Fluid Mechanical Parameters Research Articles

Study on methane hydration process in a semi-continuous stirred tank reactor

The methane hydration process is investigated in a semi-continuous stirred tank reactor. Liquid temperatures and reaction rates without stirrer are compared with those occurring with stirrer, while at the same time better stirring conditions of the methane hydration process are given by the experiments. Some basic data of fluid mechanics, for example, stirring Reynolds number, Froude number and stirrer power, are calculated during the methane hydration process, which can be applied to evaluate stirrer capacity and provide some basic data for a scaled up reactor. Based on experiment and calculations in this work, some conclusions are drawn. First, the stirrer has great influence on the methane hydration process. Batch stirring is helpful to improve the mass transfer and heat transfer performances of the methane hydration process. Second, induction time can be shortened effectively by use of the stirrer. Third, in this paper, the appropriate stirring velocity and stirring time were 320 rpm and 30 min, respectively, at 5.0 MPa, for which the storage capacity and reaction time were 159.1 V/V and 370 min, respectively. Under the condition of the on-flow state, the initial stirring Reynolds number of the fluid and the stirring power were 12,150 and 0.54 W, respectively. Fourth, some suggestions, for example, the use of another type of stirrer or some baffles, are proposed to accelerate the methane hydration process. Comparing with literature data, higher storage capacity and hydration rate are achieved in this work. Moreover, some fluid mechanics parameters are calculated, which can provide some references to engineering application.

Induced pulsing in trickle beds — Particle shape and size effects on pulse characteristics

Periodic liquid feeding of the ON–OFF type is investigated — at sufficiently high frequencies to be classified as “fast” mode of induced pulsing — in the range of mean gas and liquid flow rates corresponding to the steady “trickling flow” regime. Two of the most common types of catalyst-support particles, i.e. porous spherical and cylindrical extrudates, are employed to study the imposed pulse characteristics. Detailed information is obtained, on the axial propagation and attenuation of pulses, from instantaneous, cross-sectionally averaged holdup measurements. Key fluid-mechanical parameters studied include, aside from dynamic holdup and pressure drop, pulse celerity and intensity, as a function of fluid feed rates ( G , L ) and liquid cyclic frequency. Similar published data, for 6 mm glass spheres, are employed for comparison; it is shown that, for the particles examined, particle size has a pronounced effect, but not as significant as that of particle shape. For particles of comparable size, the cylindrical shape is associated with much greater global dynamic holdup and pressure drop, and with increased pulse attenuation. Moreover, packed extrudates exhibit a significant increase of holdup in the axial direction, recently also observed in steady trickling flow. For spherical particles, both time-average holdup and pulse celerity are practically constant along the bed for fixed L , G . Pressure drop, global holdup and pulse celerity are not affected by cyclic liquid feeding frequency, for both spherical and cylindrical extrudate particles. Based on the pulse attenuation characteristics, for the three particle types examined, recommendations are made on preferred conditions for induced pulsing (from the fluid dynamics point of view) which would maximize benefits. Overall, it appears that spherical packings hold significant advantages over cylindrical extrudates of comparable size. Finally, in view of the observed significant decay of imposed pulses along the bed, care should be exercised to properly interpret data obtained in short laboratory reactors (where pulse attenuation is limited) for scale-up of the much longer industrial beds.

A Study on Characteristics of Leak Signals of Pipeline Using Acoustic Emission Technique

This study presents an approach to leak detection of pipeline review in terms of theoretical analysis such as acoustics and hydromechanics that should be accompanied by explanation of leakage. The acoustic emission signals during leak from circular hole of different geometries were studied both analytically and experimentally. The relationships between acoustic parameters and fluid mechanical parameters also were derived analytically. A quadrupole aerodynamic model was applied for the analysis of leak from the circular hole. Computer simulation results demonstrate the effectiveness of the proposed approach. In addition, it was confirmed that the wavelet transform (WT) was an effective tool to determine source location. That is, arrival times of each frequency component needed in the velocity calculation could be determined from the peak of the magnitude of wavelet transform data on the time-frequency plane.

