Purging Flow Research Articles

An enhanced salp swarm algorithm with chaotic mapping and dynamic learning for optimizing purge process of proton exchange membrane fuel cell systems

Swarm intelligence algorithm is now a research focus for the energy optimization of fuel cell systems to improve hydrogen utilization efficiency. However, conventional algorithms exhibit poor robustness and low execution efficiency since complex constraints are involved in the fuel cell cathode purge process. Given that, this paper innovatively introduces chaotic mapping and dynamic learning mechanisms into the Salp swarm algorithm to enhance the algorithm's global search and local exploitation capabilities under complex constraints. First, we developed a three-stage nonlinear cathode purge model to describe the different water transfer behaviors in the three purging stages. Then, an optimizing function is created under the complex staged constraints to accurately reveal the energy consumption mechanism. Finally, the enhanced Salp swarm algorithm enables the rapid and accurate determination of the three-stage dynamic purge flows based on minimizing energy consumption. Compared with the fixed flow purge scheme, we found that energy consumption is reduced by 3.6 %–8.2 % under various constraints. The enhanced Salp swarm algorithm proposed in this work demonstrates an outstanding performance in the energy consumption optimization of fuel cell systems.

Utilizing periodic boundary conditions to save computational resources for assessing building natural ventilation in urban areas

For the first time in literature, we innovatively conducted CFD simulations with periodic boundary conditions to predict coupled indoor-outdoor airflows for a full-scale 3D six-floor residential building unit in urban areas with uniformly building clusters. A few influencing parameters on building ventilation performance are comprehensively analyzed, including the impacts of the surrounding buildings, wind incident angle (θ), external opening designs, cross or single-sided ventilation modes, and indoor facilities. Ventilation evaluation is contingent on factors including air change rate per hour (ACH), the corresponding ACH of purging flow rate (ACHPFR), and age of air (τ).Results show that the efficiency of natural ventilation on each floor differs from previous research conclusions after considering the impacts of surrounding buildings. Single-sided ventilation is significantly less effective than cross-ventilation in all scenarios. Most cross-ventilation cases have one-order greater ACH and ACHPFR values compared to those with single-sided ventilation. The window-to-wall ratio on the windward and leeward sides can affect the natural ventilation rate of the corresponding rooms. A large leeward opening helps to increase the ventilation rate, especially for the rooms on the upper floor, but it decreases the ventilation for the rooms near the ground. Indoor furniture has an insignificant impact on outdoor airflow and natural ventilation efficiency.

Wind-induced ventilation rate of single-sided ventilation in a building with internal partition

Wind-induced single-sided ventilation is a prevalent form of natural ventilation extensively used in buildings. Nevertheless, prior experimental investigations predominantly focused on single-zone buildings, neglecting the multizone buildings with internal partitions which is representative of more common scenarios. This study addresses this gap by investigating the impact of internal partitions on single-sided ventilation, employing a combination of wind tunnel experiment and numerical analysis. Airflow rate (AFR) was measured with a split-fibre probe and purging flow rate (PFR) was assessed by the tracer gas methodology. The PFR exhibits greater sensitivity to internal partitions in unidirectional airflow compared to bidirectional flow. Large Eddy Simulation (LES) was conducted to elucidate the intricate airflow characteristics in single-sided ventilation. The ventilation efficiency (ratio of PFR and AFR) derived from LES ranges between 0.74 and 0.79, which means that <80% of the AFR actively contributes to the removal of contaminants. Notably, the investigation discerned that the AFR of a single room approximates that of the entire room, whereas the PFR of a single room is smaller than that of the whole room. The disparities in AFR and PFR were caused by the recirculating flow, which was elaborated by the theoretical analysis.

Analysis and control strategy design for PEMFC purging process

In this study, a lumped-parameter model for shutdown purging has been developed using MATLAB/Simulink®. Data gleaned from actual operational scenarios on a fuel cell experimental platform serve as the basis for parameter identification within the model. The study encompasses a comparative analysis of purging processes under various operational parameters, including stack temperatures, purging currents, and purging flow rates. Moreover, an innovative purging strategy is proposed, employing an open-loop control mechanism to modulate the purging flow rate. The analysis reveals that an elevated stack temperature and a reduced purging current markedly enhance purging efficiency and diminish the water content at equilibrium. A negative correlation is observed between purging time and purging flow rate, with energy consumption demonstrating a U-shaped pattern across different flow rates. According to the proposed purging strategy, the optimal purging flow rate is ascertained through a Multi-dimensional Array Programming (MAP) lookup. This lookup is contingent upon stack temperature, purging current, and initial membrane water content. Validation confirms that this strategy not only truncates the purging duration but also curtails the system energy expenditure. These analytical insights and the newly-formulated purging strategy hold both theoretical and pragmatic implications for optimizing stack shutdown purging operations and advancing future purging methodologies.

