Horizontal Air Research Articles

Bag breakup of low viscosity drops in the presence of a continuous air jet

This work examines the breakup of a single drop of various low viscosity fluids as it deforms in the presence of continuous horizontal air jet. Such a fragmentation typically occurs after the bulk liquid has disintegrated upon exiting the atomizer and is in the form of an ensemble of drops which undergo further breakup. The drop deformation and its eventual disintegration is important in evaluating the efficacy of a particular industrial process, be it combustion in automobile engines or pesticide spraying in agricultural applications. The interplay between competing influences of surface tension and aerodynamic disruptive forces is represented by the Weber number, We, and Ohnesorge number, Oh, and used to describe the breakup morphology. The breakup pattern considered in our study corresponds to that of a bag attached to a toroidal ring which occurs from ∼12 < We < ∼16. We aim to address several issues connected with this breakup process and their dependence on We and Oh which have been hitherto unexplored. The We boundary at which breakup begins is theoretically determined and the expression obtained, $We = 12( {1 + {\raise0.7ex\hbox{2} \!\mathord{\left/ {\vphantom {2 3}}\right.\kern-\nulldelimiterspace}\!\lower0.7ex\hbox{3}}Oh^2 } )$We=12(1+2/3Oh2), is found to match well with experimental data {[L.-P. Hsiang and G. M. Faeth, Int. J. Multiphase Flow 21(4), 545–560 (1995)] and [R. S. Brodkey, “Formation of drops and bubbles,” in The Phenomena of Fluid Motions (Addison-Wesley, Reading, 1967)]}. An exponential growth in the radial extent of the deformed drop and the streamline dimension of the bag is predicted by a theoretical model and confirmed by experimental findings. These quantities are observed to strongly depend on We. However, their dependence on Oh is weak.

One-dimensional photonic crystal fishbone hybrid nanocavity with nanoposts

We propose and investigate a one-dimensional photonic crystal (PhC) fishbone (FB) hybrid nanocavity lying on silver substrate with a horizontal air slot. With very few PhC periods, the confined transverse-magnetic, TM10 hybrid mode concentrated within the air slot shows high quality factor over effective mode volume ratio larger than 105λ−3. Most importantly, this FB hybrid nanocavity allows formation of low-index nanoposts within the air slot without significantly affecting the mode properties. These nanoposts guarantee the structural stabilities under different environmental perturbations. Furthermore, capabilities of our proposed design in serving as optical sensors and tweezers for bio-sized nanoparticles are also investigated.

Fine coal covering for preventing spontaneous combustion of coal pile

In order to investigate the effect of fine coal covering around the bottom of coal stockpile on spontaneous combustion prevention, a two-dimensional math model was established to numerically simulate the fine coal covering coal pile and a coal pile temperature-rising experimental system was setup to study the two-dimensional heat and mass transfer characteristics of air diffusion in the horizontal direction and air heat convection in the vertical direction inside coal stockpiles covered by different thicknesses of fine coal. The results showed that (1) the fine coal located at the bottom of the coal pile can effectively inhibit air convection and diffusion, cut off oxygen replenishment, and prevent the temperature rise inside coal pile, and (2) thicker fine coal has more obvious effect. Finally, the field experiments on the fine coal covering coal piles for preventing self-ignition of coal pile were carried out successfully. The results showed that the uncovered or exposed coal piles self-ignited rapidly within a very short period (18 days), while the coal pile covered with 1 m fine coal lasted for 123 days with a maximum coal temperature of only 59.9 °C. The characteristics of temperature distribution and diffusion inside coal stockpile were studied, and the high-temperature region was found in the region 1.3 m high and 2–3 m deep in the coal pile. The effects of environment temperature and precipitation on self-ignition of coal pile were also analyzed in field experiment. The experimental results proved that the fine coal covering technology can effectively prevent the spontaneous combustion of coal stockpiles.