Hydrodynamic Shear Damage of Brewer's Yeast

The objectives of this study were to investigate the effects of mechanical agitation on the quality and fermentation performance of two types of industrial yeast slurries (one ale and one lager) and to correlate these effects to fluid mechanics parameters. Increases in pH, extracellular protease activity levels, and haze in the slurry supernatant showed satisfactory correlations with shear rate (76–228 sec−1) and shear stress (6.0–22.6 Pa) during continuous agitation at 4°C for 24 hr. The effect of shear prior to wort pitching on attenuation rate was insignificant in 12°Plato (P) and 20°P all-malt worts. However, beer quality dramatically deteriorated with regards to haze after forced aging and foam stability, which were directly affected by the intensity of agitation prior to pitching. Increased levels of mannose and glucose residues in beer haze hydolysate indicated yeast cell wall mannan and β-glucan as the main causes of increased beer haze, while the loss of foam stability was attributed to increased levels of protease activity during fermentation.

Experimental Investigation of Three Types of Clean Room Diffusers using Particle Image Velocimetry and Laser Doppler Velocimetry Techniques

The main purpose of this paper is to evaluate the main fluid mechanics parameters in the exit region of three different terminal systems commonly used for controlled environments such as clean rooms or operating theatres. Three different types of diffuser were tested i.e. a diffuser grid, a square ceiling diffuser and a swirling radial discharge diffuser. The paper presents results obtained experimentally which were carried out in order to study the flow characteristics of isothermal jets issuing from such devices. The study has been performed for four different air flow rates for each type of terminal tested. To characterise the flow with confidence and obtain high spatial resolution, a Particle Image Velocimetry technique and a Laser Doppler Velocimetry technique were used. For each case investigated, the results were plotted as velocity profile, velocity magnitude, turbulence intensity and vorticity. The study displays the particular behaviour of the flow generated by each terminal. Vorticity regions and turbulence spots were also detected and carefully localised for the investigated configurations.

On NO x emissions from turbulent propane diffusion flames

This paper presents an investigation on NO x emissions from turbulent propane diffusion flames. The study includes both experimental measurements and numerical 2D simulations and aims to provide a better understanding of the dominant physical effects associated with the NO x production in turbulent diffusion flames. Measurements of NO x emission indices (EINO x ), performed in unconfined and vertical lifted flames, have been analysed numerically. In this analysis, the effects of flame radiation, flame extinction by stretch and residence time have been studied by means of a mathematical model including a subroutine of the relevant NO chemistry. The numerically calculated values of EINO x , which are in good agreement with the experimental data, are found to be proportional to the residence time of the reaction products in the high-temperature reaction zone. The similar EINO x trends with geometrical or fluid mechanical parameters obtained without taking flame radiation or flame extinction into account reveals that the residence time is the dominant physical parameter associated with NO x scaling for the present flames.

Flow Field and Performance Characteristics of Combustor Diffusers: A Basic Study

Results of a detailed study concerning the influence of geometric as well as fluid mechanic parameters on the performance of a plane model combustor diffuser in cold flow are presented. For a qualitative insight into the complex flow field inside the prediffuser, the sudden expansion region, and the flow field around the flame tube dome, results of a flow visualization study with the hydrogen bubble method as well as with the ink jet method are presented for different opening angles of the prediffuser and for different flame tube distances. Also, quantitative data from detailed measurements with LDV and conventional pressure probes in a geometrically similar air-driven setup are presented. These data clearly demonstrate the effect of boundary layer thickness as well as the influence of different turbulence levels at the entry of the prediffuser on the performance characteristics of combustor diffusers. The possibility of getting an unseparated flow field inside the prediffuser even at large opening angles by appropriately matching the diffuser’s opening angle and the flame tube distance is demonstrated. Also, for flows with an increased turbulence level at the entrance—all other conditions held constant—an increased opening angle can be realized without experiencing flow separation. The comparison of the experimental data with predictions utilizing a finite-volume-code based on a body-fitted coordinate system for diffusers with an included total opening angle less than 18 deg demonstrates the capability of describing the flow field in combustor diffusers with reasonable accuracy.

