Airflow Conditions Research Articles

ANALISIS PERFORMA MENARA PENDINGIN MECHANICAL INDUCED DRAUGHT ALIRAN COUNTERFLOW PADA PEMBANGKIT LISTRIK TENAGA PANAS BUMI LAHENDONG UNIT 5

In the geothermal power plant process, the main cooling water system is required to maximize the power plant, one of them is using the cooling tower. The Cooling Tower is an incredibly vital cooler. So, the performance must be noted is still in accordance with initial conditions. The purpose of this research is to determined the performance of Mechanical Induced Draught counterflow Cooling Tower in Lahendong Geothermal Power Plan Unit 5 with quantitative research for 7 days with 10 hours of operational work. In Lahendong Geothermal Power Plant Unit 5. The result of this research showed the performance of Mechanical Induced Draught Counterflow Cooling Tower in Lahendong Geothermal Power Plan Unit 5. The range increased up to 14.2 C, in the morning because of the high humidity, the effectiveness which also increases in the morning and the airflow conditions which still remain. So, this research will be concluded when the performance of Mechanical Induced Draught Counterflow Cooling Tower Geothermal Power Plant Unit 5 is still in normal operation conditions and needs to do Make-up Water amounts of 387.81 m3/h.

Bifunctional ZIF-8 Grown Webs for Advanced Filtration of Particulate and Gaseous Matters: Effect of Charging Process on the Electrostatic Capture of Nanoparticles and Sulfur Dioxide.

Metal-organic framework (MOF), an emerging class of porous hybrid inorganic-organic crystals, has been applied for various environmental remediation strategies including liquid and air filtration. In this study, the role of the zeolite imidazole framework-8 (ZIF-8) was explored on the charge trapping ability and its contribution to capturing the targeted pollutants of NaCl nanoparticles and SO2 gas. Poly(lactic acid) fibers with controlled surface pores were electrospun using water vapor-induced phase separation, and the fiber surface was uniformly coated with ZIF-8 crystals via an in situ growth method. As a novel process approach, the corona charging process was applied to the ZIF-8 grown webs. The ZIF-8 promoted the charge trapping in the corona process, and the charged ZIF-8 web showed a significantly improved electrostatic filtration efficiency. Also, the charged ZIF-8 web showed an enhanced SO2 capture ability, both in the static and dynamic air flow states, demonstrating the applicability as a bifunctional filter for both particulate and gaseous matters. The approach of this study is novel in that both particulate and gas capture capabilities were associated with the charge trapping ability of ZIF-8, implementing the corona charging process to the ZIF-8 webs.

Mechanism and experimental study of arc suppression by polyphase longitudinal airflow

An arc extinguishing lightning protection device with a multi-arc extinguishing chamber structure has been gradually applied to the overhead line lightning protection, but the process and key factors of the arc building of the internal multi-phase flow suppression arc still need to be studied. In this paper, based on the theory of arc magnetohydrodynamics and Euler’s high velocity flow field model, a simplified model of arc coupled polyphase longitudinal air flow in a multi-pipe structure is established, the approximate solution of the model is made, and the development process of polyphase air flow and the extinction mechanism of the arc are obtained. At the same time, the arc quenching process of polyphase longitudinal air flow is also studied experimentally. The experimental results show that the continuous arc of power frequency can be stopped quickly and will not be reignited under the condition of polyphase air flow.

Effect of swirling flow and particle-release pattern on drug delivery to human tracheobronchial airways

The present study aims to investigate the effect of swirling flow on particle deposition in a realistic human airway. A computational fluid dynamic (CFD) model was utilized for the simulation of oral inhalation and particle transport patterns, considering the k-ω turbulence model. Lagrangian particle tracking was used to track the particles' trajectories. A normal breathing condition (30 L/min) was applied, and two-micron particles were injected into the mouth, considering swirling flow to the oral inhalation airflow. Different cases were considered for releasing the particles, which evaluated the impacts of various parameters on the deposition efficiency (DE), including the swirl intensity, injection location and pattern of the particle. The work's novelty is applying several injection locations and diameters simultaneously. The results show that the swirling flow enhances the particle deposition efficiency (20-40%) versus no-swirl flow, especially in the mouth. However, releasing particles inside the mouth, or injecting them randomly with a smaller injection diameter (dinj) reduced DE in swirling flow condition, about 50 to 80%. Injecting particles inside the mouth can decrease DE by about 20%, and releasing particles with smaller dinj leads to 50% less DE in swirling flow. In conclusion, it is indicated that the airflow condition is an important parameter for a reliable drug delivery, and it is more beneficial to keep the inflow uniform and avoid swirling flow.

