The aluminum foil is blackened on the inside of a hollow letter 'G', with the inner leg-part of the 'G' being upward as part of the upwrd curve, then following the round shape of the inner layer as a heater of the drift passing uoward thru 2 or 3 holes at the top with the middle (of ) hole being bigger, the flow thus repeating it's circuit. It overheats in less than a minute so can only demonstate overunity posing dangers of overdriving anything as such in reality. A really useful device is one that is useable, so unless you or heating a kiln or oven for cooking a huge piece of meat you are out of your league before you start. You better be ready to kick it down if it cooks some air, so build it only of small pieces of aluminum foil smoked black os one side, like a baked ptatoe wrapping.
I believe it can be possible to achieve greater temperature than the heater itself put out by channeling/focussing and feedback looping, but overunity would require you to accumulate more heat heat, in Joules, than the heater put out during its ON-time.