo millet. To design the hermetic bin the physical properties of de-hulled kodo millet such as bulk density, true density, porosity, angle of repose and co-efficient of friction were studied. The bulk density, true density, porosity, and angle of repose of de-hulled kodo millet were found to be 685.42 kg/m3, 1250 kg/m3, 45.16% and 26.1°. The co-efficient of friction of de-hulled kodo millet against the mild steel was found to be 0.781. The lateral pressure exerted on the wall surface for was 123.45 kg/m3 at the height of 0.6m. Pressure decay test was performed to check the air tightness of the hermetic bin. This hermetic bin can advocated to farmers and processors for value addition of small millets.

Full‐scale evaluation of critical control points and monitors at a reuse facility

AbstractThe hazard analysis and critical control point (HACCP) process is being widely adopted as a design, control, and operational methodology to maintain the reliability of delivering water quality that is safe for public health. This study applied the HACCP methodology to identify and assess the reliability of critical control points and critical monitors to manage acute and chronic health risks in potable reuse treatment trains. Specifically, a failure analysis was performed for full‐scale ultrafiltration and reverse osmosis critical control points to determine the reliability of critical monitors and their associated impacts on finished water quality. The results supported the use of ultrafiltration and reverse osmosis membranes as critical control points in potable reuse and identified the sensitivities of both current and emerging critical monitoring parameters, including turbidity, total organic carbon, ultraviolet absorbance at 254 nm, conductivity, fluorescence, calcium, sulfate, sucralose, and pressure decay tests.

Determination of Concentration-Dependent Gas Diffusivity in Reservoir Fluid Systems

One of the major mechanisms associated with gas injection to recover heavy oil is the molecular diffusion of gas, which reduces the viscosity of heavy oil. Numerous efforts have been made to estimate the diffusivity of such gas in heavy oil by assuming the gas diffusivity as a constant. Meanwhile, only limited attempts have been made to determine the concentration-dependent diffusivity from pressure decay test data by using analytical, semi-analytical, or numerical methods. In this study, a generalized methodology has been developed to determine the diffusivity of gas (e.g., CO2) in a heavy oil as an exponential function of gas concentration with consideration of oil swelling. More specifically, non-intrusive experimental measurement data obtained by dynamic volume analysis (DVA) are used to compute the concentration-dependent diffusivity by integrating the finite element method (FEM) with the particle swarm optimization (PSO) algorithm. Subsequently, concentration-dependent diffusivity of CO2 from the DVA experimental data can be obtained in the form of the exponential function and then converted to the function of liquid-phase viscosity. Then, the pressure decay test data are employed to determine the optimal diffusivity among the solutions of concentration-dependent CO2 diffusivity obtained from DVA test data by using Hayduk and Cheng’s formula together with the FEM. The final solution provides two coefficients for the exponential model and an exponent as well as a coefficient for Hayduk and Cheng’s model. It is found that the obtained concentration-dependent diffusivity of CO2 is reasonable and accurate as well as it can be converted for use at different pressures and temperatures through the determined coefficient and exponent for Hayduk and Cheng’s equation together with a linear relation between the natural logarithm of heavy oil viscosity and the dissolved gas concentration. Meanwhile, such findings in this study may be able to contribute to improve the gas injection projects such as vapor extraction or cyclic solvent injection processes.

Contribution of biofilm layer to virus removal in gravity-driven membrane systems with passive fouling control

