HXL Version 2.12

Heat Exchanger Library 2.12 is part of Modelon's 2024.1 release. New versions of Modelon's libraries are sold and distributed directly from Modelon, as well as approved resellers.

Version 2.12 contains the changes described below.

New features

  • All heat exchangers can now use temperature-dependent heat capacity and thermal conductivity for the solid wall. The "WallMaterial" parameter with constant properties remains for backwards-compatibility, and by default the properties specified there are used. To use temperature-dependent heat capacity and thermal conductivity, the new MaterialModel option need to be set to something other than the default which is constant properties. A table-based model is available, as well as cryogenic temperature models for different materials. When a MaterialModel is selected, parameters belonging to the selected model must also be set, for example tabulated properties versus temperature or coefficients for specific materials at low tempretures. When temperature dependent properties are used the constant density from WallMaterial is still used to compute the heat exchanger mass from its geoemtry, but the constant heat capacity and thermal conductivity given there are ignored.
  • Added Summary and Initialization component views to see relevant variables and parameters on stickies. (Known limitation: Instantiating multiple components that extend from the same class, which has the component views defined, will not have their component views appear.)

Improvements

  • Fin-on-tube heat exchangers now support moisture condensation on fin walls in case the air humidity is higher than the saturated air humidity at wall surface temperature. An example of fin-on-tube evaporator with condensing moist air was added: HeatExchanger.HeatExchangers.CrossFlowAir.FinTube.Experiments.Evaporator.
  • Revised default settings of the Advanced tab parameter condenseMoisture, which if set to false apply the simplification that outlet air humidity = inlet air humidity. All component involving air now has this set to true by default, unless the component or example name clearly suggest an application where air is heated, and thereby will not have moisture condensation.
  • In the air flow model of flat-tube & fin-on-tube heat exchangers (both "stand-alone" and "stacking" variants), there is a difference in how air specific heat capacity is computed. Previously, the default was to use the aritmethic mean value of air heat capacity at the inlet and outlet states of the air flow. This had two problems; latent heat of water condensing at the wall was neglected, and for some outlet state points (especially at exactly 0 degree C) the latent heat contribution could be so high causing simulation robustness problems.
    With this version there is a new formulation defining average specific heat capacity as the actual enthalpy difference per temperature difference in the air stream. This includes the effect of latent heat, if any, from inlet to outlet temperature of the air, and doesn't produce very high values in case the heat capacity is high at a particular state point.
    This change affects results and for backwards compatibility there is a new parameter, "cp_arithmetic_mean", introduced and the Advanced parameter tab on air channels and heat exchangers. This should only be enabled to preserve results of existing calibrated models. Other uses of the setting are not recommended.
  • Library experiments include System Views with key variables in plots or stickies.
  • Air flow sources for 2D discretized air have improved flexibility and default behaviour in which air density is used to convert to mass flow rate when either air velocity or air volumetric flow rate is prescribed. Below is a list of previous and new behavior for all affected components:
  • HeatExchanger.Sources.Segmented.HomogeneousAirFlow - previously the same density value was used for each stream tube. It was computed from ambient parameters p_amb, T_amb and the average prescribe absolute humidity per stream tube. Now there is a user input for density d that allow unique values per stream tube. By default density is computed from the ambient pressure parameter p_amb and prescribed temperature and relative humidity (both either from parameter or real inputs). With its default setting the parameter T_amb no longer has any influece.
  • HeatExchanger.Sources.Segmented.ConstantAirFlow - previously the same density value was used for each stream tube. It was computed from ambient parameters p_amb, T_amb and the average prescribed absolute humidity per stream tube. Now there is a user input for density d that allow unique values per stream tube. By default density is computed from the ambient pressure parameter p_amb and per segment prescribed temperature and relative humidity (both either from parameter or real inputs). If prescribed temperature and relative humidity have different discretization, they will both be resampled to mass flow discretization as needed for the computation of density per stream tube. With its default setting the parameter T_amb no longer has any influece.
  • HeatExchanger.Sources.Segmented.AirVelocityFromFile & HeatExchanger.Sources.Segmented.AirFlowFromFile - The behavior is unchanged but there is a new possibility to define density value per segment when enable_resampling = false. By default density is computed from p_amb, T_amb and prescribed relative humidity. If enable_resampling = true, density is computed per segment using the temperature distribution on the file.
  • Library experiments include System Views with key variables in plots or stickies.

Bug fixes

  • Fixed an error in the fan component for stack integration, HeatExchanger.Stacks.SubComponents.GeometricFan, where the fan power and flow rate were not correctly applied when the fan covered multiple air flow segments.
  • Fixed errors in what aggregate fluid mass and volume is reported in summary records and top level aggregate mass components. Previously, volumes were in some cases taken from geometry parameters directly, but if the user selected to neglect headers, the reported volume could include header volume. After these fixes, the reported mass and volume is always consistent with what is actually represented in the component during simulation. Both fin-on-tube and flat-tube heat exchangers were affected by this.
  • The air flow source component for homogeneous air flow in 2D-discretized representation, HeatExchanger.Sources.Segmented.HomogeneousAirFlow, was incorrectly applying a density factor when using the option to specify volumetric flow rate. If used to prescribe mass flow rate or air velocity, the error was not present. The erronous result when prescribing volumetric flow rate has been corrected and thus affecting results. To achive the same result as before with incorrect expression, the deprecated component HeatExchanger.Sources.Segmented.Deprecated.HomogeneousAirFlowVflowBug, can be used. User models are not converted to use this component automatically. I need to be changed manually if desired.