Mixsim2: Heat exchanger coil or tube bundle as porous media zone?
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A tank contains one or more helical heat exchanger coil(s), or bundles of vertical heat exchanger tubes in a circular arrangement. In both cases, resolving the geometry of these entities results in huge mesh cell counts. Approximating these entities by one or more cylindrical porous media zones is the appropriate way. How can this be done in MixSim?? - In MixSim, create a "Hex Region" of the type "Donut" (this can be a child either of the tank or of the shaft). Give it the correct proportions so that it represents the desired porous volume. - Adjust the "Initial Mesh Size" value for the Hex Region to a sensible value -- not larger than the "wall thickness" (i.e. half the difference between inner and outer diameter), and somewhere between the impeller's "Initial Mesh Size" and the Tank's "Initial Mesh Size". If meshing fails, try a smaller value here. - For each impeller that is inside or near this "Hex Region", please do activate the "Fix Zone Dimensions" check button. (That is usually located near the bottom end of the impeller's parameter list in MixSim's "Model Management" panel.) Adjust the values if you feel that the MRF zone should be larger than the (intentionally small) default values. But make sure there's enough space for the transition from (large) pyramid cells on the Hex Region to (small) tet cells on the MRF zone boundary. (Activating the "Fix Zone Dimensions" button is necessary because MixSim doesn't account for Hex Regions when it determines to which extent MRF zones can be enlarged automatically.) When you view the Hex Region and the visualized MRF zones in the MixSim model setup preview graphics, you may find it advantageous to use the {A,R}-{Hex,Tank,Zones} buttons in the preview graphics window. - After meshing, go to "Solve---Iterate", UNcheck "save data" and "save case", set the number of iterations to ZERO, and press "Iterate". - When MixSim is finished setting up the FLUENT case, go to "File---Control-Panel", and switch the GUI menu bar to the FLUENT GUI. - In Define---Boundary-Conditions, find the zone "hex_region_X_fluid" (X is some small, usually odd, integer number). This represents the cell zone that has been meshed with hex cells. Edit the boundary conditions for this zone, and add the "porous zone" property to it. Set the porous zone parameters. - Run iterations (using "Solve---Iterate" either in the FLUENT GUI or after switching back to the MixSim GUI. - Enjoy, including the MixSim postprocessing features! __________________________________________ If you find any problems or deficiencies with these instructions, please contact your technical support engineer or Fluent distributor, so that we can improve this. |
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