Pascal Lemaitre

Real-time global interferometric laser imaging for the droplet sizing (ILIDS) algorithm for airborne research

Our objective was to develop an airborne optical sizemeter for atmospheric water droplet characterization. We chose the ILIDS (interferometric laser imaging for droplet sizing) method. This paper details the acquisition method developed to implement the image processing and the experimental tests performed to validate the method. The purpose is to develop a strategy for real-time data analysis in order to obtain information on droplets size during flight; this work is included in the EUFAR project that is supported by the 7th Framework Program of the European Commission (FP7).

Development of a global rainbow refractometry technique to measure the temperature of spray droplets in a large containment vessel

In order to study the heat and mass transfers between a spray of droplets and the atmosphere in thermal-hydraulics conditions representative of a severe accident in a Pressurized Water Nuclear Reactor, the French Institute for Radioprotection and Nuclear Safety (IRSN) developed the TOSQAN facility. The present paper presents the development and the quantification of an optical diagnostic, global rainbow refractometry, in order to measure falling droplet temperature.

Simultaneous 3D location and size measurement of bubbles and sand particles in a flow using interferometric particle imaging.

We present a system to characterize a triphasic flow in a 3D volume (air bubbles and solid irregular particles in water) using only one CCD sensor. A cylindrical interferometric out-of-focus imaging setup is used to determine simultaneously the 3D position and the size of bubbles and irregular sand particles in a flow. The 3D position of the particles is deduced from the ellipticity of their out-of-focus image. The size of bubbles is deduced from analysis of interference fringes. The characteristics of irregular sand particles are obtained from analysis of their speckle-like pattern. Experiments are confirmed by simulations.

Influence of design and operating parameters of pneumatic concentric nebulizer on micro-flow aerosol characteristics and ICP-MS analytical performances

This paper describes the development of a very simple micro-flow pneumatic ICPMS nebulizing solution based on a commercial glass concentric slurry nebulizer and a fused-silica capillary. It appears as a well-performing, low cost system able to nebulize efficiently at a low liquid flow rate (40000 cps for a 1 ppb 238U solution at 1 μL min−1). Experimentally, it provides a practical set-up for studying the influence of not only operating conditions (liquid and gas flow rates, temperature) but also nebulizer design (nozzle configuration, capillary tip shape, capillary inner diameter). More precisely it allows the study of liquid-capillary-tip to gas-exit stick-out, i.e. recessed position (e 0) in combination with various liquid capillary inner diameters or tip shapes. This investigation brings out several practical results even if the relation between the primary aerosol characteristics (studied by three complementary techniques (PIV, shadowgraphy and ILIDS)) and the ICPMS signal measured on a tertiary aerosol is not easy to establish precisely. These results are systematically compared to the literature data, replacing them in a more global perspective. It highlights the prime importance of the nozzle configuration i.e. stick-out and liquid capillary inner diameter. The stick-out (e) parameter is of crucial importance both for the primary spray homogeneity in terms of droplet velocity distribution and for tertiary signal intensity and stability but shows no influence on the oxide ratio or on the droplet size distribution. This last characteristic may not be the most relevant criterion for low liquid uptake nebulizers, contrary to millilitre flow-rate ones. The authors hypothesize that this may be linked to the evaporation capacity of the nebulising gas largely exceeding the liquid uptake, creating a fundamentally different situation for the two types of nebulizers. This study also displays the interest of using a flat-end capillary instead of a tapered end which is the solution most commonly employed, and it highlights the existence of an optimum nozzle configuration (e > 0) in terms of sensitivity and stability, that is dependent on the capillary inner diameter.

Interferometric out-of-focus imaging of ice particles with overlapping images.

It is shown that the size and relative positions of two irregular rough particles can be analyzed using interferometric out-of-focus imaging despite the overlapping of their out-of-focus images. Simulations are confirmed by experiments done with ice particles generated in a freezing column.

