Mass flow rate through a horizontal opening at small pressure differences

Computational Fluid Dynamics (CFD) for air/water-vapor and water-liquid two-phase flow mixing with condensation in a vertical inverted U-tube is presented in this paper. This study is to investigate the flow behaviors and underlying some physical mechanisms encountered in air/water-vapor and water-liquid mixing flow when condensation is considered. Water-liquid flows upward-downward through the inverted U-tube while the air/water-vapor mixture is extracted from a side-tube just after the flow oriented downward. The CFD simulation is carried out for a side air/water-vapor mixture volume fraction (αm) of 0.2–0.7, water-vapor mass fraction (Xv) of 0.1–0.5 in the side air/water-vapor mixture and water-liquid mass flowrate (mw) of 2,4,6, and 8 kg/s. The present results reveal that, at lower air mass flow rate, no significant effect of Xv on the generated static pressure at the inverted U-tube higher part. However, by increasing the air mass flow rates, ma ≥ 0.001 at mw = 2 kg/s, and ma ≥ 0.00125 at mw = 4 kg/s, we can infer that the lowest static pressure can be attained at Xv = 0.1. This may be attributed to the increased vapor and air mass flow rates from the side tube which results in shifting the condensation from the tube highest part due to air accumulation. This leads to increasing the flow pressure and decelerating the water-liquid flow. Raising mw from 2 to 4 kg/s at the same vapor mass ratio results in a lower static pressure due to more condensation of water vapor. The turbulent intensity and kinetic energy starts to drop approximately at ma = 0.002 kg/s, and αm = 0.55–0.76 at mw = 2 kg/s for all Xv values but no noticeable change at mw = 4 kg/s occurs. These findings estimate the operational values of air and water mass flow rates for stable air entrainment from the side-tube. Increasing the air and vapor mass ratio over these values may block the evacuation process and fails the system continuance. Likewise more air entrainment from the side-tube will decelerate the water flow through the inverted U-tube and hence the flow velocity will decrease thereafter. Moreover, this study reveals that the inverted U-tube is able to generate a vacuum pressure down to 55.104 kPa for the present model when vapor condensation is considered. This generated low-pressure helps to vent an engineering system from the non-condensable gases and water vapor that fail its function if these are accumulated with time. Moreover, the water-liquid mass flow rate in the inverted U-tube can be used to sustain the required operating pressure for this system and extract the non-condensable gases with a less energy consuming system. The present CFD model provides a good physical understanding of the flow behavior for air/water-vapor and water-liquid flow for possible future application in the steam power plant.

Optimization of tube arrangement and phase change material for enhanced performance of solar air heater- A numerical analysis

Research in bidirectional data flow analysis seems to have come to a halt due to an impression that the case for bidirectional data flow analysis has been considerably weakened by a plethora of investigations based on decomposability of known bidirectional placement algorithms into a sequence of purely unidirectional components. This paper shows that the approach of decomposability is not general enough in that it derives its power from the simplifying graph transformation of edge-splitting and the favourable nature of flows in partial redundancy elimination (PRE). This follows from the fact that in the absence of edge-splitting, PRE cannot be performed using a sequence of cascaded unidirectional flows. Further, edge-splitting inherently converts data flows involved in PRE into unidirectional flows. In our opinion, this obviates the need of an alternative formulation. We also show that edge-splitting cannot convert data flows involved in "truly" bidirectional data flow problems into unidirectional flows. Thus not every bidirectional data flow problem can be converted into unidirectional flows. Besides, we argue that the premise that bidirectional analysis is more complex than unidirectional analysis, is invalid. We also mention some issues in bidirectional data flow analysis which need to be investigated.

The phase-mapping method of phase-contrast magnetic resonance angiography is shown to be based on an implicit assumption that the intravoxel velocity distribution is symmetric about its mean velocity. The effect of asymmetric distributions on the accuracy of quantitative average velocity measurements is determined analytically and verified experimentally. An explicit formulation is developed for the estimated average velocity in a voxel as a function of the true average velocity and the asymmetry of the distribution about the true average velocity. Worst-case distributions are determined for unidirectional and bidirectional flow, and the special case of laminar flow is also investigated. Computer simulations and phantom imaging experiments demonstrate the accuracy of the analysis. For voxels with unidirectional flow, the phase-mapping method produces accurate estimates of average velocity, while results for bidirectional flow indicate possible large errors unless the aliasing velocity is increased, which decreases the signal-to-noise ratio in the resultant velocity map image.

