Are you trying to implement Next Generation Science Standards? Have no idea how to do modeling with your kids? This may help.
Concepts addressed: Density, heat transfer, energy transfer, temperature, convection, conduction, radiation etc.
This modeling activity works best as a demonstration. You will need to use a heat sources, a hot plate, a pot, water and a pinwheel and you may want to have food coloring or an old-timey projector to demonstrate convection.
I recommend that you test-drive the demo, before you attempt it with the class, since the position of the pinwheel can change whether the whole thing works.
You can simplify the model by just having a pinwheel and a candle.
Grading rubrics and sample student response included.