Flow-induced vibration test of an advanced water reactor model Part 1: turbulence-induced forcing function

A 1:9 scale model of a proposed advanced water reactor was tested for flow-induced vibration. The main objectives of this test were: (1) to derived an empirical equation for the turbulence forcing function which can be applied to the full-sized prototype; (2) to study the effect of viscosity on the turbulence; (3) to verify the “superposition” assumption widely used in dynamic analysis of weakly copled fluid-shell systems; and (4) to measure the shell responses to verify methods and computer programs used in the flow-induced vibration analysis of the prototype. This paper describes objectives (1), (2), and (3); objective (4) will be discussed in a comparison paper. The turbulence-induced fluctuating pressure was measured at 49 locations over the surface of a thick-walled, non-responsive scale model of the reactor vessel/core support cylinders. An empirical equation relating the fluctuating pressure, the frequency, and the distance from the inlet nozzle center line was derived to fit the test data. This equation involves only non-dimensional, fluid mechanical parameters that are postulated to represent thefull-sized, geometrically similar prototype. While this postulate cannot be verified until similar measurements are taken on the full-sized unit, a similar approach using a 1:6 scale model of a commerical pressurized water reactor was verified in the mid-1970s by field measurements on the full-sized reactor.

On the TEHL Theory. Part I: Dimensionless Problem Formulation

Since the thermoelastohydrodynamic and elastohydrodynamic lubrication (TEHL and EHL) problems are predominantly heat transfer (HT) and/or fluid mechanics (FM) problems, it is proposed that the pertinent dimensionless quantities defined, in some instances tabulated, and commonly used in these branches of engineering science (HT and FM) should be used consistently and uniformly throughout for TEHL and EHL studies. In support of this, it is shown by some mathematical considerations that the published dimensionless quantities (in the TEHL and the EHL problems) can be converted into HT and FM parameters—such as the Reynolds number, Euler number, Eckert number, Prandtl number or Fourier modulus. It is indicated that such parameters have an immediately recognizable physical meaning.

Gas Transport in Serpentine Microporous Tubes Under Steady and Pulsatile Blood Flow Conditions

A serpentine gas exchange unit was built with cylindrical tubular microporous membranes featuring periodic arcs with a fixed curvature ratio (ratio of tube radius to radius of curvature) of 1/14 and circular angles between 30 and 360 deg. Oxygen transfer was measured under steady and pulsatile blood flow conditions in vitro and ex vivo to assess the design features which most effectively augment gas transfer. Under steady blood flow conditions, oxygen transfer increased with circular angles beyond 70 deg. Under pulsatile conditions, a wide range of geometrical and fluid mechanical parameters could be combined to enhance gas transfer performance, which eventually depended upon the secondary Reynolds number and the Womersley parameter.

Bioreactor design effects on biodegradation capabilities of VOCs in wastewater

AbstractVolatile organic chemicals are a wastewater pollution problem that can be handled by ultrafiltration, stripping, or biodegradation. Ultrafiltration and stripping transfer the dissolved organics to another phase which should then be further treated to finally destroy or utilize the organic chemicals. Biodegradation, on the other hand, converts the water soluble molecules to bio‐molecules which can then be separated or directly discharged. Biodegradation of aromatic chemicals requires air and tests have conclusively shown that traditional biodegradation designs result in VOC stripping losses to the air stream rather than biodegradation.Computer models and experimental data are presented comparing batch (plug flow), CSTR and packed bed bioreactor designs for their abilities to degrade VOC chemicals. Batch or plug flow reactors are shown to be a very poor method for biodegradation. CSTRs work well but require a large process residence time.A new packed bed column bioractor will be shown to provide much faster biodegradation and still minimize air stripping losses. Mass transfer and fluid mechanic parameters have been measured with and without biomass and compared to traditional chemical engineering correlations. The packed column minimizes the demand for air flow while increasing the throughput rate of wastewater as compared to a CSTR design. The efficiency of VOC biodegradation will be seen to be greatly improved.