High-resolution field measurements of wind-driven rain on an array of low-rise cubic buildings

Wind-driven rain (WDR) is one of the most important moisture sources with potential negative effects on the hygrothermal performance and durability of building facades. The impact of WDR on building envelopes can be understood in a better way when the WDR intensity distribution can be accurately predicted. Most field experiments of WDR reported in the literature focused on either stand-alone buildings or on buildings in geometrically complex environments. There is a need for high-resolution measurements in more generic and idealized multi-building configurations. The present study reports WDR measurements that were conducted with high spatial and temporal resolution in a test setup consisting of an array of 9 low-rise cubic building models, located in Dübendorf, Switzerland. Detailed descriptions are provided of the building models, the surroundings, the measuring instruments, the measurements of WDR, wind speed, wind direction, horizontal rainfall intensity and air temperature during three selected rain events, as well as error estimates for the WDR measurements. The datasets of rain events and WDR measurement results are made available online to download and are intended for WDR model development and validation.

CFD modelling of ventilation and dust flow behaviour above an underground bin and the design of an innovative dust mitigation system

To mitigate dust contamination in the mine intake roadway, Computational Fluid Dynamics (CFD) study was first conducted to understand the ventilation and respirable dust flow behaviour above the bin. Based on the modelling results, two possible solutions were proposed for dust control, one is modifying the ventilation system to dilute the respirable dust particles, and the other is using water mist dust droppers to suppress and capture the majority of the dust particles. Modelling results indicated that respirable dust particles could be significantly diluted at the operators’ breathing level by increasing the ventilation volume from the horizontal air intake, where 10–13m3/s of air flow rate was suggested to be a preferable quantity. The mechanism of respirable dust capture using water mist was investigated from classical theory and two phase flow theory, respectively, both of which demonstrated a good dust mitigation effect was achievable. CFD models were employed to investigate the flow behaviour of water mists when sprays were oriented at different directions above the bin. An innovative design of dust control system employing water mist technology with four nozzles was proposed and subsequently built for field implementation. An independent field dust evaluation demonstrated that a reduction up to 68% of respirable dust particles has been achieved in the vicinity of the underground bin, and an average of 40% respirable dust reduction along the belt roadway. The successful application of the new dust mitigation system also demonstrates its potential use in underground longwall faces, roadway development and subsurface tunnel excavations by roadheader.

Effects of urban parks on the local urban thermal environment

Air temperatures in and outside of 60 parks in Taipei city were surveyed to study the effect of different urban parks on their surrounding thermal gradients. Results suggest that the factors governing the temperature of park surroundings are not identical to those of park interiors. Air-temperature gradients surrounding urban parks are influenced by both the horizontal transport of cool or warm air mass above parks and the evapotranspirative air-parcels from trees, creating a cool island larger than the boundaries of cool-island parks, a heat-island larger than the boundaries of strong heat-island parks, and a cool-ring outside weak heat-island parks. Such horizontal air movement is not easily detected using remotely sensed data. During daytime, the thermal environment within a park is dominated by the amount of solar input absorbed by unshaded paved area, which, when strong, can overflow to increase the temperatures of park surroundings; at night, despite park trees causing a warming effect inside parks, park surroundings are cooled by horizontal flow of evapotranspirative air-parcels from park trees. In business and other districts used mostly during daytime, it is recommended that parks and other open spaces be designed with less than 50% paved area and at least 30% trees, shrubs, and other shadings. In residential districts that are used mostly during nighttime, parks and other open spaces are recommended to be designed with more trees. Night irrigation, a measure commonly recommended for the conservation of water, is also recommended to further enhance this nighttime cooling.

Colloidal crystallization of spindle-shaped hematite particles coated with polymer brush in deionized aqueous suspension

