An engine is a thermal machine that receives heat from a hot reservoir, transfers part of it to a cold reservoir, and converts the rest into work.

A receiver is a thermal machine that receives heat from a hot reservoir, transfers part of it to a cold reservoir, and converts the rest into work.

An engine is a thermal machine that receives heat from a cold reservoir, transfers part of it to a hot reservoir, and converts the rest into work.

A receiver is a thermal machine that receives work, allowing it to transfer heat from the cold reservoir to the hot reservoir.