.AixLib.Fluid.MassExchangers.MembraneBasedEnthalpyExchangers.BaseClasses.HeatTransfer.AdsorptionEnthalpy

Information

This model calculates the adsorption enthalpy of water vapour for an microporous absorbent. It is based on the Dubinin-Astakhov equation for sorption. All equations are taken from [1].

The actual water uptake w of the absorbent is calculated as follows.

w = w₀ exp[-F(-T ln(φ))ⁿ]

Here F and n are material specific adsorption characteristic constants. The temperature T and the relative humidty φ are inputs of the model. The maximum water uptake w₀ is calculated as following:

w₀ = ρ(T) v₀

The specific micropore volume of the adsobent v₀ has to be set as an parameter. The density of water is calculated by the following term.

ρ(T) = 1 ⁄ (A T + B⁄T)

A and B are constants with A = 1.8105⋅10^-6 m³ kg^-1 K^-1 and B = 138.08⋅10^-3 m³ kg^-1 K .

With the specific vaporization enthalpy of water Δh_v and the gas constant of water vapour R_g the specific adsorption enthalpy can be calculated by the following equation.

Δh_ads = Δh_v + R_g T[-1 ⁄F ln(w ⁄w₀)]^{1 ⁄n} [1 ⁄T + 1 ⁄(n w0 ln(w ⁄w₀) (∂w₀ ⁄∂T)]

Known Limitations

• Calculated adsorption enthalpy for high relative humidities is not reliable (increases up to very high values, as the ln-function aproximates zero).
• Not solvable for complete dry air as the ln(0) is not defined

References

[1]: Min,J.; Wang,L.: Coupled heat and mass transfer during moisture exchange across a mebrane. Journal of Membrane Science. 430 (2013). pp.150-157

Revisions

• November 23, 2018, by Martin Kremer:
  Changed RealInputs to inputs to use the model inside other models
• November 22, 2018, by Martin Kremer:
  First Implementation