LIF Technique Research Articles

Laser spectroscopy of magnetic splitting of Pr I levels in the presence of saturation effects

Laser spectroscopy is a very precise tool in determining atomic structure data. However, in the case of complex spectra, when the individual components of the spectra cannot be separated, precise analysis is hindered by the appearing saturation effect. Sometimes this effect is so large that the spectrum simulation does not provide precise results. In the present work, we present the analysis of the Zeeman spectra of seven praseodymium lines in the range of 566–652 nm, which were recorded using the LIF technique in the presence of the saturation effect. To analyze these spectra, we used a specially dedicated computer program, which allowed for very accurate matching of the simulated spectrum to the recorded experimental shape. As a result of the conducted research, we determined 14 Lande factor values, 3 of which are new.Graphic

Delineation and detection of breast cancer using novel label-free fluorescence

BackgroundAccurate diagnosis of breast cancer (BC) plays a crucial role in clinical pathology analysis and ensuring precise surgical margins to prevent recurrence.MethodsLaser-induced fluorescence (LIF) technology offers high sensitivity to tissue biochemistry, making it a potential tool for noninvasive BC identification. In this study, we utilized hyperspectral (HS) imaging data of stimulated BC specimens to detect malignancies based on altered fluorescence characteristics compared to normal tissue. Initially, we employed a HS camera and broadband spectrum light to assess the absorbance of BC samples. Notably, significant absorbance differences were observed in the 440–460 nm wavelength range. Subsequently, we developed a specialized LIF system for BC detection, utilizing a low-power blue laser source at 450 nm wavelength for ten BC samples.ResultsOur findings revealed that the fluorescence distribution of breast specimens, which carries molecular-scale structural information, serves as an effective marker for identifying breast tumors. Specifically, the emission at 561 nm exhibited the greatest variation in fluorescence signal intensity for both tumor and normal tissue, serving as an optical predictive biomarker. To enhance BC identification, we propose an advanced image classification technique that combines image segmentation using contour mapping and K-means clustering (K-mc, K = 8) for HS emission image data analysis.ConclusionsThis exploratory work presents a potential avenue for improving "in-vivo" disease characterization using optical technology, specifically our LIF technique combined with the advanced K-mc approach, facilitating early tumor diagnosis in BC.

Experimental Investigation of Mechanisms of Droplet Entrainment in Annular Gas-Liquid Flows: A Review

Entrainment of liquid from the film surface by high-velocity gas stream strongly affects mass, momentum and heat transfer in annular flow. The construction of basic assumptions for simplified physical models of the flow, as well as validation of numerical models, requires detailed experimental investigation of droplet entrainment process and the preceding stages of film surface evolution. The present paper analyzes the achievements and perspectives of application of various experimental approaches to qualitative and quantitative characterization of droplet entrainment. Optical visualization in at least two planes simultaneously may provide enough information on transitional liquid structures and detaching droplets, given that the side-view image is not obscured by the wall film. A planar LIF technique is not suitable for this purpose, since real objects are hidden by curved agitated interface and replaced by optical artifacts. To characterize the waves evolving into the transitional liquid structures, film thickness measurements in the plane of the wall are necessary. Such measurements can be achieved by intensity-based optical techniques, such as Brightness-Based LIF, near-infrared or X-ray attenuation techniques, combined with the side-view observations.

Implementation of a Single-Shot Lif Technique for 2-D Imaging of Metastable Nitrogen Molecules in a Discharge Afterglow at Sub-Atmospheric Pressures

Implementation of a Single-Shot Lif Technique for 2-D Imaging of Metastable Nitrogen Molecules in a Discharge Afterglow at Sub-Atmospheric Pressures

Laser induced fluorescence spectroscopy for detection of Aflatoxin B1 contamination in peanut oil

