Practical realization and full cycle performance of an “hourglass” system for transient thermal management based on dynamic melting

Phase change materials (PCMs) are attractive for transient thermal management of electronic devices operating either over a limited period or intermittently with occasional thermal dissipation spikes. Since the low thermal conductivity of PCMs presents a significant challenge for heat removal, various ways have been suggested to overcome this issue, which can cause overheating of the electronic devices due to the associated thermal resistance. Commonly, various thermally conductive additives, like extended surfaces, porous structures or particles, have been suggested for this purpose. The present study is an advanced exploration of an alternative approach to mitigating the high thermal resistance of PCM-based systems, based on a concept termed “dynamic PCM”. Dynamic PCMs work by applying an external load to the solid PCM, causing it to move towards the heat source during melting. The melted PCM is squeezed away, and only a thin liquid layer of practically constant thickness separates the heated surface from the solid PCM phase. Following the recent studies where this concept was introduced and confirmed in principle, the objective of the present work is to demonstrate practical implementation and operation of a sealed, cyclic system, based on the same general idea but significantly modified to meet the real-world requirements. This device is based on the “hourglass” concept, introduced and devised in a previous study. Accordingly, in the present work, a fully metallic configuration is developed to demonstrate practical operation at room temperature. The system is simple, consisting of a cylindrical tube and two end caps. The external force, required for dynamic PCM, is created by a weight which, together with the PCM, is located within the system. The heat-generating component itself serves as the driving factor for detachment of solid PCM from the envelope. As a result, the system preserves all positive features of the earlier prototype but allows for stand-alone implementation with a heat-generating component. Following the system design, fabrication and proof-of-concept runs, controlled tests at three power levels, 30 W, 40 W, and 50 W, are conducted to characterize the thermal behavior, reproducibility of results, and effective melting dynamics of the system. The heating and dynamic melting stages are successfully characterized. Then, system recharge (solidification) is explored under the conditions of free and forced convection in air. Numerical simulations, validated using the experimental results, complement the experiments while revealing important details of the underlying processes. A robust and repeatable performance of the system is demonstrated.