Low Air Flow Research Articles

Holey Ti3C2Tx nanosheets membrane with high PM removal efficiency for air pollution

Developing air filters with high efficiency, low airflow resistance, good chemical and thermal stability is a great challenge for PM purification applications. MXene membranes with controlled interlayer nano-channels and abundant hydrophilic groups exhibit excellent separation potential. However, the easy stacking between neighboring nanosheets in two-dimensional lamellar membranes increases the resistance during the separation process. In this study, metal oxides were assembled with Ti3C2Tx nanosheets by electrostatic interaction, and holey Ti3C2Tx (H-Ti3C2Tx) nanosheets with abundant through-hole structures were prepared by calcination and etching with a specific surface of 13.2 m2g−1, 6 times higher than that of Ti3C2Tx (2.2 m2g−1). H-Ti3C2Tx nanosheet membranes with transverse and longitudinal channels were produced using vacuum filtering. The membrane has excellent PM filtration performance, with filtration efficiency higher than 94.59% for PM 0.3 and 99.97% for PM 2.5 and 99.99% for PM 10.0, respectively, and the pressure drop of 120 Pa after 12 h of operation, which is better than that of pure Ti3C2Tx membrane (>1300 Pa). Excellent PM filtration was also demonstrated under high humidity conditions. Our findings provide a scalable strategy for the synthesis of holes MXene materials as well as demonstrate their potential in air purification.

Reconstruction of Vocal Fold Medial Surface 3D Trajectories: Effects of Neuromuscular Stimulation and Airflow.

Analysis of medial surface dynamics of the vocal folds (VF) is critical to understanding voice production and treatment of voice disorders. We analyzed VF medial surface vibratory dynamics, evaluating the effects of airflow and nerve stimulation using 3D reconstruction and empirical eigenfunctions (EEF). In vivo canine hemilarynx phonation. An in vivo canine hemilarynx was phonated while graded stimulation of the recurrent and superior laryngeal nerves (RLN and SLN) was performed. For each phonatory condition, vibratory cycles were 3D reconstructed from tattooed landmarks on the VF medial surface at low, medium, and high airflows. Parameters describing medial surface trajectory shape were calculated, and underlying patterns were emphasized using EEFs. Fundamental frequency and smoothed cepstral peak prominence (CPPS) were calculated from acoustic data. Convex-hull area of landmark trajectories increased with increasing flow and decreasing nerve activation level. Trajectory shapes observed included circular, ellipsoid, bent, and figure-eight. They were more circular on the superior and anterior VF, and more elliptical and line-like on the inferior and posterior VF. The EEFs capturing synchronal opening and closing (EEF1) and alternating convergent/divergent (EEF2) glottis shapes were mostly unaffected by flow and nerve stimulation levels. CPPS increased with higher airflow except for low RLN activation and very dominant SLN stimulation. We analyzed VF vibration as a function of neuromuscular stimulation and airflow levels. Oscillation patterns such as figure-eight and bent trajectories were linked to high nerve activation and flow. Further studies investigating longer sections of 3D reconstructed oscillations are needed. N/A, Basic Science Laryngoscope, 134:1249-1257, 2024.

Design of PID and ADRC based adaptively anti-disturbance quadrotor hovering controller

This paper reported an implementation of quadrotor controller, aimed at using ADRC-based controller cascaded with PID controller to overcome hovering difficulties and provide resistance to extreme wind conditions in the complex airflow environment common in typical urban low-flying environments. The main tasks of the implementation including analyzing the complexity of urban low air flow environments and exploring what challenges it brings to the hovering stability of lightweight quadcopters, as well as demonstrating the good performance of the cascade PID-ADRC controller in this case and compare it with a classic PID controller.