Influence of Argon and Helium Purging Flow Rates on the Fusion Zone in Autogenous Stationary TIG Arc Welding of 316L Stainless Steel

Influence of Argon and Helium Purging Flow Rates on the Fusion Zone in Autogenous Stationary TIG Arc Welding of 316L Stainless Steel

Diode effects on street canyon ventilation in valley city: Temperature inversion and calm geostrophic wind

In urban areas, especially in valleys, challenges from heat and pollution are common. The situation worsens due to temperature inversions, where warm air traps pollutants. A new study employed multi-scale computational fluid dynamics (CFD) to assess ventilation in valley cities, specifically during temperature inversions and calm winds. Parameters like air change rate (ACH), local mean age of air (LMAA), and purging flow rate (PFR) were used to gauge street canyon ventilation efficiency. Factors such as atmospheric stability, city-slope positioning, and surface materials are altered to analyze impacts on urban heat island (UHI) intensity and air quality.Results indicated that katabatic winds had varied effects on pollution in different city regions, influenced by atmospheric conditions. Higher temperature lapse rates led to enhanced pollutant removal near slopes due to vortex interactions, but distant regions experienced thicker inversion layers, limiting pollutant dispersion. Conversely, anabatic winds improved ventilation with distance. Under inversion conditions, slope-city distance and surface materials played roles.For katabatic winds, city positioning significantly reduced UHI intensity, lowering LMAA by around 440s. Anabatic winds' UHI impacts ranked as atmospheric conditions, city location, and surface materials. A neutral atmosphere reduced UHI by 4.5K, but increased distance between city and slopes strengthened UHI by 4.04K. Ventilation efficiency was mainly tied to atmospheric conditions, while city location impacted pollution mitigation.This research aids in understanding air quality and airflow patterns during extreme weather events, aiding urban canyon design in valleys, especially with recurring heatwaves.

Possible high COVID-19 airborne infection risk in deep and poorly ventilated 2D street canyons

AbstractDespite the widespread assumption that outdoor environments provide sufficient ventilation and dilution capacity to mitigate the risk of COVID-19 infection, there is little understanding of airborne infection risk in outdoor urban areas with poor ventilation. To address this gap, we propose a modified Wells-Riley model based on the purging flow rate (QPFR), by using computational fluid dynamics (CFD) simulations. The model quantifies the outdoor risk in 2D street canyons with different approaching wind speeds, urban heating patterns and aspect ratios (building height to street width). We show that urban morphology plays a critical role in controlling airborne infectious disease transmission in outdoor environments, especially under calm winds; with deep street canyons (aspect ratio &gt; 3) having a similar infection risk as typical indoor environments. While ground and leeward wall heating could reduce the risk, windward heating (e.g., windward wall ~10 K warmer than the ambient air) can increase the infection risk by up to 75%. Our research highlights the importance of considering outdoor infection risk and the critical role of urban morphology in mitigating airborne infection risk. By identifying and addressing these risks, we can inform measures that may enhance public health and safety, particularly in densely populated urban environments.

Pyrolysis and Oxidative Thermal Decomposition Investigations of Tennis Ball Rubber Wastes through Kinetic and Thermodynamic Evaluations

Thermal decomposition of tennis ball rubber (TBR) wastes in nitrogen and air has been studied through thermogravimetric analysis. The samples were thermally decomposed from room temperature to 950 K at heating rates of 3 to 20 K/min with a purging flow of 30 cm3/min. The degradation features and specific temperatures for two purging gases are thus compared according to the nonisothermal results. Kinetic analyses of two thermal decomposition processes have been isoconversionally performed using differential or integral methods. The activation energy as a function of mass conversion has been thus obtained over the entire decomposition range, varying from 116.7 to 723.3 kJ/mol for pyrolysis and 98.2 to 383.6 kJ/mol for oxidative thermal decomposition. The iterative Flynn-Wall-Ozawa method combined with the linear compensation effect relationship has been proposed for determining the pre-exponential factor and reaction mechanism function, resulting in chemical order reaction models of f(α) = (1 - α)5.7 and f(α) = (1 - α)5.8 for describing pyrolysis and the oxidative thermal degradation of TBR wastes, respectively. With these kinetic parameters, very satisfactory matching against experimental data has been obtained for both gases. Additionally, the thermodynamic parameters, such as the changes of entropy, enthalpy and Gibbs free energy, over the whole thermal degradation processes have also been evaluated.