Synthesis and structure of hypercoordinated germanate complexes with naphthalene-2,3-dialkoxide ligands

The synthesis of six-coordinated germanate complexes with naphthalene-2,3-dialkoxide ligands with alkali metals (Li, Na, and K) as counter ions are described. The molecular structures of lithium and potassium germanate complexes were clarified by X-ray diffraction analysis. Each germanium center atom is coordinated by six oxygen atoms to form slightly distorted octahedral configuration. All the compounds were thermally stable up to 300 °C determined by thermogravimetric analysis under air-flow conditions.

Effect of inflow conditioning for dry powder inhalers

The transport of pharmaceutical dry powder inside an optically accessible inhaler-like device is studied using both macro- and microscopic high-speed imaging. The investigation aims to systematically study the effect of inflow modifications on the dispersion characteristics of agglomerates inside a dry powder inhaler (DPI) geometry. An inhaler device was designed with geometrical features akin to commercial inhalers used in the current market and research oriented inhalers such as the Twincer®: two offset inlet channels (one with a powder pocket), a clockwise swirling chamber and a single outlet channel. At the device outlet, a vacuum pump was fitted with an actuator and calibrated to achieve a steady state inhalation with a peak flowrate of 85 and 125 L/min. Airflow conditions at the intake of the device were strategically perturbed in order to induce powder fluidisation and dispersion using turbulence grids and through physically obstructing channel streams in order to achieve changes in flow behaviour (e.g., flow separation). Complete fluidisation of the powder bed was observed with image processing enabling statistics on de-agglomerated fragment size and velocity. A range of behaviour was noted including local turbulence through introduction of a grid, bimodal fragment size behaviour for cohesive mannitol powder, as well as introduction of low velocity zones in the device through flow splitting. The geometry enables simple systematic study of inflow conditions into a DPI-like device with the data being useful for study of a given powder formulation (mannitol) and validation of computational models.

Effects of tangential supersonic airflow on the laser ablation of laminated CFRP

Ablation behaviors of laminated carbon fiber reinforced plastics (CFRP) subjected to intense continuous wave laser in the supersonic wind tunnel are investigated experimentally. Comparable laser ablation tests in other environments, i.e., static air, static nitrogen and open airflow, are also carried out. Laser ablation rate in the supersonic wind tunnel is significantly larger than those of the other environments, in particular, at least twice of that in an open tangential airflow condition. The ablation morphology can be classified into two regions, coupled ablation zone (CAZ) and downstream affected zone (DAZ). Coupled thermal-fluid-solid analysis including thermochemical ablation and thermomechanical erosion models reveals that the contribution of each laser mechanisms is distinctive at the different positions of the laser ablation pit.

Bubble Size in a Flotation Column with Oscillatory Air Supply in the Presence of Frothers

ABSTRACT Oscillatory air supply has demonstrated advantages over conventional steady air supply in froth flotation with diffused aeration, but the interaction between oscillatory air supply and frother in determining bubble size remained unclear. In the present work, we measured the size of air bubbles in a laboratory scale flotation column with common frothers such as MIBC, Dowfroth 250, and polypropylene glycol with an average molecular weight of 425 (PPG 425), with conventional steady air supply and with oscillatory air supply. The oscillatory air supply was converted from steady airflow using a fast-switching solenoid valve with the main operating parameters being switching frequency and on/off time ratio. In the absence of frother, the Sauter mean bubble diameter (d 32) remained the same with oscillatory air supply replacing steady air supply, but the d 32 decreased by 13–35% in the presence of frother. It was also found that the critical coalescence concentration (CCC) of each frother were reduced by 11–69% using oscillatory air supply to replace steady air supply. The degree of reduction in d 32 or the CCC appeared to be dependent on the oscillatory airflow condition (i.e., frequency and on/off time ratio) and frother type. The present work also confirms the recent findings by others that the CCC is not solely a material property of frothers.

