The heat flow into the engine is Q ˙ ˙ H = k H ( T H − − T H ′ ) , where k H is the heat conduction coefficient. The heat flow out of the engine is Q ˙ ˙ L = k L ( T L ′ − − T L ) . The power output of the engine is W ˙ ˙ = Q ˙ ˙ H − − Q ˙ ˙ L .