Cyclic Flow Conditions Research Articles

Applications of Passive Infrared Thermal Imaging for Detecting Delaminated Areas of Ancient Rock-cut Tunnel

Delaminations are generally developed in construction works due to numerous factors, including cyclic loading, water flow, and weather conditions. A conventional non-destructive method, such as tapping or chain dragging, is commonly used to predict subsurface delaminations. However, tapping tests may require more precision, especially for minor subsurface defects. Passive Infrared Thermal Imaging or Passive Infrared Thermography (PIRT) effectively detects sizable delaminated areas of a structure quickly. However, the inspected structural components are recommended to be exposed to direct sunlight. In this study, PIRT was used to investigate an operating ancient rock-cut tunnel and to detect potentially dangerous locations where delamination and spalling have occurred. The results prove that PIRT can effectively detect delaminated areas, even when there is only a 1-2°C atmospheric temperature difference nine hours before testing.

Assessment of Geochemical Limitations to Utilizing CO2 as a Cushion Gas in Compressed Energy Storage Systems.

Compressed energy storage (CES) of air, CO2, or H2 in porous formations is a promising means of energy storage to abate the intermittency of renewable energy production. During operation, gas is injected during times of excess energy production and extracted during excess demands to drive turbines. Storage in saline aquifers using CO2 as a cushion or working gas has numerous advantages over typical air storage in caverns. However, interactions between CO2 and saline aquifers may result in potential operational limitations and have not been considered. This work utilizes reactive transport simulations to evaluate the geochemical reactions that occur during injection and extraction operational cycles for CES in a porous formation using CO2 as a cushion gas. Simulation results are compared with similar simulations considering an injection-only flow regime of geologic CO2 storage. Once injected, CO2 creates conditions favorable for dissolution of carbonate and aluminosilicate minerals. However, the dissolution extent is limited in the cyclic flow regime where significantly smaller dissolution occurs after the first cycle such that CO2 is a viable choice of cushion gas. In the injection-only flow regime, larger extents of dissolution occur as the fluid continues to be undersaturated with respect to formation minerals throughout the study period and porosity increased uniformly from 24.84% to 33.6% throughout the simulation domain. For the cyclic flow conditions, porosity increases nonuniformly to 31.1% and 25.8% closest and furthest from the injection well, respectively.

Optimal efficiency of the Q-cycle mechanism around physiological temperatures from an open quantum systems approach

The Q-cycle mechanism entering the electron and proton transport chain in oxygenic photosynthesis is an example of how biological processes can be efficiently investigated with elementary microscopic models. Here we address the problem of energy transport across the cellular membrane from an open quantum system theoretical perspective. We model the cytochrome {b}_{6},f protein complex under cyclic electron flow conditions starting from a simplified kinetic model, which is hereby revisited in terms of a Markovian quantum master equation formulation and spin-boson Hamiltonian treatment. We apply this model to theoretically demonstrate an optimal thermodynamic efficiency of the Q-cycle around ambient and physiologically relevant temperature conditions. Furthermore, we determine the quantum yield of this complex biochemical process after setting the electrochemical potentials to values well established in the literature. The present work suggests that the theory of quantum open systems can successfully push forward our theoretical understanding of complex biological systems working close to the quantum/classical boundary.

Filter media performance under the oscillating flow condition

This work investigated the performance of two mechanical glass-fiber and one electret filter media under the oscillating flow conditions (i.e., cyclic flows in this study). DMA-classified particles of 30, 50, 100 and 150 nm, and oscillating flow conditions with the Average Suction Flow Rates (ASFRs) of 6.4, 25.6 L/min and oscillating frequency of 6, 24, 40 min−1 were chosen for the experiments. It is found in general the particle penetration of test media increases with the increase of oscillating frequency. The above-observed penetration enhancement is found to be more pronounced for small particles (i.e., 30 and 50 nm) as compared to that for large particles (i.e., 100 and 150 nm). At the flow oscillating frequency of 24 and 40 min−1, the particle penetration through filter media is also higher than it under the corresponding constant flow conditions. The increase of ASFR increases the particle penetration of filter media for all the selected particle sizes. The apparent single fiber efficiency for media A and B under cyclic flow conditions was lastly found. The obtained efficiency enables the single fiber theory to calculate the average penetration of diffusive particles through mechanical filter media under the cyclic flow conditions.

