Carnot engine scheme. Heat flows from hot souce <i>T<sub>1</sub></i> to cold source <i>T<sub>2</sub></i> through the Carnot engine <i>C</i>. In the cycle, the engine does a work <i>W</i> on the surroundings.
<a href="//commons.wikimedia.org/wiki/User:Keta" title="User:Keta">Keta</a>
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<span class="int-own-work" lang="en">Own work</span>