English

Objective: To analyze the body heat dissipation by thermography during indoor running treadmill with different airflow conditions. Materials and method: Nine male participants (23.0±2.5 years old) underwent three 45-minute moderate-intensity running sessions (60-70% reserve heart rate) on a treadmill. At each session, a different experimental condition was applied in a crossover design: without airflow (NF), and with low (LF) and high airflow (HF) generated by a fun. Thermograms were obtained with a thermal camera before exercise, during (every 10 minutes), and after exercise. Skin temperature (Tsk) was measured on regions of interest of the upper body: pectoral, brachial biceps, and upper back. A repeated measures ANOVA was used to compare Tsk over time and between conditions, considering p<0.05 as statistically significant. Results: In pectoral and brachial biceps, LF and HF conditions provided greater reductions in Tsk at all moments when compared to the NF (p<0.05). There was a higher reduction in Tsk to the HF vs LF in biceps at 30, 40, and 45 min during exercise (p<0.05). In the upper back, Tsk remained below baseline at all moments during exercise only in the HF condition (p<0.05). In NF and LF conditions, Tsk returned to baseline at 30 min during exercise (p>0.05). Conclusion: The frontal wind flow enhances body heat dissipation during moderate-intensity running in the pectoral, brachial biceps, and upper back, with a direct relationship of flow speed and Tsk reduction during exercise.

Fluid flow characteristics and convective heat transfer improvement on a gas turbine blade

AbstractThe flow field features and heat transfer enhancement are investigated on a gas turbine blade by applying the jet impingement cooling method. The distribution of the flow field and the Nusselt number (Nu) was determined on the targeted surface in the cooling channel. The injection holes of different shapes, such as circular, square, and rectangular were considered. The Reynolds numbers (Re) of the airflow in the range of 2000–5000 and aspect ratios of 0.5–2 were particularly focused. The flow vortices and recirculation in the cooling channel and their influence on the heat transfer enhancement were analyzed in detail under different airflow and geometric conditions. Decreasing the ratio of the distance between jet‐to‐target plate to the diameter of the jet orifice (H/d) increased the heat transfer rate and produced high‐intensity vortices and recirculation zones. It was noticed that the formation and generation of vortices and recirculation have important effects on the convective heat transfer rate at the impingement surface. Local Nusselt number, formation of complex vortices, and airflow recirculation in the cooling channel decreased with the increase in the distance between the jet hole and the targeted surface. It was found that with the increase in the Reynolds number of the jet, heat transfer between cold airflow and the targeted surface increased. Moreover, it was observed that the cooling performance of the round and square jet holes was better than the rectangular holes.

A Parametric Model for Local Air Exchange Rate of Naturally Ventilated Barns

With an increasing number of naturally ventilated dairy barns (NVDBs), the emission of ammonia and greenhouse gases into the surrounding environment is expected to increase as well. It is very challenging to accurately determine the amount of gases released from a NVDB on-farm. Moreover, control options for the micro-climate to increase animal welfare are limited in an NVDB at present. Both issues are due to the complexity of the NVDB micro-environment, which is subject to temporal (such as wind direction and temperature) and spatial (such as openings and animals acting as airflow obstacles) fluctuations. The air exchange rate (AER) is one of the most valuable evaluation entities, since it is directly related to the gas emission rate and animal welfare. In this context, our study determined the general and local AERs of NVDBs of different shapes under diverse airflow conditions. Previous works identified main influencing parameters for the general AER and mathematically linked them together to predict the AER of the barn as a whole. The present research study is a continuation and extension of previous studies about the determination of AER. It provides new insights into the influence of convection flow regimes. In addition, it goes further in precision by determining the local AERs, depending on the position of the considered volume inside the barn. After running several computational fluid dynamics (CFD) simulations, we used the statistical tool of general linear modeling in order to identify quantitative relationships between the AER and the following five influencing parameters, the length/width ratio of the barn, the side opening configuration, the airflow temperature, magnitude and incoming direction. The work succeeded in taking the temperature into account as a further influencing parameter in the model and, thus, for the first time, in analysing the effect of the different types of flow convection in this context. The resulting equations predict the barn AER with an R2 equals 0.98 and the local AER with a mean R2 equals around 0.87. The results go a step further in the precise determination of the AER of NVDB and, therefore, are of fundamental importance for a better and deeper understanding of the interaction between the driving forces of AER in NVDB.

