Experimental apparatus showing the piston used to apply pressure to the PCM within the container; the heat source (heating pads) is at the bottom. Credit: The Grainger College of Engineering, University of Illinois Urbana-Champaign
Have you ever gotten relief from summertime heat by draping a wet towel over your head? If so, you’ve benefited from a phase-change material (PCM): a substance that releases or absorbs energy when it transitions between two of the fundamental states of matter, such as the solid, liquid, or gas states. Your damp towel cools you because water is a PCM that absorbs heat when it’s evaporating—in other words, when it’s transitioning from the liquid state to the gas state.
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