Experimental Determination of the Effect of Disjoining Pressure on Shear in the Contact Line Region of a Moving Evaporating Thin Film

2005 ◽  
Vol 127 (3) ◽  
pp. 231-243 ◽  
Author(s):  
Sashidhar S. Panchamgam ◽  
Shripad J. Gokhale ◽  
Joel L. Plawsky ◽  
Sunando DasGupta ◽  
Peter C. Wayner,
Keyword(s):  
Fluid Flow ◽  
Contact Line ◽  
Quartz Substrate ◽  
Thin Liquid Film ◽  
Disjoining Pressure ◽  
Dispersion Constant ◽  
Line Region ◽  
Fundamental Insight ◽  
First Time

The thickness and curvature profiles in the contact line region of a moving evaporating thin liquid film of pentane on a quartz substrate were measured for the thickness region, δ<2.5 μm. The critical region, δ<0.1 μm, was emphasized. The profiles were obtained using image-analyzing interferometry and an improved data analysis procedure. The precursor adsorbed film, the thickness, the curvature, and interfacial slope (variation of the local “apparent contact angle”) profiles were consistent with previous models based on interfacial concepts. Isothermal equilibrium conditions were used to verify the accuracy of the procedures and to evaluate the retarded dispersion constant in situ. The profiles give fundamental insight into the phenomena of phase change, pressure gradient, fluid flow, spreading, shear stress, and the physics of interfacial phenomena in the contact line region. The experimental results demonstrate explicitly, for the first time with microscopic detail, that the disjoining pressure controls fluid flow within an evaporating completely wetting thin curved film.

A Study of an Oscillating Corner Meniscus With Phase Change Using Image Analyzing Interferometry

Volume 4 ◽  
2004 ◽  
Author(s):  
Sashidhar S. Panchamgam ◽  
Shripad J. Gokhale ◽  
Joel L. Plawsky ◽  
Sunando DasGupta ◽  
Peter C. Wayner
Keyword(s):  
Fluid Flow ◽  
Phase Change ◽  
Contact Line ◽  
Quartz Substrate ◽  
Thin Liquid Film ◽  
Adsorbed Film ◽  
Line Region ◽  
The Stability ◽  
First Time

The thickness and curvature profiles in the contact line region of a moving evaporating thin liquid film of pentane on a quartz substrate were measured for the thickness region, δ &lt; 2.5 microns. The critical region, δ &lt; 0.1 microns, was emphasized. The profiles were obtained using image analyzing interferometry and an improved data analysis procedure. The precursor adsorbed film, the thickness, the curvature, and interfacial slope (variation of the local “apparent contact angle”) profiles were consistent with previous models based on interfacial concepts. Isothermal equilibrium conditions were used to evaluate the Hamaker constant in-situ and to verify the accuracy of the procedures. The profiles give fundamental insights into the phenomena of phase change, pressure gradient, fluid flow, spreading, and the physics of interfacial phenomena in the contact line region. The experimental results demonstrate explicitly for the first time, with microscopic detail, that the disjoining pressure controls fluid flow within an evaporating completely wetting thin curved film and the stability of the thin film. The change in the thickness of the adsorbed film with time is demonstrated for the first time.

Experimental Evaluation of Marangoni Shear in the Contact Line Region of an Evaporating 99+% Pure Octane Meniscus

2007 ◽  
Vol 129 (11) ◽  
pp. 1476-1485 ◽  
Author(s):  
Sashidhar S. Panchamgam ◽  
Joel L. Plawsky ◽  
Peter C. Wayner
Keyword(s):  
Thin Film ◽  
Fluid Flow ◽  
Intermolecular Interactions ◽  
Contact Line ◽  
Disjoining Pressure ◽  
Operating Conditions ◽  
Working Fluid ◽  
Quartz Surface ◽  
Experimental Conditions ◽  
Line Region

Image analyzing interferometry was used to study the spreading characteristics of an evaporating octane meniscus (purity: 99+%) on a quartz surface. The thickness, slope, and curvature profiles in the contact line region of the meniscus were obtained using a microscopic data analysis procedure. The results obtained for the octane were compared to that of pure pentane (purity: >99.8%) under similar operating conditions. Isothermal experimental conditions of the menisci were used for the in situ estimation of the retarded dispersion constant. The experimental results for the pure pentane demonstrate that the disjoining pressure (the intermolecular interactions) in the thin-film region controls the fluid flow. Also, an imbalance between the disjoining pressure in the thin-film region and the capillary pressure in the thicker meniscus region resulted in a creeping evaporating pentane meniscus, which spreads over the solid (quartz) surface. On the contrary, for less pure octane, the intermolecular interactions between octane and quartz had a significantly different contribution for fluid flow, and hence, the octane meniscus of lower purity did not creep over the quartz surface. As a result, we had a stationary, evaporating octane meniscus. Using the experimental data and a simple model for the velocity distribution, we evaluated the Marangoni shear in a portion of the stationary, evaporating octane meniscus. An extremely small change in the concentration due to distillation had a significant effect on fluid flow and microscale heat transfer. Also, it was found that nonidealities in small interfacial systems, i.e., the presence of impurities in the working fluid, can have a significant effect on the thickness of the adsorbed film, the heat flux, the spreading characteristics of an almost pure fluid, and, therefore, the assumptions in modeling.

