Michel Gradeck

two-phase gas-liquid flow in horizontal corrugated channels

Abstract Experiments have been carried out for adiabatic concurrent gas–liquid flow of nitrogen and water through two corrugated test sections. This study examines flow patterns as the gas fluxes are increased. At low gas fluxes two main patterns have been observed: stratified flow for low liquid fluxes and bubble flow for greater ones. The mean wall shear stress of the two-phase flow has been measured with the electrochemical method (polarography); its analysis reveals the flow structure modification from monophasic to two-phase flow.

Inverse Heat Conduction Applied to the Measurement of Heat Fluxes on a Rotating Cylinder: Comparison Between an Analytical and a Numerical Technique

A method using either a one-dimensional analytical or a two-dimensional numerical inverse technique is developed for measurement of local heat fluxes at the surface of a hot rotating cylinder submitted to the impingement of a subcooled water jet. The direct model calculates the temperature field inside the cylinder that is submitted to a given nonuniform and time dependent heat flux on its outer surface and to a uniform surface heat source on an inner radius. In order to validate the algorithms, simulated temperature measurements inside the cylinder are processed and used by the two inverse techniques to estimate the wall heat flux. As the problem is improperly posed, regularization methods have been introduced into the analytical and numerical inverse algorithms. The numerical results obtained using the analytical technique compare well with the results obtained using the numerical algorithm, showing a good stable estimation of the available test solutions. Furthermore, real experimental data are used for the estimation, and local boiling curves are plotted and discussed.

Semi-analytical inverse heat conduction on a rotating cylinder with Laplace and Fourier transforms

This work aims to verify the feasibility of the estimation of heat fluxes during the cooling of a rotating cylinder by an impinging jet. A semi-analytical method has been developed for this two-dimensional inverse heat conduction problem (IHCP) using Laplace and Fourier transforms technique. The simulations of inversion for two representative test cases show that the estimated surface heat flux is not biased and can therefore be reconstructed.

Cooling of a Rotating Cylinder by a Subcooled Planar Jet - Influence of the Surface Velocity on Boiling Regime

Cooling from impinging jet is nearly compulsory in steel industry processing especially in Run Out Table processing and steel tube production because of the high heat transfer provided by the boiling of the subcooled water jet. As far as metallurgical phase transformations, residual stresses and deformations in the workpiece are concerned, the temperature drop during cooling must be controlled thanks to a full understanding of the heat transfer mechanisms. One of the main characteristic using jet impingement is that the transition boiling regime may exist for very high superheat and thus the Leidenfrost temperature is higher than in pool boiling; consequently, boiling curves generally have a particular shape in the transition boiling regime which is usually called “shoulder of flux”. In this study, an innovative experimental quenching device has been used for analyzing the effect of the wall velocity of the surface to be cooled on the boiling curves (i.e. heat transfer) and we especially point out that the “shoulder of flux” (i.e. transition boiling regime) is strongly dependent on the surface to jet velocity ratio (r*). We found that a very small increase of the wall velocity has a high influence on shoulder of flux collapse.

Influence of the Impact Angle and the Gravity Direction on Heat Transfer during the Cooling of a Cylinder by a Free Planar Subcooled Impinging Jet

Cooling from impinging jet is nearly compulsory in steel industry processing especially in Run Out Table processing and steel tubes production because of the high heat transfer rates provided by the boiling of the subcooled water jet. As far as metallurgical phase transformations, residual stresses and deformations in the workpiece are concerned, the temperature drop during cooling must be perfectly controlled thanks to a fully understanding of the heat transfer mechanisms. In a previous study [1] the effect of surface to jet velocity ratio on heat transfer has been characterized and it has been shown that this parameter has a significant influence on shoulder of flux collapse. In order to understand the effect of more industrial quench process parameters, an innovative experimental quenching device has been designed and built. It allowed us to make heat transfer measurements at the surface of a hot nickel cylinder impinged by a subcooled water jet, according to several angles of impact and three jet directions against gravity. The results clearly highlight an effect of these two parameters on the heat transfer mechanisms at the surface of the tube. These results allow a better understanding of the origins of temperature heterogeneities inside the tube during the quench.