Influence of typical street-side public building morphologies on the ventilation performance of streets and squares

The deterioration of the urban environment has captured the attention of governmental departments and research institutions, which aim to improve the urban environment from the perspective of optimizing urban morphology. Although ideal building arrays and residential building morphologies have been previously studied, research on the relationship between public building morphology and urban ventilation is currently scarce. Therefore, we used computational fluid dynamics (CFD) to analyze the relationship between six public building morphologies extracted from real cities and urban ventilation. This study bridges the gap between public building morphology and urban ventilation and guides the future architectural design and urban planning. The purging flow rate and age of air were used to quantify the ventilation capacity of the squares, paths, and streets in public building blocks. The results show that a square space formed by public building setbacks can form a broad space with a path and street, which is conducive to incoming wind, resulting in better ventilation capacity. Overall, public building morphologies with 8 m street-side setbacks and 16 m path-side setbacks exhibited higher superiority rates for both single and multiple public building morphologies (66.7% and 83.3%, respectively). This study concluded that a public building morphology with 8 m street-side setbacks is the best because of a high ventilation capacity (total superiority rate = 66.7%) and building packing density.

Pollutant capture efficiencies in and around the opening surface of a fume hood under realistic conditions

Fume hoods are an indispensable instrument for experimental operations dealing with hazardous chemicals, wherein safety operations are strictly adherent to regulations. Within this context, few cases exist wherein the ventilation efficiency and pollutant capture efficiency inside fume hoods are precisely analyzed and quantitatively visualized. In this study, the pollutant capture efficiencies of a fume hood were analyzed by computational fluid dynamics as functions of exhaust airflow rate and according to the posture of workers in front of the fume hood. The indices for ventilation efficiencies, that is, age of air (SVE3), net escape velocity (NEV), and local purging flow rate (L-PFR), were adopted to quantitatively evaluate the pollutant concentration distributions formed inside the fume hood. NEV analysis revealed that the presence of a worker at the front of the fume hood did not significantly affect the pollutant capture efficiency at the opening surface of the fume hood. Changing the exhaust airflow rate resulted in changes in the size of the circulation flow formed in the upper part of the chamber. The circulation flow was found to have a dominant effect on the distribution of SVE3 and on the formation of the pollutant concentration distribution in the chamber.

Effect of slow pyrolysis conditions on biocarbon yield and properties: Characterization of the volatiles

Slow pyrolysis of spruce and birch was performed at various heating programs and conditions in a horizontal quartz tube reactor heated by an electric furnace. The effects of feedstock and carbonization conditions on the yield of biocarbon, liquid and gaseous products were studied. The thermal properties, volatile matter (VM) content and the evolution profiles of volatiles from the biocarbons were characterized by thermogravimetry/mass spectrometry. The composition of volatiles was analyzed in detail by pyrolysis–gas chromatography/mass spectrometry. Increased char yield was observed when staged pyrolysis program, low purging flow rate or covered sample holder were applied. Spruce produced more charcoal than birch due to the higher lignin content of softwood. The amount and the evolution profiles of the main gaseous products were similar from spruce and birch biocarbons prepared under the same conditions. The relative amount of aromatic and polyaromatic compounds in VM drastically decreased with increasing carbonization temperature.

A combined framework of integrating optimized half-open spaces into buildings and an application to a realistic case study on urban ventilation and air pollutant dispersion

The project planning activities of urban air quality and breathability have increasingly become the noticed issues around the world in recent times. In this study, the incorporation of half-open spaces into the ground corners of high-rise buildings is accomplished by slightly modifying the building morphology as a feasible solution. A unified procedure is proposed via a combined framework of parametric CFD study and multivariable regression analysis to optimize the half-open space design for improving ventilation performance and air quality. The influences of four design parameters on wind flow characteristics are investigated, including (i) the building height, (ii) the width of street canyon, (iii) the height of half-open space, and (iv) the width of half-open space. Using the results from this combined framework, CFD simulations are then extended to inspect the effectiveness of merging optimized half-open space layouts into high-rise buildings as the deterministic analysis in a realistic case study. Both CFD simulations are validated with the wind tunnel data for a generic urban array and on-site measurements for a realistic case study. The predictions are discussed to evaluate the outcomes of urban breathability and air pollutant dispersion by the indices of air change per hour (ACH) and purging flow rate (PFR). The incorporation of optimized half-open spaces into constructions can greatly improve urban ventilation and air pollutant dispersion in the pedestrian pathway layer. To complete the combined framework for a realistic high-rise urban area, the optimized half-open space design can increase ACH* and PFR by 75% and 57%, respectively, in the pedestrian pathway layer, as compared to the case of original half-open space design. This strategy relies on the database formulated from the CFD results of varied building morphologies in the generic urban array to realize the optimized design in a more effective and time-saving manner when applying to realistic cases.