Colloidal crystallization of highly monodisperse spindle-shaped hematite particles coated with poly(poly(ethylene oxide) methyl ether methacrylate) brush (SHB) was studied by reflection spectroscopy and optical microscopy. SHB suspensions were deionized exhaustively with the mixtures of cation- and anion-exchange resins more than 6 months. The liquid thin film along the vertical cell wall above the horizontal air–liquid interface showed the strong color bands. Furthermore, the reflection spectra composed of many sharp peaks shifted continuously toward shorter wavelengths with time. These observations support the presence of thin film of SHB suspension, where the width is thickened downward by the gravity and the layered liquid further flow downward with time. The rigidities of SHB crystals in the bulk phase estimated from the optical microscopy in the sedimentation equilibrium were 0.007 to 0.7 Pa as SHB concentration increased from 0.006 to 0.35 wt.%. The fluctuation parameter, b-factors of the anisotropic crystals, was from 0.025 to 0.035 and decreased slightly as particle concentration increased. Rigidities and the fluctuation parameters of SHB suspensions support that the elastic properties of the anisotropic-shaped colloidal crystals are close to those of typical crystals of colloidal spheres. Compression of the SHB crystals by the gravity is also suggested in the sedimentation equilibrium state.

A Study on Unsaturated Zone Characterization and Feasibility of Soil Vapor Extraction at a DNAPL-contaminated Site in Korea

This study aimed at characterizing unsaturated zone at the source zone area contaminated by DNAPL and investigating feasibility of soil vapor extraction (SVE). Five boreholes with three multi-level screens at the depth of 3.0~4.5 m, 5.5~7.0 m, and 8.0~12.0 m were installed at the source zone. Pneumatic tests were performed to determine the permeability of porous medium. Permeability was estimated to be 81.6 to 203.7 darcy, depending on the applied solutions, which was contradicted by grain size analysis of cored soil samples leading to 3.51 darcy. This is due to air flow through gravel pack during the early stage of pneumatic test. Pressure-drawdown curve in the late stage also well showed the leaky aquifer type, indicating air leakage to the ground. Air flow tests were also carried out to investigate air flow connectivity between multi-level wells, indicating that the horizontal air flow was well developed between the lower screens of the wells, not between the upper and middle screens due to the leakage to the surface. For the SVE test, there was no noticeable variation in TCE vapor concentration between three different test runs: 1. 8 hours daily for 5 days, 2. 24 hours together with air blowing at another well (BH1), 3. five consecutive days. Even for five-day consecutive test, total amount of removed TCE was estimated only to be as low as 46.5 g.

Air/mist cooling in a rectangular duct with varying shapes of ribs

A numerical investigation of turbulent forced convection in a three-dimensional channel with periodic ribs on the lower channel wall is conducted. The lower wall is subjected to a uniform heat flux condition while the upper wall insulated. This study was conducted to investigate the forced convection, flow friction, and performance factor in a horizontal air and air/mist cooled rectangular duct, with various shaped ribs. Calculations are carried out for square ribs (case A), triangular ribs (case B), and trapezoidal ribs (case C and case D) cross sections over a range of Reynolds numbers (8000–20,000), constant mist mass fraction (6%), and fixed rib height and pitch. To investigate turbulence model effects, computations based on a finite volume method are carried out by utilizing three turbulence models: the standard k-ω, Omega Reynolds stress, and shear stress transport turbulence models. The predicted results from using several turbulence models reveal that the shear stress transport turbulence model provides better agreement with available measurements than others. It is found that the average mist cooling enhancement is about 1.8 times. The air/mist provides the higher heat transfer enhancement over air with trapezoidal-shaped ribs (38°, case C).

Laying-up of sterile instruments in the operating theatre: equal or superior protection by using a horizontal unidirectional air flow system

