共查询到20条相似文献,搜索用时 31 毫秒
1.
Concentration measurements during mass transfer across liquid-phase boundaries using planar laser induced fluorescence (PLIF) 总被引:1,自引:0,他引:1
A non-intrusive optical measuring technique, the planar laser induced fluorescence is described to investigate mass transfer
of a fluorescent dye (rhodamine B) across an interface between two partial immiscible liquids (1-butanol and water). The spatial
resolution of the measurement technique used for the mass transfer investigations was 31.6 μm. The measured concentration
profiles do not correspond with those, which were expected on the basis of usual theories. A solution equilibrium at the phase
boundary could not be found.
Received: 21 January 1999/Accepted: 4 May 1999 相似文献
2.
R. J. Exton R. J. Balla B. Shirinzadeh M. E. Hillard G. J. Brauckmann 《Experiments in fluids》1999,26(4):335-339
A new concept for flow visualization is demonstrated in which fluorescence from locally seeded iodine is viewed in the wake
of simple aerodynamic models at Mach 6. Localized seeding is performed by painting a small area of a ceramic model with a
tincture of iodine. When the model is injected into the flow, the adsorbed iodine is entrained into the boundary layer, follows
the model contour, and ultimately mixes into the wake region. Planar “snapshots” of the wake flow are taken by exciting the
iodine with an ArF excimer laser sheet at 193 nm and observing the fluorescence in the 210–600 nm region with an intensified
CCD camera.
Received: 17 July 1997/Accepted: 12 August 1998 相似文献
3.
Whole field measurement of temperature in water using two-color laser induced fluorescence 总被引:2,自引:0,他引:2
A technique is described that measures the instantaneous three-dimensional temperature distribution in water using two-color
laser-induced fluorescence (LIF). Two fluorescent dyes, Rhodamine B and Rhodamine 110, are used as temperature indicators.
A laser light sheet scanned across the entire measurement volume excites the fluorescent dye, and an optical system involving
a color beam splitter gives the intensity distribution of the individual fluorescent dyes on two separate monochrome CCD cameras.
The ratio of these fluorescence intensities at each point of the image is calibrated against the temperature to eliminate
the effect of the fluctuation of illuminating light intensity. A stable thermally stratified layer was measured by this system
to evaluate the total accuracy of the measurement system. The random error of the measurement was ±1.4 K with 95% confidence.
Measurements of thermal convection over a heated horizontal surface show temperature iso-surfaces having typical structures
such as plumes, ridges and thermals.
Received: 1 October 1997/Accepted: 23 March 1998 相似文献
4.
The unsteady mixed convection boundary layer flow over a vertical cone is considered to investigate the combined effects of
the buoyancy force, thermal and mass diffusion in the presence of the first order chemical reaction and surface mass transfer.
The unsteadiness is caused by the time dependent free stream velocity varying arbitrarily with time. The governing boundary
layer equations are transformed into a non-dimensional form by a group of non-similar transformations. The resulting system
of coupled non-linear partial differential equations is solved numerically by the combination of quasi-linearization technique
and an implicit finite difference scheme. Numerical computations are performed for different values of the parameters to display
the velocity, temperature and concentration profiles graphically. Both accelerating and decelerating free stream velocities
are considered. Numerical results are presented for the velocity, temperature and concentration profiles as well as for the
skin-friction coefficient, local Nusselt number and local Sherwood number. The obtained results are compared with previously
reported ones and are found to be in excellent agreement. 相似文献
5.
6.