A “sweet-spot” for fluid-induced oscillations in the conditioning of stem cell-based engineered heart valve tissues

Fluid-induced shear stresses are involved in the development of cardiovascular tissues. In a tissue engineering framework, this stimulus has also been considered as a mechanical regulator of stem cell differentiation. We recently demonstrated that the fluid-oscillating effect in combination with a physiologically-relevant shear stress magnitude contributes to the formation of stem cell-derived de novo heart valve tissues. However, the range of oscillations necessary to induce favorable gene expression and engineered tissue formation is unknown. In this study, we took a computational approach to establish a range of oscillatory shear stresses that may optimize in vitro valvular tissue growth. Taking a biomimetic approach, three physiologically-relevant flow waveforms from the human: (i) aorta, (ii) pulmonary artery and (iii) superior vena cava were utilized to simulate pulsatile flow conditions within a bioreactor that housed 3 tissue specimens. Results were compared to non-physiological pulsatile flow (NPPF) and cyclic flexure-steady flow (Flex-Flow) conditions. The oscillatory shear index (OSI) was used to quantify the fluid-induced oscillations occurring on the specimen surfaces. The range of mean OSI under the physiological conditions investigated was found to be 0.18 ≤ OSI ≤ 0.23. On the other hand, NPPF and Flex-Flow environments yielded a mean OSI of 0.37 and 0.11 respectively, which were 46% higher and 45% lower than physiological conditions. Moreover, we subsequently conducted OSI-based human bone marrow stem cell (HBMSC) culture experiments which resulted in preferential valvular gene expression and phenotype (significant upregulation of BMP, KLF2A, CD31 and α-SMA using an OSI of 0.23 in comparison to a lower OSI of 0.10 or a higher OSI of 0.38; p < .05). These findings suggest that a distinct range or a “sweet-spot” for physiological OSI exists in the mechanical conditioning of tissue engineered heart valves grown from stem cell sources. We conclude that in vitro heart valve matrix development could be further enhanced by simultaneous exposure of the engineered tissues to physiologically-relevant magnitudes of both fluid-induced oscillations and shear stresses.

In vitro assessment of small charged pharmaceutical aerosols in a model of a ventilated neonate

Aerosolized medications may benefit infants receiving mechanical ventilation; however, the lung delivery efficiency of these aerosols is unacceptably low. In vitro experiments were conducted to evaluate aerosol delivery through conventional and modified ventilation systems to the end of a 3mm endotracheal tube (ETT) under steady state and realistic cyclic flow conditions. System modifications were employed to investigate the use of small charged particles and included streamlined components, a reduction in nebulizer liquid flow rate, synchronization with inspiration, and implementation of a previously designed low-flow induction charger (LF-IC), which was further modified in this study. Cyclic flow experiments implemented a modern ventilator with bias airflow and an inline flow meter, both of which are frequently excluded from in vitro tests but included in clinical practice. The modified LF-IC system demonstrated superior delivery efficiency to the end of the ETT (34%) compared with the commercial system (~1.3%) operating under cyclic ventilation conditions. These findings indicate that commercial systems still provide very low lung delivery efficiencies despite decades of innovation. In contrast, the modified system increased dose delivery to the end of the ETT by 26-fold. Despite initial concerns, the charged aerosol could be efficiently delivered through the small diameter ETT and reach the lungs. Future studies will be required to determine if the applied particle charge can eliminate expected high exhalation aerosol loss and will require the development of a realistic lung model.

