Surface Tension Effect Essay

Buyevich et al. [22] in their unique finding argued that surface tension effect which otherwise believed to be an effective force in pressing the bubble to a heated wall, result in an effective force that tend to transform the bubble into sphere, thereby facilitating bubble detachment. They obtained this finding by analyzing the behaviour of a vapour bubble modeled as a spherical segment, formed at a nucleation site on a heated horizontal wall and in separated form the wall by microlayer of intervening liquid.

The outcomes of above studies clearly show that boiling heat transfer mechanism is influenced by nucleation site density, bubble departure diameter and bubble emission frequency. Therefore, a brief review on these parameters has been made in the following section.

It is now widely accepted that nucleation site density depends upon the surface physical properties, surface finish, wall superheat and liquid physical properties. Some notable studies on nucleation site density are discussed here.

Jakob & Linke [80] were apparently the first to find a linear relationship between the nucleation site density and the heat flux for boiling of water at low heat fluxes by usually counting the number of nucleation sites. However, later studies [81, 54, 95, 116, 55, 137, 57, 89, 46, 119, 158, 153] on relationship between nucleation site density and heat flux reveals that a non-linear relationship exists between these two quantities. The results of various investigators on non-linear relationship between nucleation site density and heat flux is listed in following Table