Quasi real-time analysis of mixed-phase clouds using interferometric out-of-focus imaging: development of an algorithm to assess liquid and ice water content

According to changes in aircraft certifications rules, instrumentation has to be developed to alert the flight crews of potential icing conditions. The technique developed needs to measure in real time the amount of ice and liquid water encountered by the plane. Interferometric imaging offers an interesting solution: It is currently used to measure the size of regular droplets, and it can further measure the size of irregular particles from the analysis of their speckle-like out-of-focus images. However, conventional image processing needs to be speeded up to be compatible with the real-time detection of icing conditions. This article presents the development of an optimised algorithm to accelerate image processing. The algorithm proposed is based on the detection of each interferogram with the use of the gradient pair vector method. This method is shown to be 13 times faster than the conventional Hough transform. The algorithm is validated on synthetic images of mixed phase clouds, and finally tested and validated in laboratory conditions. This algorithm should have important applications in the size measurement of droplets and ice particles for aircraft safety, cloud microphysics investigation, and more generally in the real-time analysis of triphasic flows using interferometric particle imaging.

Study of Heat Transfer and Mass Transfer in a Spray for Containment Application: Analysis of the Influence of Spray Temperature at the Injection Point

Abstract During the course of a hypothetical severe accident in a nuclear power plant, spray may be activated in order to reduce static pressure in the containment. The Institut de Radioprotection et de Sûreté Nucléaire (IRSN) has developed the TOSQAN experiment to provide a better understanding of the heat transfer and mass transfer that take place between a spray and the surrounding confined gas in such a situation. This paper studies how the temperature of the spray at the injection point influences the dynamics of a test. To carry out this analysis, we performed two spray tests: spray test 101 (ST101), which served as a reference, and spray test 107 (ST107), which had exactly the same initial and boundary conditions except for the temperature of the spray at the injection point, which varied from 25°C to 58°C. First, we present the entire scenario for ST101 and ST107 and the results of the tests. We then focus our analysis on the intercomparison of the thermal-hydraulic behavior induced by the spray temperature at the injection point and the wall temperature. This intercomparison is divided into two parts: global and local.

SUMP INFLUENCE ON CONTAINMENT THERMAL HYDRAULIC: RESULTS OF THE TOSQAN TESTS

This paper presents the results of the TOSQAN tests performed in the field of the TOSQAN sump program undertaken by the Institut de Radioprotection et de Surete Nucleaire (IRSN). This work is devoted to study the heat and mass transfers induced by the water sump towards the containment atmosphere, for typical accidental thermal hydraulic conditions in PWR.Copyright

Influence of Sump on Containment Thermal Hydraulics: Synthesis of the TOSQAN Tests

During the course of a severe accident in a nuclear power plant, water can be collected in the sump containment through steam condensation on walls, cooling circuit leak, and by spray systems activation. Therefore, the sump can become a place of heat and mass exchanges through water evaporation and steam condensation, which influences the distribution of hydrogen released in containment during nuclear core degradation. The objective of this paper is to present the analysis of semi-analytical experiments on sump interaction between containment atmosphere for typical accidental thermal hydraulic conditions in a pressurized water reactor (PWR). Tests are conducted in the TOSQAN facility developed by the Institut de Radioprotection et de Surete Nucleaire in Saclay. The TOSQAN facility is particularly well adapted to characterize the distribution of gases in a containment vessel. A tests’ grid was defined to investigate the coupled effect of the sump evaporation with wall condensation, for air steam conditions, with noncondensable gases (He, SF6), and for steady and transient states (two depressurization tests).

Study of Aerosol Particle Scavenging by Rain, Experiments and Modelling

The understanding and the anticipation of the environmental fallout in case of severe nuclear accidents with radioactive releases is crucial for the environment. In this study we aim to improve our knowledge on the aerosol particles scavenging, in particular the washout by raindrops with a diameter larger than 1 mm.