Laminar flow past three closely spaced monodisperse spheres or nonevaporating drops

A basic understanding of the highly nonlinear interaction effects of multiple, closely spaced spheres or droplets on the fluid flow patterns and fluid mechanics parameters is of importance for the improved design of a variety of fluid-particl e systems. Streamlines, vorticity contours, flow separation angles, and individual drag/interaction coefficients are presented for steady laminar axisymmetric flow past a linear array of three spheres or droplets. A finite element method has been used to solve the complete Navier-Stokes equations for the system parameter ranges of 1 < Red < 200 (particle Reynolds numbers) and 2 < dy < 6 (dimensionless particle spacings). The verified computer simulation results indicate that the separation angles and effective drag coefficients of interacting spheres deviate significantly from solitary spheres at all Reynolds numbers. The differences between solid spheres and nonevaporating water drops in air with stress-induced internal circulation are only marginal.

Convective mixing mechanisms in high frequency intermittent jet ventilation.

A liquid flow visualization technique was used to identify the location of neutrally buoyant bead clouds injected into airway models during flows simulating high frequency intermittent jet ventilation (HFIJV) in neonatal lungs. The motions of these bead clouds show that the convective or bulk mixing that occurs during HFIJV is made up of two parts; a turbulent convective exchange with the atmosphere caused by the jet in the trachea and a streaming motion along the airways driven by an interaction between the jet and the expansion and contraction of the airways due to their compliance. These convective streaming motions combine with molecular diffusion to produce augmented diffusion which transports O2 and CO2 between the trachea and the peripheral alveoli. Optimizing HFIJV (as well as other forms of HFV) depends on maximizing these airway convective streaming flows which depend on many more lung and fluid mechanical parameters than are necessary to describe conventional mechanical ventilation.

Oxygen and CO 2 transfer of a polypropylene dimpled membrane lung with variable secondary flows

Gas transfer performance is presented for one form of the Oxford membrane lung in which vortex mixing is induced in blood flow across a dimpled polypropylene membrane. Dimensional analysis has been used to define the parameters characterizing mass transfer in the device, and of three fluid mechanical parameters: Reynolds number based on peak pulsation velocity, Strouhal number, and ratio of mean to oscillatory flows, only the first has been found to affect mass transfer significantly in the ranges studied. For oxygenation, rated flows in excess of 5 l min −1 m −2 are measured. A new definition is presented for a rated flow for extracorporeal CO 2 removal and values in excess of 1.2 l min −1 m −2 are obtained.

Measurement of turbulence intensity in the center of the canine ascending aorta with a hot-film anemometer.

The blood flow velocity near the central axis of the canine ascending aorta was measured with a hot-film anemometer. The cardiac output and the heart rate were controlled at will by means of an extracorporeal circulation and by atrial pacing. The turbulent component of the blood flow velocity was calculated using an ensemble average technique. Ensemble average turbulent intensity was also calculated to show the time course of turbulence in the aorta. The ratio of the mean turbulence intensity to the time mean sectional average velocity in the aorta was constant in most animals regardless of the changes in fluid mechanical parameters. The correlation between the frequency parameter and the relative mean turbulence intensity was weakly positive. The power spectrum of the turbulence was also calculated.

