High Velocity Air Stream Research Articles

Microstructural, chemical and physical characterisation of the Shot-Earth 772

The material analysed in the present paper is a specific mixture of the shot-earth (named shot-earth 772) produced by introducing, into a high velocity air stream, 7 parts of excavated soil, 7 parts of aggregates and 2 parts of cement (by volume), and by adding about 3% of water (by volume) at the spraying nozzle. The mixture stream is projected at high velocity onto a surface, where the impact compacts the material. A thorough investigation on the microstructural, chemical and physical properties of the shot-earth 772 is performed.

Comparison of convergent/divergent ramp on fuel mixing of single jet at supersonic crossflow

Interactions of high-velocity air stream with cross fuel jet have great impacts on fuel mixing and flame stability in the combustion chamber. This work investigates the influence of adding inclined ramp upstream of the solitary jet on fuel mixing and distribution at supersonic cross-stream of Mach=4. The chief focus of our work is to unveil the impacts of momentum of air stream on the diffusion and distribution of fuel jet. Computational fluid dynamic method is applied for the computational modeling of flow structure and achieving mixing zone downstream of fuel jet. Effects of the convergent and divergent ramp, as well as slope angle of the ramp on fuel stability and distribution downstream of a single jet, are exclusively studied. The addition of an intrusive device upstream of a single fuel jet provides a potential means of enhancing combustor efficiency by assisting combustion products to diffuse into the main combustor flow via deflection of airstream behind the ramp. Our outcomes indicate that the mixing effectiveness of divergent ramp with a slope angle of 30 deg is about 55% more than a divergent ramp with a slope of 10 deg.

Use of Different Cooling Methods in Pig Facilities to Alleviate the Effects of Heat Stress-A Review.

Simple SummaryHeat stress triggers behavioural and physiological response and thus negatively affects productivity in livestock. Among farm species, pigs are especially susceptible to exposure to high air temperatures. The evaporative pad cooling system, high pressure fogging, sprinkling as well as elevating of air velocity and floor cooling are the methods most often used in pig facilities to alleviate the effects of heat stress. This article mainly discusses issues linked with the effectiveness of the various cooling methods on improving the indices of animal welfare.An increase in the frequency of hot periods, which has been observed over the past decades, determines the novel approach to livestock facilities improvement. The effects of heat stress are revealed in disorders in physiological processes, impaired immunity, changes in behaviour and decreases in animal production, thus implementation of cooling technologies is a key factor for alleviating these negative consequences. In pig facilities, various cooling methods have been implemented. Air temperature may be decreased by using adiabatic cooling technology such as a high-pressure fogging system or evaporative pads. In modern-type buildings large-surface evaporative pads may support a tunnel ventilation system. Currently a lot of attention has also been paid to developing energy- and water-saving cooling methods, using for example an earth-air or earth-to-water heat exchanger. The pigs’ skin surface may be cooled by using sprinkling nozzles, high-velocity air stream or conductive cooling pads. The effectiveness of these technologies is discussed in this article, taking into consideration the indicators of animal welfare such as respiratory rate, skin surface and body core temperature, performance parameters and behavioural changes.

Acoustic Behaviour of Nonwovens

The article reviews the acoustic properties of nonwoven fabrics. sound absorption coefficients (SACs) of needle-punched and thermal-bonded nonwovens produced from polyester (PET) fibers with various cross sections, i.e., hollow, round and hexaflower, blended with a low melt PET, was reported. Efforts have been taken to develop relatively lightweight and fibrous acoustic webs. Nonwoven webs that contain bicomponent filaments with islands-in-the-sea cross sections were produced by spun bonding, which involves the extrusion of sea and island polymer melts through dies, cooling and attenuating the bicomponent filaments by high-velocity air streams. Nylon 6 and polyethylene were used as the island and sea polymers, respectively.

