Philippe Géoris

Investigation of thermocapillary convection in a three-liquid-layer system

We present the first experimental results on Marangoni-Benard instability in a symmetrical three-layer system. A pure thermocapillary phenomenon has been observed by performing the experiment in a microgravity environment where buoyancy forces can be neglected. This configuration enables the hydrodynamic stability of two identical liquid-liquid interfaces subjected to a normal gradient of temperature to be studied. The flow is driven by one interface only and obeys the criterion based on the heat diffusivity ratio proposed by Scriven & Sternling and Smith. The measured critical temperature difference for the onset of convection is compared to the value obtained from two-dimensional numerical simulations. The results of the simulations are in reasonable agreement with the velocimetry and the thermal experimental data for moderate supercriticality. Numerically and experimentally, the convective pattern exhibits a transition between different convective regimes for similar temperature gradients. Their common detailed features are discussed

Oscillatory instability in multilayer systems

The paper presents the space experimental results on Marangoni–Benard instability in a real symmetric three-layer system with close values of thermal diffusivities of fluids. For the first time a pure thermocapillary phenomenon has been experimentally observed under microgravity conditions where buoyancy forces can be neglected. The experimental results confirm the existence of theoretically predicted oscillatory instability, essentially connected with the interaction of the interfaces. Nonlinear regimes of the oscillatory convection are investigated by means of the finite-difference method.

Nonlinear Marangoni oscillations in multilayer systems

Nonlinear regimes of Marangoni convection in a real symmetric three-layer system with close values of thermal diffusivities of fluids are investigated. The predictions of the linear stability theory and experiments concerning the appearance of oscillations, are justified. The transitions between different oscillatory flow regimes have been studied.

Water Conditioning Assembly for Hermes ECLSS

This paper presents results of new development work carried out in the context of the Water Conditioning Assembly (WCA) which is part of the Liquid Management Section (LMS) of the Hermes Environmental Control and Life Support Subsystem (ECLSS) (see ref [1] and [2]). Its task is to condition and monitor the quality of highly pure water which has been produced in two fuel-cell stacks by the oxidation of hydrogen. This water will be used for different cooling elements (e.g. water evaporator, water sublimator) and as potable water for drinking and food purposes. The assembly consists mainly of: - a hydrogen separator, providing for removal of dissolved and gaseous residual hydrogen from the fuel-cell water. The passive method of gettering the hydrogen (H 2) in a palladium (Pd) matrix at ambient temperature has been used. - a monitoring and measurement device, measuring the contaminants concentration of the water by means of an electrical conductivity meter joined with a temperature sensor, placed downstream of the H2-separator. - a water disinfection device using iodine. - a gas trap, based on diffusion through a filter, avoiding the blockage of the H2 separator, and placed upstream of that device. This paper presents the selected design concepts of the main constituents. Based on these concepts breadboard models of the H 2 separator and of the water quality monitoring device are described. The results of several test series, namely for: - functional efficiency - hydraulics - matrix expansion - contamination by KOH - influence of temperature - relation between conductivity and pH value are presented. The conclusions and the analysis for further development work are then explained.