Now that all the flows & pressures are tuned, it’s time to add in the thermal effects and tune them. The idea here is to get the fluid to exit links at the correct temperature, given the desired inlet & wall temperatures. You can start replacing the previous constraints that were set up before. Replace them one at a time with a proper tuning that achieves the desired exit temperature (i.e. not using overrides or infinite HTC).

For convection links, constrain the desired wall temperature and adjust the HTC until you get the correct exit temperature and heat flux.

• For links that define HTC directly, such as GunnsFluidHeatExchanger, then if there is vendor data giving the HTC then you can start with that and tweak it as needed. See GunnsFluidHeatExchanger for more help.

• For links that define thermal geometry, such as GunnsFluidValve and similar, then you should start with the known geometry of the passage and tweak these terms as needed. See the GunnsFluidValve for more help. Some additional hints:
  • GunnsDraw shape data thermalLength: increasing this raises the effective HTC and heat transfer.
  • GunnsDraw shape data thermalDiameter: increasing this lowers the effective HTC and heat transfer.
  • GunnsDraw shape data surfaceRoughness: increasing this raises the effective HTC and heat transfer.
  • In run-time, the link replaces thermalLength with mThermalSurfaceArea, and surfaceRoughness with mThermalROverD. You can tweak these along with mThermalDiameter, which comes from thermalDiameter:
    • mThermalSurfaceArea: increasing this raises the effective HTC and heat transfer.
    • mThermalDiameter: increasing this lowers the effective HTC and heat transfer.
    • mThermalROverD: increasing this raises the effective HTC and heat transfer.
  • These thermal terms do not affect the main fluid flow conductance of the link.

We use conduction in the GunnsFluidTank to cause the stored gas to heat back up to the shell temperature after it had cooled down due to expansion during outflow.

The tank models the heat flux as a function of the fluid’s thermal conductivity (a fluid property which you don’t set) and the tank geometry (surface area & shell radius). The model is not very accurate so you may need to tune the mSurfaceArea and mShellRadius terms to get the temperature rate and flux where you want it.

You can use the tank’s built-in edit controls to edit the gas temperature inside. Use this in conjunction with setting the mShellTemperature to help tuning.

Most conductor links have a mExpansionScaleFactor term that is used to scale the temperature change due to gas expansion across the link. This model is most accurate for isentropic flows, but it can also be tuned to model isenthalpic expansion for a specific flow condition. See here for more info.

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