Evaluation of Respirator Filter Media under Inhalation-only Conditions

ABSTRACTFilter media for respirator applications are typically exposed to cyclic flow condition instead of constant flow adopted in the standard filter media tests. The objective of this study is thus to investigate the effects of breathing frequency (BF) and peak inhalation flow rate (PIFR) on the peak particle penetration of respirator filter media, especially for particles at the most penetration particle sizes under the constant flow condition having equivalent mean inhalation flowrate (MIFR). Five respirator filter media were evaluated under inhalation-only conditions. Three BFs and three PIFRs were selected for the testing. Our study evidenced that both BF and PIFR would increase the peak particle penetration under the cyclic inhalation-only conditions. It is further found that, for each filter media, the peak particle penetration at various PIFRs could be merged into one curve via the newly-defined peak penetration ratio (i.e., the ratio of peak particle penetration at cyclic flow condition to the penetration at the constant flow condition having the equivalent MIFR) and the curve is only a function of BF. The above observation indicates that the increase of peak particle penetration resulted from the increase of PIFR is simply because of the increase of MIFR. The effect of BF on the peak particle penetration is clearly observed using the defined penetration ratio. Based on our finding a semi-theoretical model was further proposed to estimate the peak particle penetration of respirator filter media under inhalation-only conditions.

Gold nanoparticle interactions with endothelial cells cultured under physiological conditions.

PEGylated gold nanoparticles (AuNPs) have an extended circulation time after intravenous injection in vivo and exhibit favorable properties for biosensing, diagnostic imaging, and cancer treatment. No impact of PEGylated AuNPs on the barrier forming properties of endothelial cells (ECs) has been reported, but recent studies demonstrated that unexpected effects on erythrocytes are observed. Almost all studies to date have been with static-cultured ECs. Herein, ECs maintained under physiological cyclic stretch and flow conditions and used to generate a blood-brain barrier model were exposed to 20 nm PEGylated AuNPs. An evaluation of toxic effects, cell stress, the release profile of pro-inflammatory cytokines, and blood-brain barrier properties showed that even under physiological conditions no obvious effects of PEGylated AuNPs on ECs were observed. These findings suggest that 20 nm-sized, PEGylated AuNPs may be a useful tool for biomedical applications, as they do not affect the normal function of healthy ECs after entering the blood stream.

Advanced testing method to evaluate the performance of respirator filter media

ABSTRACTFilter media for respirator applications are typically exposed to the cyclic flow condition, which is different from the constant flow condition adopted in filter testing standards. To understand the real performance of respirator filter media in the field it is required to investigate the penetration of particles through respirator filters under cyclic flow conditions representing breathing flow patterns of human beings. This article reports a new testing method for studying the individual effect of breathing frequency (BF) and peak inhalation flow rate (PIFR) on the particle penetration through respirator filter media. The new method includes the use of DMA (Differential Mobility Analyzer)-classified particles having the most penetrating particle size, MPPS (at the constant flowrate of equivalent mean inhalation flow rate, MIFR) as test aerosol. Two condensation particle counters (CPCs) are applied to measure the particle concentrations at the upstream and downstream of test filter media at the same time. Given the 10 Hz sampling time of CPCs, close-to-instantaneous particle penetration could be measured. A pilot study was performed to demonstrate the new testing method. It is found that the effect of BF on the particle penetration of test respirator filter media is of importance at all the tested peak inhalation flow rates (PIFRs), which is different from those reported in the previous work.

Performance of an improperly sized and stretched-out loose-fitting powered air-purifying respirator: Manikin-based study