Erosive Wear Testing of Laser Clad and HVOF Coatings for Drilling in Mining

Drilling is a major cost factor to mining operations (exploration, drill and blast operations), and wear of components is a significant driver of drilling costs. For drilling, the so-called Down-the-Hole (DTH) hammers or Reverse Circulation (RC) hammers are used. These drills break the rock through repetitive impact. Cuttings are removed via a high-velocity air stream. The main wear mechanism for these hammers was found to be erosion. To combat erosive wear, laser clad coatings with a Nimatrix and different-sized fused tungsten carbides FTC (WC/W2C) (angular and spherical) and monocrystalline WC were developed. In addition, hard Fe-based HVOF coatings were investigated. Wear-resistant steel, WCCoCr HVOF, electroplated chrome and a high-chrome cast iron as bulk served as references. An erosion-testing apparatus which follows ASTM G76 was developed. Testing was carried out at incident angles from 15-90°. Coating performance was assessed via volume loss, obtained using 3D profilometry. At low angles, the WCCoCr coating lost the least volume, and at high angles a Ni/WC laser clad coating with spherical FTC provided the best erosion resistance. Imperfections like cracks, pores and voids serve as weak points where material loss out of the surface commences.

Surface rheological properties alter aerosol formation from mucus mimetic surfaces.

The effects of surface tension and surface viscoelastic properties on the formation of aerosol droplets generated from mucus-like viscoelastic gels (mucus mimetics) during shearing with a high velocity air stream were investigated. Mucus mimetic samples were formulated with similar composition (94% water and 6% dissolved solids, consisting of mucins, proteins, and ions), surface tension (via the addition of surfactant to the mimetic surface) and bulk viscoelastic properties (via crosslinking of mucin macromolecules in the mimetic) to that of native non-diseased tracheal mucus. The surface tension of the mucus mimetic was decreased by spreading one of two surfactants, dipalmitoyl phosphatidylcholine (DPPC) or calf lung surfactant (Infasurf®), on the mimetic surface. Aerosols were generated from the mimetic surfaces during simulated coughing using an enhanced simulated cough machine (ESCM) operating under controlled environmental conditions. The size distribution of aerosol droplets generated during simulated coughing from the surfactant-coated mimetic surfaces was multimodal, while no droplets were generated from the bare mimetic surface due to its high surface viscoelastic properties and high surface tension. The concentration of aerosols generated from the DPPC-coated mimetic was higher than that of the Infasurf®-coated mimetic, even though the surface tension of the two interfaces was the same. The experimental results suggest that a balance of surface elastic behavior and surface viscous behavior is required for the generation of aerosols from the viscoelastic surfaces.

Theoretical aspects of synchronization in transverse galloping aeroelastic instability

We investigate, for the first time to the best of our knowledge, theoretical aspects of synchronization in transverse galloping aeroelastic instability. The current study is a generalization of previous studies that considered the dynamics of a single-cylinder, and therefore, precluded the option to study synchronization. Here, we consider both the deterministic and stochastic dynamics of a system comprising two weakly coupled cylinders, which are attached to the ground with linear springs and dashpots, and are immersed in a high velocity airstream. We derive the conditions for the instability threshold. We give a detailed and simplified procedure to compute the amplitudes, phase differences, and frequencies of the synchronized solutions. We calculate quantitative measures of the amplitude and phase noises, including an explicit calculation of the phase noise reduction due to synchronization, which can enhance the performance of transverse galloping-based energy harvesters. Furthermore, we provide simple mappings for the amplitudes and phase difference dynamics, which we show to be highly useful for understanding both the deterministic and the stochastic dynamics of the amplitudes and the phase difference dynamics from geometric point of view.

