Influence of the presence of vapor diffusion from a wetted non-adiabatic boundary upon the sensible heat transfer between a boundary wall and a gas stream



The evaporation of a liquid from a wetted surface into a gas stream has consequences which are of fundamental importance in the analysis of sensible heat transfer at the boundary. The presence of a relatively high concentration of vapor in the region adjacent to the surface influences the physical properties of the fluid and the vapor concentration gradient affects the heat transfer mechanism.

Experimental equipment was devised to measure the sensible heat transfer coefficients at the inside surface of a porous ceramic tube from which water was being evaporated. Series of tests were carried out for non-adiabatic wall conditions over ranges of the Reynolds Number from 5,600 to 16,000, tube diameter from 1.360 to 3.300 inches, bulk air temperature from 150 to 220°., and wall vapor pressures from 0.35 to 2.20 p.s.i.a.

Over the range of vapor pressures and evaporation rates investigated, the sensible heat transfer coefficients were not observed to depart significantly from those predicted by generally accepted relationships for the dry wall case.