Jet Flow Rate Research Articles

An experimental study on bubble entrainment and flow characteristics of vertical plunging water jets

When a vertical liquid jet plunges into a liquid surface after passing through a surrounding gas phase it entrains a large amount of gas bubbles into the receiving pool, and forms a large submerged two-phase region with a considerable interfacial area. At the intersection of the plunging jet and the liquid surface, free-surface instabilities develop, and gas entrainment may be observed. In this study, a set of experiments were performed on plunging water jets injected vertically downward through short circular nozzles lN/dN⩽5 onto a free water surface. The effect of the operation conditions including initial jet diameters dN, initial jet velocity VN, and jet length x1 on the flow characteristics such as the inception velocity of the gas entrainment Ve, the bubble penetration depth Hp, the gas entrainment rate Qa, the centerline jet velocity Vc, and the axial jet velocity distribution Vx below the free water surface were evaluated. A flow visualization technique using a CCD camera, which allowed simultaneous measurements of several magnitudes, was used to investigate such flows. This technique provided a direct measurement of the interfacial behavior between the entrained air bubbles and the liquid ambient.The results obtained showed that the nondimensional bubble penetration depth Hp/dN decreased with the dimensionless jet length x1/dN up to 25, after this point it was almost constant. Also, the bubble penetration depth was found to increase with the jet velocity and nozzle diameters. The entrainment rate tended to increase when the jet velocity increased and its functional dependence was divided into three regions depending on the jet velocity. The value of Qa was also found to increase as x1 and dN increased for the same jet flow rate. The jet centerline velocity decay Vc was measured and found to be a function of: the jet impact velocity V1 with the plunge water surface, the jet diameter d1 and the plunge depth x. The axial velocity distributions Vx/Vc were found to be approximately Gaussian distributions for all the cases when plotted against r/bu. Empirical relationships were proposed to predict the jet parameters and when were compared with the available experimental data and correlation of other authors a good agreement was found.

Self-oscillation regimes of the penetration of free conical thin-walled turbulent jets through a fluid surface

Certain results of an experimental investigation of hydrodynamic effects occurring, when free thin-walled turbulent jets issuing from a conical slot nozzle with a vertical axis penetrate through the surface of a fluid in a rectangular reservoir, are presented. The ranges of the jet flow rate and the spacing between the nozzle and the free surface, on which stable regular transverse self-oscillations of the boundaries of dome-shaped jets are observable, are determined. For fixed values of the conicity angle α = 60° and the nozzle slot width δ = 0.1 cm the characteristic form of the dependence of the self-oscillation period on the jet flow rate and the spacing between the slot nozzle and the free surface (dome height) is presented. The self-oscillation regime generation mechanism, together with the possible reasons for the revealed bifurcation changeover of the oscillation mode at certain values of the governing parameters and the hysteresis effects, are discussed. The salient features of the flows occurring on the surface and within the fluid beneath the dome are described.

Experimental investigation of the performance of a novel foam generator for dust suppression in underground coal mines

Dust in underground coal mines is a serious threat to workers’ health and safety. Foam is used as an efficient means of dust suppression in these confined workplaces. A novel foam generator has been designed to overcome the problem of bottlenecks due to the complex operation and high cost of existing foam technology. Experimental performance testing and evaluation showed that a 20–40m3/h gas source for generating foam is produced by a small 0.4–0.6m3/h flow-rate jet, and the device consumes as little as 4–6kg/h of foaming agent. It requires only a normal pipeline water pressure, eliminating the need for a compressed air supply (compressor, pipelines and/or hoses). Its simplified structure combines the advantages of safe, reliable and convenient operation with compact size. The marked reduction in the consumption of water and foaming agent significantly reduces foam production cost. The foam generator was tested at a coal face and successfully controlled dust produced by a longwall double-drum shearer.