ABSTRACTThe objective of this study was to investigate the protection level offered by a Powered Air-Purifying Respirator (PAPR) equipped with an improperly sized or stretched-out loose-fitting facepiece using constant and cyclic flow conditions. Improperly sized PAPR facepieces of two models as well as a stretched-out facepiece were tested. These facepieces were examined in two versions: with and without exhaust holes. Loose-fitting facepieces (size “large”) were donned on a small manikin headform and challenged with sodium chloride (NaCl) aerosol particles in an exposure chamber. Four cyclic flows with mean inspiratory flows (MIFs) of 30, 55, 85, and 135 L/min were applied using an electromechanical Breathing Recording and Simulation System (BRSS). The manikin Fit Factor (mFF) was determined as the ratio of aerosol concentrations outside (Cout) to inside (Cin) of the facepiece, measured with a P-Trak condensation particle counter (CPC). Results showed that the mFF decreased exponentially with increasing MIF. The mFF values of the stretched-out facepiece were significantly lower than those obtained for the undamaged ones. Facepiece type and MIF were found to significantly affect the performance of the loose-fitting PAPR. The effect of the exhaust holes was less pronounced and depended on the facepiece type. It was concluded that an improperly sized facepiece might potentially offer relatively low protection (mFF < 250) at high to strenuous workloads. The testing was also performed at a constant inhalation flow to explore the mechanism of the particle-facepiece interaction. Results obtained with cyclic flow pattern were consistent with the data generated when testing the loose-fitting PAPR under constant flow conditions. The time-weighted average values of mFF calculated from the measurements conducted under the constant flow regime were capable of predicting the protection under cyclic flow regime. The findings suggest that program administrators need to equip employees with properly sized facepieces and remove stretched-out ones from workplace. Manufacturers should emphasize the importance of proper sizing with their user instructions.

Numerical simulation of airflow and micro-particle deposition in human nasal airway pre- and post-virtual sphenoidotomy surgery.

In the present study, the effects of endoscopic sphenoidotomy surgery on the flow patterns and deposition of micro-particles in the human nasal airway and sphenoid sinus were investigated. A realistic model of a human nasal passage including nasal cavity and paranasal sinuses was constructed using a series of CT scan images of a healthy subject. Then, a virtual sphenoidotomy by endoscopic sinus surgery was performed in the left nasal passage and sphenoid sinus. Transient airflow patterns pre- and post-surgery during a full breathing cycle (inhalation and exhalation) were simulated numerically under cyclic flow condition. The Lagrangian approach was used for evaluating the transport and deposition of inhaled micro-particles. An unsteady particle tracking was performed for the inhalation phase of the breathing cycle for the case that particles were continuously entering into the nasal airway. The total deposition pattern and sphenoid deposition fraction of micro-particles were evaluated and compared for pre- and post-surgery cases. The presented results show that sphenoidotomy increased the airflow into the sphenoid sinus, which led to increased deposition of micro-particles in this region. Particles up to 25 μm were able to penetrate into the sphenoid in the post-operation case, and the highest deposition in the sphenoid for the resting breathing rate occurred for 10 μm particles at about 1.5%.

Viable Viral Efficiency of N95 and P100 Respirator Filters at Constant and Cyclic Flow

The growing threat of an influenza pandemic presents a unique challenge to healthcare workers, emergency responders, and the civilian population. The Occupational Safety and Health Administration (OSHA) recommends National Institute for Occupational Safety and Health (NIOSH)-approved respirators to provide protection against infectious airborne viruses in various workplace settings. The filtration efficiency of selected NIOSH-approved particulate N95 and P100 filtering facepiece respirators (FFRs) and filter cartridges was investigated against the viable MS2 virus, a non-pathogenic bacteriophage, aerosolized from a liquid suspension. Tests were performed under two cyclic flow conditions (minute volumes of 85 and 135 L/min) and two constant flow rates (85 and 270 L/min). The mean penetrations of viable MS2 through the N95 and P100 FFRs/cartridges were typically less than 2 and 0.03%, respectively, under all flow conditions. All N95 and P100 FFR and cartridge models assessed in this study, therefore, met or exceeded their respective efficiency ratings of 95 and 99.97% against the viable MS2 test aerosol, even under the very high flow conditions. These NIOSH-approved FFRs and particulate respirators equipped with these cartridges can be anticipated to achieve expected levels of protection (consistent with their assigned protection factor) against airborne viral agents, provided that they are properly selected, fitted, worn, and maintained.