A system for the preparation of sterilized instruments with unidirectional horizontal air flow (UDHF) has several advantages over a unidirectional down flow system (UDDF). The advantages are based on the installation of the system being more flexible and easier to use, no cooling of the air flow being necessary and less air being needed for circulation, resulting in reduced energy use. The objective of this study was to determine whether a system with UDHF performs equal or superior to a system with UDDF in terms of prevention of contamination of the air (the presence of particles and micro-organisms) during the laying-up process. The degree of protection (DP) offered by two UDHF system variants and two UDDF system variants was determined for several static set-ups and a dynamic simulation of the process. In addition to determining the level of protection for several categories of particle size, colony-forming units (CFU) were also measured during process simulations. When maximum protection (no particles present) is considered, the UDHF systems performed significantly better than the UDDF systems for particles ≥2.5μm. When particles were present, there was no significant difference between systems for particles ≥0.3 and ≥0.5μm. However, the performance of the UDHF system was superior to that of the UDDF system (DP) for particles ≥1.0μm representing the bacteria-carrying particles. During the process measurements, no CFU were found with the UDDF system in 64% of the measurements, compared with 90% for the UDHF system (P=0.012). The UDHF system offers equal or superior protection to the UDDF system against contamination of the clean area within which the laying up takes place. Despite our finding that the differences did not always reach statistical significance (due to low background concentrations), there is a clear trend, from the small-sized particles (≥1.0μm) up to the largest sizes considered, including bacteria-carrying particles, that demonstrates the superiority of the horizontal flow system. The UDHF system offers a more robust solution than the UDDF system, provided that good work instructions are given and the height of the table and height of the plenum are properly adjusted.

Effects of air temperature and air flow rate control on the tipburn occurrence of leaf lettuce in a closed-type plant factory system

This study aimed to establish a practical method to reduce tipburn symptoms on leaf lettuce cultivars in a closed plant factory system, focusing on air temperature conversion at specific plant growth stages and artificial air flow application strategies using pre-screened tipburn-sensitive cultivars. Inter-conversion effect of day temperature among 18, 22, and 25°C, 12 days after transplanting on tipburn occurrences, were compared with stable day temperature condition. Horizontal air flow rates were controlled at 0.28 (Low), 0.55 (Medium), and 1.04 m·s−1 (High). Tipburn occurrences were highly variable depending on the lettuce cultivars tested. Following the initial screening of 28 leaf lettuce cultivars under 3 different light intensity conditions (ranging from 150 to 250 mol·m−2·s−1), two cultivars exhibiting relatively higher percentages of tipburn were selected for the following air temperature and air flow treatments. None of the temperature treatments effectively reduced tipburn symptom, while adjusting the temperature to a lower day temperatures at 12 days after transplanting only had a minor effect on lettuce growth and tipburn occurrence. In contrast, stable horizontal 24-hour air flow rates above 0.28 m·s−1 effectively reduced tipburn symptom, with no significant differences being found among the tested air flow rates, while above 65% of tipburned plants were found in the control plot of 0.08 m·s−1 flow rate. When stable air flow was applied, compared to the control, there was an increase in the absolute calcium content and a decrease in the calcium content difference between the inner and outer lettuce leaves. This calcium balance change may have occurred due to the enhanced transpiration in the inner parts of plants. This study showed that stable horizontal air flow application along cultivation beds is more effective than air temperature control in decreasing tipburn symptoms in a closed plant factory system.

Effectiveness of horizontal air flow fans supporting natural ventilation in a Mediterranean multi-span greenhouse

Natural ventilation is the most important method of climate control in Mediterranean greenhouses. In this study, the microclimate and air flow inside a Mediterranean greenhouse were evaluated by means of sonic anemometry. Experiments were carried out in conditions of moderate wind (≈ 4.0 m s-1), and at low wind speed (≈ 1.8 m s-1) the natural ventilation of the greenhouse was supplemented by two horizontal air flow fans. The greenhouse is equipped with a single roof vent opening to the windward side and two side vents, the windward one being blocked by another greenhouse close to it, while the leeward one is free of obstacles. When no fans are used, air enters through the roof vent and exits through both side vents, thus flowing contrary to the thermal effect which causes hot air to rise and impairing the natural ventilation of the greenhouse. Using fans inside the greenhouse helps the air to circulate and mix, giving rise to a more homogeneous inside temperature and increasing the average value of normalized air velocity by 365 %. These fans also increase the average values of kinetic turbulence energy inside the greenhouse by 550 % compared to conditions of natural ventilation. As the fans are placed 4 m away from the side vents, their effect on the entrance of outside air is insufficient and they do not help to reduce the inside temperature on hot days with little wind. It is therefore recommended to place the fans closer to the side vents to allow an additional increase of the air exchange rate of greenhouses.