An Insertion Rate Model for Pile Installation in Sand by Jetting

Abstract The use of jetting is an approach to aid the installation of piles, especially in areas that have hard but relatively shallow subsurface soil layers. Jetting piles for a portion of their installation depth minimize their exposure to excessive driving stress and provide energy savings and noise reduction. However, the literature offers little information regarding the appropriate selection of jetting parameters, such as flow rate and jet velocity, which are needed to produce the desired installation times as a function of soil strength. This paper presents a model for estimating pile jetting parameters based on the results from laboratory and field testing. The model is based on an idealization of the applied shear stress that is produced by the jet as well as the soil resistance to pile insertion. The model is applied to 19 field installations where the jetted depths of the piles range from 10–34 ft. The field data yield ratios of 6–20 for the jet flow rate (Qw) to the rate of the pile volume insertion in terms of time (Qp), with the lower ratios associated with higher jet velocities. The proposed model yields an estimated Qw/Qp that is within +/− 20 % of the measured values.

Low-mixing coaxial nozzle for effective personalized ventilation

The aim of this work was to study the performance of a novel coaxial nozzle for personalized ventilation that can be used as an add-on to ceiling diffuser. The coaxial nozzle minimizes air entrainment between the central fresh air stream and the room air. It allows effective delivery of clean air to the breathing zone while the recirculated conditioned air is supplied to the space by the associated ceiling diffuser. Detailed 3-D Computational Fluid Dynamics (CFD) simulations were performed and numerical results on velocity, temperature, and CO2 concentration fields agreed well with experimentally measured values. The effect of the jet flow rate, temperature, and inclination angle on air quality at the breathing zone of the occupant was then investigated. The proposed coaxial personalized ventilation achieved high air quality in the breathing zone demonstrated by a personal exposure effectiveness of 32% at fresh airflow rate of 10 L s−1 per person. It contributed also to the attainment of temperature differences up to 2℃ between the occupant’s microenvironment and the rest of the room air leading to considerable energy savings compared to the mixed convection air conditioning.

Tomography images to analyze the deformation of the cavern in the continuous‐flow mixing of non‐Newtonian fluids

Tomography, an efficient nonintrusive technique, was employed to visualize the flow in continuous‐flow mixing and to measure the cavern volume (Vc) in batch mixing. This study has demonstrated an efficient method for flow visualization in the continuous‐flow mixing of opaque fluids using two‐dimensional (2‐D) and 3‐D tomograms. The main objective of this study was to explore the effects of four inlet‐outlet configurations, fluid rheology (0.5–1.5% xanthan gum concentration), high‐velocity jet (0.317–1.660 m s−1), and feed flow rate (5.3 × 10−5−2.36 × 10−4 m3 s−1) on the deformation of the cavern. Dynamic tests were also performed to estimate the fully mixed volume (Vfully mixed) for the RT, A310, and 3AM impellers in a continuous‐flow mixing system, and it was found that Vfully mixed was greater than Vc. Incorporating the findings of this study into the design criteria will minimize the extent of nonideal flows in the continuous‐flow mixing of complex fluids and eventually improve the quality of end‐products. © 2013 American Institute of Chemical Engineers AIChE J, 60: 315–331, 2014

Noise generation by open inverse diffusion flames

The acoustic spectra of noise radiation from a turbulent non-premixed inverse diffusion flame were measured and the effect of the point of observation, air jet Reynolds number and overall equivalence ratio on the spectra were examined. The tests were conducted in a wide range of air and fuel flow rates and both the non-reacting and reacting cases were considered and discussed. For the non-reacting case, the noise emitted from the cold flow is mainly generated by the central air jet, with only a small role played by the fuel jets. The dominance of the noise produced by the air jet is confirmed by the observation that the cold flow noise is a strong function of the air jet flow rate or air jet Reynolds number. The spectral features of the noise from the combusting flames differ significantly from those of the cold flow noise due to the chemical reactions. Upon combustion, the noise radiated from the flames significantly overwhelms the corresponding cold flow noise in the range of frequency under consideration (80–3000 Hz). The distance of the point of observation only affects the magnitude of the sound pressure level while both the shape and magnitude of the sound pressure level are influenced by the azimuth of the point observation. The total sound pressure level increases with Re, while the effect of Ф on the total sound radiation level indicates that the highest level of noise occurs as complete combustion is approached.

Characterization and psychophysical studies of an air-jet lump display.

