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1.
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
2.
Single shot spatially and spectrally resolved laser induced predissociation fluorescence measurements in a shock layer around a cylinder in a pulsed supersonic free stream are presented. Fluoresence signals were produced using the tuned output of an argon fluoride excimer laser to excite a mixture of rovibrational transitions in molecular oxygen. The signals produced along a line inside the shock layer were focussed onto a two dimensional detector coupled to a spectrometer, thus allowing spectral and spatial resolution of the fluoresence. In this way, it was possible to detect two fluoresence signals from two different transitions simultaneously, allowing the determination of vibrational temperatures without the need for calibration. To minimize problems associated with low signal to noise ratios, background subtraction and spatial averaging was required.This article was processed using Springer-Verlag TEX Shock Waves macro package 1.0 and the AMS fonts, developed by the American Mathematical Society. 相似文献
3.
Planar laser induced fluorescence in aqueous flows 总被引:2,自引:0,他引:2
J. P. Crimaldi 《Experiments in fluids》2008,44(6):851-863
Planar laser-induced fluorescence (PLIF) is a non-intrusive technique for measuring scalar concentrations in fluid flows.
A fluorescent dye is used as a scalar proxy, and local fluorescence caused by excitation from a thin laser sheet can be related
to dye concentration. This review covers quantitative PLIF in aqueous flows, with discussions of fluorescence theory, experimental
methods and equipment, image processing and calibration, and applications of the technique. 相似文献
4.
Dual emission laser induced fluorescence for direct planar scalar behavior measurements 总被引:1,自引:0,他引:1
In this paper, a new method of measuring scalar behavior in bulk aqueous fluid flows is presented. Using a simple ratiometric
scheme, laser induced fluorescence from organic dyes can be normalized so that direct measurements of a scalar in the flow
are possible. The technique dual emission laser induced fluorescence (DELIF) relies on normalizing the fluorescence emission
intensity of one dye with the fluorescence emission intensity of a second dye. Since each dye fluoresces at a different wavelength,
one can optically separate the emission of each dye. This paper contains an overview of the basic ratiometric technique for
pH and temperature measurements as well as the spectral properties of nine water soluble dyes. It also covers the three most
significant sources of error in DELIF applications. To demonstrate the technique, steady state turbulent jet mixing and temperature
fields in a thermal plume were quantified. The accuracy was camera limited at under 3% of the fluorescence ratio which corresponds
to 0.1 pH units or 1.8 °C.
Received 7 June 1996/Accepted 17 June 1997 相似文献
5.
Digital holographic interferometry is a hybrid optical-digital technique for determining the phase of an interferogram. This technique improves the accuracy of interferometric measurement of fluid properties and enhances the utility of interferometric flow visualization. Displays of the interferometric phase produce excellent images of weakly refracting two-dimensional flows and can be used to produce integral projection images of three dimensional flows which differ from and complement schlieren and shadowgraph images. The technique is explained herein and examples of its use in both continuous wave and pulsed interferometry are presented.This work was presented in part at the 1985 Optical Society of America Annual Meeting 相似文献
6.
We present a noninvasive technique to measure instantaneously two-dimensional temperature distributions in liquid flows by means of two-color planar laser induced fluorescence (PLIF) of rhodamine B. This technique allows absolute temperature measurements by determining the relative intensities on two adequate spectral bands of the same dye and a reference measurement at a known temperature. Demonstration measurements on a heated turbulent jet injected into a coflow at ambient temperature are presented. The mean temperature field is investigated, as well as the temperature fluctuations. The results are compared to those obtained by means of a usual single-color PLIF technique. 相似文献
7.
D. J. Shlien 《Experiments in fluids》1987,5(5):356-356
Conclusion An inexpensive, yet effective method of generation of a light sheet has been presented. Use of two such lenses at angles to eachother could produce unusual regions of illumination. 相似文献
8.
Temporal sequences of planar laser-induced fluorescence (PLIF) images of several high-speed, transient flowfields created in a reflection-type shock tunnel facility were acquired. In each case, the test gas contained either nitric oxide or the hydroxyl radical, the fluorescent species. The processes of shock reflection from an endwall with a converging nozzle and of underexpanded free jet formation were examined. A comparison was also made between PLIF imaging and shadow photography. The investigation demonstrated some of the capabilities of PLIF imaging diagnostics in complex, transient, hypersonic flowfields, including those with combustion.Nomenclature
A
spontaneous emission rate
-
A
las
cross sectional area of laser sheet
-
B
laser absorption rate
-
C
opt
constant dependent on optical arrangement, collection efficiency, etc.