Objective: To assess endoscopically the hemodynamic function of arterioarterial (AA) anastomoses in twin-twin transfusion syndrome (TTTS) and monochorionic selective intrauterine growth restriction(IUGR).Materials and methods: The videotapes of TTTS and IUGR patients undergoing laser surgery between July 1997 and December 2001 were reviewed for the presence of AA anastomoses. The hemodynamicequator was defined as the site within the AA anastomosis with color flashing. AA anastomoses were classified as having unidirectional flow, having bi-directional flow, or being non-functional, dependingon whether the hemodynamic equator reached a returning vein to one, both, or neither twin, respectively. TTTS was classified in stages as previously described.Results: AA anastomoses were presentin 35/183 (19.1%) of TTTS and in 12/24 (50%) IUGR patients. Of these, the hemodynamic equator was visible in 8/35 (22.8%) TTTS patients (all in stage III, and mostly in atypical stage III) and in 6/12 (50%)IUGR patients (overall 14/47, 29.8%). Of the 14 patients with a visible hemodynamic equator, 13 (92.8%) AA anastomoses showed unidirectional (9/13, 69.2% from the smaller to the larger twin) flow, and only1/14 (7.1%) showed bi-directional flow.Conclusion: The hemodynamic equator is visible in approximately 30% of patients with AA anastomoses. Within this group, most AA anastomoses behave as functionalarteriovenous anastomoses, and the direction of flow can be from the smaller to the larger twin or vice versa. The data suggest a correlation between sonographic findings and placental vascular design,also implying possible interfetal oxygenation differences. Further assessment of the functional behavior of AA anastomoses is warranted to understand the pathophysiology of TTTS and selective IUGR.

This study investigated the influence of a cyclist on crowd behaviors on a shared road. A series of mixed traffic experiments of a cyclist and a crowd of pedestrians were conducted in a circular wide track under different densities and moving directions. The influence of the cyclist on the fundamental diagram of pedestrians showed a clear difference under unidirectional and bidirectional scenarios. The cyclist restricted the pedestrian flow evidently in the unidirectional flow, while in bidirectional flow, a critical density around 0.9 ped m−2 was observed, where the restriction on the motion of the crowd was not noticeable unless the critical density was reached. The speed of the cyclist also depended on the relative moving direction, but the discrepancy became negligible when the following effect was eliminated. The lane formation was quantitatively analyzed with Otsu’s method. The results showed that the formed lanes were more concentrated in bidirectional flow than unidirectional flow. When two lanes were formed, the distances between the lanes were larger in unidirectional flow. These differences could be explained by the cognition difference of pedestrians in mixed traffic under unidirectional and bidirectional scenarios. It was observed that a major effect of the cyclist on the crowd behavioral mechanism was the generation of backward propagated density waves. A Y-shaped pattern for the formation of high-density clusters was discovered, which implied that stable high-density clusters were likely to form as the forward propagated and backward propagated density waves merged. Moreover, in bidirectional flow, the generated backward propagated density wave could also promote the fading of stable high-density clusters by reducing the heterogeneity of density distribution. Our study helps to achieve a better understanding and modeling of the dynamics of pedestrian–cyclist in mixed traffic.

Piston gauges are well-known standard instruments in the field of pressure metrology. But it is difficult to use them for small differential pressure measurements, because the pressure must be balanced against at least the weight of the piston, which generally corresponds to a pressure of several kilopascals. It is also difficult to reduce the pressure fluctuations caused by the rotation of the piston or the cylinder to lower than 0,1 Pa. A novel type of piston gauge has been developed in order to solve these problems and to measure small differential gas pressures in the range 1 Pa to 10 kPa with a sensitivity of about 5 mPa. This piston gauge uses two special features, of which one compensates for the weight of the piston and the other centralizes the piston in the cylinder without rotation. These mechanisms enable an electronic balance to measure the force produced on the piston by a small differential pressure.

