When energy in a transformation is lost where does it go?

Answer 1

There are usually losses in a machine such as a heat engine, where thermal energy is converted to mechanical energy. Losses occur in the cooling system which has to keep the machine at a suitable temperature for its component materials, ie the radiator in your car, the exhaust system which carries away quite a lot of thermal energy, and frictional losses in moving parts. In a power station where the turbine operates on the Rankine cycle most of the heat losses occur in the condenser where steam is condensed back to water to refeed the boilers. The rejected heat goes into the environment, either into the atmosphere via cooling towers or directly into a river, lake, or the ocean. In an aircraft engine the losses go directly into the atmosphere in the exhaust.

Generally these losses are not recoverable because the rejected heat is at a low temperature or the vehicle is moving freely. However in some situations heat can be rejected at usable temperature and used for district heating etc.