Influence of sea polymer removal on sound absorption behavior of islands-in-the-sea spunbonded nonwovens

This work presents the results of efforts focused on the development of relatively lightweight and fibrous acoustic webs. For this objective, nonwoven webs that contain bicomponent filaments with islands-in-the-sea cross sections were produced by spunbonding, which involves the extrusion of sea and island polymer melts through dies, cooling and attenuating the bicomponent filaments by high-velocity air streams. Nylon 6 and polyethylene were used as the island and sea polymers, respectively. Webs were hydroentangled with high-pressure water jets prior to the dissolving process to obtain fiber entanglement. Sea polymer was removed from the spunbonded nonwovens by using a reflux dissolution setup. Weight, thickness, air permeability, pore size and sound absorption coefficients of the nonwoven samples were measured before and after the sea polymer removal. Results demonstrated that sea polymer removal led to further bicomponent filament fibrillation, which affected sound absorption positively. The structure with the higher number of island fibers had better acoustical properties. Lightweight and fibrous acoustic nonwovens can be obtained with the method given in this study.

Effect of sea component dissolution on fibrous structure of islands-in-the-sea spunbond nonwovens

This work presents the preliminary results of our efforts that focused on the development of lightweight and more fibrous nonwoven. For this objective, nonwoven webs that contain bicomponent filaments with island-in-the-sea cross section was produced by spunbonding, which involves extruding of sea and island polymer melts through dies, cooling, and attenuating the bicomponent filaments by high velocity air streams. Nylon-6 and Polyethylene were chosen as the island and sea polymers, respectively. Bonding process was applied to web first to keep structural integrity after removing the sea polymer. The web was hydroentangled with high speed water jets prior to the dissolving process to obtain fiber entanglement. Xylene, which is one of the few chemical that can dissolve Polyethylene, was used for the dissolution of the sea component from the fibrous structure of the spunbond nonwoven. Removal of the sea polymer from spunbond nonwovens that contain bicomponent filaments with islands-in-the-sea cross section was achieved by the developed dissolution process. Weight, thickness, and area of the nonwoven samples changed after the dissolution. After removing the sea polymer, spunbond nonwoven contains only thin island fibers and also gets lighter. Lightweight and more fibrous nonwovens can be obtained with the method given in this study.

Computer-automated silica aerosol generator and animal inhalation exposure system

Inhalation exposure systems are necessary tools for determining the dose response relationship of inhaled toxicants under a variety of exposure conditions. The objective of this study was to develop an automated computer controlled system to expose small laboratory animals to precise concentrations of uniformly dispersed airborne silica particles. An acoustical aerosol generator was developed which was capable of re-suspending particles from bulk powder. The aerosolized silica output from the generator was introduced into the throat of a venturi tube. The turbulent high-velocity air stream within the venturi tube increased the dispersion of the re-suspended powder. That aerosol was then used to expose small laboratory animals to constant aerosol concentrations, up to 20 mg/m3, for durations lasting up to 8 h. Particle distribution and morphology of the silica aerosol delivered to the exposure chamber were characterized to verify that a fully dispersed and respirable aerosol was being produced. The inhalation exposure system utilized a combination of airflow controllers, particle monitors, data acquisition devices and custom software with automatic feedback control to achieve constant and repeatable exposure environments. The automatic control algorithm was capable of maintaining median aerosol concentrations to within ±0.2 mg/m3 of a user selected target concentration during exposures lasting from 2 to 8 h. The system was able to reach 95% of the desired target value in <10 min during the beginning phase of an exposure. This exposure system provided a highly automated tool for conducting inhalation toxicology studies involving silica particles.

Random Field Sampling for a Simplified Model of Melt-Blowing Considering Turbulent Velocity Fluctuations

In melt-blowing very thin liquid fiber jets are spun due to high-velocity air streams. In literature there is a clear, unsolved discrepancy between the measured and computed jet attenuation (thinning). In this paper we will verify numerically that the turbulent velocity fluctuations causing a random aerodynamic drag on the fiber jets—that has been neglected so far—are the crucial effect to close this gap. For this purpose, we model the velocity fluctuations as vector Gaussian random fields on top of a k–ϵ turbulence description and develop an efficient sampling procedure. Taking advantage of the special covariance structure the effort of the sampling is linear in the discretization and makes the realization possible. Numerical results are discussed for a simplified melt-blowing model consisting of a system of random ordinary differential equations.