Experimental Evaluation of Marangoni Shear in the Contact Line Region of an Evaporating 99+ % Pure Octane Meniscus

2006 ◽  
Author(s):  
Sashidhar S. Panchamgam ◽  
Joel L. Plawsky ◽  
Peter C. Wayner
Keyword(s):  
Thin Film ◽  
Fluid Flow ◽  
Intermolecular Interactions ◽  
Contact Line ◽  
Disjoining Pressure ◽  
Operating Conditions ◽  
Working Fluid ◽  
Quartz Surface ◽  
Experimental Conditions ◽  
Line Region

Image analyzing interferometry was used to study the spreading characteristics of an evaporating meniscus containing octane (purity: 99+ %) on a quartz surface. The thickness and curvature profiles in the contact line region of the meniscus were obtained using a microscopic data analysis procedure. The results obtained for the octane were compared with that of pure pentane under similar operating conditions. Isothermal experimental conditions of the meniscus were used for the in-situ estimation of the retarded dispersion constant. The experimental results for the pure pentane demonstrate that the disjoining pressure (the intermolecular interactions) in the thin film region controls the fluid flow. Also, an imbalance between the disjoining pressure in the thin film region and the capillary pressure in the thicker meniscus region resulted in a creeping evaporating pentane meniscus, which spread over the solid (quartz) surface. On the contrary, for less pure octane, the intermolecular interactions between octane and quartz had a significantly different contribution for fluid flow and hence the octane meniscus of lower purity did not creep over the quartz surface. As a result, we had a stationary, evaporating octane meniscus. Using the experimental data and a simple model for velocity distribution, we evaluated the Marangoni shear in a portion of the stationary, evaporating octane meniscus. An extremely small change in the concentration due to distillation had a significant effect on fluid flow and microscale heat transfer. Also, it was found that non-idealities in small interfacial systems, i.e. the presence of impurities in the working fluid, can have a significant effect on the thickness of the adsorbed film and therefore the spreading characteristics of an almost pure octane meniscus.

Experimental Study of Evaporation in the Contact Line Region of a Thin Film of Hexane

1985 ◽  
Vol 107 (1) ◽  
pp. 182-189 ◽  
Author(s):  
P. C. Wayner ◽  
C. Y. Tung ◽  
M. Tirumala ◽  
J. H. Yang
Keyword(s):  
Liquid Film ◽  
Contact Line ◽  
Thin Liquid Film ◽  
Bulk Composition ◽  
Transport Processes ◽  
Shear Stresses ◽  
Strong Function ◽  
Thickness Profile ◽  
Line Region ◽  
Curvature Gradient

The transport processes in the contact line region (junction of evaporating thin liquid film, vapor, and substrate) of stationary steady-state evaporating thin films of hexane with various bulk compositions were studied experimentally. The substrate temperature distribution and liquid film thickness profile were measured, analyzed, and compared with previous results on other systems. The results demonstrate that small changes in the bulk composition significantly alter the characteristics of the transport processes in the contact line region. The curvature gradient at the liquid-vapor interface is a strong function of evaporation rate and composition. Concentration and temperature gradients give interfacial shear stresses and flow patterns that enhance contact line stability.

Microscale Temperature Measurements Near the Contact Line of an Evaporating Thin Film in a V-Groove

2009 ◽  
Author(s):  
C. P. Migliaccio ◽  
H. K. Dhavaleswarapu ◽  
S. V. Garimella
Keyword(s):  
Thin Film ◽  
Contact Line ◽  
Quartz Substrate ◽  
Constant Heat Flux ◽  
Electrical Heating ◽  
Thin Film Evaporation ◽  
Meniscus Shape ◽  
Liquid Feeding ◽  
Line Region ◽  
Balance Analysis

Thin-film evaporation of heptane in a V-groove geometry is experimentally investigated. The groove is made of fused quartz, and electrical heating of a thin layer of titanium coated on the backside of the quartz substrate provides a constant heat flux. The effects of liquid feeding rate on the temperature suppression in the thin-film region and on the meniscus shape are explored. High resolution (∼6.3 μm) infrared thermography is employed to investigate the temperature profile in the thin-film region, while a goniometer is used to image the meniscus shape. An approximate heat balance analysis is used to estimate the fraction of total meniscus heat transfer which takes place in the contact line region.

scholarly journals The Role of Contact Line (Pinning) Forces on Bubble Blockage in Microchannels

2015 ◽  
Vol 137 (3) ◽  
Author(s):  
Mahshid Mohammadi ◽  
Kendra V. Sharp
Keyword(s):  
Contact Line ◽  
Contact Angle Hysteresis ◽  
Thin Liquid Film ◽  
External Pressure ◽  
Working Fluid ◽  
Dry Bubble ◽  
Contact Line Pinning ◽  
First Time ◽  
Capillary Pressure Gradient

This paper highlights the influence of contact line (pinning) forces on the mobility of dry bubbles in microchannels. Bubbles moving at velocities less than the dewetting velocity of liquid on the surface are essentially dry, meaning that there is no thin liquid film around the bubbles. For these “dry” bubbles, contact line forces and a possible capillary pressure gradient induced by pinning act on the bubbles and resist motion. Without sufficient driving force (e.g., external pressure), a dry bubble is brought to stagnation. For the first time, a bipartite theoretical model that estimates the required pressure difference across the length of stagnant bubbles with concave and convex back interfaces to overcome the contact line forces and stimulate motion is proposed. To validate our theory, the pressure required to move a single dry bubble in square microchannels exhibiting contact angle hysteresis has been measured. The working fluid was de-ionized water. The experiments have been conducted on coated glass channels with different surface hydrophilicities that resulted in concave and convex back interfaces for the bubbles. The experimental results were in agreement with the model's predictions for square channels. The predictions of the concave and convex back models were within 19% and 27% of the experimental measurements, respectively.

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