Asterios Pantokratoras 《Transport in Porous Media》2009,76(3):309-325
A steady laminar boundary layer flowing along a vertical plate immersed in a Darcy–Brinkman porous medium saturated with water
at 4°C is studied. The plate temperature varies sinusoidally along the plate between 0 and 8°C where the density of water
varies parabolically and is almost symmetrical at about 4°C. Except for the existence of the buoyancy force, it is assumed
that either the plate moves upwards or the ambient water moves upwards (moving stream). The results are obtained with the
direct numerical solution of the boundary layer equations taking into account the temperature dependence of water thermophysical
properties (ρ, μ and c
p). Results are presented for the wall temperature gradient and the wall shear stress along the plate for free convection and
mixed convection. Temperature and velocity profiles are also presented. 相似文献
7.
A novel particle tracking system working with a high particle concentration for the measurement of flow fields beneath water
waves is described. It features a 1–4 cm thick light sheet parallel to the main wave propagation direction so that the seeding
particles stay long enough in the illuminated area to enable tracking over several wave periods. An area of up to 14.0×10.0 cm2 is observed by a CCD camera with up to 200 fields/s. The polychromatic scattering theory of small particles in a light sheet
illumination is investigated, enabling the segmentation of individual particles at high particle concentration.
Received: 12 July 1995/Accepted: 18 April 1997 相似文献
8.
A technique has been developed to measure void fraction using X-rays in a 10 cm thick pool of molten tin with gas injection
at various flow rates. Visualization of the multiphase mixture using high energy X-rays can be performed at imaging rates
of 220 fps with 256×256 pixel resolution or at 30 fps with 480×1128 pixel resolution. The images are subsequently processed
to obtain two dimensional distributions of the chordal average void fraction in the mixture. The estimated relative uncertainty
of the measurement is discussed in detail and shown to be of the order of 10% of the reported value.
Received: 6 June 1997/Accepted: 2 December 1997 相似文献
9.
Laboratory measurement of suspended sediment concentration using an Acoustic Concentration Profiler (ACP) 总被引:2,自引:0,他引:2
Vertical profiles of suspended sediment concentration have been gathered in a laboratory flume using a 2.25 MHz acoustic
transducer. The acoustic concentration profiler (ACP) was calibrated in a vertical duct for homogeneous concentrations of
two uniformly sized sediments. The transducer was then transferred to a 6 m horizontal flume where concentration profiles
were measured in steady and unsteady flows. For the steady flow tests, concentration measurements made with the ACP and with
suction samplers are compared. The results demonstrate that the ACP provides an accurate method of non-intrusively measuring
sediment concentrations of more than 2.5% by volume.
Received: 24 September 1998/Accepted: 12 April 1999 相似文献
10.
K. A. Yih 《Heat and Mass Transfer》1998,34(1):55-61
A boundary layer analysis is used to investigate the heat and mass transfer characteristics of mixed convection about a vertical
flat plate embedded in a saturated porous medium under the coupled effects of thermal and mass diffusion. The plate is maintained
at prescribed surface temperature/concentration (PST/PSC) or prescribed heat/mass flux (PHF/PMF). The nonsimilar governing
equations are obtained by using a suitable transformation and solved by Keller box method. Numerical results for the local
heat transfer rate and the local mass transfer rate are presented for various parameters. The local heat and mass transfer
rates increase with increasing n and m and buoyancy parameter ξ. When buoyancy parameter ξ is very small (large) the value of local Nusselt and the local Sherwood
number correspond with the pure forced (free) convection, respectively. Increasing buoyancy ratio N (or N
*) increases the local heat and mass transfer rates. It is apparent that Lewis number has a pronounced effect on the local
mass transfer rate than it does on the local heat transfer rate. Furthermore, increasing Lewis number decreases (increases)
the local heat (mass) transfer rate.
Received on 8 December 1997 相似文献
11.
