We can compress all of this information into a tidy diagram. Take some time to understand the diagram and what is represented there.

Figure %: Entropy and Energy in a Heat Engine

Other Devices

Looking back at , there is nothing to prevent us from trying to reverse the process entirely. That is, we could try to input work to take heat from a low temperature to a high temperature. The only difference in the diagram is that the unwanted entropy created inside the device never works to our advantage and makes the outputted entropy greater than that inputted.

If you think about it, the description given above is exactly that of a refrigerator; it uses work (electrical work) to remove heat from inside the refrigerator, which is at a low temperature, and dump it into the environment at a higher temperature.

Two more common devices follow the same basic setup. An air conditioner is essentially a large refrigerator, where the inside of the refrigerator is exchanged for the inside of a house or car. A heat pump is an air conditioner in which we now swap the input and output. Therefore we extract heat from a cold environment to heat a warmer environment.

All of these devices work in essentially the same manner, which is a beautiful result of thermodynamics.