Development of tactile displays to enhance palpation of lumps during robot-assisted minimally invasive surgery is challenging due to size and weight constraints, motivating a pneumatic actuation strategy. This work describes the quantitative and psychophysical assessment of an air-jet tactile display that creates a lump percept by directing pressurized air through an aperture onto the finger. The air pressure and aperture size are meant to control the hardness and size, respectively, of the perceived lump. Jet impingement pressure and flow rate were measured by capacitive tactile sensors and mass flow meters at varying aperture sizes and pressures. The air-jet pressure profile width evolves as jet theory predicts and is largely independent of supply pressure (and therefore jet exit velocity). The method of constant stimuli was used to determine the just noticeable differences (JNDs) for the air pressure and aperture size. Qualitative results indicate that subjects perceive the stimulus as a "lump-like" shape. Pressure JNDs ranged from 19.6-24.4 kPag and aperture size JNDs ranged from 0.50-0.66 mm. No significant correlation exists between the supply pressure and changes in perceived lump size. However, pressure JNDs show significant (p < 0.001) inverse correlation with aperture size, with improved discrimination at larger apertures, where a greater finger pad area is stimulated.

Jets to control scour around circular bridge piers

It is common for engineers to use countermeasures to protect hydraulic structures against scour. This study aims to explore the effect of jet injection through the pier body as a pier-scour countermeasure. Laboratory experiments were conducted in two different flow depths (10.5 and 28 cm) using 1-jet and 3-jet injections, different jet locations, and angles between the jets under clear-water conditions. The experimental data showed that the most optimal case in terms of pier-scour depth reduction occurred for lower flow depth, higher jet flow rate, and angle between the jets equal to 90°. Moreover, the jets are able to reduce the scour depth, scour volume and upstream slope of the scour hole up to 37.5%, 57%, and 25% for flow depth of 10.5 cm and 31.2%, 37%, and 57% for flow depth of 28 cm, respectively. By increasing the number of jets, turbulent kinetic energy increases, leading to the pier-scour depth decreasing.

基于格子玻尔兹曼方法的单孔射流鼓泡床的离散颗粒模拟

This paper presents a discrete simulation of bubbling bed with jet flow at a single orifice using a lattice Boltzmann method based discrete particle model proposed by us. This algorithm is based on four-way coupling discrete particle simualtion whereas governing equations of fluid flow solved by modified lattice Boltzmann method with consideration of the effect of porosity and relative slip velocity between particle and fluid and interaction between particles modelled by time-driven hard-sphere model. The EMMS drag model is adopted for coupling between solid and gas phase. We first investigated the influence of particle diameter and gas jet velocity on bubble formation. The results show that bubble size reduces with increasing of particle diameter under the same gas injet velocity, while bubble size increases with increasing of gas jet velocity. Then the relationship of bubble detached from the bottom of bed with particle size and jet flow rate is explored. The results show that with the change of particle size and jet flow rate, bubble detached time is almost the same. We also found that the enlargement of solid initial bed has an effect on bubble size and shape. The bubble tends toward a circular shape with a wider bed of solids and become smaller with increasing of solid initial bed height. Finally we reproduced the phenomenon of bubble inducement that bubble tends move toward an empty region.

0602 空気を用いた非接触微小粒子除去における流量及び対象物振動の影響(OS6-1 噴流,後流およびはく離流れ現象の探求と先端的応用,OS6 噴流,後流およびはく離流れ現象の探求と先端的応用)

Recently, low cost cleaning technique has been demanded to remove small particle that causes quality and yield ratio loss in manufacturing process. In this study, in order to investigate the particle removal characteristics of suction and jet flow in terms of energy saving, we performed particle removal experiment. Furthermore, to enhance the particle detachment, we investigated the effect of surface vibration for particle detachment. For consideration of the experimental results, we analyzed the flow field by using FLUENT. As a result, the particle removal efficiency of jet flow is higher than that of suction flow, even jet flow rate is about 80 percent lower than that of suction flow rate. And the wall shear stress generated by jet flow acts on wide region compare to the suction flow. It was also found that the inertia force due to vibration could assist the particle removal.

