MULTIPHASE MEDIA AND PHASE CHANGE 3
STUDY ON THE EFFECTS OF FREE CONVECTION AND ELEVATED PRESSURE ON
TRANSIENT DROPLET EVAPORATION
Ali Chérif A., Bouaziz M., Chesneau X., Daïf A.
Laboratoire de Mécanique, Acoustique et Instrumentation
Université de Perpignan
52, Avenue de Villeneuve, 66860 PERPIGNAN Cedex
In this paper, we present a model for pure fuel droplet evaporation at high pressure with natural convection. The principle of the method uses the film theory : heat and mass transfer between droplet surface and ambiant gas takes place in a thin film around the droplet. In addition, in order to take natural convection into account, we first of all write and resolve local equations for a limited gas phase around a porous sphere. With this calculation, we able to estimate the corresponding mean Nusselt and Sherwood numbers in terms of mass and thermal Grashof numbers and thus determine the thickness of the gas film. In the first section of this paper, we present the numerical method and the correlation obtained for taking natural convection into account. In the last section of this paper, we present a comparison between our numerical results and experimental and numerical results in the appropriate literature.
TRANSIENT COOLING WITH SOLIDIFICATION OF A THERMODEPENDANT YIELD STRESS FLUID FLOWING IN A DUCT
K. JAVAHERDEH, C. NOUAR, M. LEBOUCHÉ AND R. DEVIENNE
LEMTA CNRS 875 et Université Henri Poincaré, Nancy I
2, Avenue de la Forê de Haye
54504 Vandoeuvre-les-Nancy France
This study is dedicated to the cooling of Herschel-Bulkley fluids flowing in circular pipes. These fluids exhibit yield effect, their rheological comportment law being =S+K.n and also some thermodependancy, the consistency being a function of the temperature according to K = a.exp-bk.T. We present numerical results concerning the temporal development and also some experimental results for stationary situations.
TRANSIENT HEAT AND MASS TRANSFER DURING THE FORMATION OF SUPERHEATED SPHERICAL BUBBLES
A. C. Mezavilla, C. M. Hackenberg
COPPE/UFRJ - Chemical Engineering Dept.
C.P. 68502, Rio de Janeiro, RJ. 21945-970 - Brazil
In this work a thermofluid dynamic model, with known moving boundary, is proposed in order to study the heat and mass transfer, including phase change, during the formation of superheated bubbles in orifices immersed in a continuous liquid phase. From the obtained results it is possible to determine not only the total amount of the continuous phase evaporated mass per bubble, but also the internal and interfacial temperatures and concentrations profiles. For the mathematical description of the heat and mass transfer and surface evaporation, during bubble formation, the bubble growth is determined by constant gas flow and bubble frequency in each orifice. In order to determine the solution to this moving boundary value problem a linearized liquid-vapor equilibrium equation is utilized at the interface. The integral transform method has been applied and a maple-v code was written in order to calculate numerical results from the analytical solutions of the resulting ODE matrix system.
LOCAL STRUCTURE OF THE GAS-LIQUID FLOW IN HORIZONTAL CORRUGATED CHANNELS - FLOW PATTERNS AND WALL SHEAR STRESS
Michel GRADECK* et Michel LEBOUCHE**
LEMTA CNRS URA 875. 2, avenue de la forêt de Haye. BP 160.
54504 Vandoeuvre cedex. France
Experiments have been carried out to determine the local structure of the gas-liquid flow in two corrugated channels. First, the different flow patterns were identified using a combination of visual and video observation and have been mapped on a two-dimensional graphic using the superficial velocities. The measurement of the wall shear stress by electrochemical method allowed us to give a fine description of the local two-phase flow structure.