Storage-enhanced thermal management for mobile devices

During regular use, mobile devices generate significant amounts of heat. In this paper, we discuss the use of phase-change materials (PCM) as an energy storage medium to lower the energy consumption of temperature control devices in mobile systems. We adopt a systems perspective and show that the fundamental effect of latent-heat storage is to increase the time constant of the response of the system to changes in heat input without affecting the gain. We also demonstrate that PCM-based cooling reduces energy consumption when used in conjunction with active cooling in a hierarchical control structure, and establish a connection between the dynamics of the integrated system, energy savings and the quantity and geometric properties of the PCM elements. Composite heat sinks consisting of PCM elements confined in a matrix material with high thermal conductivity represent a promising practical implementation of PCM-based cooling. Using a first-principles model and a novel algorithm, we present a method for optimizing the size and number of the PCM elements in the matrix, which effectively amounts to “tuning” the PCM-based controller. We study the PCM-enhanced thermal management of a computer microchip to illustrate the theoretical concepts.