Date of Award
Master of Science (MS)
As the demand for smaller and faster electronics increases, it becomes increasingly challenging to effectively manage the generated heat without hindering device performance in applications whose thermal profiles are dominated by pulsed thermal loads. Heat propagation in a system can be characterized by steady or transient state heat transfer. In steady state, the temperature at any particular point remains constant after thermal equilibrium is reached. In a transient state, the temperature within a system varies over time. The changing parameters and time dependency associated with a transient regime make heat transfer calculations far more complex than in a steady state. Thus, many electronic devices are designed for steady state operation under peak loading conditions and the associated increased temperatures. However, these peak conditions occur infrequently, leading to unnecessary system overdesign.
Phase change materials (PCMs) are heat mitigation materials for transient conditions. These materials can maintain a nearly constant temperature during the phase transformation of pure or eutectic substances,which are used as thermal buffers in electronic devices, especially in applications with intermittent loading profiles or transient power spikes. This work specifically focuses on organic and metallic PCMs. Organic PCMs are characteristically lightweight, have a high specific latent heat, and are inexpensive. Despite these advantages, low thermal conductivity limits their widespread application. As an alternative, metallic PCMs have high volumetric latent heat and thermal conductivity values. This study introduces a new concept of combining the two PCMs into a material composite that exploits the advantageous physical characteristics and thermal properties of each material for specific transient thermal electronic applications.
This research aims to mitigate the overdesign of electronic packaging by incorporating melamine microencapsulated paraffin spheres embedded in a Field’s metal (32.5Bi/51In/16.5Sn wt%) matrix to dissipate heat. Four PCM concentrations are synthesized, with paraffin volumetric fractions of 21.8%, 40.3%, 50.1%, and 61.2%. The collected data is compared to distinct organic and metallic PCM performance records available in the literature. The results can guide future innovative composite studies.
To characterize the PCM composites, differential scanning calorimetry (DSC), scanning electron microscopy (SEM), micro-computed tomography (micro-CT), and time-domain thermoreflectance (TDTR) techniques are employed. Manual mixing most effectively combined the two PCMs after particle dispersion analysis in comparison to the other combination techniques. The physical experiments are validated by computer-modeled simulations. An explicit model of a dynamic system is created to characterize the interactions between the size of the particles, heat flux, and temperature propagation. The computer model provides insight into the material characteristics and interactions that facilitate predicting specific trends at various temperatures. In a high pulse rate scenario, with time scale matching, the onset of the steady state regime in a transient system is delayed by approximately 50%. The novel PCM fabrication approach presented here decreases the device package size, limits the associated weight, increases the system performance, and minimizes the composite cost (SWaP-C). The synthesized composites have enormous potential for cooling specific electronics-based applications due to the organic to metallic PCM ratio, tailorable material properties, and application-specific phase change onset temperature. This study provides a new foundation for future composite research that maximizes the advantages of systematically combining organic and metallic PCMs.
Dr. Damena Agonafer
Dr. Katharine Flores, Dr. Julio D’Arcy, Dr. Michael Fish, and Dr. Lauren Boteler