Dust and tropical PMx aerosols in Cape Verde: Sources, vertical distributions and stratified transport from North Africa

We investigated the sources and processes affecting the vertical distribution of tropical PMx aerosols (particulate matter -PM- smaller than 10, 2.5 and 1 μm, PM10, PM2.5 and PM1, respectively) in the low troposphere of Santo Antão and São Vicente islands, in Cape Verde archipelago, a region where a better understanding of aerosols is needed due to their involvement in tropical meteorology and their impact on air quality, ocean and climate. We found that local sources had a low-scale impact. From transect measurements at ground level, we found that PMx levels were predominantly low, except near to PMx sources, where distinctive PM1 / PM2.5 ratios were measured, linked to vehicle exhaust (0.96), biomass burning (0.67) and Cape Verdean dust (0.36) emissions. The depth of the marine boundary layer (MBL) and the vertical distributions of PMx showed wide variability prompted by meteorological conditions. The trade winds prevailed in the MBL, whereas other airflows were situated above it: North-Atlantic, African easterly airflow and Saharan Air Layer. Under North-Atlantic airflow conditions, the MBL extended to 1400 m above sea level (m.a.s.l.). Above this altitude, PMx concentrations decreased quickly (< 3 μg/m3) due to the free troposphere conditions. Under Saharan dust conditions, the MBL was confined to just 70 m.a.s.l., whereas a complex dust stratification was observed above, characterized by alternating dry air layers with high dust loads (PM10 ~ 100 μg/m3) and more humid air layers with lower aerosol loads (PM10 ~ 40 μg/m3). Within the dry easterly African airflow occurring above the marine stratocumulus typical of the MBL top (placed at 500 m.a.s.l.), we detected layers enriched in hydrophilic aerosols (PM10: ~ 8 μg/m3). These were imbedded in relatively humid air (RH ~48%), probably linked to secondary aerosol formation by in-cloud processes in the marine stratocumulus situated below. We found that PMx transport from North Africa, both under dust and dust-free conditions, is associated with complex vertical stratifications, even within the dusty Saharan Air Layer.

Energy efficiency and physical integrity of maize grains subjected to continuous and intermittent drying

ABSTRACT Grain drying is a common process, due to its need for the maintenance of quality, but it is the activity with the highest energy demand among the postharvest stages. Thus, this study aimed to evaluate the effect of different tempering times on the energy efficiency of drying process and maintenance of cell membrane integrity of maize grains harvested with moisture content at 0.34 ± 0.01 d.b. The grains were dried in an experimental fixed-bed dryer with control of temperature and air flow conditions. The experiment was conducted in a completely randomized design with five tempering times (0, 4, 8, 12 and 16 hours) and four repetitions, where zero corresponds to continuous drying, while the remaining times correspond to the intermittent dryings. The grains were dried at the temperature of 100 ºC and air flow of 15.4 m3 min-1 t-1 until reaching moisture content of 0.16 ± 0.03 d.b. For intermittent drying, the process was interrupted with 0.22 ± 0.02 d.b. and restarted after the tempering time. The increase of tempering time led to reductions in effective drying time, specific energy consumption, electrical conductivity and damage and increase in the drying rate and overall energy efficiency. Intermittent drying reduced the drying time, being 30.25% more efficient than continuous drying.