Good Manufacturing Practices (GMP) related to sterile product aseptic manufacturing environments rely on protective airflow mechanisms to ensure the control over airborne contamination. Alongside the protective airflow, pressure differentials that drive airflow cascade ensure GMP compliant contamination control of airborne contamination that may include Microbial carrying particles (MCPs). Airflow visualisation qualification by smoke studies has been clarified as a GMP requirement in EU & PICS Annex 1. The scope of Annex 1 applies to manufacture of sterile medicinal products together with bioburden control processes where bioburden in intermediates, substances, APIs and non-sterile products can also impact patient safety so a wide scope of protective airflow applications is applied. As a GMP requirement (included in 2008 version of Annex 1): It should be demonstrated that air-flow patterns do not present a contamination risk, e.g. care should be taken to ensure that air flows do not distribute particles from a particle generating person, operation or machine to a zone of higher product risk.' Within Annex 1: 2023, the concept of First Air has emerged as a critical element. First Air is defined as “filtered air that has not been interrupted prior to contacting exposed product and product contact surfaces with the potential to add contamination to the air prior to reaching the critical zone.” The requirement for extensive smoke studies and the integration of First Air protection as a mandated aspect in GMP regulations has brought to the fore an imperative need for a deeper comprehension of airflow dynamics and their implications on sterile product Aseptic manufacturing. This shift beckons us to explore the nuances of protective airflow, particularly in the context of Computational Fluid Dynamics (CFD) analyses, to discern the efficacy of airflow patterns in different scenarios. Stakeholders involved in Annex 1 implementation have been impacted by introduction of the First Air protection requirement, considering design and in qualification via smoke study airflow visualisation. Such requirements must follow QRM principles where process understanding and knowledge of contamination hazards are essential to mitigate risks in compromise of product quality and potential harm to patients. Risk mitigations must take a Quality by Design (QbD) approach as monitoring alone does not provide assurance of product sterility or in meeting defined bioburden limits.

He II liquid/vapour phase separator for large dynamic range operation

This paper presents a Computational Fluid Dynamic (CFD) simulation for dry air/water-liquid and two-phase flow mixing in a vertical inverted U-tube using the mixture multiphase and turbulence models. This study is to investigate the flow behaviors and underlying some physical mechanisms encountered in dry air/water-liquid flow in the inverted U-tube. Water flows through the inverted U-tube while the dry air is entrained using the side-tube installed after the water flow downward. The inverted U-tube is tested at water mass flow rates of 2,4,6 and 8 kg/s, air mass flow rates, 0.000614–0.02292 kg/s, with dry air volume fractions 0.2–0.9. The obtained results are compared with the experimental data for model validation and the present CFD model is able to give an acceptable agreement. Also, the results show that, at water mass flow rate of 2 kg/s, there are vortices and turbulent intensity disturbances are noticed at the inverted U-tube higher part, which refers to an air entrainment occurrence from the side-tube. Theses disturbances starts to be stabilized at air mass flow rate around 0.00736 kg/s and air volume fraction, αa = 0.75. This means, if the air mass flow rate increases above this limit, the air entrainment may be blocked. On the other side, at water mass flow rate of 4 kg/s, there are little noticed disturbances until air mass flow rate of 0.00368 kg/s and αa = 0.43 and thereafter stabilized. After this point for water mass flow rate of 4 kg/s, increasing air mass flow rate may block the water flow and the whole inverted U-tube system possible stop flowing. Therefore, this study is able to estimate the required operational conditions and mass ratios for stable air entrainment process. Beyond these operational conditions, air entrainment may be blocked and the whole system discontinues its normal induced gravitational flow. In addition, this study proves that the inverted U-tube is able to generate a vacuum pressure up to 53.382 kPa based on the present geometrical configuration. This generated low-pressure by the inverted U-tube can be used for engineering applications which are working under vacuum and need continuous evacuating form the dry air and non-condensable gases. Furthermore, these findings motivate the utilizing of inverted U-tube for the air evacuation purposes for less power consuming in power plants.

MANY rock beds are used to damp out the large fluctuations in temperature obtained when air is heated by a solar collector, or to alter the phase relationship between the input and output temperature variations. Rock beds could often operate with continuous, unidirectional air flow. A solution to the Schumann equations for a sinusoidal temperature input and unidirectional flow, found in the chemical engineering literature, is presented. This solution has the form • T + T e~ mean amp sin(co(t - bx) ) where a and b can be expressed in terms of the bed characteristics and the air velocity. Discrete results from the steady-state performance of a rock bed can be fitted to a sine function by using a least-squares fit technique. A model rock bed was constructed, and experimental results were used to obtain sets of values of N^^^ vs. NRC, these were compared with values from the literature. The model was also subjected to a periodic temperature variation that simulated the output from a solar collector. As predicted from the mathematical analysis, the output was dominated by the fundamental frequency, because the harmonic terms were highly damped. The paper finishes with a discussion of the use of the steady-state periodic solution in design. It is shown that attenuation or phase lag can be controlled quite easily, but control of both may not be economical. The discussion emphasizes the improvement in understanding gained by reducing the many experimental variables to a few dimensionless groups.