Coating and Characterization of Mock and Explosive Materials

This project develops a method of manufacturing plastic-bonded explosives by using use precision control of agglomeration and coating of energetic powders. The energetic material coating process entails suspending either wet or dry energetic powders in a stream of inert gas and contacting the energetic powder with atomized droplets of a lacquer composed of binder and organic solvent. By using a high-velocity air stream to pneumatically convey the energetic powders and droplets of lacquer, the energetic powders are efficiently wetted while agglomerate drying begins almost immediately. The result is an energetic powder uniformly coated with binder, that is, a PBX, with a high bulk density suitable for pressing. Experiments have been conducted using mock explosive materials to examine coating effectiveness and density. Energetic materials are now being coated and will be tested both mechanically and thermally. This allows for a comprehensive comparison of the morphology and reactivity of the newly coated materials to previously manufactured materials.

Demonstration of a Wire Suspension for Wind-Tunnel Virtual Flight Testing

This paper describes the development of a wire suspension system for dynamic testing of missiles in a wind tunnel. The system restrains the missile, permits motion in 3 rotational degrees of freedom, and measures forces on the model. The apparatus allows testing of missile control systems in the wind tunnel, reducing the cost and risk of a flight-test program. Hydraulic actuators control cable tension and model position. Bearings provide free roll and pitch, whereas yaw motion is created by the cable actuation system and a repetitive-learning controller. The paper describes the cable arrangement, force balance, bearings, closed-loop hydraulic control, and the repetitive-learning controller. Two sets of tests were conducted with the broad ocean area missile (a sidewinder variant) in the HighVelocity Air Stream facility at the China Lake Naval Weapons Center. The tests, conducted at M 0:4–0:6, demonstrate functionality of the system in a series of missile pitch and yaw maneuvers. The learning controller is shown to learn an s maneuver in the yaw plane.

Liquid jet in a high Mach number air stream

The instability of circular liquid jet immersed in a coflowing high velocity air stream is studied assuming that the flow of the viscous gas and liquid is irrotational. The basic velocity profiles are uniform and different. The instabilities are driven by Kelvin–Helmholtz instability due to a velocity difference and neckdown due to capillary instability. Capillary instabilities dominate for large Weber numbers. Kelvin–Helmholtz instability dominates for small Weber numbers. The wavelength for the most unstable wave decreases strongly with the Mach number and attains a very small minimum when the Mach number is somewhat larger than one. The peak growth rates are attained for axisymmetric disturbances ( n = 0) when the viscosity of the liquid is not too large. The peak growth rates for the first asymmetric mode ( n = 1) and the associated wavelength are very close to the n = 0 mode; the peak growth rate for n = 1 modes exceeds n = 0 when the viscosity of the liquid jet is large. The effects of viscosity on the irrotational instabilities are very strong. The analysis predicts that breakup fragments of liquids in high speed air streams may be exceedingly small, especially in the transonic range of Mach numbers.

Generator of Fine Polydisperse Aerosol

A simple and inexpensive laboratory generator of test aerosol is described. The generator is based on the principle of pneumatic atomization of a solution of a soluble compound by high-velocity air stream. After evaporation of solvent from produced droplets, solid particles are formed. The generator provides continuous unattended long-term operation with constant aerosol output. The performance characteristics of the generator were evaluated by spraying solutions of NaNO3 and (NH4)2SO4. The generator produced polydisperse aerosol in a fine region of particle sizes with a geometric mean diameter of 52.1 nm and a geometric standard deviation of 1.90 for the NaNO3 concentration in the sprayed solution 30 g/l. The total number concentration of the produced aerosol was 3.14 × 107 cm-3 at a nominal air flow rate 78 l/min. The number concentration of particles increased with increasing flow rate of solution, solute concentration and pressure of compressed air through the atomizer or with decreasing total air flow rate through the generator. The change in any of these variables can be used to adjust the particle number concentration. NaNO3 aerosol generation rate was 0.172 mg/min for the NaNO3 concentration in the sprayed solution 30 g/l.

