Thankyou for your response.

Yes in two-phase interaction, I am using VOF method (evaporation and condensation model)

CASE EXPLANATION: In My case fluid is flowing over the tubes of heat exchanger I want to do when water flowing downward direction how much of water will get evaporated from inlet to outlet of the tube ( as tube are at higher temp taking constant wall temp case)

I want to know coeff of value how to find out this  as mentioned in equation 16 (referring to the below link)