Employing a fan to improve the wintery heating performance of solar air collectors with phase-change material: An experimental comparison

Solar Air Collectors integrated with Phase-Change Material (SAC-PCM) were widely used for wintery heating with the superiority of overcoming the mismatch shortcoming between supply and demand time from solar heating. However, the traditional SAC-PCM had the low-efficiency heat output due to the low air flow of natural convection. Based on this, a fan was proposed to enhance air flow and thereby, increase the heat output from SAC, so an experiment was built to compare the thermal performance between SAC-PCM and SAC-PCM with a fan (SAC-PCM-F). The experimental result showed that the fan enhanced the outlet wind speed from 0.8 m/s-1.55 m/s to 2.15 m/s-2.3 m/s and by employing the fan, the heat output was easier from SAC-PCM and the average temperatures of outlet air were increased 4.18 °C in all day with the average temperature difference of outlet and inlet air increased by 1.17 °C. Employing the fan could improve indoor average temperature by 1.17 °C, while the daily heat output was increased by 146.02% by employing the fan and the heat collecting efficiency was increased from 24.92% to 61.32%

To optimize gas flaring in Kirkuk refinery in various seasons via artificial intelligence techniques

Unavoidable flaring in downstream oil industry causes pollutant emission in large amounts which is potentially harmful to nearby cities or farms. Hence one must manage exhaust toxic gases to raise enough in atmosphere or redirect from such places. Since Kirkuk refinery in north Iraq is next-door to agricultural farms on west yet to residential areas on east optimizing its layout for flare stacks is something acute. In this work we wrote codes in MATLAB software to simulate incomplete rather than complete oxidation as well as pollutant generation reactions. Then we made use of FLEUENT software to simulate pollutant propagation in Kirkuk oil purifier complex yet also farther to city as well as farms with respect to seasonal air currents on lowest troposphere layer. Finally, we set neural network approach to train on simulation data thereafter to unify outcomes to turn into a fast technique for layout optimization. Results show that optimization process efficiency relies on air current velocities as well as its direction. At intermediate air flow rates optimum layout includes only a selective portion of existent flare stacks. Outcomes also illustrate that heuristic techniques that have stronger local search such as particle swarm or artificial immune system can improve flare layout in seasons with intermediate air currents here summer plus early months in autumn while approaches with weak local search like Monte Carlo are more appropriate in winter for which we have no or low air flows in Kirkuk governorate.

Nasal Pressure Derived Airflow Limitation and Ventilation Measurements are Resilient to Reduced Signal Quality.

Obstructive sleep apnea is a disorder characterized by partial or complete airway obstructions during sleep. Our previously published algorithms use the minimally invasive nasal pressure signal routinely collected during diagnostic polysomnography (PSG) to segment breaths and estimate airflow limitation (using flow:drive) and minute ventilation for each breath. The first aim of this study was to investigate the effect of airflow signal quality on these algorithms, which can be influenced by oronasal breathing and signal-to-noise ratio (SNR). It was hypothesized that these algorithms would make inaccurate estimates when the expiratory portion of breaths is attenuated to simulate oronasal breathing, and pink noise is added to the airflow signal to reduce SNR. At maximum SNR and 0% expiratory amplitude, the average error was 2.7% for flow:drive, -0.5% eupnea for ventilation, and 19.7 milliseconds for breath duration (n = 257,131 breaths). At 20 dB and 0% expiratory amplitude, the average error was -15.1% for flow:drive, 0.1% eupnea for ventilation, and 28.4 milliseconds for breath duration (n = 247,160 breaths). Unexpectedly, simulated oronasal breathing had a negligible effect on flow:drive, ventilation, and breath segmentation algorithms across all SNRs. Airflow SNR ≥ 20 dB had a negligible effect on ventilation and breath segmentation, whereas airflow SNR ≥ 30 dB had a negligible effect on flow:drive. The second aim of this study was to explore the possibility of correcting these algorithms to compensate for airflow signal asymmetry and low SNR. An offset based on estimated SNR applied to individual breath flow:drive estimates reduced the average error to ≤ 1.3% across all SNRs at patient and breath levels, thereby facilitating for flow:drive to be more accurately estimated from PSGs with low airflow SNR.Clinical Relevance- This study demonstrates that our airflow limitation, ventilation, and breath segmentation algorithms are robust to reduced airflow signal quality.

