If the past is prolog, the Papp engine produced very little if any heat. The same will be true for the Mills engine.
Mills engine energy production will come from two places: pressure/shock wave expansion with associated plasma movement and the production of excess electrons. These two energy sources were the source of the over unity power production derived from the Papp engine and these sources should be the same for the Mills engine. The one important engine design idea that has not made it into Mills' head yet is the requirement to setup positive feedback loops that leverage these two energy sources to optimize Mills engine power production. I fear that Mills fantasy doctrinaire will blind Mills to these important engine design priorities in the design and the development of the Mills engine. Can Mills discard the science religion that has fed him and built a legion of faithful and adoring followers be abruptly discarded in altruistic pursuit of truth and subsequent open source engine design success? It will never happen.