Experimental investigation on influence of porous material properties on drying process by a hot air jet

The drying process of porous media is a subject of scientific interest, and different mathematical approaches can be found in the literature. A previous paper by the same authors showed that the celebrated Martin correlation for hot air jet heat and mass transfer yields different degrees of accuracy (from 15% to 65%, increasing at high values of input power) if tested on different fabrics, the remaining conditions being the same. In this paper the fabric drying has been experimentally investigated more in depth. A dedicated experimental apparatus for hot jet drying was assembled and operated, in which a hot jet impinges perpendicularly onto a wet fabric. A calibrated orifice was adopted to measure the jet flow rate, with an accuracy better than 3%. The drying power was determined by continuously weighing with a precision scale a moistened patch exposed to the drying jet. The effect of the time of the exposure and the initial amount of water has been evaluated for each sample. During the hot jet exposure, the temperature distribution over the wet patch has been observed by an infrared thermo-camera. A mathematical model of water transport inside and outside the fabric was developed, in order to evidence the governing transport resistances. The theoretical predictions have been compared with the experimental results, and showed the necessity to modify correlations and models accounting for fabric properties.

Free-surface electrospray technique using a multi-hole array

The main obstacle of the electrospray method; especially cone-jet mode, to apply many industry fields is low throughput of electrospray method. One of the functioning modes of electrospray labeled multi-jet mode is alternative mode to solve to problem and to achieve high throughput. Because of the positional instability and polydispersity of generated droplet size, multi-jet mode is rarely studied to compare with cone-jet mode. To eliminate this shortcoming, we exploited free surface electrospraying system using arrayed hole at the side of the nozzle. For evaluation of the nozzle system, the electric current and size distribution of electrosprayed droplets were measured under various experimental conditions. The electric current in the multi-jet mode obeyed the same power law as the single cone-jet mode as a function of flow rate. In particular, both modes produced almost the same size distribution of droplets for a given average jet flow rate.

Study on Nozzle Array Structure Fluidic Gyroscope

This paper reports about a nozzle array structure fluidic gyroscope. The gyro used setting sub-nozzle around the main nozzle to inhibit the attenuation which had been caused by the main nozzle jet column spread out and to increase the angular velocity difference of sensitive element in the thermal resistance wire when the jet flow rate had been input, thereby to improve the performance of the jet gyro. The test results showed that: a resolution of better than 0.1°/s nozzle formation jet gyro sensitivity better than 10mv/(0.1°/s), the measurement range is better than ± 60°/s; non-linearity of better than 1%.The impact of the gyroscope impact resistance capability, small size and wide range of applications.

Experimental study of heat transfer coefficient on hot steel plate during water jet impingement cooling

Experiments were performed, under transient conditions, to investigate the heat transfer phenomena of stationary hot steel plate under multiple top circular jets on run-out table. Based on inverse heat conduction model, a two-dimensional finite difference program was developed to calculate the local surface convective heat transfer coefficients and corresponding temperatures. The cooling water jet flow rate was varied from 15L/min to 35L/min and its effect on the convective heat transfer coefficient and surface temperature was analyzed. The results show that heat transfer coefficients are nonlinear functions of surface temperature. The cooling flow rate has no effect on heat transfer coefficient and surface temperature at stagnation point. Within 70mm distance from stagnation line, heat transfer coefficient ratio changes slightly from 0.87 to 0.97. Beyond surface temperature of 350°C, heat transfer coefficient ratio decreases with increasing distance from stagnation line.

Oil-in-water emulsification using confined impinging jets

A confined impinging jet mixing device has been used to investigate the continuous sunflower oil/water emulsification process under turbulent flow conditions with oil contents between 5% (v/v) and 10% (v/v). Various emulsifiers (Tween20, Span80, Whey Protein, Lecithin and Sodium Dodecylsulphate) varying in molecular weights have been studied. Mean droplet sizes varied with the emulsifiers used and smallest droplets were obtained under fully turbulent flow regime, i.e. at the highest jet flow rate and highest jet Reynolds Number conditions. Sodium Dodecylsulfate (SDS) produced droplets in the range of 3.8μm while 6μm droplets were obtained with Whey Protein. Similar droplet sizes were obtained under fully turbulent flow conditions (610mL/min; Reynolds Number=13,000) for oil content varying between 5% (v/v) and 10% (v/v). To investigate the smallest droplet size possible in the device, the emulsion was passed through the geometry multiple times. Multi-pass emulsification resulted in reduction in droplet size indicating that longer residence in the flow field under high shear condition allowed for breakage of droplets as well as the time for the emulsifier to stabilize the newly formed droplets, decreasing the impact of coalescence. This was confirmed by timescale analysis of the involved process steps for the droplet data obtained via experiments. Dependence of mean droplet size on the o/w interfacial tension and peak energy dissipation was also investigated.