Investigation into the Hydration Behavior of K2CO3 Packed Beds: An NMR Study

K2CO3 is seen as a promising heat storage material, available for applications in the domestic sector. For practical purposes, the material is hereby often employed in a packed bed containing millimeter-sized particles. To gain more insight into the hydration behavior of these packed beds, quantitative NMR measurements, capable of following the in-situ hydration behavior, are presented for the first time. It is found that hydration behavior varies significantly, depending on the specific hydration conditions that are chosen. At low airflows hydration is found to proceed via a hydration front, while higher airflows cause the hydration front to widen. Since an increase in flow rate coincided with an increase in the supplied water vapor, hydration is eventually found to proceed in a uniform manner. A comparison between TGA and NMR measurements shows that the overall packed bed hydration kinetics hereby transition to the reaction kinetics of single K2CO3 particles.Graphical

Membrane bubble aeration unit: Experimental study of the performance in lab scale and full-scale systems

The transfer of oxygen is limited at the gas/liquid interface by the low solubility of oxygen in water. Fine bubble diffusers have a standard oxygen transfer efficiency (SOTE) lower than 30% in a full-scale system. Porous membranes can be employed as diffusor to improve the efficiencies taking the advantage of the high exchange interfacial area and the low volume of equipment. The aim of this work is to study the feasibility of membrane systems for aeration in a full-scale system. Several membrane modules were prepared using hollow fibers hydrophobic membranes and compared with the traditional disk diffusor currently employed in wastewater treatment. The mass transfer coefficient (KLa) and SOTE were assessed by carrying out the aeration tests in both lab-scale and full-scale systems exploring different operating parameters such as system flow rate, the geometry of the module and the surface of the device. The advantage and disadvantages of employing membranes in the aeration process were highlighted. The membrane unit showed better overall mass transfer efficiency increasing from 28% at the lab-scale to 34% in the full-scale system. Unlike the conventional disk diffusers, it has been found that the membrane aerator can operate with significantly lower air flow rates, which leads to a doubling of the efficiency. Moreover, the membrane surface generating the bubbles can be easily increased while maintaining the same module footprint, which in turn allowing a further increase of efficiency from 9% to 24%. However, important phenomena of scaling were observed on the membrane surface.

Automated fault detection and diagnosis of airflow and refrigerant charge faults in residential HVAC systems using IoT-enabled measurements

While automated fault detection and diagnosis (AFDD) in residential heating, ventilation, and air-conditioning (HVAC) using smart thermostat data is gaining increasing attention in recent times, it still requires in-depth investigation for market adoption, especially with real-life data. This paper proposes an Internet of Things (IoT) - based approach that adds a smart sensor to the smart thermostat data to carry out AFDD. The approach uses a model which predicts enthalpy change across the evaporator and compares the prediction to the measured enthalpy change. Deviations which exceed analytically determined thresholds then signal faults in the HVAC system. The faults detected are either installation related or degradation related. Experimental tests were carried out in four homes located in Norman, Oklahoma. From the tests, installation issues like indoor/outdoor mismatch were detected in two homes, while a 30% low charge and low indoor airflow rate were detected in one home. The results show that the proposed AFDD algorithm was able to successfully detect two prevalent faults, namely low indoor airflow and low refrigerant charge. Unlike most of the smart thermostat-based approaches, the proposed IoT-based approach can detect and diagnose both faults but only require one additional sensor which is provided by smart thermostat manufacturers.

A comparative study of property-constant and property-variable icing models

ABSTRACT Icing on cold surfaces is ubiquitous in many natural and engineering processes, and various icing models have been proposed with little advice given on model selection. Here, we calculate the ice accretion characteristics using property-constant and property-variable icing models under different airflow parameters. The ice thickness, water film thickness, temperature profile, critical ice thickness, and critical time are compared. The property-variable icing model yields a larger ice thickness at the early icing stage but a smaller one at the later stage. The water film appears earlier, and the water film thickness is larger in the property-variable model. The temperature profiles are a logarithmic curve and a straight line in the property-variable and property-constant models. The property-variable model yields a shorter critical time and a smaller critical ice thickness. A smaller liquid water content, airflow velocity, and collection efficiency or a lower airflow temperature enlarges the difference in the ice accretion characteristics between the property-variable and property-constant models. The property-variable icing model is recommended when the airflow coefficient is smaller than 50. The findings in this work provide guidance for the model selection in icing prediction.

