Les documents ci-dessous ont été publiés au terme de mon stage de DEA. Le sujet en est le comportement hydraulique d’un mélange eau + billes de propylène simulant un coulis de glace. Ils proposent des modèles de prévision des pertes de charge en conduite cylindrique.
FRICTION LOSSES FOR FLOW OF CONCENTRATED SLURRIES
Benoit STUTZ, Patrick REGHEM, Olivier MARTINEZ
Laboratoire de Thermodynamique et Energétique
64013 PAU, France
The aim of this work is to study the hydraulic behaviour of ice slurries. The solid phase is replaced by polypropylene particles with a density close to that of ice to determine the behaviour of ice/water mixture in adiabatic conditions. The experimental tests are carried out using a slurry flow facility, consisting of a flow loop though which the different piping elements are installed. Friction losses in horizontal pipes, bends, contractions, and enlargements have been measured. The pressure drops depend strongly on the flow pattern.
For suspended particles regimes, the Blasius law based on Reynolds numbers defined from water viscosity and mixture density, is appropriate. Inversely, for moving bed regimes, pressure losses depend on the concentration of the solid phase.
Two models of pressure losses in pipes have been developed. The first one is a correlation. The second one uses the Bingham fluid to model the flow of solid-liquid mixture. An extended Reynolds number is introduced. The Blasius law computed by replacing the classical Reynolds number with the extended Reynolds number is found to be applicable to the two-phase flow in its full range.
FLOW OF SLURRIES OF PARTICLES WITH DENSITY CLOSE TO THAT OF WATER
B.Stutz, P. Reghem, O. Martinez
Université de Pau et des Pays de l’Adour, Avenue de l’Université, 64000 Pau, France
The purpose of this work is to investigate the friction factor for slurries of particles with density close to that of water. The use of particles with density close to that of ice aims to get explanations of new generation of liquid-solid coolant in adiabatic conditions. The solid particles are 3mm-diameter polypropylene sphere, of density 869 kg/m3. The test section consists of horizontal transparent PVC pipes 22 and 45mm in diameter. Friction losses are measured using differential pressure transducers. Velocity distribution within the water layer is measured using Pitot tube. Flow pattern and particle behaviour are observed using visualisation device.
Different flow pattern can be observed in fully turbulent conditions. The transition between the flow pattern depends on the Froude number. Three predicting models of pressure losses in pipe have been used. The first one consists in correlating experimental data using dimensional analysis. The second one uses rheological model : extended Reynolds number based on the empirical Bingham model is introduced. The Blasius law computed by replacing the classical Reynolds number with the extended Reynolds number is found to be applicable to the two-phase flow in its full range. The third one is a two-layer model that contains the effect of pipe diameter. The model treats the flow as being constituted of two layers: a stationary or a moving bed at the top of the pipe and a heterogeneous flow suspension below. The friction coefficient between the bed layer and the pipe is estimated by performing momentum balance using the experimental results (pressure drop, visualisation and distribution of the local velocity within the heterogeneous flow suspension. The validity of the hypothesis of the two-layer model are discussed.