Retention performance of woven geotextiles subjected to cyclic-flow conditions

ABSTRACT: Woven geotextiles are widely used as filters in geotechnical, hydraulic, and environmental applications. Depending on the application, geotextile filters can be subjected to uni-directional, bi-directional, or cyclic-flow conditions, with cyclic flow occurring in two directions repeatedly over time. The selection of a suitable geotextile filter is of critical importance, particularly for cyclic-flow conditions. Cyclic-flow conditions can rapidly lead to an excessive loss of fine soil particles and failure of a soil–geotextile system. Although these conditions are frequently encountered, limited work has been done to evaluate the retention behavior of geotextiles under cyclic-flow conditions. In this study, the retention performance of nine different woven geotextiles with five different soils under cyclic-flow conditions was modeled using a bi-directional hydrodynamic filtration test (BHFT). Based on the results of this research, a retention criterion of AOS/d85 of 1.62 is proposed for woven geotextiles subjected to cyclic-flow conditions, where AOS is the apparent opening size of the geotextile or O95 as determined by dry sieving ( ASTM D4751 ) and d85 is the soil particle diameter corresponding to 85% by weight of finer soil particles. Additionally, an allowable soil-loss limit less than 5000 g/m2 is proposed.

Study of erythrocyte aggregation at pulsatile flow conditions with backscattering analysis

In vivo red blood cell aggregation will vary under pulsatile flow but few studies have been reported due to various difficulties in generating physiological flow conditions and detecting RBC aggregation. The present study developed a microfluidic system that generates cyclic pulsatile flow through a microchannel. Backscattered light signals from human blood were recorded over time and analyzed for RBC aggregation in pulsatile flow. Four different blood samples (control, normal RBCs in PBS, hardened RBCs in autologous plasma, and hardened RBCs in PBS) were examined. In a cyclic pulsatile flow condition, light intensity-time curve for the control and hardened RBCs in plasma exhibited apparent critical shear stresses that were similar to the respective values measured at a single pulse flow condition. During entire cycles of pulsatile flow, the measured critical shear stress remained nearly constant. We conclude that the critical shear stress can be observed in cyclic pulsatile flow and would be an important index to represent in-vivo pulsatile blood flow rheology.

N95 and P100 Respirator Filter Efficiency Under High Constant and Cyclic Flow

This study investigated the effect of high flow conditions on aerosol penetration and the relationship between penetration at constant and cyclic flow conditions. National Institute for Occupational Safety and Health (NIOSH)-approved N95 and P100 filtering facepiece respirators and cartridges were challenged with inert solid and oil aerosols. A combination of monodisperse aerosol and size-specific aerosol measurement equipment allowed count-based penetration measurement of particles with nominal diameters ranging from 0.02 to 2.9 μm. Three constant flow conditions (85, 270, and 360 L/min) were selected to match the minute, inhalation mean, and inhalation peak flows of the four cyclic flow conditions (40, 85, 115, and 135 L/min) tested. As expected, penetration was found to increase under increased constant and cyclic flow conditions. The most penetrating particle size (MPPS) generally ranged from 0.05 to 0.2 μm for P100 filters and was approximately 0.05 μm for N95 filters. Although penetration increased at the high flow conditions, the MPPS was relatively unaffected by flow. Of the constant flows tested, the flows equivalent to cyclic inhalation mean and peak flows best approximated the penetration measurements of the corresponding cyclic flows.

Experimental study of a hydrocyclone under cyclic flow conditions for fine particle separation

The difficulty in separating fine particles is described in this paper. The basic separating principle of hydrocyclones and the cyclic experimental research facilities are also introduced. Based on a solid–liquid hydrocyclone used for separating fine particles, the effect of the cyclic flow conditions on hydrocyclone's performance is studied. Effects of the cyclic period ratio, cyclic flowrate amplitude ratio, Reynolds number, gas liquid ratio, and the cyclical signal type on the hydrocyclone's fine particle separation performance, with emphasis on the relative overflow purifying rate, are all studied in detail. The results show that the separation efficiency of the hydrocyclone operating under cyclic flow conditions can be higher than that in steady conditions when the cyclic period ratio is about 0.68 and the cyclic flowrate amplitude ratio is around 2%. The rectangular wave seems to be the best cyclic signal for enhancing the hydrocyclone's separation efficiency.