Study on the Effect of Air Circulator on Temperature Distribution in an Oyster Mushroom Farm

Purpose: Recently, domestic and abroad consumption of mushroom has been increasing. Especially, oyster mushroom has been the most consumed product, sharing one third of the mushroom market. The air temperature differences between relative positions of the mushroom farms were needs to be minimal. However, in reality, the air temperature differences ranged from 2 to <TEX>$5^{\circ}C$</TEX>. Because of this, the mushrooms are non-uniform growth as well as decrease in both quality and quantity. Although air circulators have been employed by oyster mushroom farms to minimize air temperature differences, no experiments have been performed to illustrate the effect of the air circulators. Methods: This experiment is designed to analyze the effect of the air circulation by constructing a prototype air circulator and measuring the air temperature when the circulator was position at different heights (50 cm, 150 cm, 200 cm) from the floor in the center. Result: The horizontal plane air temperature of the first growing bed when the air circulator was installed 50cm above the floor in the center, once not using the air circulators and the other time using the air circulators, yielded the air temperature differences of <TEX>$8.6^{\circ}C$</TEX> and <TEX>$1.8^{\circ}C$</TEX> and deviations of 2.82 and 0.60, respectively. The third growing bed's air temperature differences were <TEX>$10.0^{\circ}C$</TEX>, <TEX>$1.6^{\circ}C$</TEX> and deviations 3.28, 0.64, each respectively. These outcomes proved that the use of air circulators minimized the air temperature difference and deviation. The use of air circulators helped minimize the air temperature differences and the derivations in oyster mushroom farm. Conclusion: The use of air circulators helped balance the air temperature distribution in oyster mushroom farm.

Silicon Nitride Horizontal Air-Slot Microdisk Resonators With a Nanocrystal Si Emitting Layer

Silicon nitride (SiN) microdisk resonators with a 40-nm horizontal air slot and a nanocrystal Si (nc-Si) emitting top layer are investigated. The whole structure is fabricated using only a single deposition and lithography step, with the light-emitting layer self-aligned to excite the slot-mode within the air slot. The nc-si are excited via top-pumping using a UV laser diode, and the visible light emission from nc-Si is coupled into the whispering gallery mode (WGM) with the light concentrated in the air slot. The WGM resonances are observed via side-photoluminescence setup using a Si charge-coupled device. The feasibility of applying this structure as a biosensor is demonstrated, with an estimated surface sensitivity of 2.8 nm/nm.

Novel Radon Sub-Slab Suctioning System

A new principle for radon protection is currently presented which makes use of a system of horizontal pressurised air ducts located within the lower part of the rigid insulation layer of the ground-floor slab. The function of this system is based on the principles of pressure reduction within the zone below the ground-floor construction. For this purpose a new system of prefabricated lightweight elements is introduced. The effectiveness of the system is demonstrated for the case of a ground-floor reinforced concrete slab situated on top of a rigid insulation layer (consisting of a thermal insulation layer located on top of a capillary-breaking layer) mounted in turn on stable ground. The new system of prefabricated lightweight elements consists of the capillary-breaking layer and a pressure-reduction zone which is working as the radonsuction zone. The radon-suctioning layer is formed from a grid of horizontal air ducts with low pressure which are able to remove air and radon from the ground. Results showed the system to be effective in preventing radon infiltrating from the ground through the ground-floor slab, avoiding high concentrations of radon being accumulated inside houses. For the system to be effective, the pressure within the ducts must be lower than the pressure inside the house. The new principle was shown to be effective in preventing radon from polluting the indoor air by introducing low pressure in the horizontal grid of air ducts. A lower pressure than the pressure inside the building must be established. The prefabricated lightweight elements were integrated into the insulation layer below the material of the ground-floor slab. The element and the insulation material were made of expanded polystyrene. The new element can be handled by one man on site.