A technique for measuring near instantaneous concentration profiles of a fluid injected through a narrow inclined slot at
the wall into a high unit Reynolds number flat plate turbulent boundary layer is discussed. The concentration profiles are
determined by measuring the light intensity emitted from a fluorescent dye, premixed into the injectant flow, as the injectant
convects through an excitation laser beam. The fluorescence intensity is quantified by an electronically shuttered single
stage microchannel plate image intensifier coupled to a linear photodiode array. This instrumentation provided the high spatial
and temporal resolution required for these boundary layer concentration profile measurements. The laser induced fluorescence
technique is being used to study the diffusion of injected polymer solutions away from the near wall region of the boundary
layer where these solutions are effective in reducing drag. The diffusion of slot injected water has also been examined and
the present results are in excellent agreement with previous studies. 相似文献
12.
The mixing characteristics of a round, turbulent, unsteady jet were studied experimentally. A gravity-driven flow was created
by releasing dyed fluid from a vertical tube into a large water tank. The jet velocity increased from zero to a maximum and
then decreased continuously such that each run lasted about s. The jet dilution was examined by an optical absorption technique
that measured the line integral of concentration across the jet diameter. These measurements revealed that the portion of
the unsteady jet corresponding to the deceleration phase dilutes more than the steady jet. The molecular scale mixing, as
deduced from an acid-base neutralization reaction, corroborated the finding that the jet mixes in a shorter distance than
the steady jet.
Received: 22 August 1996/Accepted: 4 February 1997 相似文献
13.
We describe the capabilities of coherent high resolution radar to observe remotely the effects of an upwelling subsurface
flow on the water surface. This observation is possible because the radar radiation backscatters very strongly from surface
features with dimensions similar to its wavelength, in this case X-band at 0.03 m. This technique provides imaging capability
with relatively high spatial resolution (∼0.3 m) and fast time sampling (∼0.006 s) over a large surface area. The processed
data reveal both the line-of-sight velocity spectrum of moving water surface features, and their water surface radar backscatter
cross-section. We believe that the surface features are generated by subsurface vortices oriented normal to the surface. The
vortices are advected with the bulk flow of the jet. Our radar observations of the down-stream flow from a submerged waterjet
that is directed parallel to the surface are consistent with those previously measured by laser velocimetry.
Received: 25 February 1994/Accepted: 16 May 1996 相似文献
14.
We present experimental results using Filtered Rayleigh Scattering to make planar measurements of velocity, temperature and
pressure in ambient air and in a Mach 2 free jet. The ambient air measurements are used to identify and calibrate experimental
uncertainties. The Mach 2 measurements demonstrate the usefulness of the technique for making accurate planar measurements
in a high speed flow. The measured values for velocity, temperature and pressure in the Mach 2 jet ranged, through a shock
system, from 205 to 235 m/s, 150 to 170 K and 700 to 1000 torr, with estimated uncertainties of ±5.4 m/s, ±3.2 K and ±38 torr
(±2 to 3%, ±2% and ±4–5%, respectively).
Received: 10 December 1996/Accepted: 14 July 1997 相似文献
15.
The spatial-temporal progressions of the leading-edge stagnation, separation and reattachment points, and the state of the
unsteady boundary layer developed on the upper surface of a 6 in. chord NACA 0012 airfoil model, oscillated sinusoidally within
and beyond the static-stall angle, were measured using 140 closely-spaced, multiple hot-film sensors (MHFS). The MHFS measurements
show that (i) the laminar separation point and transition were delayed with increasing α and the reattachment and relaminarization
were promoted with decreasing α, relative to the static case, (ii) the pitchup motion helped to keep the boundary layer attached
to higher angles of attack over that could be obtained statically, (iii) the dynamic stall process was initiated by the turbulent
flow separation in the leading-edge region as well as by the onset of flow reversal in the trailing-edge region, and (iv) the
dynamic stall process was found not to originate with the bursting of a laminar separation bubble, but with a breakdown of
the turbulent boundary layer. The MHFS measurements also show that the flow unsteadiness caused by airfoil motion as well
as by the flow disturbances can be detected simultaneously and nonintrusively. The MHFS characterizations of the unsteady
boundary layers are useful in the study of unsteady separated flowfields generated by rapidly maneuvering aircraft, helicopter
rotor blades, and wing energy machines.
