High Velocity Air Jet Research Articles

Indoor particle dispersion due to hand dryer in public washroom: an in silico study

Hand dryer in public washroom has been reported likely to be a reservoir of drug-resistant bacteria. When a hand dryer being used, the high-velocity air jet from the dryer outlet can carry aerosol particles to hand surfaces, the user, and indoor space. This in silico study considered the effect of different airflow speed of hand dryers on the dispersion of particles in different diameters with and without the user. The aim of this study was to apply the computational fluid dynamics (CFD) method based on the discrete phase model to investigate the trajectory of indoor particles from the hand dryer in public washroom. The CFD results showed that, when the user was using the hand dryer, 42.3% of the particles were distributed on the wall against the user, and 31.6% were distributed on the user’s body, including their hands. When no one was standing in front of the hand dryer, 87.6% of the particles fell on the ground. The blocking of user’s hand dispersed the particles to a wide range, particularly for the larger diameter particles which were scattered on the user’s body or on the ground. In addition, the dispersion proportion of particles did not vary with the speed of airflow, but the area of particles distribution became larger as the speed increased. Our findings suggest that the contamination of the indoor environment caused by the hand dryer could not be ignored, incorporating filters into hand dryers is essential. Furthermore, our work offers valuable insights for optimizing the design of hand dryers.

Numerical Investigation of Gasper Air Jet Dynamics in an Aircraft Cabin

Computational fluid dynamics (CFD) is used to analyze the jet interaction of side-vent and gaspers and their influence on cough jets in aircraft cabins. A control device is designed and proposed to be attached to the existing gasper outlet to widen narrow, high-velocity air jet into a widespread air curtain. It forms a shield around the passenger's face, controlling cough droplets from infected passengers entering the co-passengers breathing zone and pushing the high-velocity cough jet toward the floor. A detailed study on flow distribution with existing gaspers and the newly designed control device is presented. The influence and efficacy of the control device in achieving desired flow spread, droplet spread, and intrusion control into co-passengers breathing zones are evaluated. The simulation showed significant droplets were reaching window and aisle passenger breathing zones in the existing gasper, whereas no droplet was found when the control device was introduced.

Using sonic crystals to separate the acoustic from the flow field of a fluidic transducer

Ultrasonic testing is a widely applied measurement method in materials research and medicine. Commonly, a transducer is coupled to the specimen directly or via a liquid coupling agent. While reducing acoustic transmission losses significantly, this procedure is time-consuming and cannot be used for sensitive specimens. Air-coupled ultrasound is a viable alternative in such cases, although suffering from very high acoustic transmission losses between transducer, air and specimen.The recently introduced fluidic transducer (FT) generates ultrasound by utilizing the instability of a supersonic air jet switched inside a fluidic amplifier. Since only air is used as the working medium and no vibrating surfaces are used for ultrasound generation, the transducer is able to efficiently generate large acoustic pressure amplitudes. The resulting acoustic field shares its directivity with the ejected high-velocity air jet. Thus, the acoustic energy needs to be redirected from the jet axis in order to make the fluidic transducer applicable to sensitive specimens.In this study, the effectivity of using sonic crystals (SCs) for this redirection is investigated using acoustic and flow measurements. SCs are air-permeable while being reflective to large acoustic frequency bands. It was shown that both a defect waveguide and a mirroring strategy successfully redirected the acoustic field from the air jet. Furthermore, the interaction of flow and SC showed strong acoustic quenching if the SC was placed too close to the FT outlet. Blockage of the jet entrainment due to the SC may result in slightly higher off-axis flow velocities locally, which should be considered in sensitive applications.

High-pressure ESI-MS made easy using a plug-and-play ion source and its application to highly conductive aqueous solutions.

The performance of a compact high-pressure electrospray ionization (HP-ESI) source that can be readily used for commercial atmospheric pressure ionization (API) mass spectrometers is reported. The ion source employs a converging-diverging outlet nozzle, and ions/droplets generated inside the high-pressure compartment are carried by the high-velocity air jet toward the mass spectrometry (MS) ion inlet placed under the atmospheric pressure. With the use of a shielding electrode, the HP-ESI can also be operated with its emitter held at ground potential. This feature prevents the flow of current from the emitter to other electrically grounded components and facilitates the connection of ion source to liquid chromatography (LC) columns or capillary electrophoresis. Sensitive detection of proteins from highly conductive aqueous solutions such as 0.1% trifluoroacetic acid (TFA) solution and the prevention of electrochemical artifacts by the grounded emitter operation are demonstrated.