Testing and Evaluation of an Updraft Gasifier Using Saba Banana Peel as Feedstock

Saba bananas are widely produced in the Philippines, mainly for food production. The peel of saba was characterized, and some physical properties of it were measured. The heating value, fixed carbon, volatile matter, ash, and moisture content of the peel were also determined. In predicting the elemental composition, the equation of Parikh et al. (2007) was used, yielding an air-to-fuel ratio of 6.92 kgair/ kgbiomass for combustion. A laboratory-scale prototype updraft gasifier was fabricated and tested for efficiency by boiling water on it. The size of the peel affects the ignition time of the syngas and the burning rate of the biomass. Flow rate affects the amount of heat produced and the equivalence ratio during gasification. Thermal efficiencies in different settings are less than 20% due to system heat loss. The highest efficiency was obtained with a low airflow setting, while the lowest efficiency was yielded at a high airflow setting. At an equivalence ratio of 0.208, about 500g of saba peel produced around 1562.63 kJ of heat with a thermal efficiency of 17.46%. For higher efficiency of the peel, it is recommended to design a gasifier that would decrease the system heat loss and process the biomass into briquettes or pellets for a more uniform mass and size distribution.

Experimental and Numerical Study on the Combined Jet Impingement and Film Cooling of an Aero-Engine Afterburner Section

The recent advancement of cooling methodologies for critical components such as turbine blades, combustor liners, and afterburner liners has led to the development of a combination of impingement and film cooling. The present study proposes an efficient cooling technique for a modern aero-engine afterburner liner based on the combination of jet impingement and film cooling. To achieve this, a numerical model is devised to model the film flow over a corrugated liner with several jets impinging over it. The numerical model is validated in a set of in-house experiments as well as against experimental data available in the literature. The experiment is performed for a limited temperature range (i.e., with a low-density ratio). However, the numerical simulations are carried out by varying the blowing ratio from 0.3 to 0.6. The density ratio during the simulations is kept at 3.5. The minimum distance between the impinging plate and the liner is kept at h/D = 1. A detailed analysis of the numerical results indicates a significant drop in the temperature distribution over the liner surface because of the employed cooling technique. The present study also reveals that, under similar operating conditions, the combined jet impingement and film cooling system has the ability to achieve the targeted cooling effect at a lower bleed air flow rate due to its higher effectiveness than that of the standard film cooling arrangement.

Modeling of closed-circuit ball milling of cement clinker via a PBM with a variable Tromp curve for classification

Full-scale closed-circuit cement ball milling was modeled using a true unsteady-state simulator (TUSSIM), based on a transient cell-based population balance model (PBM) with a set of differential algebraic equations (DAEs). As a major novelty, the PBM for the mill was coupled with a dust load-dependent, variable Tromp curve for the air classifier. Results from the dynamic simulations suggest that lower air flow rate or higher rotor speed of the classifier not only led to a finer product but also increased the dust load of the classifier feed. When the dust load was too high, operational failure due to overloading of the whole circuit was detected. Finally, TUSSIM was used for process optimization with a global optimizer-DAE solver to identify the air classifier's parameters that yielded desirable cement quality while maximizing production rate. We have demonstrated that the optimization could increase production rate by 7% compared to the baseline process.

Experimental study and modeling analysis of sewage sludge smoldering combustion at different airflow rates

Sewage sludge is a major by-product of wastewater treatment, and its unfavorable properties are frequently a key restriction of disposal technologies, resulting in high costs and ineffective waste management. Smoldering combustion is a new technique for disposing of organic solid waste with high moisture content, which efficiently recovers energy with minimal igniting energy requirements. The objective of this study is to investigate the effects of airflow rate on sewage sludge (SS) smoldering combustion by combining experimental and modeling analyses. Results show that air channeling easily forms at the reactor's edge, intensifying the smoldering reaction and forming a concave smoldering front. The minimum airflow rate required for self-sustaining smoldering is 0.3 cm/s. As the airflow rate increases, convective heat transfer becomes dominant over conduction and radiation, resulting in a surge in smoldering temperature and velocity at 0.6 cm/s, followed by a linear increase. The maximum airflow rate at which the smoldering process can propagate stably during SS disposal is 8 cm/s. The expressions of the smoldering characteristics are obtained by using the activation energy asymptotic approach, and the calculated and experimental values show the same trend of variation, with good agreement at low airflow rate conditions. Sensitivity analysis shows that porosity φ is the most crucial parameter affecting smoldering temperature and velocity.