The Aflatoxin B1 (AFB1) contamination in peanut oil is harmful and widespread. In this study, a laser induced fluorescence spectroscopy (LIF) system was developed for rapid and non-invasive screening of four varieties of peanut oils contaminated with different levels of AFB1. Discriminant analysis was conducted to classify the four varieties of peanut oils into acceptable (AFB1 < 20 μg kg−1) and contaminated (AFB1 ≥ 20 μg kg−1) levels. The results of single-step modelling, which directly classify the whole 540 peanut oils into acceptable and contaminated levels, could achieve an accuracy of 95% and 93% for calibration and validation sets respectively. Considering the fluorescence spectra could easily be influenced by the difference of physicochemical properties of different varieties of peanut oils, two-steps modelling method was conducted. In the first step, the total 540 peanut oils were classified into four varieties with all accuracy of 100% based on 600–800 nm, by using LDA algorithm. In the second step, the AFB1 contamination levels of each variety were discriminated. The classification accuracy was increased by at least 5% by conducting two-steps modelling. The results of quantitative analysis showed that for single variety, PLSR based on 400–600 nm could achieve accurate quantitative prediction. The feasibility of LIF technique for the rapid and nondestructive detection of AFB1 contamination in different varieties of edible oils was proved in this study. Further research will focus on the detection of naturally infected oils.

Measuring temperature of emulsion and immiscible two-component drops until micro-explosion using two-color LIF

In this research, we measure the temperatures of the non-combustible component (water) in a fuel droplet by 2-Color LIF before its micro-explosive fragmentation. We use two types of droplets based on water and tetradecane: a two-component immiscible droplet with water in the core and tetradecane as the envelope; a pre-mix emulsion. In both cases, the relative volume fraction of water in a droplet is 9%, and that of the combustible component (tetradecane) is 91%. To provide the micro-explosive dispersion of droplets, we use a scheme with the conductive heating in the range of 250 °C to 550 °C. Using the high-speed 2-Color LIF technique, we observe the coalescence of water micro-droplets in emulsion droplets and intense disruption of the water core in a two-component droplet when heated. The temperature in two zones are measured. The temperature difference may range from 1 °C to 10 °C. In the puffing regime, the droplet temperature is 1–3 °C higher than in the micro-explosion regime at the same temperatures of the heated metal substrate surface. Within a certain interval of the heating time, the temperatures of water in a two-component droplet and in an emulsion droplet become comparable.

Estimation of the flows mixing efficiency inside T-micromixer with an external perturbation for low Reynolds numbers

The flow pattern regimes and mixing quantities in case of an external perturbation for low Reynolds numbers in a T-shape microchannel were studied experimentally using the LIF technique. Formation of a hydrodynamic wave travelling along the outlet channel for the stratified regime was discovered. The wave amplitude is 0.057Wout. The wavelength corresponding to distance between two nearest pits is 3.86Dh. The change of mixing efficiency between undisturbed and perturbated flows in each of the considered sections is less than 6%. However, the arising of wave causes a decrease in the distance at which the flows are completely mixed.

Investigation of the perturbation flow in a T-microchannel using the LIF technique

Investigation of the perturbation flow in a T-microchannel using the LIF technique

Ambient Tracer-LIF for 2-D quantitative measurement of fuel concentration in gas jets

A novel ambient tracer LIF technique with addition of tracer into ambient gas is proposed in this study to quantitatively measure the two dimensional (2-D) fuel concentration distribution in high-pressure gas jets. Firstly, the fundamental principle of the ambient tracer-LIF technique is described, and the equation of fuel concentration in a jet is deduced from the ambient fluorescence intensity. In the ambient tracer-LIF technique, the on-site calibration can be performed, and much more degrees of freedom in selection of tracers or target fuels can be achieved in principle. Then, the experiments are carried out with the high pressure gas injected into the environment doped with acetone in an optical accessible constant volume vessel. The fluorescence in the ambient is induced by using the 266 nm laser, and is recorded by the ICCD camera. The dedicated image processing is implemented to reduce the uncertainty and obtain the quantitative fuel concentration distribution in the jet. The uncertainties of the measurement results are evaluated, including both the systematic and random errors. The uncertainty propagation analysis shows that the measurement uncertainty increases with the local fuel concentration decreasing, and at the boundary regions of the jet, where the mixture is over lean, the relative uncertainty goes up to 26%. Finally, the temporal variations of the fuel concentration distribution in the gas jet are presented, and the effects of injection pressure are discussed. These results are believed to be valuable for development of numerical models and combustion system designs.

