Low-cost LED system for fluorescent dye detection

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On the numerical and experimental study of spray cooling

International audienceThe spraying of an impinging jet is an effective way to cool heated surfaces. The objective of this study is to develop a numerical model to predict the heat transfer with phase change between a hot plate surface and a two-phase impinging jet. Different twophase modeling approaches (Lagrangian and Eulerian methods) are compared. The influence of the spray nozzle operating conditions and of the distance between the nozzle exit and the surface impact is analyzed. The numerical results are compared with measurements obtained on an experimental test bench. The confrontation numerical/experimental is carried out by comparing the distribution of temperature atthe surface of the plate and the heat transfer coefficient. This comparison shows that it is the Eulerian model which seems most capable to take into account the evaporation of the droplets in contact with the heated plate. However, the simulation performed with this model show a strong dependence of the results to the turbulence model used

Numerical and experimental study of spray cooling of a heated metal surface

International audienceThe spraying of an impinging jet is an effective way to cool heated surfaces. The objective of this study is to develop a numerical model to predict the heat transfer with phase change between a hot plate surface and a two-phase impinging jet. Different two-phase modeling approaches (Lagrangian and Eulerian methods) are compared. The influence of the spray nozzle operating conditions (pressure, flow rate, droplets size) and of the distance between the nozzle exit and the surface impact is analyzed. The numerical results are compared with measurements obtained on an experimental test bench. The confrontation numerical/experimental is carried out by comparing the distribution of temperature at the surface of the plate and the heat transfer coefficient. This comparison shows that it is the Eulerian model which seems most capable to take into account the evaporation of the droplets in contact with the heated plate and consequently, which gives results more in agreement with the experiments. However, the simulation performed with this model show a strong dependence of the results to the turbulence model used

Development and testing of a pressure probe for centerline static pressure measurement in supersonic nozzles and ejectors

International audienceThis work describes the development and testing of a system for measuring static pressure along the axis of supersonic flow devices such as convergent–divergent nozzles or ejectors. The pressure probe consists of a capillary tube positioned at the ejector centerline. A hole is perforated perpendicularly on the wall of the thin tube to capture and deport the static pressure measurement to a piezoelectric sensor located at one extremity of the tube outside the ejector. The measurements obtained are compared with numerical results from computational fluid dynamics simulations and wall pressure measurements. The first tests demonstrate the good capability of the pressure probe to detect shocks occurring in the flow and to provide continuous axial distributions of the static pressure

Visualization of flow instabilities in supersonic ejectors using Large Eddy Simulation

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CFD Design Study of a Pressure Probe for Centerline Static Pressure Measurement in Supersonic Ejectors

International audienceThe measurement of the static pressure of the flow inside a supersonic ejector can be achieved by using a thin tube with a radially drilled hole to capture the flow pressure, and which is inserted along the ejector axis. This paper presents a numerical study by CFD permitting to predict the disturbances generated by the presence of the probe in the ejector. Also this study allows guiding the design of the probe, in particular of the capillary tube diameter for the least disturbed measurement. A probe prototype has been built and tested on an ejector test bench

Flow visualization in supersonic ejectors using laser tomography techniques

International audienceThis paper presents flow imaging techniques developed for investigating flow in ejectors. These visualization techniques use the laser sheet method but differ from each other by the kind of the illumination source, the polarization direction of the incident light and thetype of the scattering tracers. Each of these methods enables the visualization of specific phenomena (shock structure, flow instabilities, mixing process). Although the flow visualizations are primarily qualitative, they allow the determination of the flow regime, the measurement of the non-mixing length, can indicate suggestions for the design of ejectors and provide the possibility to validate numerical simulations

Flow Velocity Investigation by Particle Image Velocimetry in Supersonic Air Ejector

International audienceEjectors are devices usually made of two convergent-divergent coaxial nozzles which are used to convert pressure energy into kinetic energy. These devices involve very complex phenomena which strongly affect their performance. Flow visualization methods are often used to provide precious information as for the nature of the flow within the ejectors and the comprehension of the physical phenomena encountered. Unfortunately, the visualization methods used successfully until now in these systems are primarily qualitative techniques. Some attempts at quantitative flow visualization by Particle Image Velocimetry have been carried out in quite specific applications but with mitigated results due to the complicated conditions of investigation. The objective of this paper is to present an attempt at PIV measurements in a supersonic air ejector. Several ejector operating conditions and flow seeding methods are considered. The velocity fields obtained are compared with CFD simulations of the flow and allow the rigorous validation of numerical models

Flow velocity investigation by Particle Image Velocimetry measurements in a supersonic air ejector

International audienceEjectors are devices usually made of two convergent/divergent coaxial nozzles which are used to convert pressure energy into kinetic energy. These devices involve very complex phenomena which strongly affect their performance. Flow visualization methods are often used to provide precious information as for the nature of the flow within the ejectors and the comprehension of the physical phenomena encountered. Unfortunately, the visualization methods used successfully until now in these systems are primarily qualitative techniques. Some attempts at quantitative flow visualization by Particle Image Velocimetry have been carried out in quite specific applications but with mitigated results due to the complicated conditions of investigation. The objective of this paper is to present an attempt at PIV measurements in a supersonic air ejector. Several ejector operating conditions and flow seeding methods are taken into consideration. The velocity fields obtained are compared with CFD simulations of the flow and allow the rigorous validation of numerical models

On the Use of Laser Tomography Techniques for Validating CFD Simulations of the Flow in Supersonic Ejectors

International audienceThis paper reviews some possibilities offered by several flow visualization methods to validate numerical simulations of the flow in supersonic air ejectors. The visualizations techniques are all based on the laser sheet method but differ from each other by the kind of the illumination source, the polarization direction of the incident light and the type of the scattering tracers. Each of these methods enables the visualization of specific flow phenomena (shock structure, condensation and mixing processes, flow instabilities). The experimental flow visualizations obtained using these methods are compared with numerical flow visualizations and are proven very effective to help in the validation of CFD simulations