Passive gravity-driven membrane (PGM) filtration is a type of gravity-driven membrane (GDM) filtration operated with passive physical fouling control measures that add limited to no complexity to the system (e.g. permeate flux interruptions, gravity-driven air scouring, system draining), allowing a greater permeate flux to be sustained. A key aspect of PGM/GDM systems is the development of a structurally loose and permeable biofilm layer on the membrane that enables a sustainable flux to be achieved and has also been associated with improved removal of humic acids, polysaccharides, proteins, assimilable organic carbon and microcystins. The present study investigated if the biofilm layer of PGM systems also contributes to virus removal, for both intact and breached PGM systems. Breach sizes considered ranged from 20 to 180 µm. Challenge tests (CTs) identified an increase of 2.0+ in the log removal value (LRV) for viruses in both intact and breached PGM systems when a biofilm layer was present, suggesting that the biofilm layer is capable of bridging the gap over integrity breaches, acting as a secondary barrier to contaminants that would otherwise bypass treatment by flowing through the breach. Pressure decay tests (PDTs), however, did not identify the same increase in LRVs as that of CTs, suggesting that the standard PDT approach cannot consider the contribution of the biofilm layer to the removal of small material such as viruses. An alternative integrity testing protocol for PGM systems was developed using a modified PDT approach that takes into account the additional removal provided by the biofilm layer. This alternative protocol is also simpler and requires less frequent testing, contributing to the simplification of overall operation of PGM systems in small/remote communities and decentralized applications.

Effect of GOR on Gas Diffusivity in Reservoir-Fluid Systems

Summary Molecular diffusion plays a dominant role in various reservoir processes, especially in the absence of convective mixing. In general, gas diffusion in oils depends on several factors such as pressure, temperature, oil viscosity, and gas/oil ratio (GOR). Out of these factors, the effects of GOR and live-oil-compositional changes on diffusivity are rare or not available in the literature. The current work fills this gap and presents the experimental observations on the effect of GOR on gas diffusivity in reservoir-fluid systems. Synthetic live oils were created by combining stock-tank oil (STO) and methane in various ratios. Constant-composition-expansion (CCE) experiments were performed with these oils to obtain their bubblepoints and liquid densities in relation to GOR. Methane diffusivity in these oils was obtained from pressure-decay (PD) tests at high-pressure/high-temperature (HP/HT) conditions. The diffusion and solubility parameters were estimated from PD data using the diffusion model and integral-based linear regression presented in previous work (Ratnakar and Dindoruk 2015, 2018). The experimental and modeling methodologies are presented here in sufficient detail to allow readers to replicate and evaluate the results. In this work, we experimentally investigated the effect of GOR on methane diffusivity in oils at HP/HT conditions using PD tests. In particular, We present experimental data for bubblepoints and liquid density of synthetic oils with various GOR values. For the range of GORs considered, these measurements show that the bubblepoint pressure increases linearly with GOR. Late-transient solution (LTS) of the PD model was used to obtain diffusivity parameters by regressing against experimental data. It is found that as the GOR value increases (that is, when oil becomes lighter), the diffusivity value increases, which is in accordance with the Stokes-Einstein relation. Most importantly, an empirical correlation is developed on the basis of a limited data set to describe the variation in diffusivity values with GOR. This can be important when experimental data are available for the STO but not for the live oils. It can also be extremely useful in gas-injection processes where the amount of gas dissolved in the oil varies, leading to variations in diffusivity.

Effect of CO2 mass transfer on rate of oil properties changes: Application to CO2-EOR projects

The performance of any CO2-EOR project relies on the capability of CO2 to change the oil properties at a reasonable period of time. The rate of mass transfer of CO2 into a specific oil controls the rate of oil properties changes. Additionally, the rate of CO2 transfer into an oil sample is dependent on CO2 thermodynamic state which is a function of pressure and temperature. Hence, this study aims to investigate the mass transfer of CO2 into a crude oil at gas and also supercritical state to estimate the rate of resultant changes of the oil properties at these two different states. To do so, two mass transfer pressure decay tests were conducted to study the molecular diffusion of CO2 in a light crude oil at both supercritical and gas states. Later, a mathematical model was used to determine the mass transfer parameters, i.e. diffusion coefficient (D) and interface mass transfer coefficient (k), and the dynamic concentration distribution of CO2 within the oil phase. As a part of this study, the time-dependent changes of the crude oil properties due to the molecular diffusion process of CO2 were also obtained for both supercritical CO2 and CO2 at gas state. For this purpose, the results of pressure decay experiments were combined with the results of additional experiments carried out to measure PVT properties of the CO2-oil system including CO2 solubility, oil swelling, oil viscosity, and interfacial tension (IFT) at various pressures and a constant temperature. The measured mass transfer parameters, i.e. D and k, were found to be higher for CO2 at supercritical state than that at gas state. The higher diffusivity of the supercritical CO2 in the oil resulted in faster changes of the oil properties as compared to the rate of properties changes by CO2 gas. For instance, it took 2 h for the oil to be swollen by 30% when it was in contact with CO2 at supercritical state as compared to 10 h at gas state. In the case of oil viscosity, for example, during 9 h, 58% reduction in oil viscosity was resulted by supercritical CO2 as compared to 25% reduction by CO2 gas. The results of this study can be used for better planning of CO2-EOR projects and particularly for CO2 Huff and Puff where the soaking time needs to be optimized properly.