Flame length elongation behavior of medium hydrocarbon pool fires in cross air flow

This paper presents an experimental investigation on flame lengths of medium pool fires under horizontal cross air flows. Square pool fires with dimensions of 10cm, 15cm, 20cm, and 25cm, using ethanol and heptane as typical fuels, are burned under cross air flows ranged in 0–2.5m/s. The burning rates are measured by an electronic balance with accuracy of 0.1g. The flame geometrical characteristics are recorded by a CCD (Charge-Coupled Device) digital camera, in which the mean flame length is quantified based on flame appearance intermittency spatial distribution. Results show that the cross air flow enhances the mass burning rate in a linear function of flow speed. Such enhancement effect is more prominent, indicated by a higher enhancement rate (β), for heptane than that for ethanol. This fuel type effect on β can be accounted for by a thermochemical property-Heat Release Parameter of the fuel (R, ratio of heat of combustion to heat of effect evaporation, R=ΔHc/ΔHfg). The normalized value of β/R is in a linear function of reciprocal of pool length (β/R∼d−1) and independent of fuel. The flame length is found to be elongated by the cross air flow due to the enhancement of the fuel burning (evaporation), as also being more remarkable for heptane than ethanol. A generalized model (Eq. (18)) is proposed to approximate the elongated flame length (ℓf), in relation to an amended dimensionless Froude number of ugd·sΔHcMfuelΔHfg·Mo2ρaYo2,∞, as incorporating globally both the thermochemical property (represented by R parameter, ΔHcΔHfg), molecular property and reaction molar stoichiometric ratio (represented by sMfuel) of the fuel, as well as the ambient oxygen molar concentration factor (represented by Mo2ρaYo2,∞).

Measurement of the Cosmic Ray primary spectrum with ARGO-YBJ experiment

The study of cosmic ray physic of 1012 – 1015 primary cosmic energy is one of the main goals of ARGO-YBJ experiment. The detector, located at the Yangbajing Cosmic Ray Laboratory (Tibet, 4300 m a.s.l., 606 g/cm2), is an EAS array consisting of a continuous carpet of RPCs. The low energy threshold of the detector allows to study an energy region characterized by the transition from the direct to the indirect measurements. In this talk we will report on the measurement of the cosmic ray energy spectrum at different zenith angles. The phenomenology of horizontal air shower (θ > 70°) will be described and discussed.

Landspout across Novi Beograd, 24 may 2012: Synoptic analysis

In this study we have analysed a case of the landspout across Novi Beograd on 24 May 2012. We have used a synoptic analysis method in the research and the description of the landspout event is based on visual evidence and photographs. According to the available data, it can be concluded that there were favourable conditions for a landspout development since there was a process and an increased amount of instability. The landspout occured within the northeast stream which moved over Belgrade and further toward the southeast and west. Based upon synoptic data analysis, it can?t be said that there was a cold air advection. Surface air was warm enough, but not the air in the upper layers of the atmosphere. The conditions for a landspout development were favourable - high relative air humidity and increased vertical and horizontal air currents.

Amplification of wind waves in reservoirs of finite depth

A method for predicting the generation and amplification of waves from the zone of generation to large fetches, where infragravity waves occur in water of finite depth, is developed from a physical model of interaction between a horizontal air flow and a water surface caused by periodic formation of vortices in the viscous air layer. The model describes the origination of multiple frequencies, and the displacement of wave energy to low-frequency region over a fetch.

On the possibility of neutrino flavor identification at the highest energies

High energy astrophysical neutrinos carry relevant information about the origin and propagation of cosmic rays. They can be created as a by-product of the interactions of cosmic rays in the sources and during propagation of these high energy particles through the intergalactic medium. The determination of flavor composition in this high energy flux is important because it presents a unique chance to probe our understanding of neutrino flavor oscillations at gamma factors >10^21. In this work we develop a new statistical technique to study the flavor composition of the incident neutrino flux, which is based on the multipeak structure of the longitudinal profiles of very deep electron and tau neutrino horizontal air showers. Although these longitudinal profiles can be observed by means of fluorescence telescopes placed over the Earth's surface, orbital detectors are more suitable for neutrino observations owing to their much larger aperture. Therefore, we focus on the high energy region of the neutrino spectrum relevant for observations with orbital detectors like the planned JEM-EUSO telescope.