-
D
nozzle throat diameter
-
E
p
laser pulse energy
-
f
J
Boltzmann fraction of absorbing state
-
g
spectral convolution of laser and absorption lineshapes
-
k
Boltzmann constant
-
M
s
incident shock Mach number
-
N
noise, root-mean-square signal fluctuation
-
P
static pressure
-
P
1
initial pressure of test gas in shock tube
-
P
a
free jet ambient pressure
-
P
s
stagnation pressure
-
Q
electronic quenching rate of excited state
-
S
PLIF signal
-
t
time between shock reflection and image acquisition
-
T
static temperature
-
T
s
stagnation temperature
-
a
mole fraction of absorbing species 相似文献
9.
Planar Laser Induced Fluorescence (PLIF) is used to obtain a series of two-dimensional concentration distributions in large scale (order of 5 m) time-varying thermally stratified flows. Density gradients due to turbulent fluctuations within the image area were found to cause reflection and refraction of the laser light sheet, reducing the usual simplicity of the PLIF method. To compensate for these effects, a variable local attenuation coefficient has been introduced to relate the attenuation of the laser sheet due to the concentration of the fluorescent dye and its spatial gradient. A mathematical algorithm for image restoration has been developed and applied to produce two-dimensional surface temperature mappings using fluorescent dye as an indicator. The algorithm has been verified using a set of temperature probes placed in the flow. It is found that this method provides both powerful flow visualization and adequate non-intrusive concentration measurements for large scale investigations of density stratified flows. 相似文献
10.
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
11.
12.
13.
The characteristics of the critical heat flux (CHF) for downward flow were studied experimentally with an Inconel 600 circular tube test section in a water test loop at low-flow rate (0 200 kg/m2s) and low-pressure (0.1 0.7 MPa) conditions. The attention was given to the effects of upstream conditions—upper plenum and inlet throttling. Two totally different kinds of CHF behaviors were observed. It seems appropriate to interpret them as flooding-type CHF and dryout in annular flow. The CHF in downward flow may vary from extremely unstable flow CHF as low as near the flooding CHF value to stable flow CHF as high as that of upflow, depending on the upstream conditions of the test section. The CHF correlation by Mishima and that by Weber were proposed for the presentation of the lower and upper limits of the CHF for downward flow in a vertical tube at low-flow rate and low-pressure conditions. 相似文献
14.
Mario Alonso Peter J. Kay Phil J. Bowen Robert Gilchrist Steve Sapsford 《Experiments in fluids》2010,48(1):133-142
This paper describes the development of a laser induced fluorescence (LIF) technique to quantify the thickness and spatial
distribution of transient liquid fuel films formed as a result of spray–wall interaction. The LIF technique relies on the
principle that upon excitation by laser radiation the intensity of the fluorescent signal from a tracer like 3-pentanone is
proportional to the film thickness. A binary solution of 10% (v/v) of 3-pentanone in iso-octane is used as a test fuel with
a Nd:YAG laser as the excitation light source (utilising the fourth harmonic at wavelength 266 nm) and an intensified CCD
camera is used to record the results as fluorescent images. The propagation of the excitation laser beam through the optical
piston is carefully controlled by total internal reflection so that only the fuel film is excited and not the airborne droplets
above the film, which had been previously shown to induce significant error. Other known sources of error are also carefully
minimised. Calibrated temporally resolved benchmark results of a transient spray from a gasoline direct injector impinging
on a flat quartz crown under atmospheric conditions are presented, with observations and discussion of the transient development
of the fuel film. The calibrated measurements are consistent with previous studies of this event and demonstrate the applicability
of the technique particularly for appraisal of CFD predictions. The potential utilisation of the technique under typical elevated
ambient conditions is commented upon. 相似文献
15.
Planar laser induced fluorescence technique for measurements of concentration fields in continuous stirred tank reactors 总被引:1,自引:3,他引:1
A new non-intrusive method based on laser sheet visualization and image processing has been developed to measure the instantaneous
concentration fields of a non-reacting fluorescent dye in a continuous stirred tank reactor. The method consists of measuring
the fluorescence intensity of a tracer excited by a thin planar laser sheet and in transforming it into an instantaneous concentration
field of tracer by a calibration procedure. This allows the characterization of mixing in a plane defined as the cross section
of the flow by the laser sheet. Flow visualization images have been recorded on video tape and subsequently digitized. The
relationship between the intensity of the fluorescent light and the grey level of the images has been established. The first
result is the instantaneous field of dye concentration. A contacting parameter between the fluids coming from the two inlet
sources, and emphasizing the average state of the mixing, has been defined and its field has been determined. The field of
temporal variance, which characterizes the segregation of the investigated zone, has also been computed.