A Novel Model of Pressure Decay in Pressure-Driven Membrane Integrity Tests Based on the Bubble Dynamic Process

The membrane integrity is estimated using a pressure decay test based on the bubble dynamic process of membrane defects. The present work builds a schematic diagram for a bubble formation model of a pressure decay test, proposes a simulation model of pressure decay rate (PDR) in the membrane gas chamber by means of numerical simulation using microdefect bubble dynamic behavior, and tries to establish the main factors influencing the back-calculated defect size resolution. Results obtained from the variations in the membrane gas chamber pressure and the PDR allowed for accurate determination of the membrane defect size, and the PDR was found to be relatively dependent on the gas chamber volume and the initial applied test pressure. The measured data about PDR using controlled experimental parameters was in good agreement with the trend found in the prediction model, proving that the pressure decay test process is in essence a bubble dynamic process. Furthermore, the back-calculated defect size resolution was found to decrease with the increase in gas chamber volume and PDR as well as with the decrease in applied pressure.

Analysis and Interpretation of Pressure-Decay Tests for Gas/Bitumen and Oil/Bitumen Systems: Methodology Development and Application of New Linearized and Robust Parameter-Estimation Technique Using Laboratory Data

Summary Diffusion mixing is a dominant process in the absence of convective mixing in various reservoir processes, such as carbon dioxide (CO2) flooding of fractured reservoirs, heavy-oil and bitumen recovery, solution-gas-drive processes, and the gas-redissolution process in a depleted reservoir. In these processes, the diffusivity governs the rate and extent of mixing of light hydrocarbons/nonhydrocarbons with the oil that enhances the oil recovery through in-situ viscosity reduction. It is one of the key parameters for the design and understanding of displacement processes. Because of its significance in various aspects of oil-recovery processes, several experimental and theoretical studies were recently performed on the measurement of gas diffusivity in oils. Experimental work most commonly uses the pressure-decay (PD) concept because of its simplicity and the potential extraction of other necessary parameters, such as Henry's constant. However, the parameter estimation from these tests is dependent on nonlinear regression, which might have several issues such as nonconvergence, nonuniqueness or multiplicity in solution, and high sensitivity toward noise and the time span of the data. Therefore, in this paper, Ratnakar and Dindoruk (2015) is extended and New experimental data are provided from a PD test for CO2 diffusion into bitumen at 80°C and approximately 700 psi. A robust inversion technique for parameter estimation is presented for exponentially decaying late-transient data, which can be used with any PD model used in the literature. The validity and applicability of the inversion technique is demonstrated against numerical data that are generated for a PD system by solving a diffusion model with continuity in the state variable (using Henry's constant) and molar flux at the gas/oil interface. Most importantly, the issues with the nonlinear-regression technique are resolved using the linearized technique. The inversion technique presented in the work is dependent on a combination of linear regression and numerical integration using a modified, more-convenient form of the fundamental equations rather than a nonlinear regression on the fundamental equations as derived. This integral-based linear representation avoids the multiple solutions and can be used with limited data sets and/or when noise in the experimental data is significant, especially in industrial-grade experiments.

