Figure-of-merit for phase-change materials used in thermal management

•A FOM for PCMs in thermal management is evaluated numerically and experimentally.•Realistic boundary conditions leading to no explicit analytical solution are studied.•The FOM is important in selecting PCMs, while sensible heat is a lesser design factor.•Adding a PCM has little effect on an application’s maximum steady-state duty cycle.•A high-FOM PCM is experimentally shown to manage heat spikes in a smartphone.