Convective mixing of miscible liquids in a rotor-stator spinning disk reactor

Convective mixing of two miscible liquids injected into a rotor-stator spinning disk reactor (RS-SDR) has been studied using an LIF technique and CFD simulations. The fluids are ammonia water and fluorescein ammonia water solutions. The RS-SDR has a rotor 100 mm in diameter and a thin circular cavity 0.10–0.15 mm in height between the rotor and stator. Laminar flow conditions for rotation speeds up to 120 rpm and total flow rates up to 8 mL/min are considered. The fluorescein solution is injected from the second off-center hole into the cavity filled with the ammonia water supplied from the central hole. The LIF technique visualizes a spiral streak pattern formed downstream of the second injection hole. This streak pattern is analyzed to calculate the local mixedness of the two fluids. It is determined that the mixedness increases for lower flow rates, while it is less sensitive to rotation speed and cavity height. The CFD simulations indicate that the spiral streak pattern is deformed and stretched in the radial direction to form a densely layered structure of the two fluids. The development of the mixedness along the streak pattern is correlated well with Reinlet/Recavity, where Reinlet and Recavity are the Reynolds numbers for the injected flow and the azimuthal flow in the cavity, respectively. This Reynolds number ratio is shown to be related to the Rossby number and the position and radius of the second injection hole. The proposed correlation is based on a linear combination of injection mixing and rotation mixing. The mixedness decreases with Reinlet/Recavity because the injection mixing decreases with Reinlet while the rotation mixing increases with Recavity.

Dual emission LIF technique for pH and concentration field measurement around a rising bubble

Mass transfer plays an important role in chemical engineering applications involving multiphase systems. Several techniques have been developed in the field to measure the global mass concentration in multiphase chemical reactors. However, because of the complexity of multiphase processes, only few techniques are able to provide local and quantitative information. In this study a dual-emission Laser Induced Fluorescent technique (LIF) has been developed to locally measure the mass transfer of a rising CO2 bubble in a quiescent fluid. Details of the pH field with an overall precision of ±0.04 pH units, dissolved CO2 concentration, and the mass transfer evolution in the bubble wake can now be measured quantitatively. It is capable to provide quantitative comparison with simulation results and as such experimental validation of multiphase CFD models.

Investigation of mixture formation in a diesel spray by tracer-based laser-induced fluorescence using 1-methylnaphthalene

The paper presents a proof-of-principle study for the simultaneous imaging of temperature and fuel partial density in a realistic diesel spray using tracer-based planar laser-induced fluorescence (Tracer-PLIF). The fluorescence of 1-methylnaphthalene (1-MN) is characterized in a flow cell with respect to temperature and pressure in nitrogen atmosphere at IC engine conditions with excitation at 266nm. The strong spectral red-shift of 1-MN with increasing temperature is used for two-color-LIF. The fuel partial density is determined with only one detection channel. This technique is further applied for investigation of temperature and fuel partial density in a diesel spray studied at 5MPa and 800K in an injection chamber. Averaged images are presented for a pilot injection revealing a maximum temperature difference between fuel jet and ambience of about 150K with a maximum fuel partial density of about 220g/m3. Between 1300 and 1700µs after visible start of injection, the mixing temperature increases by up to 50K and the fuel partial density decreases by about 20g/m3 because of gas entrainment. The suitability of the LIF technique for single-shot measurements is further demonstrated by studying the cyclic spray variations, which allows for a detailed understanding of mixture formation in IC engine combustion. This enhanced tracer-based LIF-technique for the first time allows for a simultaneous quantification of temperature and fuel partial density at elevated temperatures, which are highly relevant for diesel engines.