An analytical method of estimating diffusion coefficients of gases in liquids from pressure decay tests

We present an exact solution of quasi‐equilibrium model, based on pressure decay technique, to measure diffusion coefficient. The results of the quasi‐equilibrium model are compared with the traditional equilibrium model and it was found that the latter is only a special case of former one. We provide new approximate solution to estimate diffusion coefficient that is more convenient to use, compared with the previously reported approaches. It also reveals that our solution is capable of taking into account greater portion of the collected pressure decay test data and is more accurate. Based on the developed solution, estimation approaches, including linear method and exponential method, are presented and applied to analyze synthetic and experimental pressure‐decay data. The quasi‐equilibrium model is also compared with the traditional equilibrium model. The results reveal that analysis of the test data using equilibrium model may introduce large error in estimation of diffusion coefficient. © 2018 American Institute of Chemical Engineers AIChE J, 65: 434–445, 2019

Comparison of methods to assess the integrity and separation efficiency of ultrafiltration membranes in wastewater reclamation processes

Membrane filtration is used in many water reuse applications, thanks to its high separation efficiency with regard to particles, bacteria, cysts and in the case of ultrafiltration even viruses. However, the separation performance of a membrane system can be affected and the permeate quality can be reduced or increased by phenomena such as membrane damage, membrane fouling or microbiological regrowth on both permeate and retentate side of the membrane. Thus, in order to guarantee a sufficiently high permeate quality, the separation efficiency of a membrane system has to be assessed sensitively, reliably and, if possible, continuously.In the here presented study, a variety of different analytical methods was tested to assess the separation efficiency of ultrafiltration membranes in a pilot-scale wastewater reclamation system. After intentionally damaging the membrane to different degrees, its integrity was monitored by pressure decay testing and permeate turbidity measurements, and by continuously monitoring the concentration of micro- and nanoparticles in the permeate stream. The microbiological permeate quality was not only assessed by plate counting, but also by flow cytometric measurements. The results showed that the membrane integrity is primarily affected by physical damaging, as detectable by pressure decay testing, while the permeate quality strongly depends on particle-membrane interactions such as formation of a fouling layer or clogging of membrane defects. Nanoparticle counting was found to be a very sensitive method to continuously monitor the membrane’s separation efficiency. Additionally, flow cytometry revealed that bacterial regrowth on the permeate side can affect the microbiological permeate quality in particular.

Pressure-decay testing of pleural air leaks in intact murine lungs: evidence for peripheral airway regulation.

The critical care management of pleural air leaks can be challenging in all patients, but particularly in patients on mechanical ventilation. To investigate the effect of central airway pressure and pleural pressure on pulmonary air leaks, we studied orotracheally intubated mice with pleural injuries. We used clinically relevant variables – namely, airway pressure and pleural pressure – to investigate flow through peripheral air leaks. The model studied the pleural injuries using a pressure‐decay maneuver. The pressure‐decay maneuver involved a 3 sec ramp to 30 cmH20 followed by a 3 sec breath hold. After pleural injury, the pressure‐decay maneuver demonstrated a distinctive airway pressure time history. Peak inflation was followed by a rapid decrease to a lower plateau phase. The decay phase of the inflation maneuver was influenced by the injury area. The rate of pressure decline with multiple injuries (28 ± 8 cmH20/sec) was significantly greater than a single injury (12 ± 3 cmH2O/sec) (P < 0.05). In contrast, the plateau phase pressure was independent of injury surface area, but dependent upon transpulmonary pressure. The mean plateau transpulmonary pressure was 18 ± 0.7 cm H2O. Finally, analysis of the inflation ramp demonstrated that nearly all volume loss occurred at the end of inflation (P < 0.001). We conclude that the air flow through peripheral lung injuries was greatest at increased lung volumes and limited by peripheral airway closure. In addition to suggesting an intrinsic mechanism for limiting flow through peripheral air leaks, these findings suggest the utility of positive end‐expiratory pressure and negative pleural pressure to maintain lung volumes in patients with pleural injuries.