LINEAR INSTABILITY ANALYSIS OF THE VISCOUS LONGITUDINAL PERTURBATION ON AN AIR-BLASTED LIQUID SHEET

This article describes the evolution of sinusoidal waves propagating on a water sheet surrounded by two high-velocity co-flowing air streams. The analysis is based on linear instability theory and includes viscosity in both gas and liquid perturbations, while for the stationary velocity profiles the flows have been treated as inviscid. To discern the role of the gas dynamics, air and water velocities have been varied independently. Flow conditions have been selected to compare the numerical predictions with experimental measurements of oscillation frequencies, wavelengths, and growth rates. The dispersion diagrams show a broad viscosity-enhanced zone, a consequence of considering viscosity in the gas perturbation.

Contribution to droplet breakup analysis

Abstract A basic experiment has been developed to investigate the secondary breakup of droplets in high velocity airstreams. Monosized droplets are injected in the mixing layer of two co-flowing airflows. Various conditions have been tested, different initial drop sizes, different air and droplet velocities to evaluate the influence of the Weber number on breakup regimes. An image processing technique has been developed to measure droplet diameter. Comparisons with numerical simulation conclude this work.

Design and performance of a high velocity air–sand jet impingement erosion facility

This paper describes the design, construction and capabilities of a high velocity air–sand erosion rig. It has been designed with the aid of computational fluid dynamics to approximately simulate the erosion conditions often experienced by subsea choke valves used in the offshore oil industry. It has also been designed to evaluate the erosion performance of CVD diamond coatings at sonic velocity. The rig is of the gas-blast design in which solid particles, typically sand 60–660 μm in size, are injected into a high velocity air stream and accelerated down a 16-mm-diameter tube, 1 m in length, before striking the sample under test. Tests can be carried out with particle velocities of up to 340 m/s under a wide range of sand fluxes, impact angles and standoff distances. The results of pressure, velocity and sand flux calibration work are described. In addition, preliminary experimental data on tests carried out on mild steel, bulk and sprayed tungsten carbide are also presented. The flexibility of the air–sand rig allows the erosion behaviour of materials to be studied under a wide range of conditions.

Design of a shrouded probe for airborne aerosol sampling in a high velocity airstream

In this paper, we present our design of a shrouded probe for high velocity airborne aerosol sampling of particles in the size range 0.1–15 μm diameter. We address many of the problems associated with traditional samplers and discuss the use of a shrouded sampling probe, designed with the aid of computational fluid dynamics, to solve these problems. Techniques for solving the equations governing the fluid motion and individual particle motions are discussed, and the aspiration efficiency of the sampler is calculated. We verify our computational procedures by calculating the airflow and aspiration efficiency of the shrouded probe recently used by McFarland et al. (1989, Environ. Sci. Technol. 23, 1487–1492). The final design includes an evaluation of different inlet tip contours and shroud diameters and their effects on the flow characteristics near the probe inlet, as well as the results of placing a second shroud around the probe to further reduce the velocity of the airflow near the probe inlet. We conclude by presenting a calibration curve for our sampler which can be used to reconstruct freestream particle concentrations and size distributions based on measurements with the sampler.

Thermocoagulation with Hot Air in Thoracic Surgery

Thermocoagulation with hot air is a new hemostatic procedure. During pulmonary surgery oozing blood and air leaking can be controlled by sweeping a high velocity air stream of about 420°C Cover a pulmonary surface stripped of visceral pleura. The hot air thermocoagulator can also control oozing of blood from the epicardium.