Inerting Strategy for a Demonstration-Scale Hot Cell Facility Based on Experiences from Pilot-Scale Argon Cell Facility Operation and CFD Analysis

Pyroprocessing is being developed at Korea Atomic Energy Research Institute (KAERI), and in recent years, all process equipment required for integrated processes have been examined in the PyRoprocess-integrated Inactive DEmonstration (PRIDE) facility. Based on the successful operation of a pilot-scale facility, a conceptual design for this scale-up facility was actualized. Implementing a “demonstration-scale” hot cell facility is challenging as it is intended to supersede PRIDE and satisfy the increased requirements of larger-scale facilities. This study focused on an inerting strategy for a larger-scale (demonstration-scale) hot cell facility to achieve conditions equivalent to those in a pilot-scale gas-tight argon cell facility. The study applies the inerting strategy to a demonstration-scale hot cell facility beyond that of the currently existing pilot-scale hot cell facility and performs computational fluid dynamics (CFD) simulation with various flow rates to determine an appropriate approach for inerting the target facility. To this end, practical constraints on the simulation are introduced based on experiences from the existing pilot-scale facility. The results show that the purging flow rate should be accurately predicted, and a variable flow rate should be applied to achieve hot cell inerting effectively. The required purging time and amount of inerting source are essential factors in the larger-scale hot cell facility. The study results can be helpful in the design of large hot cell facilities operated under inert conditions.

Study on PSA Oxygen producing process under plateau region: Effect of purging flow rate on oxygen concentration and recovery

The effect of purging flow rate and oxygen product concentration and recovery rate under different altitude conditions (50 m-4540 m) was studied on the PSA oxygen production platform. The results show that the higher the altitude, the less the purging flow rate consumption in PAS process. Product oxygen recovery rate at altitudes of 50 m, 2810 m, 3080 m, 3550 m, 4140 m and 4540 m is 39.6%∼42%, 42%∼47%, 43%∼46%, 43.4%∼45.5%, 42%∼46% and 48%∼52.5% respectively. At the same altitude, the oxygen recovery first increases and then decreases with the increase of purging flow rate, and there is an optimal balance between oxygen recovery and purging flow rate. This study can provide reference for the regulation of oxygen production process of PSA at high altitude.

Periodic Flow Purging System for Harvesting Fibers from Screens

ABSTRACT Fiber length is believed to be an important factor in determining various toxicological responses to asbestos and other bio-persistent fibers. Length classification of fibers thus is crucial for toxicological assessment. Nylon mesh screens have been shown to be effective in separating fibers by length. In this note, we report development of a purging flow system for harvesting fibers from a nylon net screen, with the aim of separating airborne fibers by length. We evaluated the performance of this purging flow system by examining the lengths of glass fibers collected on a screen. Fibers aerosolized by vortex shaking were provided to 10 µm and 20 µm mesh screens, and the fibers collected on each screen were purged periodically with a backflow. The length of the purged fibers was measured and compared to that of fibers washed from the screen. The mean length of fibers on the screen is larger than that of the fibers in the original test aerosol. The mean length of the backflow purged fibers is smaller than that of the fibers from the washed screen. The results indicate that the purging flow system with screens can harvest the longer fibers from the original aerosol.

Inhalation airflow and ventilation efficiency in subject-specific human upper airways

The present numerical study investigated the transportation time of the inhaled chemicals in three realistic human airway models by adopting a methodology from the field of the building ventilation. Two indexes including “scale of ventilation efficiency 3 (SVE3)” and “local purging flow rate (L-PFR)” were used to evaluate the respective arrival time and staying time under different inhalation flow rates. The general trend of the SVE3 was predicted as expected and the exceptions within the nasal cavities were attributed to the uneven allocation of the inhaled flow between the internal channels and the formation of the vortex circulation therein. The complicated situation of the L-PFR was also explained by the structure constrains. Moreover, the variation of the two indexes with the flow rate was sensitive to the inter-subjective differences but the distribution pattern was not changed significantly. By combining the SVE3 and L-PFR, it could help with assessing the potential effect of the inhaled chemicals on the human health for engineering applications to which the relative impacts are more interested than the absolute value. But for the precise evaluation regarding a specific chemical, comprehensive simulation is still necessary with the surface adsorption included under realistic respiration cycles.