Mechanically Robust and Recyclable Cross-Linked Fibers from Melt Blown Anthracene-Functionalized Commodity Polymers.

Melt blowing combines extrusion of a polymer melt through orifices and attenuation of the extrudate with hot high-velocity air jets to produce nonwoven fibers in a single step. Due to its simplicity and high-throughput nature, melt blowing produces more than 10% of global nonwovens (∼$50 billion market). Semicrystalline thermoplastic feedstock, such as poly(butylene terephthalate), polyethylene, and polypropylene, have dominated the melt blowing industry because of their facile melt processability and thermal/chemical resistance; other amorphous commodity thermoplastics (e.g., styrenics, (meth)acrylates, etc.) are generally not employed because they lack one or both characteristics. Cross-linking commodity polymers could enable them to serve more demanding applications, but cross-linking is not compatible with melt processing, and it must be implemented after fiber formation. Here, cross-linked fibers were fabricated by melt blowing linear anthracene-functionalized acrylic polymers into fibers, which were subsequently cross-linked via anthracene-dimerization triggered by either UV light or sunlight. The resulting fibers possessed nearly 100% gel content because of highly efficient anthracene photodimerization in the solid state. Compared to the linear precursors, the anthracene-dimer cross-linked acrylic fibers exhibited enhanced thermomechanical properties suggesting higher upper service temperatures (∼180 °C), showing promise for replacing traditional thermoplastic-based melt blown nonwovens in certain applications. Additionally, given the dynamic nature of the anthracene-dimer cross-links at elevated temperatures (> ∼180 °C), the resulting cross-linked fibers could be effectively recycled after use, providing new avenues toward sustainable nonwoven products.

Micro electrical discharge machining in nitrogen plasma jet

Dielectric, such as kerosene-based oil, deionized water or air, is an essential part of electrical discharge machining (EDM). It directly influences machining performance of the EDM process. While there is large tool electrode wear during machining in liquid dielectric, micro EDM in gas dielectric exhibits almost no tool electrode wear. However, small discharge energy, low dynamic viscosity and low debris concentration of micro EDM in gas creates narrow discharge gap, causing frequent occurrence of abnormal discharge. In this paper, nitrogen plasma jet (NPJ) is used as a dielectric to increase the discharge gap of micro EDM in gas. The machining characteristics of micro EDM in NPJ are investigated and compared with those in other dielectrics. It was found that the discharge distance, machining efficiency and surface quality are significantly improved in NPJ, compared to those in gas under the same conditions. The coaxial high-velocity air jet is helpful to reduce short circuits. Experimental results reveal that NPJ is a viable dielectric in micro EDM.

Spray mist cooling heat transfer in glass tempering process

Energy saving is a very important issue in glass plants, especially in a glass tempering process, where very high velocity air jet impingement is applied during the cooling process of glass tempering. In fact, air compressor energy may be reduced by a spray cooling due to its high heat transfer capabilities. Presently, in this paper, both pure air and water mist spray cooling are investigated in the glass tempering process. The test results indicate that thin and low-cost tempered glass can be made by mist cooling without fracture. It is possible to find the optimal water flux and duration of mist application to achieve a desirable temperature distribution in the glass for deep penetration of the cooling front but without inducing cracking during the tempering. The use of mist cooling could give about 29 % air pressure reduction for 2-mm glass plate and 50 % reduction for both 3- and 4-mm glass plates.

Attrition of methanol to olefins catalyst with high-velocity air jets at elevated temperature

The air jets method proved to be an important tool for assessing attrition propensity of fluidized bed catalyst in the laboratory, but the influence of test temperature and test time has seldom been considered. This paper focuses on the influence of test temperature and test time on the attrition mechanism of methanol to olefins (MTO) catalyst in high velocity air jets. The attrition time was prolonged to 144h in current study. It has been found that test time should be carefully chosen in order to achieve an equilibrium attrition rate. A short test time is not sufficient to understand the attrition mechanism. Test temperature affects the attrition mechanism significantly. At room temperature the abrasion and fragmentation were found coexisting while at 500°C the abrasion is dominant. The abrasion of MTO catalyst at 500°C results in a severe generation of superfine powder that is hard to capture by downstream cyclones, which is in accordance with the findings in industrial MTO unit. Apparently the attrition test at room temperature cannot reflect the generation of superfine powder. Both test time and test temperature should be carefully considered when the air jets method is used in the attrition study in laboratory.