Flow visualization and mixing quantification in a rod bundle using laser induced fluorescence

Laser induced fluorescence technique (LIF) was applied to visualize and quantitatively analyze fluid mixing in a fuel rod bundle geometry. A test facility has been designed and constructed at Harbin Engineering University (HEU) utilizing the matching index of refraction (MIR) approach. Single-phase experiments on the fluid mixing between subchannels were performed. Fluorescent dye tracer Rhodamine B (RhB) was injected in the sub-channels in the upstream of a spacer grid to visualize the fluid mixing process. Laser sheet was formed by optics system to emit the fluorescence, and a high-speed camera was used to record the fluorescence information to reconstitute the concentration distribution. The concentration contour maps were analyzed to illuminate the fluid mixing phenomenon in the rod bundle, and the influence of spacer grid was explored in detail. In addition, the coefficient of variation (COV) analysis was conducted to quantify the fluid mixing, and the phenomenon difference between the injection positions was investigated. The analysis results, which were in accordance with the previous studies, indicate that LIF technique is applicable in the study of flow inside rod bundle geometry. The whole-field measurement technique developed in this study is expected to provide a new insight on the research of flow inside fuel rod bundle geometry, which should be useful in the evaluation of CFD codes and spacer grid performance.

Isomer discrimination of PAHs formed in sooting flames by jet-cooled laser-induced fluorescence: application to the measurement of pyrene and fluoranthene

Jet-cooled laser-induced fluorescence is a spectroscopic method, specifically developed for the study of PAHs formed in flames. This technique has already been used to measure different aromatic species in sooting low-pressure methane flames such as benzene, naphthalene, and pyrene. The use of the LIF technique to excite PAHs drastically cooled down inside a supersonic jet offers the possibility to get selective and quantitative profiles of PAHs sampled from sooting flames. In this paper, we demonstrate the ability of this experimental method to separate the contribution of two mass isomers generated in sooting flames which are the pyrene and the fluoranthene. The selectivity of the method is demonstrated by studying the spectral properties of these species. The method is then applied to the measurement of both these species in two sooting flames with different equivalence ratios and stabilized at 200 torr (26.65 kPa). The sensitivity of the technique has been found to reach a few ppb in the case of fluoranthene measurements.

Time-resolved measurement of concentration fluctuations in a confined bubbly flow by LIF

The present work investigates the mixing of a low-diffusivity dye in a swarm of bubbles at high Reynolds number confined in a Hele-Shaw cell for gas volume fractions ranging from 1.4 to 5.4%. A patch of a fluorescent dye is injected within the swarm and, during its mixing, its concentration is measured at a given location in an observation volume of 4.5 mm2 by means of Laser Induced Fluorescence at a frequency of 250 Hz. A spectrometer is used to analyse the light issued from the observation volume and to distinguish the fluoresced light from other light sources. Simultaneously, the bubble distribution around the observation volume is imaged with a high speed camera synchronised with the spectrometer in order to assess the LIF technique in bubbly flow. Thanks to the good time resolution, rapid and intense concentration fluctuations corresponding to dye patches passing through the observation volume are recorded and are superimposed to a slow global evolution. This slow global evolution shows first an increase of the concentration and then an exponential decrease due to the mixing by bubble-induced agitation. This exponential decay, which is incompatible with a diffusion process, is consistent with the transport by dye capture in bubbles wakes that are quickly dampened by the shear-stress at the walls. The one-point statistics of the concentration fluctuations (probability density function and spectrum) also point out that mixing in a confined bubbly flow is intermittent and convective.

超解像度LIF法を用いた血管内皮細胞表面近傍の物質濃度分布計測

超解像度LIF法を用いた血管内皮細胞表面近傍の物質濃度分布計測

Single-shot volumetric laser induced fluorescence (VLIF) measurements in turbulent flows seeded with iodine.