Purge-assisted and temperature-controlled headspace solid-phase microextraction combined with gas chromatography–mass spectrometry for determination of six common phthalate esters in aqueous samples

This study describes a novel procedure, namely, purge-assisted and temperature-controlled headspace solid phase microextraction combined with gas chromatography/mass spectrometry, which is used to determine six phthalate esters in aqueous samples. The optimum conditions for obtaining extraction efficiency, such as the extraction fiber type, extraction temperature, nitrogen gas purging flow rate, addition of salts, extraction time, headspace condenser cooling temperature, sample stirring rate, and fiber position parameters were investigated by using single-factor experiment (one-factor-at-a-time) and orthogonal experimental design (OED) methods. Under the optimal conditions, the linear range of detection of the proposed method was 0.2–50 ng/mL with coefficients of determination between 0.992 and 0.995. Limits of detection for six phthalate esters were 0.04–0.18 ng/mL. The application of the proposed method for the determination of trace phthalate esters in real samples was investigated by analyzing bottled water sample and brewed hot coffee successfully.

Localized Purging Methodology to Minimize Oxidation During Gas Tungsten Arc Welding of 304L Stainless Steel Pipes

In reprocessing plant with high-density piping, inert gas purging for gas tungsten arc welding (GTAW) of 304L stainless steel pipes to minimize oxidation is difficult at some places due to complexity of design and access limitations. One typical example is terminal joints. During GTAW of the terminal joints, oxidation due to inadequate purging is observed, apart from weld defects. Since the pipe joints are not amenable for inspection after commissioning, it is essential to ensure integrity of each pipe joint weld by stringent quality assurance measures and volumetric nondestructive testing such as radiographic testing. Oxidation of any magnitude and any linear defect indications at root are not acceptable as they promote corrosion at the root side of the pipe welds during service. Conventional full volume flow purging is time-consuming and expensive depending on the volume of the processing tank. Other well-established localized purging methods such as water-soluble dams and thermally disposable barriers are not feasible for most of the terminal joints. This paper presents development and implementation of an alternate localized purging methodology that uses a perforated copper flask to address oxidation and associated weld defect formation during the welding of SS 304L pipe terminal joints. This methodology is found to be faster and cost-effective than the conventional full volume flow purging methodology.

Experimental Investigation of Purging Saline Solution from a Dead-End Water Pipe

Salty groundwater might find its way into dead end legs of a water distribution network and thus efforts are required to clean such parts of the network. This paper reports, for the first time, the results of a visual study for laboratory experimental investigation on the purging process of saline water from a dead-end water pipe using fresh water. Three purging locations and a number of purging flow rates were considered to identify the effect of purging location and purging flow rate on the time required to completely remove saline water from the dead-end pipe. Image processing analysis techniques were used to capture data from the experimental lab setup. A universal gray-intensity to salinity curve was experimentally found to formulate a color intensity to salinity mapping. A script code based on Octave numerical package was written for this regard to determine the temporal variation of the total dissolved salt (TDS) value within the dead leg pipe. It is generally noted that, as Reynolds number gets higher, the time removal ratio (t/ts) gets bigger. It is also noted that, as a purging location gets farther from the dead end, the time required for the complete removal of TDS increases exponentially.

An experimental study to investigate typical temperature conditions in fuel tanks of European vehicles

Vehicular evaporative emissions have been recognized as an important source of volatile organic compounds to the environment and are of high environmental concern since these compounds have been associated to the formation of surface ozone and secondary organic aerosols. Evaporative emissions occur during any vehicle operation. In Europe, a revised legislative test procedure has been recently introduced to better control evaporative emissions during parking. However, emissions related to normal driving conditions—the so-called running losses—have received less attention compared with the other categories. The current study aims at giving some insights to the prevailing temperature conditions in fuel tanks of typical European vehicles during normal driving operation. The effects of ambient air temperature, trip duration, vehicle speed, and fuel tank level on the temperature reached by the fuel inside the tank under different real-world operating conditions were studied. Tank temperature can exceed 40 °C depending on ambient and driving conditions. Ambient temperature was found to be the most important parameter affecting the tank temperature. Trip duration and driving pattern may also have an influence on the tank temperature particularly when long trips combined with high vehicle speed are examined. Additionally, the difference between tank and ambient temperature was examined during the individual trips and was found to vary between 1 and 10 °C depending on the testing conditions. The most important parameters affecting the delta temperature were found to be the trip duration and the maximum vehicle speed. Finally, the purging strategy of two of the test vehicles was monitored, and the parameters affecting the purging flow rate were investigated. No strong correlation between the canister flow rate with ambient temperature, vehicle speed, or fuel level was observed in either of the tested vehicles. Substantially different canister flow rate levels between the two vehicles point to different purging strategies.