On high spatial resolution scalar measurement with LIF

Wang, G. R.; Fiedler, H. E.

doi:10.1007/s003489900084

Cited by 16 publications

(9 citation statements)

References 0 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…When a fluorescent dye is continuously irradiated by a laser, the signal will eventually degrade owing to photobleaching and/or thermal blooming effects (i.e. Sahar & Treves 1977;Koochesfahani 1984;Benson et al 1985;Saylor 1995;Crimaldi 1997;Wang & Fiedler 2000). Therefore, upon exiting the laser, the beam was first passed through a high-speed optical chopper (Scitec 310CD).…”

Section: Optical Set-upmentioning

confidence: 99%

Differential diffusion of high-Schmidt-number passive scalars in a turbulent jet

2008

View full text Add to dashboard Cite

The separate evolution, or differential diffusion, of high-Schmidt-number passive scalars in a turbulent jet is studied experimentally. The two scalars under consideration are disodium fluorescein (Sc≡ ν/D= 2000) and sulforhodamine 101 (Sc= 5000). The objectives of the research are twofold: to determine (i) the Reynolds-number-dependence, and (ii) the radial distribution of differential diffusion effects in the self-similar region of the jet. Punctual laser-induced fluorescence (LIF) measurements were obtained 50 jet diameters downstream of the nozzle exit for five Reynolds numbers (Re≡uod/ν = 900, 2100, 4300, 6700 and 10600, whereu0is the jet exit velocity,dis the jet diameter, and ν is the kinematic viscosity) and for radial positions extending from the centreline to the edges of the jet cross-section (0 ≤r/d≤ 7.5). Statistics of the normalized concentration difference,Z, were used to quantify the differential diffusion. The latter were found to decay slowly with increasing Reynolds number, with the root mean square ofZscaling asZrms≡ 〈Z2〉1/2∝Re−0.1, (or alternatively 〈Z2〉 ∝Re−0.2). Regardless of Reynolds number, differential diffusion effects were found to increase away from the centreline. The increase in differential diffusion effects with radial position, along with their increase with decreasing Reynolds number, support the hypothesis of increased differential diffusion at interfaces between the jet and ambient fluids. Power spectral densities ofZwere also studied. These spectra decreased with increasing wavenumber – an observation attributed to the decay of the scalar fluctuations in a turbulent jet. Furthermore, these spectra showed that significant differential diffusion effects persist at scales larger than the Kolmogorov scale, even for moderately high Reynolds numbers.

show abstract

Section: Optical Set-upmentioning

confidence: 99%

Differential diffusion of high-Schmidt-number passive scalars in a turbulent jet

2008

View full text Add to dashboard Cite

show abstract

“…at 550 550-680, max. at 590 [20,92] local temperature increases [16]. Both phenomena should be strictly avoided.…”

Section: Principle Of the Lif Techniquementioning

confidence: 99%

“…Another important aspect which has to be kept in mind is the photobleaching and the thermal blooming effect. Wang and Fiedler described this phenomenon in 2000 although its influence on experimental results has been found earlier, i.e., by Saylor in 1995, who investigated the photobleaching of disodium fluorescein in water . Photobleaching is a phenomenon where the emission light intensity of a laser dye decays with time, due to photodecomposition or collisional quenching.…”

Section: Principle Of the Lif Techniquementioning

confidence: 99%

“…The thermal blooming occurs, since energy of the laser light will be partially converted to emmited light and partially to heat due to the quantum yield of fluorescence and photobleaching. At higher laser intensity the measuring volume will be affected and the local temperature increases . Both phenomena should be strictly avoided.…”

Section: Principle Of the Lif Techniquementioning

confidence: 99%

See 1 more Smart Citation

Laser‐Induced Fluorescence in Multiphase Systems

et al. 2018

View full text Add to dashboard Cite

Nowadays, multiphase flows occur in many different applications in everyday life or industrial context. Consequently, the understanding of transport phenomenolgy between the participating phases is a crucial task of recent and prospective research. When it comes to the optimization of absorption and chemical reaction tasks in process industry, in‐depth knowledge concerning mass transfer is required. The laser‐induced fluorescence (LIF) imaging is therefore a promising optical measurement technique to characterize concentration fields with high spatial and temporal resolution. This review gives an overview of the different fields of research within which LIF measurements are carried out, with focus on gas‐liquid systems. Chances and obstacles of recently publicated results as well as experiences of LIF methods regarding multiphase flows are presented and discussed.

show abstract

“…This indicates that increasing or decreasing the dye concentration C does not affect the first-order photobleaching process, if in the absence of light absorption. Finally, the local fluorescent intensity I f ,local can be calculated accordingly as [25] I f ,local = q f IC (10) with q f being a fluorescence quantum yield factor.…”

Section: Lifpa Photobleaching Modelmentioning

confidence: 99%

Numerical Simulation of the Photobleaching Process in Laser-Induced Fluorescence Photobleaching Anemometer

et al. 2021

View full text Add to dashboard Cite

At present, a novel flow diagnostic technique for micro/nanofluidics velocity measurement—laser-induced fluorescence photobleaching anemometer (LIFPA)—has been developed and successfully applied in broad areas, e.g., electrokinetic turbulence in micromixers and AC electroosmotic flow. Nevertheless, in previous investigations, to qualitatively reveal the dynamics of the photobleaching process of LIFPA, an approximation of uniform laser distribution was applied. This is different from the actual condition where the laser power density distribution is normally Gaussian. In this investigation, we numerically studied the photobleaching process of fluorescent dye in the laser focus region, according to the convection–diffusion reaction equation. The profiles of effective dye concentration and fluorescence were elucidated. The relationship between the commonly used photobleaching time constant obtained by experiments and the photochemical reaction coefficient is revealed. With the established model, we further discuss the effective spatial resolution of LIFPA and study the influence of the detection region of fluorescence on the performance of the LIFPA system. It is found that at sufficiently high excitation laser power density, LIFPA can even achieve a super-resolution that breaks the limit of optical diffraction. We hope the current investigation can reveal the photobleaching process of fluorescent dye under high laser power density illumination, to enhance our understanding of fluorescent dynamics and photochemistry and develop more powerful photobleaching-related flow diagnostic techniques.

show abstract

On high spatial resolution scalar measurement with LIF

Cited by 16 publications

References 0 publications

Differential diffusion of high-Schmidt-number passive scalars in a turbulent jet

Differential diffusion of high-Schmidt-number passive scalars in a turbulent jet

Laser‐Induced Fluorescence in Multiphase Systems

Numerical Simulation of the Photobleaching Process in Laser-Induced Fluorescence Photobleaching Anemometer

Contact Info

Product

Resources

About