This work reports the experimental demonstration of single-shot visualization of turbulent flows in all three spatial dimensions (3D) based on volumetric laser induced fluorescence (VLIF). The measurements were performed based on the LIF signal of iodine (I2) vapor seeded in the flow. In contrast to established planar LIF (PLIF) technique, the VLIF technique excited the seeded I2 vapor volumetrically by a thick laser slab. The volumetric LIF signals emitted were then simultaneously collected by a total of five cameras from five different orientations, based on which a 3D tomographic reconstruction was performed to obtain the 3D distribution of the I2 vapor in the target flow. Single-shot measurements (with a measurement duration of a few ns) were demonstrated in a 50 mm × 50 mm × 50 mm volume with a nominal spatial resolution of 0.42 mm and an actual resolution of ~0.71 mm in all three dimensions (corresponding to a total of 120 × 120 × 120 voxels).

Simultaneous velocity measurements and the coupling effect of the liquid and gas phases in slug flow using PIV–LIF technique

The analysis of a two-phase slug flow is of immense importance due to its vast applications in many industrial problems. A number of experimental and analytical studies have been carried out to study this complex and unwanted phenomenon. Mostly, these studies were limited to the liquid phase and to the statistical parameters and formation mechanism. So far, no attempt has been made to study the phase interaction and coupling effects of both phases simultaneously, which is more important in understanding this complex flow behavior. This kind of study requires the instantaneous velocity fields of both phases simultaneously. Therefore, in this study a PIV–LIF technique has been applied to study two-phase (liquid–gas) slug flow in a laboratory facility. Water and gas were considered as working fluids, and slug flow was generated in a nearly horizontal pipe with an inclination of 1.16° to consider the terrain slugging mechanism. Liquid and gas phases were seeded simultaneously with fluorescent and titanium dioxide tracer particles, respectively. Two CCD cameras installed with low pass and band pass filters were used to capture images for separate phases. Instantaneous velocity field for both liquid and gas phases was measured simultaneously. To extract the coherent structures and for the analysis of turbulence in liquid and gas phase, the proper orthogonal decomposition (POD) analysis technique was applied to the velocity fields. Large energy containing modes were successfully revealed by POD. The energy distribution of spatial modes for both phases was also measured and compared.

Experimental study and modelling of NOx formation in high pressure counter-flow premixed CH4/air flames

Nitric oxide (NO) is an atmospheric pollutant responsible for the destruction of the ozone layer and the creation of photochemical smog. As a result, NOx emissions from combustion sources are regulated in most industrialised countries. The need to control NOx emissions while also promoting more efficient use of fossil energy resources requires a better understanding of combustion processes, especially the chemical kinetics of NOx formation. NO formation in high-pressure flames is a research area of great practical interest as high pressure exists in practically all power-generation and propulsion engines and it is known that pressure influences the combustion chemistry. In the present work, NO mole fraction profiles were measured by Laser Induced Fluorescence in laminar high pressure (up to 0.7MPa) counter-flow lean CH4/air (E.R.=0.7) flames. Inherent problems linked to the application of the NO LIF technique in high pressure environment were addressed. The experimental NO profiles were then compared with modelling using the OPPDIF code and the three detailed kinetic mechanisms: the GDFkin®3.0_NCN mechanism developed by Lamoureux et al. and the two mechanisms from the Gas Research Institute: GRImech 2.11 and GRImech 3.0. A kinetic analysis based on rate of production/consumption analyses was performed to better understand the differences between the three mechanisms. Finally, the GRImech3.0 mechanism was modified with three updated prompt-NO submechanisms proposed in the literature and the consequences on the N-containing species mole fractions predictions are discussed.

On the behaviour of thin liquid layers at curved solid edges

AbstractThe knowledge of the behaviour of thin liquid layers on solid surfaces is of fundamental interest as far as basic research and applications like technical covering or lubrication processes are concerned. The subject is currently of increasing importance, particularly due to stronger requirements of thin liquid layer functionalities. We therefore studied the development of the liquid layer thickness distribution field as well as the liquid layer disturbance propagation on a plane solid surface in the vicinity of a curved solid edge experimentally using LIF technique. The investigation focusses on the influence of the initial layer thickness as well as on liquid properties like viscosity and surface tension on the liquid film behaviour, especially close to solid edges. Selected experimental results are shown highlighting relevant quantities with respect to disturbance propagation and validation. (© 2014 Wiley‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)