イヌ上行大動脈中心軸付近の乱流強度

The turbulence intensity near the central axis of the canine ascending aorta was measured with a hot-film anemometer. The cardiac output and the heart rate were controlled arbitrarily by the use of an extracorporeal circulation called open-loop method and of an atrial pacing. Drugs other than anesthetics were not used.Blood flow velocity waveforms showed high-frequency fluctuations appearing near at the peak systolic velocity and persisting all the way through the deceleration phase of systole. These fluctuations were regarded as turbulence.We designed a computer method for separating the turbulence from the physiological changes of the blood flow velocity. The mean turbulence intensity was defined as the square root of the time integral of the ensemble average square of the turbulence velocity; the integration interval was the whole deceleration phase of the ensemble average blood flow velocity. The relative mean turbulence intensity was defined as the ratio of the mean turbulence intensity to the time mean sectional average velocity in the aorta. It was constant in most animals regardless of the changes in fluid mechanical parameters. In some animals, however, the relative mean turbulence intensity was dependent upon the peak Reynolds number. The relative mean turbulence intensity positively correlated with the frequency parameter, but the correlation was not so strong. The amplitude ratio (ratio of the peak velocity to the mean velocity) failed to make its role clear in the turbulence phenomena in the present experiments.

Heat transfer with stratified gas‐liquid flow

AbstractThis article presents a method for predicting local Nusselt numbers for heat transfer to a stratified gas‐liquid flow for turbulent liquid/turbulent gas conditions. A mathematical model based on the analogy between momentum transfer and heat transfer is developed and tested, using heat transfer and fluid mechanics data taken for air/water flow in a 63.5 mm I.D. tube. The fluid mechanics parameters required for the prediction of the heat transfer characteristics are obtained in the manner outlined elsewhere. Liquid phase Nusselt numbers predicted by the analogy are shown to be in agreement with experimental results for large and small amplitude wavy interfacial conditions. The circumferential average gas phase Nusselt numbers are in rough agreement with the Dittus‐Boelter equation for single phase flow based on flow through a conduit of irregular shape. There is a tendency for the average gas phase Nusselt numbers to scatter about predicted values because of the effects of splashing and droplet deposition on the tube wall in the vicinity of the gas‐liquid interface.

Thermal entrance effects in stratified gas—liquid flow: experimental investigation

A study of heat transfer in the thermal entrance region for horizontal concurrent airwater flow over a flat plate has been carried out to complement theoretical studies of the phenomenon. Measurements of the heat transfer characteristics and fluid mechanics parameters have been made for constant wall temperature and constant wall heat flux boundary conditions. The results for smooth surfaces and for hydrodynamically unstable liquid films are compared with the theory for non-rippling films. Theory and experiment are compared in terms of dimensionless parameters that characterize the system, in terms of wall temperature and wall heat flux profiles and as local Nusselt numbers vs. position.

Skin Effect in Magneto-Fluid Dynamic Traveling Wave Devices

Electromagnetic propagation through an infinite circular cylindrical traveling wave tube in which a conducting fluid of constant conductivity is moving axially with uniform speed is studied. Asymptotic solutions valid for |αR0|«1 and |αR0»1, where α is the complex separation constant and R0 the tube radius, are obtained and analyzed. Concentrating specifically on the axial body force per unit tube length induced in the fluid, the |αR0|»1 solution indicates, fixing the current sheet input and geometry, that the magnitude of the induced axial force is a marked function of the dimensionless parameter β, equal to the magnetic Reynolds number based on wavespeed and wavelength multiplied by the slip. The body force rises linearly with β for small β, reaches a peak and then, because of the inability of the electromagnetic field to penetrate into the conductor with increasing β (skin effect), falls like β−1/2 for large β. From the practical viewpoint, the results suggest the adjustment of the electrical and fluid mechanical parameters so that operation occurs at that value of β which optimizes the force. It is further indicated, especially for moderate to high β operation, that for efficient utilization and conservation of working fluid mass and electrical energy, injection and acceleration take place in an annulus close to the coils rather than throughout the entire cross section.