Received: 17 June 1997 / Accepted: 10 December 1997 相似文献
16.
Adrian Postelnicu 《Heat and Mass Transfer》2007,43(6):595-602
The heat and mass transfer characteristics of natural convection about a vertical surface embedded in a saturated porous medium
subjected to a chemical reaction is numerically analyzed, by taking into account the diffusion-thermo (Dufour) and thermal-diffusion
(Soret) effects. The transformed governing equations are solved by a very efficient numerical method, namely, a modified version
of the Keller-box method for ordinary differential equations. The parameters of the problem are Lewis, Dufour and Soret numbers,
sustentation parameter, the order of the chemical reaction n and the chemical reaction parameter γ. Local Nusselt number and local Sherwood number variations and dimensionless concentration
profiles in the boundary layer are presented graphically and in tables for various values of problem parameters and it is
concluded that γ and n play a crucial role in the solution. 相似文献
17.
Noninvasive measurement techniques were developed to obtain the surfactant concentration and the velocity field of a vortex
pair interacting with a contaminated free surface. The optical method of second-harmonic generation (SHG) was utilized to
determine the time-varying concentration of a surfactant at a point on the surface, and the established technique of digital
particle image velocimetry (DPIV) was used for the measurement of the velocity field. The evolution of the initially uniform,
insoluble monolayer along with the vorticity field are described. One of the present limitations is the temporal resolution
of the concentration measurements which is of order 5 Hz. The extension of the SHG technique to high Reynolds number, turbulent
flows is discussed.
Received: 24 January 1996 / Accepted: 17 July 1996 相似文献
18.
An imaging technique that uses backlighting has been developed to measure drop sizes in annular two-phase flows with small
concentrations of drops in the gas phase. Advantages over conventional photography are realized in that data collection and
analysis times are shortened considerably, and consistent unbiased results can be expected. A magnification of 1.9 was used
to measure drops above 50 μm. A drop size distribution was obtained for an air–water system as a superficial gas velocity
of 30 m/s and a liquid flow of 20 g/s. The data are used to substantiate a theory for the rate of deposition.
Received: 6 February 1997/Accepted: 3 February 1998 相似文献
19.
The non-similar solution of an unsteady mixed convection laminar boundary layer flow over a vertical cone in the presence of non-uniform surface mass transfer through slot has been obtained while the axis of cone is inline with the flow. The unsteadiness is caused by the time dependent free stream velocity. The governing boundary layer equations are transformed into a non-dimensional form by a group of non-similar transformations. The resulting coupled non-linear partial differential equations have been solved numerically by the combination of quasi-linearization technique and an implicit finite difference scheme. Numerical computations are performed for different values of the parameters to display the velocity and temperature profiles graphically. Both accelerating and decelerating free stream velocities are considered. Numerical results are reported to display the effects of non-uniform single and double slot suction (injection) on skin friction and heat transfer coefficients at the wall. Further, the effects of Prandtl number, buoyancy and mass transfer (suction or injection) parameters at different stream-wise locations for various times on velocity and temperature profiles, and on skin friction and heat transfer coefficients are also presented in this paper. 相似文献
20.
Particle image velocimetry with optical flow 总被引:4,自引:0,他引:4
An optical Flow technique based on the use of Dynamic Programming has been applied to Particle Image Velocimetry thus yielding
a significant increase in the accuracy and spatial resolution of the velocity field. Results are presented for calibrated
synthetic sequences of images and for sequences of real images taken for a thermally driven flow of water with a freezing
front. The accuracy remains better than 0.5 pixel/frame for tested two-image sequences and 0.2 pixel/frame for four-image
sequences, even with a 10% added noise level and allowing 10% of particles of appear or disappear. A velocity vector is obtained
for every pixel of the image.
Received: 18 July 1997/Accepted: 5 December 1997 相似文献