Liquid $\text{'}$B$\text{'}$ is flowing in laminar motion down a vertical wall. The film begins far enough the wall so that the velocity, Vz$,$ depends only on y for z$>=0.$ For Oz L$,$ the wall is made of species $\text{'}$A$\text{'}$ that is slightly soluble in $\text{'}$B$\text{'}.$ Assume that $\text{'}$A$\text{'}$ will not diffuse very far into the falling film so that $\text{'}$A$\text{'}$ will be present only in a very thin boundary layer near the solid surface. The species A is dissolving into a falling film of liquid B$,$ moving a fully developed parabolic velocity profile. Also, assume transport of $\text{'}$A$\text{'}$ in z direction is by convection and in $\text{'}$y$\text{'}$ direction by diffusion only. Obtain the expression for estimation of molar flow of $\text{'}$B$\text{'}$ across the entire mass transfer surface at y $=0.$