Thermal optimization of flat plate closed-loop oscillating heat pipes using microencapsulated phase change materials suspensions in hollow evaporator sections: an experimental study

Flat plate closed-loop oscillating heat pipes (FP-CLOHPs) are efficient devices that use oscillatory fluid motion for heat transfer between evaporator and condenser sections. This study presents a novel approach to enhance thermal performance by modifying the working fluid's properties instead of expanding the FP-CLOHP structure. It investigates the effects of microencapsulated phase change materials (ME\PCMs) combined with water and polyethylene glycol, specifically focusing on 2% and 5% volume suspensions. The study analyzes varying filling ratios (25%, 50%, and 75%) and inclination angles (0 degrees, 30 degrees, 60 degrees, and 90 degrees) on thermal resistance, temperature differences between the evaporator and condenser, and the time to reach a critical temperature of 80 degrees C. Results reveal that the 2%vol ME\PCM suspension outperforms both deionized water and the 5%vol ME\PCM suspension, showing lower thermal resistance and longer time to reach critical temperature. An optimal filling ratio of 50% is established, providing a 6% and 32% thermal resistance improvement over the 25% and 75% ratios, respectively. The vertical orientation (90 degrees inclination) achieves the lowest thermal resistance, aided by gravitydriven fluid circulation. Overall, this innovative design significantly enhances heat transfer efficiency compared to conventional FP-CLOHP configurations.