ICONE23-1467 Behavior of Entrainment Droplet formed by High Velocity Air Jet Flow in Stagnant Water

ICONE23-1467 Behavior of Entrainment Droplet formed by High Velocity Air Jet Flow in Stagnant Water

Flow properties of CO2 sorbent powders modified with nanosilica

In this work, the flow behavior of a CO2 sorbent precursor (natural limestone) and a modified sorbent precursor, obtained by dry mixing the natural limestone and a silica nanostructured powder, is investigated. After dry mixing, small silica nanoparticle aggregates are seen to coat the limestone particle surface, which serves to decrease interparticle adhesion thus improving powder flowability. The tensile strength of the modified material subjected to small consolidation stresses has been tested before and after calcination. In addition, laser diffraction particle size analysis has been performed to test the mechanical strength of the aggregates as they are pre-dispersed in-situ by high energy processes such as high velocity air jets or ultrasonication in a liquid. The results also indicate that calcination leads to an increase of the average size of the limestone/nanosilica composite aggregates whose mechanical strength is enhanced as compared to that of calcined limestone aggregates.

Inviscid and Viscous Numerical Models Compared to Experimental Data in a Small Data Center Test Cell

Both localized power densities and overall power consumption within the data center continue to rise, following the same upward trend as the information technology (IT) equipment stored within the data center. Air cooling this increasing power has proved a significant challenge at both the IT equipment and data center level. In order to combat this challenge, computational fluid dynamics and heat transfer (CFD/HT) models have been employed as the dominant technique for the design and optimization of both new and existing data centers. This study is a continuation of earlier comparisons of CFD/HT models to experimentally measured temperature and flow fields in a small data center test cell. It compares an inviscid model, a laminar flow model, and three turbulence models to six sets of experimentally collected data. The six sets of data are from two different IT equipment rack power dissipations using three different layouts of perforated tiles. Insight into the location of the deviation between the different CFD/HT models and experimental data are discussed, along with the computational effort involved in running the models. A new grid analysis was performed on the different CFD/HT models in order to try to minimize computational effort. The inviscid model was able to run with a smaller grid size than the viscous models and even for the same size grid was found to run 30% faster than the fastest viscous model. Due to both the reduced grid size and computational effort (due to the simpler equation set), the inviscid model ran over thirty times faster than the next fastest model. The fact that the inviscid model ran the fastest is not surprising, however what was not expected is that the inviscid model was also found to have the smallest deviations from the experimental data for all six of the cases. This is most likely due to the arrangement of the data center test cell with the relatively few high velocity air jets and large open space around the IT equipment. More tightly packed data centers with higher air velocities and turbulent mixing conditions will certainly produce different results than those found in this study.

Attrition of Ca‐based CO2‐adsorbents by a high velocity gas jet

Attrition of Ca‐based adsorbents is a subject of interest that determines the efficiency of the Ca‐looping process for CO2capture. In this article, we report an experimental test to assess the mechanical strength of cohesive Ca‐based adsorbents based on particle sizing by laser diffractometry. In this technique, the powder sample is dispersed, either by a high velocity air jet (dry dispersion) or by a liquid before the particle size distribution (PSD) is measured. In the dry dispersion unit, particle aggregates are subjected to high energy collisions intended to cause their fragmentation. The PSDs obtained at a low dispersive air pressure for calcined CaO shows that there is a remarkable population of large aggregates due to strong van der Waals of attraction. A second population consists of compact small aggregates, which are relatively stronger due to material sintering at interparticle contacts. As the dispersive air pressure is increased, these aggregates are broken. Their size scales as a power law of the jet air velocity in agreement with the prediction of a fracture mechanics theory of brittle materials. In contrast, the population of large aggregates of a modified adsorbent, consisting of a CaO/nano‐silica composite, is not significative, which can be attributed to the effect of nano‐silica in decreasing the van der Waals attractive force. Moreover, the small compact aggregates of the composite are broken at a lower rate with the dispersive air pressure. The enhanced strength of these composite aggregates is further supported by the PSDs obtained for samples dispersed in a liquid and previously excited by high energy ultrasonication. © 2012 American Institute of Chemical Engineers AIChE J, 59: 1096–1107, 2013

Does the United States Pharmacopeia Throat Introduce De-agglomeration of Carrier-Free Powder from Inhalers?