Oxidative pyrolysis of pellets from lignocellulosic anaerobic digestion residues and wood chips for biochar and syngas production

Compared to pyrolysis in an inert atmosphere, oxidative pyrolysis for biomass conversion is autothermal and decreases the concentration of tars in the produced gases. The aim of this work is to study a fixed bed reactor for oxidative pyrolysis on a laboratory scale with a capacity of 1.5 kg/h of lignocellulosic anaerobic digestion residues (Pellets-DR) at a temperature range of 600 °C and under a low specific airflow of 0.012 kg/m2.s. Wood chips (WC-P16F05) were used as a reference to evaluate the potential of Pellets-DR conversion to biochar and syngas using oxidative pyrolysis. Oxidative pyrolysis produced only 10% and 6% of tars on a fuel dry and ash-free basis for Pellets-DR and wood chips, respectively, which is equivalent to a concentration of 25 g/Nm3 and 38.6 g/Nm3 in gases. Ultimate and proximate analysis of biochar produced from both types of biomasses showed that the main element present was carbon in the case of wood chips (87.8%). However, carbon is present in only 48.33% of the biochar from Pellets-DR. The main difference between Pellets-DR and wood chips was also found in biochar’s low heating value (LHV), which is estimated to be 31.9 MJ/kg for wood chips and 13.01 MJ/kg for Pellets-DR. The propagation of the oxidation zone was inversely proportional to biomass density, and it plays a key role during biomass oxidative pyrolysis; it was about 0.14 cm/min and 0.5 cm/min for Pellets-DR and wood chips, respectively. Air flux was the most important factor affecting the oxidation zone propagation velocity, but in this study, low values of air flux meant that changes in air flux did not have a significant effect on the yield and the composition of the products. Regardless of its high ash content, Pellets-DR may have the potential to be converted into biochar and syngas by oxidative pyrolysis.

Temperature and flame structure imaging in kerosene swirl-stabilized spray flames at low air flow using TLAF and OH-PLIF

Air flowrate is an important parameter for airbrast nozzles and low air inlet flow rate in airbrast type combustors will lead to worse atomization, combustion instability, and increased pollutant emissions. Using non-linear excitation regime two-line atomic fluorescence (NTLAF) thermography imaging and planar laser-induced fluorescence of hydroxyl radical (OH-PLIF), temperature and flame structure in the near-nozzle area are investigated at different low air flow rate to study the combustion deterioration of kerosene swirl-stabilized spray flames. In this concerned area, combustion occurs mainly at the near-wall region but a few OH signals are present at the centerline region except for the kerosene LIF particles. With the air supply getting low, the near-wall OH signals get low, corresponding to the change of indium Stokes and anti-Stokes fluorescence. The temperature in the centerline region is presented to be reduced and the region for the temperature threshold filter expands, indicating the reduction of the downstream hot combustion products brought back by weak swirl, which is closely related to the extremely low air flowrate. Under extremely low air flow rate, the highly fluctuating temperature and weak gas-liquid mixed combustion at the centerline area may tend to cause combustion instability or ignition failure.

Effect of multi parameter synergy on the upgrading characteristics of wide size moist coal

ABSTRACT Through composite dry separation, effective precipitation and impurity removal can be achieved, improving the quality of raw coal. This paper mainly systematically analyzes the synergistic control mechanisms of airflow velocity, airflow transition layer height and control angle on the upgrading characteristics of moist coal. The results show that Zone I is a high airflow area, and when v = 2.12 m/s, it can effectively destroy the original static stable structure of low-density particles, increase the degree of freedom of particle accumulation volume, and achieve effective precipitation of particles. Zone II is a medium air volume area, and when v = 1.78 m/s, the high-density particle group in this area has the weakest obstruction effect on airflow, which can achieve efficient particle precipitation. Zone III is a low airflow area, where the dispersion of high-density particle groups increases at v = 1.36 m/s. The airflow can effectively act on the particles through the bed layer, reducing their surface water. When the height (H) of the gas transition layer is 49-52 mm and the regulatory perspective is 20–25, the distribution uniformity of the gas flow in the bed is the best. After separation and upgrading, the moist coal concentrate yield is 78.3%, ash content is 10.05%, as well as the possible deviation E value is 0.1 g/cm3.