The effect of decongestion on nasal airway patency and airflow

Nasal decongestant reduces blood flow to the nasal turbinates, reducing tissue volume and increasing nasal airway patency. This study maps the changes in nasal anatomy and measures how these changes affect nasal resistance, flow partitioning between superior and inferior cavity, flow patterns and wall shear stress. High-resolution MRI was applied to capture nasal anatomy in 10 healthy subjects before and after application of a topical decongestant. Computational fluid dynamics simulated nasal airflow at steady inspiratory flow rates of 15 L.min^{-1} and 30 L.min^{-1}. The results show decongestion mainly increases the cross-sectional area in the turbinate region and SAVR is reduced (median approximately 40% reduction) in middle and lower parts of the cavity. Decongestion reduces nasal resistance by 50% on average, while in the posterior cavity, nasal resistance decreases by a median factor of approximately 3 after decongestion. We also find decongestant regularises nasal airflow and alters the partitioning of flow, significantly decreasing flow through the superior portions of the nasal cavity. By comparing nasal anatomies and airflow in their normal state with that when pharmacologically decongested, this study provides data for a broad range of anatomy and airflow conditions, which may help characterize the extent of nasal variability.

Study on improvement for the prediction accuracy of natural circulation flow rate by investigating void fraction correlation

Natural circulation is a key technology for developing the molten core cooling system without an external power source from the lessons of the severe accident at Fukushima-Daiichi Nuclear Power Station. This study is devoted to quantify the void fraction which is an important parameter for the driving force of natural circulation flow, and to evaluate the effect of the void fraction correlation on the prediction accuracy of the natural circulation flow rate. Test was conducted at atmospheric pressure and room temperature, using the upward air–water two phase flow. Vertical tubes with an inner diameter of 36 and 25 mm were used as the test section. The void fraction was measured by three different methods: quick-closing valve method, pressure drop method, and conductive void-probe method. The following conclusions are obtained from this study: (1) The data of the natural circulation flow rate, void fraction and pressure drop for the upward air–water two phase flow at atmospheric pressure and room temperature were obtained to develop and verify the new model. (2) By improving the void correlation, it was found that the prediction accuracy of the natural circulation flow rate could be improved by about 10% to 5%, that is, the prediction error can be halved in the range of this study. (3) The natural circulation flow rate for 25 mm test section was saturated with increasing the air flow rate at higher air flow condition. The model cannot predict this tendency. From the point of design of the actual molten core cooling system, the model improvements in this region are necessary in the future.

Efficiencies assessment of an indoor designed solar air heater characterized by V baffle blocks having staggered racetrack-shaped perforation geometry

The outcome of an experimental study carried to maximize the thermal efficiency of a rectangular section solar air heater duct having V-baffle blocks with staggered racetrack-shaped openings are presented in this paper. The investigation encompasses the methodology to determine first the baffle blocks' optimum parameters yielding the thermohydraulic performance factor (η) value greater than unity and then finalizing the 'best optimum parameters' that maximize the duct's thermal (ηth) and effective (ηeff) efficiencies. The thermal and fluid flow characteristics are studied under a constant heat flux at the duct's top wall for turbulent airflow condition. The effect of relative roughness height (e ⁄H) ranging from 0.4 to 0.7, relative pitch (p ⁄e) ranging from 2 to 10 and Reynolds number (Re) ranging from 5000 to 15000 are investigated on 45° V-baffle blocks with apex pointing both in downstream and upstream directions. The result shows that the air jets issuing through racetrack openings intensify the turbulence in the wake of baffle blocks leading to a substantial rise in Nusselt number (Nu) and friction factor (f) relative to smooth duct. The V-down baffle blocks obtain the maximum enhancement of Nusselt number and friction factor over the smooth duct with range 1.358 to 4.559 and 4.03 to 39.07, respectively. The V-down baffle blocks' parameters, e/H of 0.5, p/e of 4 and Re of 13021, provides a maximum value of thermohydraulic performance factor as 1.435. V-up baffle block with e/H of 0.7, p/e of 6 at Re of 12,322 reports the highest thermal and effective efficiencies values as 96.6% and 91.8%, respectively.

