Integral relations for the heat and mass transfer resistivities of the liquid–vapor interface

2006 ◽  
Vol 370 (2) ◽  
pp. 258-274 ◽  
Author(s):  
Eivind Johannessen ◽  
Dick Bedeaux
Keyword(s):  
Mass Transfer ◽  
Heat And Mass Transfer ◽  
Vapor Interface ◽  
Integral Relations ◽  
Liquid Vapor

The Role of Surfactant Adsorption Rate in Heat and Mass Transfer Enhancement in Absorption Heat Pumps

2000 ◽  
Author(s):  
Michael S. Koenig ◽  
Gershon Grossman ◽  
Khaled Gommed
Keyword(s):  
Mass Transfer ◽  
Surface Tension ◽  
Heat And Mass Transfer ◽  
Heat Pumps ◽  
Surfactant Adsorption ◽  
Relaxation Rates ◽  
Dynamic Surface ◽  
Vapor Interface ◽  
Enhanced Absorption ◽  
Liquid Vapor

Abstract The importance of heat and mass transfer additives in absorption chillers and heat pumps has been recognized for over three decades. However, a universally accepted model for the mechanisms responsible for enhanced absorption rates has yet to be proposed. The Marangoni effect — an instability arising from gradients in surface tension at the liquid-vapor interface — is generally accepted as the cause of the convective flows that enhance transfer rates. Certain surfactant additives can significantly improve absorption rates and thus reduce the overall transfer area required by a given machine. Any means available that can increase the efficiency and acceptability of absorption machines is to be welcomed, as this technology provides an alternative to vapor compression systems which is both environmentally friendly and more versatile with regards to energy sources. This study investigates the rate at which a surfactant additive adsorbs at a liquid-vapor interface. The residence time of the falling liquid solution in an absorber is quite short. An effective additive must not only reduce the surface tension of the solution; it must do so quickly enough to cause the Marangoni instability within the short absorption process time. The entrance region of an absorber features a freshly exposed interface at which no surfactant has adsorbed. A numerical model is used to analyze surfactant relaxation rates in a static film of additive-laced solution. Kinetic parameters for the combination of the working pair LiBr-H2O and the additive 2-ethyl-1-hexanol are derived from data in the literature for static and dynamic surface tension measurements. Bulk, interfacial and boundary parameters influencing relaxation rates are discussed for surfactant adsorption occurring in the absence of absorption, as well as for concurrent adsorption and stable vapor absorption. Initial solution conditions and absorption driving force are shown to impact the potential for instability in the effect they have on the rate of interfacial additive adsorption.

A New Computational Method to Track a Liquid/Vapor Interface With Mass Transfer, Demonstrated on the Concentration Driven Evaporation From a Capillary Tube, and the Marangoni Effect

2005 ◽  
Author(s):  
Jeremy Rice ◽  
Amir Faghri
Keyword(s):  
Mass Transfer ◽  
Marangoni Convection ◽  
Capillary Tube ◽  
Marangoni Effect ◽  
Solution Procedure ◽  
Computational Method ◽  
Interface Tracking ◽  
Vapor Interface ◽  
Tracking Technique ◽  
Liquid Vapor

A new computational liquid/vapor interface tracking technique is developed to model an interface between a liquid and a vapor including mass transfer. This technique does not require the use of an additional transport equation, as does the VOF method, while still being implemented without a complicated solution procedure. This new interface tracking technique is used to capture the liquid/vapor interface in a capillary tube of 100 μm scale. The diffusion driven evaporation process is studied, along with the Marangoni convection that is caused by the temperature gradient along the interface. The results are qualitatively and quantitatively compared to existing experimental data.

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