Study of the performance of double pass solar air heater of a new designed absorber: An experimental work

The electrical distribution system has evolved with embedded computer systems that can better manage the electrical fault that occurred around the feeders. Such random events can affect the reliability indices of overall systems. Computerized management system for distribution operation has been improving with the advanced sensing technologies. The general research question is here to articulate is the responsiveness for utility crew to pinpoint the exact location of a fault based on the SCADA fault indicators from pole-mounted feeder remote terminal units (FRTUs). This has been a tricky question because it relies on the information received from the sensors that can conclude fault with logic's of over currents. The merit of this work can benefit at large the grid reliability because of time-saving in searching the exact location of a fault. The main contribution of this thesis is to utilize the 3-phase unbalanced power flow method to incrementally search for narrowing the localization of electrical short circuits. This is known as the reversal of the typical short circuit approach where a location of the fault is presumed. The 3 topological configurations of simulation studied in this thesis exhibit the typical radial configuration of a distribution feeder have been researched based on unidirectional and bidirectional power flow simulation. The exact fault location is carried in two steps. Firstly, a bisection search algorithm has been employed. Secondly, an incremental adjustment to match the simulated currents of fault with the measurements is conducted. Finally, the sensitivity analysis of a search can be improved with the proposed algorithm that leads to matching of telemetered and calculated values. The analysis of exact fault location is carried in unidirectional and bidirectional flow of power. Distributed energy resources (DER) such as residential PV at a household level as well the wind energy changes affect the protective relaying within a feeder as well as the reconfigurability of the switching sequences. Furthermost, the bidirectionality of power flow in an unbalanced manner would also be a challenging issue to deal with the power quality in automation. Finally, the simulation results based on unidirectional and bidirectional power flow are extensively discussed along with the future scope.

The impact of middle turbinate resection (MTR) on olfaction remains a point of debate in the current literature. Few studies have objectively evaluated olfactory cleft airflow following MTR; thus, the mechanism by which MTR may impact olfaction is poorly understood. It is not known whether the postsurgical changes in airway volume, flow, and resistance increase odorant transport or disrupt the patterns of normal airflow. Computational fluid dynamics can be used to study the nasal airway and predict responses to surgical intervention. To evaluate the functional impact of MTR on nasal airflow, resistance, and olfaction. Five maxillofacial computed tomography scans of patients without signs of significant sinusitis or nasal polyposis were used. Control models for each patient were compared to their corresponding model after virtual total MTR. For each model, nasal airway volume, nasal resistance, and air flow rate were determined. Odorant transport of 3 different odorants in the nasal cavity was simulated based on the computed steady airflow field. Total airflow significantly increased following bilateral MTR in all patient models ( P < .05). Consistent with our airflow results, we found a decrease in nasal resistance following MTR. MTR significantly increased area averaged flux to the olfactory cleft when compared to controls for phenylethyl alcohol (high-sorptive odorant). Results for carvone (medium sorptive) were similarly elevated. MTR impact on limonene, a low flux odorant, was equivocal. MTR increases nasal airflow while decreasing the nasal resistance. Overall, olfactory flux increased for high sorptive (phenylethyl alcohol) and medium sorpitve (l-carvone) odorants. However, the significant variation observed in one of our models suggests that the effects of MTR on the nasal airflow and the resultant olfaction can vary between individuals based on individual anatomic differences.

The level of airtightness is increasing in newly built Australian apartments. Due to the COVID-19 pandemic, restrictions have forced many people to work from home. An appropriate ventilation rate is needed to decrease virus transmission and provide occupants with a healthy environment. As occupants tend not to open windows, they need to be informed about the potential benefit of using trickle ventilators, in connection with exhaust systems, to ventilate their apartments. In 2022, a provision for lower rates of continuous ventilation (10 L.s−1 for the bathroom exhaust system and 12 L.s−1 for the kitchen exhaust system) was considered for inclusion in the National Construction Code of Australia. This provision was not adopted; however, this is still a valid reference for good practice. Based on this provision for continuous ventilation, our study aims to investigate the airflow velocity and the ventilation efficiency to remove the carbon dioxide (CO2) generated across winter and summer seasons in a Melbourne apartment occupied by two adults and a child over four hours.The study's objectives are 1) to connect two modelling approaches (Computational Fluid Dynamics and nodal networks), and 2) to investigate the potential benefits of using trickle ventilators across winter and summer seasons. The results show that wind conditions have limited effects (4% decrease in the extracted air flow rate) if the extraction network output is protected from the wind. Comparing winter and summer conditions, we found that indoor airflows differed, highly influenced by the temperature difference between outside and inside. We observed that the airflow patterns were more inclined to create “CO2 pockets” during winter, which could increase virus transmission due to ineffective ventilation in this area. However, in winter, ventilation performed better in reducing the CO2 concentration in the kitchen/living room area and the whole apartment than it did during summer.