From adsorption to condensation: The Zeta adsorption isotherm approach

The Zeta Adsorption Isotherm is based on the hypothesis that molecules adsorb on a solid surface as a collection of molecular clusters. The theory is extended to the steady, thermal disequilibrium states where a vapour at a temperature T^V is exposed to a solid surface at a lower temperature, T^S, and the adsorption of the vapour on a homogenous solid surface is examined analytically and experimentally. The uv-visible interferometer technique is used to measure the amount of vapour adsorbed under these steady, thermal disequilibrium states and the results give a strong support to the predicted amount adsorbed. The Zeta Adsorption Isotherm which is based on the assumption of the existence of molecular clusters is applied to predict the subcooling required for the adsorbate to make a disorder-order phase transition. The theory was used along with the Gibbsian thermodynamics to develop a method for predicting the wetting condition on a vertically oriented silicon surface exposed to the heptane vapour in a gravitational field. The measurements indicate the larger amount of vapour is adsorbed at the lower potential energies. The wetting condition is taken to be reached when the adsorbed vapour is transformed into a liquid film. Further, the surface tension of solid-vapour interface and the solid-liquid interface are calculated, and the condition for drainage of the liquid from the Si surface is predicted. It is shown that when the surface tension of the solid-liquid interface is reduced to zero, gravity would cause the larger molecular clusters to drain down the surface. The experimental observations support this prediction. Finally, the proposed method is applied to toluene and octane and heptane vapours adsorbing on Si. Dropwise condensation is observed experimentally for toluene vapour while filmwise condensation is observed for the other two vapours. From the distribution of the clusters in the adsorbate, the conditions for the initiation of the liquid phase are predicted and the surface tensions are determined for these three systems of vapours. The results are compared, and the mechanism which determines the condensation mode of the vapour condensing on the Si surface is investigated.

Department dc:contributor.department

Mechanical and Industrial Engineering

Year dc:date.issued

2018

Author dc:creator

• Yaghoubian Ghouchani, Sima

Advisor dc:contributor.advisor

• Ward, Charles A.

• Adsorption
• Dropwise condensation
• Filmwise condensation
• Gibbsian thermodynamics
• Zeta adsorption isotherm

Handle dc:identifier.uri

http://hdl.handle.net/1807/92068

OAI identifier oai:identifier

oai:utoronto.scholaris.ca:1807/92068