We hypothesize that the USP induction port may de-agglomerate carrier-free powder emitting from dry powder inhalers (DPIs). Aerosols emitting from a range of DPIs (Spinhaler®, Turbuhaler® and Osmohaler™) and induction ports (USP throat, straight tube, Alberta idealized mouth-throat geometry (AG)) were sized by laser diffraction. Total drug recovery was obtained by HPLC and fine particle fraction computed. Air flow patterns were simulated using Computational Fluid Dynamics (CFD). The straight tube did not de-agglomerate emitted powder. However, the USP throat and AG further de-agglomerated powders from the Spinhaler, but not the Turbuhaler and Osmohaler. While budesonide powder deposited similarly in all induction ports, deposition was significantly higher in the AG for both DSCG and mannitol. CFD revealed agglomerates impacting on the USP throat with higher localized velocity compared with the straight tube. CFD further showed a more complex flow pattern with high-velocity air jets in the AG, which explains the higher FPF for DSCG and the lower FPF for mannitol using the AG. The USP throat further de-agglomerated the emitted powder from the DPI when it did not sufficiently disperse the powder. Other tools such as laser diffraction may be used for cross-examining to avoid artifacts in the results.

Limestone Particle Attrition in High-Velocity Air Jets

Experiments were carried out with limestone particles of several narrow size intervals (125–180, 250–300, 355–425, 500–600, 600–710, 710–850, and 850–1037 μm) for times ranging from 0.5 to 144 h in a high-velocity jet apparatus to provide a more comprehensive understanding of jet attrition. The theory of cumulative damage for fatigue is applied to explain the particle attrition mechanisms and to build an attrition model. Fines generation processes differed for limestone particles of different initial sizes, especially in the initial stage, because of the effects of rough surfaces and cumulative damage needed for attrition. In the model, the fines generation rates in the initial stage was well fitted by an exponential function with an index inversely proportional to the particle volume until stable stages were reached, whereas the rate of fines generation during the stable stage appeared to be constant for narrowly sized limestone particles.

Isothermal Jet Suction Through the Lateral Openings of a Cylindrical Funnel

This paper discusses the computation of air entrainment in to the louvers of a cylindrical funnel as a result of a high-velocity isothermal air jet placed inside the funnel having different lengths of protrusion and different funnel diameters. The experimental setup consists of a cylindrical Perspex tube with circular louvers cut around it. The flow through the nozzle is measured with a rotameter, and the velocity at the cylinder outlet is measured with a hot wire anemometer. The numerical simulation is carried out by solving the conservation equations of mass and momentum for the funnel with a surrounding computational domain so that the suction can take place at the louver entry. The resulting equations have been solved numerically using finite volume technique in an unstructured grid employing eddy viscosity based two-equation k-e turbulence model of Fluent 6.3. It has been found from the experiment and the CFD computation that there exists an optimum funnel diameter for which the mass ingress into the funnel is highest, and also there exists an optimum protrusion length of the nozzle that entrains maximum air flow into the funnel. For isothermal air suction the mass ingress into the funnel does not depend on the inclination of the funnel, whereas for low velocity and high temperature of the nozzle fluid the mass ingress in to the funnel depends on the inclination of the funnel. After a critical nozzle velocity (Gr/Re2 < 0.5), the mass ingress into the funnel does not again depend on the inclination of the funnel. An approximate relation for the entrance length of a sucking pipe has also been developed from the present CFD solution. The original contribution of the paper is the setting of a computational methodology for computing various conditions of suction flow in to a funnel while having the numerical confidence by comparing the CFD result with a small-scale experimental measurement in the laboratory.

Numerical investigation of air suction through the louvers of a funnel due to high velocity air jet

The present investigation predicts the suction flow rate from the atmosphere through the louvers of a funnel (used in naval and merchant ships) when the high velocity exhaust comes out from a nozzle or a set of nozzles placed inside the funnel. Conservation equations of mass and momentum have been solved for the funnel with a surrounding computational domain so that the suction can take place at the louvers entry. The resulting equations have been solved numerically using finite volume technique in an unstructured grid employing eddy viscosity based two equation k- ε turbulence model. It has been found from the computation that the air suction rate into the funnel increases with the increase in louvers opening area, nozzle flow rate and height of the funnel. There exists optimum protrusion of the nozzle into the funnel for which maximum suction of air can be achieved with a prescribed nozzle flow rate and all other parameters of the funnel remaining fixed. Similarly there also exists optimum funnel diameter where the suction rate of air becomes the highest with all other parameters remaining fixed. There also exists optimum louver opening area on the funnel where the suction rate becomes the maximum as a function of the funnel diameter. The inclination of the funnel with respect to the vertical has no effect on mass ingress of air into it. An optimum nozzle diameter could be decided for a particular funnel diameter by considering the funnel suction rate and the back pressure developed by the nozzle per meter length of the pipe containing the nozzle (intersection of the two curves gives the optimum point of operation).