Nanofluid impingement jet heat transfer

Experimental investigation to study the heat transfer between a vertical round alumina-water nanofluid jet and a horizontal circular round surface is carried out. Different jet flow rates, jet nozzle diameters, various circular disk diameters and three nanoparticles concentrations (0, 6.6 and 10%, respectively) are used. The experimental results indicate that using nanofluid as a heat transfer carrier can enhance the heat transfer process. For the same Reynolds number, the experimental data show an increase in the Nusselt numbers as the nanoparticle concentration increases. Size of heating disk diameters shows reverse effect on heat transfer. It is also found that presenting the data in terms of Reynolds number at impingement jet diameter can take into account on both effects of jet heights and nozzle diameter. Presenting the data in terms of Peclet numbers, at fixed impingement nozzle diameter, makes the data less sensitive to the percentage change of the nanoparticle concentrations. Finally, general heat transfer correlation is obtained verses Peclet numbers using nanoparticle concentrations and the nozzle diameter ratio as parameters.

Parallel CFD simulation of flow in a 3D model of vibrating human vocal folds

Accurate computation of highly unsteady and massively separated airflow in human vocal folds during phonation, which is fundamental for the understanding and modeling of the aeroacoustic processes involved in human voice production, requires CFD simulations on large 3D dynamic meshes. This work presents a 3D model of flow past vibrating vocal folds solved by cell-centered finite volume method, verification of the solver on a benchmark cylinder cross-flow problem, grid dependence study and parallel scalability results obtained on a heterogeneous Linux computational cluster with 12 Intel Xeon dual-processor dual-core and 17 AMD Opteron dual-processor single-core nodes. Transient computations on dynamic meshes with up to 3.2M elements were performed on two geometries modeling convergent and divergent glottis with an angle of 20 degrees. In the results, the jet deflection angle, flow rate, glottal velocity and pressure, drag and lift force and jet contours (including phase-averaged data) are compared for these two configurations.

Particle removal process during application of impinging dry ice jet

In this study, we have investigated the application of dry ice blasting to remove fine particles adhering to surfaces and examined the removal process. The removal efficiency, area, and frequency have been analyzed using images captured with a high-speed microscope camera. In addition, the temperature of the dry ice jet has been measured in order to evaluate the dry ice particles and their effects on the particle removal process. The removal processes due to the impacts of primary dry ice particles and their agglomerates occurred in two stages corresponding to slow and rapid particle removals. High removal efficiency was achieved when the impacts of the agglomerates were dominant during the particle removal at approximately −70°C. Furthermore, we have investigated the effects of the jet flow rate on the removal area and frequency and proposed a system parameter to determine the optimum jet flow rate for efficient particle removal.

Self-oscillatory regimes of cavitation interaction between counter-streaming fluid flows

The effects of unsteady cavitation interaction between a coaxial system of a continuous water jet and a surrounding annular gas jet and a counter-streaming water flow in a cylindrical tube is investigated both experimentally and numerically. The distinctive features of the mechanism of the formation of regular self-oscillatory interaction regimes and their salient features are studied. The dependence of the mean self-oscillation frequency on the ratio of the counter-streaming water flows is determined at different gas jet flow rates. The Froude number effect on the self-oscillation frequency is analyzed. The dependence of the maximum value of the longitudinal displacement of the nose of a developed oscillating cavity penetrating into the counter stream and of the displacement amplitude on the flow rate of the supplied gas is determined. The idea on the pressure distribution in the cavity in different stages of flow development is obtained. The nature of the dependence of the self-oscillation frequency on the degree of tube flow blockage by the cavity is established.