Profile of the liquid film wetting a channel

Abstract

International audienceWe have developed a simple optical technique to investigate the characteristics of liquid films wetting solid surfaces. To validate this technique, we have studied the wetting film that separates a train of lamellas moving through a channel. Total reflection of the laser beam on the wetting film/air interface is used to extract the profile and the thickness of the wetting film. For quasistatic movement of lamellas, we show that the thickness is well described by a capillary number power law

Liquid meniscus friction on a wet plate: Bubbles, lamellae, and foams

“…Bretherton [13] and Park and Homsy [14] adapted this calculation to the case of a confined bubble and predicted the pressure drop associated with the bubble motion. Experimental results mainly report on the film thickness deposited by long bubbles in cylindrical tubes [13,[15][16][17][18][19][20] or on solids pulled out of a bath ( [8] and references therein, [21]), for a typical range of capillary number [10 −6 ; 10 −3 ]. The viscous force acting on the meniscus, or the pressure drop, have been measured for different systems including bubbles separated by liquid slugs [22,23] or lamella [1,[24][25][26][27] moving in tubes, and foams in 2D [28] or 3D geometries [29,30].…”

Experimental investigation of a moving contact line in a channel

“…Using an Abbe refractometer, we veried that the glycerol concentration in the wetting lm deduced from the optical index is equal to the one in the solution. Many theoretical and experimental studies [19][20][21][22][23][24][25][26] attempted to explain the thickness evolution by a Ca 2/3 power law. In the Ca range [5 Â 10 À3 to 10 À2 ], the data are well described by the Ca 2/3 dependence and the ratio of the lm thickness to the hydraulic channel diameter D H is constant and is equal to 0.02 (ref.…”

“…Using a recently developed optical method, 24 we studied the shape of an air-liquid interface moving in a rectangular glass channel. For a large range of capillary numbers, we measured the prole of the contact line and compared it with previous simulations.…”

“…Imbibition and wetting phenomena are well understood in some dynamic cases. [13][14][15][16][17][18] The thickness of the thin liquid lm wetting the channel walls increases monotonically with the capillary number Ca [19][20][21][22][23][24][25][26] (Ca ¼ mV/s, where V is the velocity of the gas-liquid interface, m is the viscosity of the liquid and s is the interfacial tension), following a power law where the value of the exponent remains a matter of controversy. For different ow regimes of the liquid lm, from the capillary-dominated to the viscous-dominated ones, direct investigation of its prole in the case of perfect wetting (contact angles less than 1 ) is lacking.…”

“…For different ow regimes of the liquid lm, from the capillary-dominated to the viscous-dominated ones, direct investigation of its prole in the case of perfect wetting (contact angles less than 1 ) is lacking. By using a recently developed optical technique, 24 we study here the moving contact line for a large range of Ca, from 10 À4 to 10 À1 .…”