Bernard Desmet

Local convective heat exchanges from a rotor facing a stator

Abstract The local convective heat transfer from a rotor with a 310 mm outer radius is studied experimentally at a distance of 3 mm from a coaxial crown-shaped stator with a 176 mm inner radius and a 284 mm outer radius. The experimental technique is based on the use of a thermally thick rotor heated from behind by infrared radiation. The local heat flux distribution from the rotor surface is identified by resolving the Laplace equation by finite difference method using the experimental temperature distribution as boundary conditions. The tests are carried out with the single rotor and the stator/rotor system for local rotational Reynolds numbers ranging from 2.0·104 to 1.47·106 and thus sweeping across the laminar, transition and turbulent flow regimes. The local and mean Nusselt numbers for the single disc are compared with those obtained experimentally for the stator/rotor system. The flow structure in the space between the rotor and the stator is analysed by Particule Image Velocimetry.

Influence of fin spacing and rotational speed on the convective heat exchanges from a rotating finned tube

Abstract The convective heat transfer from fins to air at rest has been evaluated for rotating annular fins. The fin cooling is studied using infrared thermography. The heat transfer coefficient can be obtained from a fin’s thermal balance, during its cooling process and its temperature–time evolution. The influence of the fin rotational speed and the fin spacing on the convective exchanges is studied. The tests were carried out for rotational Reynolds numbers (based on the shaft diameter and the shaft peripheral speed) ranging from 400 to 30xa0000, for different fin spacings. A correlation of the experimental data has been found. The relative influences of the rotational forced convection and the gravitational natural convection on the heat transfer from the fin surface have also been analyzed.

Echange thermique convectif local dans la zone de recirculation en aval d’une marche

Resume L’echange thermique local par convection sur la paroi situee a l’aval d’une marche descendante est analyse pour trois conditions de l’ecoulement a l’amont de la marche: ecoulement uniforme en dehors d’une couche limite laminaire ou d’une couche limite turbulente ainsi que dans le cas d’un ecoulement en regime etabli. Les flux thermiques locaux sont obtenus a partir des temperatures de surface d’une paroi thermiquement epaisse mesurees par thermographie infrarouge et utilisees comme conditions limites d’un calcul numerique. L’analyse porte sur les positions du point de transfert maximum ainsi que sur l’influence de l’epaisseur de la couche limite sur la valeur du nombre de Nusselt maximum.

Échanges convectifs locaux sur une couronne d'un disque en rotation

Abstract This article sets out an experimental technique for the determination of the local convective heat transfer coefficients on the surface of a rotating disc. This technique is based on the use of thermally thick walls, on infrared thermography as a method of surface temperature determination, and on the numerical solution of the energy equation to evaluate the local convective exchanges. The tests were carried out on a disc with a large temperature difference between its periphery and its interior. The rotational Reynolds number varies from 2·10 4 to 1.4·10 6 , extending from the laminar to the turbulent regime. The experimental results are compared with the ones taken from the literature and show the influence of the disc geometry and of the nature of the temperature distribution law on its surface on the convective heat transfer.

Etude des échanges convectifs sur un arbre aileté tournant, soumis à un courant d’air parallèle aux ailettes

Abstract L’evaluation du coefficient d’echange moyen convectif avec l’air est realisee sur des ailettes circulaires en rotation et soumises a un courant d’air parallele a leurs faces. Un banc d’essais a ete concu pour mesurer, par thermographie infrarouge, le refroidissement d’une ailette. Le bilan thermique dans une ailette pendant son refroidissement permet d’obtenir l’expression du coefficient d’echange thermique a partir de la variation temporelle de temperature dans l’ailette. Les essais ont ete realises pour des nombres de Reynolds du courant d’air (bases sur le diametre de l’arbre et la vitesse du courant d’air) jusqu’a 40 000 et des nombres de Reynolds rotationnels (bases sur le diametre et la vitesse peripherique de l’arbre) entre 400 et 27 500. Les influences relatives des nombres de Reynolds et du nombre de Grashof traduisant la convection naturelle due a la pesanteur sur le transfert de chaleur a la surface de l’ailette ont ete analysees.

Étude des phénomènes de transferts thermiques dans les stérilisateurs à vapeur

Abstract Study of heat transfer phenomena in a vapor sterilizer . Steam sterilization occupies a preferential place in the hospital hygiene. Hospital infection designates any sickness contracted in a hospital, allocated to microorganisms which affected sick people or hospital staff. The research work aims at studying heat transfer phenomena in a vapor sterilizer. The interactions between the different modes of heat transfer confer great complexity to this problem. The development of calculation method, zonal method , allowed to predict the field of temperature and heat transfer to optimise vapor sterilizers. This work presents the results of experiments carried out on a cycle of instrument sterilization. The main motivations of this study are the droplets of water which remain pasted to the load at the end of the drying process.