.AixLib.Fluid.MassExchangers.MembraneBasedEnthalpyExchangers.EnthalpyExchanger

Information

This model combines two AirDuctModels with a MembraneModel to form a model of a membrane-based counter-flow enthalpy exchanger.

Usage

Here will follow some hints for parametrization of the model.

• Heat and mass transfer are resolved locally by defining the paramter n.
  The higher the number of segments are, the better the accuracy, but also the higher the simulation time.
  Please note, that using a highly distributed air duct the Nusselt/ Sherwood number needs to be calculated locally (see parameters for heat and mass transfer).
• By using the parameter nParallel a parallel arrangement of several membrane and air ducts can be realized.
• The air ducts in membrane-based enthalpy exchangers are normally divided in width by webs that provide mechanical stability.
  This subdivision influences the heat and mass transfer. This is represented by the parameter nWidth. If this effect should be neglected set nWidth to one.
• Two correlations are implemented to describe the convective heat and mass transfer. By setting the parameter recDuct to false a correlation for a flat gap according to Stephan [1] is used. Else a correlation for rectangular Ducts according to Muzychka et. Al. [2] is used.
• The membrane model summarizes the complete membrane structure consisting of the thin membrane layer and the supportive layer as producers normally declare the overall thickness.
  Therefore, reasonable values for the parameter thicknessMembrane lie in between 10 to 300 μm.
• The permeability describes the water transport through the membrane. It is given in the unit Barrer. Values in the order of 1E5 till 1E8 are reasonable. You can choose between a constant pemerability (default) or a variable permeability which can be set from outside.
• The enthalpy exchanger is modelled for a counter-flow arrangement. By setting the parameter couFloArr to false the cross-flow portion will be calculated by a heat and mass flow reduction based on the Efficiency-NTU-Method (see Publications).

References

[1]: Stephan, K.: Waermeuebergang und Druckabfall bei nicht ausgebildeter Laminarstroemung in Rohren und ebenen Spalten. Chemie-Ing.-Techn. Vol. 31, no. 12, 1959 pp. 773-778

[2]: Muzychka, Y. S.; Yovanovich, M. M. : Laminar Forced Convection Heat Transfer in the Combined Entry Region of Non-Circular Ducts ; Transactions of the ASME; Vol. 126; February 2004

Publications

• Kremer, M.; Mathis, P.; Mueller, D. (2019): Moisture Recovery - A Dynamic Modelling Approach. E3S Web Conf., Volume 111, p.01099. DOI: 10.1051/e3sconf.

Assumptions

Please note, that the heat and mass transfer models implemented in this model only provide accurate transfer models for laminar flow, which is common for enthalpy exchangers.

Contents

Name	Description
Medium	medium in the air ducts

Revisions

• October 13, 2020 by Martin Kremer:
  Deleting heat capacitor for housing due to errors in heat transfer caused by heat capacitor.
• April 23, 2019, by Martin Kremer:
  Adding heat capacitor for the housing of the enthalpy exchangers.
• January 16, 2019, by Martin Kremer:
  Redeclaring sub model parameters as final. Enabling air duct models for changes on top level.
• November 23, 2018, by Martin Kremer:
  Adding model for adsorption enthalpy. Adding humidity sensor needed for adsoprtion model.
• November 20, 2018, by Martin Kremer:
  Changing mass transfer calculation: Now using permeability and thickness of membrane instead of permeance.
• November 5,2018 by Martin Kremer:
  Correcting error in calculation of heat and mass flow with cross flow coefficient.
• August 21, 2018, by Martin Kremer:
  First implementation.