Received: 15 December 1995/Accepted: 28 April 1996 相似文献
16.
Caprice Gray Chris B. Rogers Vincent P. Manno Robert D. White 《Experiments in fluids》2011,51(1):281-293
Dual emission laser induced fluorescence (DELIF) is a technique for measuring the instantaneous thin fluid film thickness in dynamic systems. Two fluorophores within the system produce laser induced emissions that are filtered and captured by two cameras. The ratio of the images from these cameras is used to cancel the effect of the laser beam profile on the image intensity. The resultant intensity ratio can be calibrated to a fluid film thickness. The utilization of a 2-dye system when applied to Chemical Mechanical Polishing (CMP) is complicated by the fluorescence of the polymeric polishing pad and the light scattering particles in the polishing slurry. We have developed a model of DELIF for CMP with 1-dye employing the polishing pad as the second fluorophore. While scattering particles in the slurry decrease the overall intensity of the individual images, the contrast in the image ratio increases. Using the 1-dye DELIF system to measure thin slurry films, our model results indicate that a cubic calibration may be needed. However, experimental results suggest a linear calibration is achieved for slurry films between 0 and 133???m thick with scattering coefficients as high as 8.66?mm?1 at a wavelength equal to 410?nm. 相似文献
17.
A first application of encapsulated thermochromic liquid crystals (TLCs) for visualizing temperature fields in pressurized
liquids was studied experimentally. By means of a tempered high-pressure optical cell, investigations were performed in a
wide temperature range and at pressures up to 7000 bar. The measured calibration curves of isochromes in the pressure/temperature
domain as well as photographically documented temperature fields at high pressure are presented and discussed. The results
found illustrate that TLCs provide an efficient instrument for investigating thermofluiddynamical processes even at high pressure.
Received: 13 February 1998/Accepted: 9 December 1999 相似文献
18.
Calibrated multichannel electronic interferometry, a new technique for quantitative flow visualization of transient phenomena, is discussed. This technique uses an interferometer combined with diffraction gratings to generate three phase shifted interferograms simultaneously which are used to perform multichannel phase shifting. The optical system is calibrated with no phase object present using standard piezoelectric phase shifting, and this calibration information is stored as an electro-optic hologram. The calibration information is used along with the three phase-shifted interferograms that exist with a phase object present to perform time-resolved phase shifting. Examples using natural convection and separated flows are presented. 相似文献
19.
The paper describes a flow visualization technique (direct injection method) used in low-speed wind-tunnel studies. Mixture of titanium tetrachloride and carbon tetrachloride is used to produce closely spaced parallel streaklines of white smoke of long duration. The technique is described in detail and representative photographs of various flow patterns are presented. 相似文献
20.
Mark F. Reeder Jim W. Crafton Jordi Estevadeordal Joseph DeLapp Charles McNiel Don Peltier Tina Reynolds 《Experiments in fluids》2010,48(5):889-900
Flow visualization, particle image velocimetry (PIV), and laser Doppler velocimetry (LDV) are among the most useful tools
available for experimental aerodynamics studies. Implementation of these techniques, however, requires that seed material
be introduced into the flow. The undesirable qualities of the seeding material often prevent the use of flow visualization
and velocimetry techniques in many test environments. This is particularly true for large-scale, closed-circuit tunnels where
facility operators must weigh the risks of facility contamination, sensor damage, and safety concerns that might result from
the introduction of seed particles. Identification of a practical clean seeding material that minimizes or eliminates these
concerns would enable flow visualization and velocimetry techniques to be deployed in these facilities. Here, we demonstrate
two seeding systems that have the potential to provide such a solution. The first system is a new concept which uses liquid
carbon dioxide that can be made to form discrete particles as it expands from a high-pressure tank. PIV measurements are demonstrated
in several flows, including supersonic and subsonic tunnels, using these residue-free seed particles. The second system utilizes
a combination of steam and liquid nitrogen to produce an aerosol or fog that serves as flow seeding. Water- or steam-based
seeding has been previously demonstrated for flow visualization in subsonic tunnels; here however, we utilize this seed material
for PIV and LDV measurements as well as for flow visualization in a large supersonic tunnel. 相似文献