.Buildings.Fluid.HeatExchangers.BaseClasses.MassExchange

Information

This model computes the mass transfer based on similarity laws between the convective sensible heat transfer coefficient and the mass transfer coefficient.

Using the Lewis number which is defined as the ratio between the heat and mass diffusion coefficients, one can obtain the ratio between convection heat transfer coefficient h in (W/(m^2*K)) and mass transfer coefficient h_m in (m/s) as follows:

h ⁄ h_m = ρ c_p Le^(1-n) ⁄ h_m

where ρ is the mass density, c_p is the specific heat capacity of the bulk medium and n is a coefficient from the boundary layer analysis, which is typically n=1/3. From this equation, we can compute the water vapor mass flow rate n_A in (kg/s) as

n_A = G_c ⁄ (c_p Le^(1-n)) (X_s - X_∞),

where G_c is the sensible heat conductivity in (W/K) and X_s and X_∞ are the water vapor mass per unit volume in the boundary layer and in the bulk of the medium. In this model, X_s is the saturation water vapor pressure corresponding to the temperature T_sur which is an input.

Contents

Name	Description
Medium	Fluid medium model

Revisions

• April 12, 2017, by Michael Wetter:
  Removed temperature that is no longer needed.
  This is for issue Buildings #704.
• December 14, 2012 by Michael Wetter:
  Renamed protected parameters for consistency with the naming conventions and fixed error in the documentation.
• August 13, 2008 by Michael Wetter:
  First implementation.