Temperature Control of Handheld Electronic Devices using Latent Heat Energy Storage
The processing power of handheld electronic devices, has increased rapidly over the last decade. Modern handheld devices are thin (<9 mm) and utilize passive temperature control strategies. The combination of these three factors has resulted in temperature control becoming a major obstacle to continued development. This work investigates the use of latent heat thermal energy storage (LHTES) modules to improve the temperature control of tablet computers. LHTES modules, utilizing solid-liquid phase change materials (PCM), were designed and tested. Modules of this type store energy during periods of high heat dissipation and release it at a later time when the device is less active. Numerical and experimental studies were used to investigate the design requirements for LHTES temperature control modules as well as the magnitude of performance improvement which they can provide. A key aspect of designing these systems is identifying the appropriate PCM, more specifically, what transition temperature is optimum. A numerical model of a tablet computer was created. Simulations with LHTES modules having transition temperatures between 35 and 47°C, showed that PCMs with lower transition temperatures allowed the tablet computer to operate longer without overheating. Phase change materials with transition temperatures between 35 and 40°C were found to be optimal. Two organic PCMs, n-eicosane (Tm=35.6 °C) and PT37 (Tm=36.4 °C), were selected. A simplified experimental setup was used to both investigate the thermal characteristics of LHTES temperature control modules, and validate the techniques used in the numerical model. These experiments compared the performance of LHTES modules using n-eicosane and dodecanoic acid (Tm=43 °C). It was found that n-eicosane was superior. The experiments also confirmed that the numerical techniques were effective. An experimental platform which simulated a tablet computer was built and used to test the effectiveness of an LHTES module based on n-eicosane. It was found that the module improved the temperature control of the simulated tablet computer, increasing the operational time before overheating by 30% and better controlling the temperature of the heat source.