A numerical study on flow structure and combustion mechanism of supersonic mixed inflow with transverse jet

The flow mixing mechanism between sonic fuel jet and supersonic mixed inflow is one of the key technologies in rocket-based combined cycle engines. In this study, the flow mechanism of different supersonic airflow conditions on the flow field is discussed. The variable parameters are the Mach number and total pressure of the airflow. The three-dimensional Reynolds-averaged Navier-Stokes equations, two equations of the shear stress transport k-ω turbulence model, and the Eddy-dissipation concept reaction model are adopted to evaluate the flow field structure. The results reveal that the shear layer between the airflow and the rocket gases gradually slopes downward with the increase of Mach number. The bow shock induced by the jet develops to the upper wall and cuts off the shear layer vortex. Additionally, as the Mach number of the airflow decreases, the mixing and combustion efficiencies gradually increase. The Mach number has a slight influence on the penetration depth. Furthermore, when the total pressure of the airflow increases, the penetration depth and mixing efficiency sharply increase.

The break phenomenon of self-pulsation for liquid-centered swirl coaxial injectors

Self-pulsation boundaries that spray switches between stable and self-pulsated behaviors are experimentally obtained under water and air flow conditions for a liquid-centered swirl coaxial injector configured with different recess lengths. The underlying mechanisms responsible for self-pulsation are investigated comprehensively. Results show that for the non-recessed injector, self-pulsation only occurs in a relatively narrower region, associated with weaker spray oscillation with the amplitude less than 2 mm2/Hz correspondingly. In particular, for the injector with larger recess length, a break region is generated with increasing the momentum flux ratio. It is indicated that spray transforms from the self-pulsated behavior to the stable behavior, and develops into self-pulsated behavior once again. The break phenomenon of self-pulsation reveals a destabilizing/stabilizing effect created by the violent gas-liquid flow dynamics. Self-pulsation occurring on either side of the break region is found to be caused by different mechanisms. As such, self-pulsation of the liquid-centered swirl coaxial injector is classified into two types. The first type occurs in the injectors configured with relatively small recess length, or with large recess length before the occurrence of the break phenomenon. This self-pulsation is caused by the periodic blockage of the conical liquid sheet. Whereas, the second type is attributed to the periodic squeezing influences of annular gas on the conical liquid sheet, corresponding to the self-pulsation occurring in the injectors with larger recess length and after the disappearance of the break phenomenon.

Aerodynamic wake oscillator for modeling flow-induced vibration of tandem cylinders with short spans

The tandem cylinders immersed in an oncoming flow undergo violent flow-induced vibration (FIV). The cylinders with short spans, in the specific conditions of airflow and mass damping, experience the galloping-like but self-limited vibration. It promotes a coupling instability, controlled by the shear layers and wake vortices. The peculiar behavior of FIV for tandem cylinders is the interference between transverse galloping and vortex-induced vibration (VIV), which lacks a modeling approach through classical theories. Based on the quasi-steady assumptions, a mathematical model including two semicoupled structural oscillators and a reduced wake oscillator was established to simulate the vibration responses. A nonlinear aerodynamic damping coefficient and an empirical interfered force were introduced to the model, revealing the unexplored interference mechanism between two cylinders with short spans. The model with calibrated parameters can reproduce the nonlinear and bifurcated vibration responses of cylinders, providing a quantitative agreement with the experimental data. Although the model only works for high Scruton numbers and loses high fidelity in predicting the vibration amplitudes of the downstream cylinder in several cases, the vital velocity thresholds, amplitude-velocity trends and maximum amplitudes can be precisely obtained. This model is conducive to preacquiring the FIV responses of tandem industrial structures, including steel stacks, bladeless wind turbines, low-power energy-harvesting devices, etc.

Investigation of fluid-structure Interaction of fuel element in high speed and high temperature air cooled reactor

The high-speed and high-temperature air is the coolant of the open-cycle reactor. The state of air has effect on the dynamic characteristics of the fuel element which may do harm to the reactor. Therefore, the Fluid-Structure Interaction of air and fuel element is studied. Firstly, the methods are validated. Subsequently, the physical properties and boundaries are determined. In addition, the effects of heat flux, inlet Mach number, temperature and pressure on the FSI characteristics of the fuel element are investigated. The results reveal that the heat flux, Mach number and temperature have effects on the dynamic characteristics indirectly. However, the effects on the deformation, force and stress can be ignored. The pressure has direct impact on the fluid force. There is no vibration with the fuel element when the flow is steady. The research can lay basis for the selection of the air flow state in the open-cycle reactor.