Interaction of fuel spray and air swirl on the combustion of residue oils

Effervescent atomization technology was applied in Waste Lubricant Oils (WLO) combustion. The tests were conducted in a 150 kW prototype boiler with a horizontally oriented cylindrical shape combustion chamber in which the combustion process was studied in terms of the interaction between a swirling air flow and fuel spray pattern. The combustion performance was assessed by continuously monitoring gaseous emissions, particularly carbon monoxide (CO) emission. Two different air feeding strategies were tested, varying in swirl number and six different configurations of the injection nozzle orifice. Three nozzles had a single orifice varying in diameter and discharge end geometry, and the others had three divergent orifice arrangement varying in cone angle and diameter. At the same time, the gas-to-liquid ratio (GLR) of the effervescent atomizer was also investigated, allowing to draw important illations about its influence on the combustion efficiency. The results show that the use of effervescent atomizers allows to burn of WLO, with CO emissions as low as 15 ppm at 8% of oxygen (O2) when using a three orifice of 1 mm with 15° of cone angle nozzle. This result was achieved by applying high-intensity combustion air flow swirl. However, the one orifice nozzles with penetrant spray pattern combined with low swirl intensity air flow also produced satisfactory results. With CO emissions of 27 ppm at 8% of O2 with a 1.2 mm single orifice nozzle. Furthermore, it was also demonstrated that the increment of the GLR in a range between 0.25 and 0.35 can be responsible for the reduction of 40 to 50% of the CO emissions when burning WLO.

CFD analysis of Part-Load operation of an Open-Circuit Induced-Draft cooling tower

Evaporative towers are the most widely used systems for cooling water in industrial processes. These systems, however, are characterized by high energy and water consumptions. Therefore, technologies and operating strategies for optimization of these devices are highly recommended. The heat exchange, which takes place inside an evaporative tower is very complex and not easy to model. In this work, an induced-draft evaporative tower is modelled by means of computational fluid dynamics (CFD), which is relatively new in this field of application. A numerical model, based on the adoption of sub-models for the heat exchange between the water droplets and humid air in the filling region, is developed and validated with experimental data, laying the foundation for further analysis in the future. The achieved results can be considered reliable and accurate as the numerical uncertainty is approximately 4 %. The study aims at evaluating and analyzing the thermo-fluid-dynamic quantities that characterize the heat exchange, with reference to water outlet temperature, cooling capacity, and evaporated water flow rate. In particular, partial load operation are analyzed. The conditions refer to the simultaneous reduction of water and air flow rates. The study shows that both at full load operation and by reducing water and air flow rates to 60 % of the design value while maintaining a constant water/air ratio, the tower process parameters are kept very close to the design ones. Under these conditions, the evaporated water is halved (∼0.05 kg/s instead of ∼ 0.1 kg/s maintaining air flow at full load). Moreover, by adopting lower water and air flow rates a significant reduction of the electric power requested by the fan, from 15 kW at full load to about 8 kW at part load, is achieved.

Modelling the ingress and charge enhanced deposition behaviour of radioactive aerosols in dwellings

Radioactive aerosols of accidental origin can travel long distances once airborne and although dwellings can provide some shelter, ingressed radioactive aerosol has been shown to be injurious to human health. Modelling approaches have been widely used to study indoor aerosol behaviour, but such approaches have not to date considered the self-charging nature of radioactive aerosol and the consequent effect upon aerosol deposition. In this work, a multi-zone modeling tool is used to simulate indoor aerosol concentrations in the individual rooms of a bungalow and semi-detached dwelling, for three radioactive aerosol particles sizes (0.5, 1.0, 2.0 μm, with aerosol deposition enhancement due to particle charge), two plume types (5 h and 24 h), and a range of representative dwelling airflow conditions (low air flow LAF and high air flow HAF1), including mechanical extract ventilation (HAF2). When comparing the time series of aerosol concentrations in different rooms, lower concentrations of charged aerosol, relative to uncharged, were observed, suggesting charge-enhanced deposition, and this phenomena is more striking during a 24 h plume compared to 5 h plume, where the difference between the two is up to 50% in one of the zones of the dwelling. The concentration comparison of charged aerosols concentration between LAF and HAF1 cases also showed that during a 5 h plume, the aerosol concentration is twice as high for the HAF1 case. These simulation results demonstrate that the effect of charged-enhanced aerosol deposition should be considered when assessing the benefits of sheltering in a building in the event of a nuclear accident.