Fabrication and characteristics of plasma facing SiC/C functionally graded composite material

A bulk SiC/C functionally graded material (FGM) having a compositional gradient from carbon (C) to silicon carbide (SiC) was obtained by powder metallurgy method with SiC, B and amorphous C powders as starting materials. The average graphite ratio of C was 66% higher than ordinary graphite. Compared with CVI and CVD SiC/C FGM and SiC coating, hot-pressed SiC/C FGM has high effective thermal conductivity while the thickness of SiC layer is 1 mm or so. Under cyclic high-temperature heat flow conditions, SiC/C FGM did not suffer cracking and was shown to be superior in resistance to thermal fatigue. The plasma-relevant performance indicated that it has excellent high-temperature erosion resistance.

Realistic Filter Performance Evaluation-Cyclic Stabilization Test

The Multi-pass filter test is the most common method to evaluate the performance of hydraulic filters. The test is conducted at a constant flow rate at constant temperature and very high dirt ingression in order to evaluate filter performance at accelerated test condition. This standard test does not represent operating condition of the modern hydraulic control systems. In order to precisely represent filter performance in the field in the laboratory, the Cyclic Stabilization Test (CST) has been developed. The CST can reliably measure the ability of the filter to control contamination in an even lower ingression environment. It also simulates cyclic flow condition to measure filter performance. In this paper, the CST is proposed as a more effective method for filter performance evaluation method.

Solute transport during cyclic flow in saturated porous media

We consider materials with large pores interconnected by thin long channels saturated with an incompressible fluid. In the absence of fluid flow, solute transport in the porous network is diffusion controlled, however, solute transport can be enhanced when the porous network is subjected to a cyclic flow with zero time average velocity. We develop a mathematical model to analyze this physical phenomenon and obtain an effective macroscale diffusion coefficient for solute transport which dependends on cyclic flow conditions and the geometry of the porous network.

Airflow structures and nano-particle deposition in a human upper airway model

Considering a human upper airway model, or equivalently complex internal flow conduits, the transport and deposition of nano-particles in the 1–150 nm diameter range are simulated and analyzed for cyclic and steady flow conditions. Specifically, using a commercial finite-volume software with user-supplied programs as a solver, the Euler–Euler approach for the fluid-particle dynamics is employed with a low-Reynolds-number k– ω model for laminar-to-turbulent airflow and the mass transfer equation for dispersion of nano-particles or vapors. Presently, the upper respiratory system consists of two connected segments of a simplified human cast replica, i.e., the oral airways from the mouth to the trachea (Generation G0) and an upper tracheobronchial tree model of G0–G3. Experimentally validated computational fluid-particle dynamics results show the following: (i) transient effects in the oral airways appear most prominently during the decelerating phase of the inspiratory cycle; (ii) selecting matching flow rates, total deposition fractions of nano-size particles for cyclic inspiratory flow are not significantly different from those for steady flow; (iii) turbulent fluctuations which occur after the throat can persist downstream to at least Generation G3 at medium and high inspiratory flow rates (i.e., Q in⩾30 l/min) due to the enhancement of flow instabilities just upstream of the flow dividers; however, the effects of turbulent fluctuations on nano-particle deposition are quite minor in the human upper airways; (iv) deposition of nano-particles occurs to a relatively greater extent around the carinal ridges when compared to the straight tubular segments in the bronchial airways; (v) deposition distributions of nano-particles vary with airway segment, particle size, and inhalation flow rate, where the local deposition is more uniformly distributed for large-size particles (say, d p=100 nm) than for small-size particles (say, d p=1 nm); (vi) dilute 1 nm particle suspensions behave like certain (fuel) vapors which have the same diffusivities; and (vii) new correlations for particle deposition as a function of a diffusion parameter are most useful for global lung modeling.