Passive thermal management using phase change materials

The trend of enhanced functionality and reducing thickness of mobile devices has led to a rapid increase in power density and a potential thermal bottleneck since thermal limits of components remain unchanged. Active cooling mechanisms are not feasible due to size, weight and cost constraints. This work explores the feasibility of a passive cooling system based on Phase Change Materials (PCMs) for thermal management of mobile devices. PCMs stabilize temperatures due to the latent heat of phase change thus increasing the operating time of the device before threshold temperatures are exceeded. The primary contribution of this work is the identification of key parameters which influence the design of a PCM based thermal management system from both the experiments and the numerical models. This work first identifies strategies for integrating PCMs in an electronic device. A detailed review of past research, including experimental techniques and computational models, yields key material properties and metrics to evaluate the performance of PCMs. Subsequently, a miniaturized version of a conventional thermal conductivity measurement technique is developed to characterize thermal resistance of PCMs. Further, latent heat and transition temperatures are also characterized for a wide range of PCMs. In-situ measurements with PCMs placed on the processor indicate that some PCMs can extend the operating time of the device by as much as a factor of 2.48 relative to baseline tests (with no PCMs). This increase in operating time is investigated by computational thermal models that explore various integration locations, both at the package and device level