Assessing the accuracy of energy turbulent diffusion dispersion correlation in a porous two-fluid model dedicated to PWR core simulations

International audienceCATHARE is a 2-fluid thermal-hydraulic code, capable of simulating thermal and mechanical phenomena occurring in the primary and secondary circuits of Pressurized Water Reactor under a wide variety of accidental situations. One of the medium-term objectives of system code CATHARE-3 is modeling a PWR core at assembly scale to simulate various accidental situations such as the loss of coolant accident (LOCA) and steam line break accident. This requires the monophasic and two-phase models that adapted to the assembly scale. However, there exists 3D models for the whole core and sub-channel scale models, which have a certain degree of validation. For more macroscopic three-dimensional models, we only have global validations without local measurements, which is necessary for the validations of each closure law's separate effects. The objective of my PhD project is improving the sub-channel scale models and developing the assembly scale models in CATHARE-3 system code with the sub-channel scale simulations and experiments results

Hydrodynamic dispersion within porous biofilms

Many microorganisms live within surface-associated consortia, termed biofilms, that can form intricate porous structures interspersed with a network of fluid channels. In such systems, transport phenomena, including flow and advection, regulate various aspects of cell behavior by controlling nutrient supply, evacuation of waste products, and permeation of antimicrobial agents. This study presents multiscale analysis of solute transport in these porous biofilms. We start our analysis with a channel-scale description of mass transport and use the method of volume averaging to derive a set of homogenized equations at the biofilm-scale in the case where the width of the channels is significantly smaller than the thickness of the biofilm. We show that solute transport may be described via two coupled partial differential equations or telegrapher's equations for the averaged concentrations. These models are particularly relevant for chemicals, such as some antimicrobial agents, that penetrate cell clusters very slowly. In most cases, especially for nutrients, solute penetration is faster, and transport can be described via an advection-dispersion equation. In this simpler case, the effective diffusion is characterized by a second-order tensor whose components depend on (1) the topology of the channels' network; (2) the solute's diffusion coefficients in the fluid and the cell clusters; (3) hydrodynamic dispersion effects; and (4) an additional dispersion term intrinsic to the two-phase configuration. Although solute transport in biofilms is commonly thought to be diffusion dominated, this analysis shows that hydrodynamic dispersion effects may significantly contribute to transport

Compositional and micro-morphological characterisation of red colourants in archaeological textiles from pharaonic Egypt

When the imagination conjures up an image of an Egyptian mummy, it is normally one of a human body wrapped with undyed linen bandages. However, the reality was much more colourful, as shown by the set of red mummy shrouds and textile fragments from Pharaonic Egypt considered in this work. The textiles were subjected to scientific investigation with the main aim of shedding light on the sources of red colour and on the possible reasons for the different levels of colour fading. The red colourants were investigated using various non-invasive and micro-invasive approaches. The results pointed towards the presence of three sources of red colour, which, in increasing order of lightfastness, are safflower (Carthamus tinctorius), madder (Rubia spp.), and red ochre. Micro-morphological observations and elemental analyses also enabled some hypotheses to be formulated regarding the application of these colourants to the textiles. The results not only deepen our knowledge of dyeing technologies in ancient Egypt and shed new light on the function of red shrouds and textiles as part of the funerary practices of Pharaonic Egypt, but are also essential in planning the display and future preservation of these mummies and their associated textiles