(1) Defining Regions to Regions

region-to-regions    RegionsHeatSourceFeature-r2r-0 Lattice Lattice

Here Lattice is the name for the region where we apply heat source.

Here RegionsHeatSourceFeature-r2r-0 is the name for the region-to-regions

Add RegionsHeatSourceFeature for it

model-feature-r2r  ConjugatedFlowModel flow-set    reg-set-1  RegionsHeatSourceFeature RegionsHeatSourceFeature-r2r-0

or

model-feature-r2r  EnergyModel flow-set    reg-set-1  RegionsHeatSourceFeature RegionsHeatSourceFeature-r2r-0

(3) write the output file

write-sim        outputFixedT.stree

(4) Edit the outputFixedT.stree.

Search for RegionsHeatSourceFeature and set the heat source.