On the failure of a brittle material by high velocity gas jet impact

Failure of brittle solid bodies due to the impingement of a high velocity air jet on the body surface is studied, experimentally and theoretically. Using the linear elastic theory and stress distribution analysis, a general criterion for the failure of brittle materials impacted by a gas jet is derived. Several special cases of jet–solid body interaction including failure of thin and thick layers and cylindrical objects immersed in a crossflow gas stream are investigated and proper material failure criteria are developed. These criteria correlate the minimum jet peak impact pressure (PIP) required to break the material to the material's tensile strength and Poisson's ratio. A series of experiments were performed using a laboratory-scale apparatus. Gypsum cast on steel tubes forming cylindrical samples was used as the model brittle material. Experimental data and high-speed breakup movies are employed to understand the gas jet–solid body interaction and to validate the theoretical criteria developed for the material failure. It is deduced that the failure of cylindrical samples impacted by a gas jet is by the formation and propagation of cracks. However, when the impact jet diameter is small, the cracks cannot propagate, and the material is failed due to localized surface pitting. One of the practical applications of this research is in Kraft recovery boilers, where high velocity supersonic steam jets are employed to remove deposits accumulated on the outer surfaces of the steam tubes.

Experimental Investigation of a Novel Combustor Modelfor Gas Turbines

The present study describes the performance of a novel combustor model for gas turbines. The working principle of this combustor is based on the establishment of a large recirculation zone in the combustion chamber, where part of the inlet air is mixed with the combustion products. Efficient mixing is achieved by the use of high-velocity inlet air jets. Six different inlet air geometries have been analyzed under nonreacting and reacting conditions at atmospheric pressure. Laser-Doppler anemometry was employed to characterize the mean velocity and turbulent kinetic energy fields as a function of the air mass flow rate and geometry configuration. Measurements of mean gas species concentration (O 2 , CO 2 , CO, HC, and NO x ) at the model exhaust are reported as a function of the equivalence ratio for all configurations. The isothermal data revealed that the recirculation ratio is mainly a function of the geometry, with a minor dependence on the experimental conditions. Under reacting conditions, the data revealed that NO x emissions are low regardless of the combustor operating conditions and geometry. However, the air inlet configuration has a strong effect in combustor efficiency.

Thermal stress analysis of cordierite materials subjected to thermal shock

Cordierite disks were obtained by slip casting and sintering at 1,450 °C for 2 h. Sintered disks were indented at the center of one flat surface. The fracture strength of indented disks was measured in biaxial flexure. The critical temperature differential was determined by sudden cooling of the center of the indented surface at high temperature, using a high-velocity air jet at room temperature. The initial temperature was successively increased by 10 °C until crack propagation was detected with the naked eye. Temperature and stress distributions during air impinging were calculated by a finite element analysis. The heat transfer coefficient was estimated by fitting experimental temperature profiles. A radial variation of the coefficient that considers its increment beyond the stagnation region and a diminution toward the disk periphery was assumed. The calculated cordierite thermal stresses were analysed in relation to experimental data. Also, the comparison with alumina tested in similar conditions was included.

Fracture Analyses of Alumina Subjected to Mechanical and Thermal Shock Biaxial Stresses

Disks of commercial alumina were fabricated by slip casting and sintering. Two surface finishes were performed: coarse (denoted as “C”) using a 70 grit diamond wheel and fine (denoted as “F”) with 120 and 320 grit SiC papers. The machined surfaces were analyzed by SEM, profilometry, and residual stresses measurements. The fracture strength was evaluated in biaxial flexure, and the thermal shock resistance was tested by cooling with a high-velocity air jet. The fracture of the specimens under both conditions was studied analyzing crack patterns and fracture surfaces in relation to the surface machining and type of loading, i.e., mechanical and thermal stresses.