Pascal Lavieille

Heat and Mass Transfer in Capillary-Pumped Liquid Films in Square Cross-Section Minichannels

This study addresses heat and mass transfer during the vaporization of a liquid in a heated square cross-section mini-channel. A theoretical model is developed in steady state using the radius of curvature as a variable. One-dimensional simulations have been performed. An analysis of this model reveals that heat and mass transfer is governed by two main groups of non-dimensional numbers (i.e., Reynolds × Boiling and Weber × Boiling2 numbers). Maps of heat transfer performance are thus proposed according to these non-dimensional numbers. A reduced model is finally derived, allowing the main parameters to be expressed (such as the extended meniscus length) analytically.

Complete Convective Condensation Inside Small Diameter Horizontal Tubes

An experimental study of complete convective condensation inside narrow channels is presented in this paper. Two-phase flows patterns and their transition (annular, annular-wavy, slug and bubbly flow) are visualized for the two tube diameters under study. A significant difference is observed for the two sizes of tube. Experimental results of the bubble radius decrease are then determined and compared to a model of bubble collapse in a subcooled and infinite liquid.Copyright

Heat Transfer Enhancement in Short Corrugated Mini-Tubes

Heat transfer phenomena are studied with standing waves inside the tubes for static and moving sinusoidal corrugated walls. The past studies have been done on big-size (dimensions in m) and micro-sized circular tubes (dimensions in μm). We are focusing on intermediate size tubes (dimensions in mm). Numerical simulations, using finite volume commercial software, were performed to study the effects of spatial wavelengths on heat transfer enhancement and associated pressure drop. We imposed 5, 10, 15 and 20 3D sinusoidal radial sine waves along the length of the tube. Heat transfer characteristics of static corrugated wavy walls were calculated for various imposed Reynolds numbers (1 < Re < 120) and amplitude of the wave was varied from 1 to 20 % of the diameter of the tube. For static wall case, upon increasing the number of sine waves, the Nusselt number starts to decrease; the associated pressure drop and friction factor increases very rapidly at the highest values of amplitude. On the other hand, in comparison to the static corrugated wall tube, the pressure drop is reduced by 20–80 % and heat transfer is enhanced by 35–70 % for highest amplitude when frequencies in the range 0 < f < 60 Hz are imposed on tube wall to make the corrugated tube moving in transverse direction.

Experimental Study of Capillary Pumping During Vaporization in a Square Cross Section Microchannel

An experimental study is undertaken to investigate microcapillary pumped loop (micro-CPL) evaporator behaviours. The experimental set-up is made of a horizontal square cross section glass microchannel which is locally heated up in order to analyze vaporization. A specific procedure allowed us to investigate the capillary pumping due to vaporization: the mass flow rate according to heat flux applied is determined. A laser-induced fluorescence technique has been used to observe phases distribution in the microchannel during vaporization, especially the liquid raising in the corners. The extended meniscus zone length has been determined as a function of the heat flux using image processing.Copyright