Benoit Fond

Bio: Benoit Fond is an academic researcher from Otto-von-Guericke University Magdeburg. The author has contributed to research in topics: Particle image velocimetry & Phosphor. The author has an hindex of 11, co-authored 29 publications receiving 563 citations. Previous affiliations of Benoit Fond include Imperial College London.

High-speed planar thermometry and velocimetry using thermographic phosphor particles

Abstract: Simultaneous gas-phase temperature and velocity imaging using micrometer-size thermographic phosphor particles seeded into the flow is demonstrated at a 3 kHz repetition rate. The velocity field is measured using a standard particle image velocimetry approach, while the temperature is determined from the temperature sensitive phosphorescence emission of the particles following excitation at 355 nm. Since the particles are very small, they rapidly assume the temperature and velocity of the surrounding gas. A single shot temperature precision of better than 5 % was achieved at 500 K. Time-resolved measurements in the wake of a heated cylinder are presented, demonstrating the utility of these imaging diagnostics to observe transient, coupled heat and mass transfer phenomena.

Simultaneous temperature, mixture fraction and velocity imaging in turbulent flows using thermographic phosphor tracer particles

Abstract: This paper presents an optical diagnostic technique based on seeded thermographic phosphor particles, which allows the simultaneous two-dimensional measurement of gas temperature, velocity and mixture fraction in turbulent flows. The particle Mie scattering signal is recorded to determine the velocity using a conventional PIV approach and the phosphorescence emission is detected to determine the tracer temperature using a two-color method. Theoretical models presented in this work show that the temperature of small tracer particles matches the gas temperature. In addition, by seeding phosphorescent particles to one stream and non-luminescent particles to the other stream, the mixture fraction can also be determined using the phosphorescence emission intensity after conditioning for temperature. The experimental technique is described in detail and a suitable phosphor is identified based on spectroscopic investigations. The joint diagnostics are demonstrated by simultaneously measuring temperature, velocity and mixture fraction in a turbulent jet heated up to 700 K. Correlated single shots are presented with a precision of 2 to 5% and an accuracy of 2%.

Thermochromic luminescent nanomaterials based on Mn4+/Tb3+ codoping for temperature imaging with digital cameras

Abstract: A new thermographic nanocrystalline Sr4Al14O25 :Mn4+, Tb3+ phosphor was developed including the optimization of the concentrations of both dopants and of the synthesis conditions. The combination of the thermally quenched luminescence from the Mn4+ ions to the almost temperature independent emission from Tb3+ provides a sensitive luminescent thermometer (SR=2.8%/oC at 150oC) with strong emission colour variability. In addition, a figure of merit for this luminescence thermochromism was proposed, as the relative sensitivities of the x and y CIE coordinates, which for this phosphor reaches at 150°C SR(x)=0.6%/oC and SR(y)=0.4%/oC, respectively. Non-contact thermal imaging was demonstrated with this phosphor using a single consumer digital camera and exploiting the ratio of red (R) and green (G) channels of the RGB images thereby confirming the high applicative potential of Sr4Al14O25 :Mn4+, Tb3+ nanocrystals for thermal sensing and mapping.

Characterisation of the luminescence properties of BAM:Eu 2+ particles as a tracer for thermographic particle image velocimetry

Abstract: Thermographic phosphor particles are seeded into the flow as tracers for simultaneous temperature and velocity measurements in fluids. Several studies using different phosphors as gas-phase tracers have been published in recent years. However, little is known about their emission characteristics when they are dispersed as individual particles in the fluid. In this paper, the luminescence properties of BAM:Eu2+ particles, a phosphor with favourable characteristics (short luminescence lifetime, blue emission spectrum, high quantum efficiency), are thoroughly investigated in the gas phase. Using a recently developed particle-counting tool, the emission intensity per particle is measured over a wide range of conditions, including for various temperatures from 300 to 920 K, in air and in pure nitrogen. The luminescence emission per particle is shown to drop with temperature, but to be insensitive to the seeding density and to the oxygen content over the tested range. Together with a spectroscopic study, and a statistical error analysis, these results are used to predict the temperature precision of the technique under various conditions for different filter combinations and to assess the current upper temperature limit of this phosphor for practical applications. Potential additional sources of uncertainty are also investigated, including cross-dependencies of the measured intensity ratio on the seeding density, excitation fluence and oxygen partial pressure in the gas phase. Only a weak dependence on the laser fluence is observed, while the measured intensity ratio is shown to be insensitive to both seeding density and the oxygen volume fraction. Finally, the saturation behaviour of the phosphorescence emission is examined, through theoretical considerations and measurements performed with different excitation schemes in an attempt to increase signal levels. In conclusion, this paper confirms that BAM:Eu2+ is a very suitable tracer for measurements in turbulent flows up to 900 K.

Particle Image Velocimetry

Abstract: conferencia sobre "Particle Image Velocimetry" de les 13:00-14:00 a la Sala de Juntes de l'FNB impartida pel professor Peter Bueken da l'Antwerp Maritime Acedemy (Belgica)

Whole Field Measurement of Temperature in Water Using Two-Color Laser Induced Fluorescence

Abstract: 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.

Trends in luminescence thermometry

Abstract: Following astonishing growth in the last decade, the field of luminescence thermometry has reached the stage of becoming a mature technology. To achieve that goal, further developments should resolve inherent problems and methodological faults to facilitate its widespread use. This perspective presents recent findings in luminescence thermometry, with the aim of providing a guide for the reader to the paths in which this field is currently directed. Besides the well-known temperature read-out techniques, which are outlined and compared in terms of performance, some recently introduced read-out methods have been discussed in more detail. These include intensity ratio measurements that exploit emissions from excited lanthanide levels with large energy differences, dual-excited and time-resolved single-band ratiometric methods, and phase-angle temperature readouts. The necessity for the extension of theoretical models and a careful re-examination of those currently in use are emphasized. Regarding materials, the focus of this perspective is on dual-activated probes for the luminescence intensity ratio (LIR) and transition-metal-ion-activated phosphors for both lifetime and LIR thermometry. Several particularly important applications of luminescence thermometry are presented. These include temperature measurement in catalysis, in situ temperature mapping for microfluidics, thermal history measurement, thermometry at extremely high temperatures, fast temperature transient measurement, low-pressure measurement via upconversion nanoparticle emission intensity ratios, evaluation of the photothermal chirality of noble metal clusters, and luminescence thermometry using mobile devices. Routes for the development of primary luminescence thermometry are discussed in view of the recent redefinition of the kelvin.