where h is a heat transfer coefficient and
Text the temperature of the external fluid far from the boundary, the moisture flux is described by the equation
where Mv is the molar mass of water vapor,
hm is a moisture transfer coefficient and
cv,ext the vapor concentration of the external fluid far from the boundary.
In Ref. 21, the heat and mass boundary layer analogy is used to express the moisture transfer coefficient
hm as a function of the heat transfer coefficient
h:
where Le is the Lewis number, D is the vapor diffusion coefficient in air,
k is the thermal conductivity,
ρ is the density, and
Cp is the specific heat capacity of the external fluid evaluated at the same conditions as those specified in the heat transfer correlation used to compute
h.