It expands. You change your constraints on your system, you heat it up some more, then you take the heat source away, and you put it back in contact with the atmosphere. And you cool it a little bit, change the constraints, cool it a little bit more, and heat, and you've got a closed cycle engine.

让它与大气接触冷却,改变约束，使它继续冷却，然后又再次加热,这就是循环热机，我们以前也研究过，更复杂的机器。

麻省理工公开课 - 热力学与动力学课程节选

So the way I've got things written here, q1 Heat's flowing from the hot reservoir to the engine that runs in a cycle.

我把这些都这些这里，是正的，q1，is，positive,热从高温的热源,传到循环工作的热机，对外做功。

麻省理工公开课 - 热力学与动力学课程节选