The experimental investigation focused on the performance of a multi-turn closed loop pulsating heat pipe (CLPHP) with inner and outer diameters of 2 mm and 3.1 mm, respectively. This investigation was conducted under various conditions, including different fill ratios of 50% and 60%, with heat input applied at the bottom in a vertical orientation. The study employed two different working fluids: water and a water-based nanofluid containing SiO₂ at varying concentrations (0.1%, 0.5%, and 1%). The addition of SiO₂ nanoparticles was intended to enhance the performance of the CLPHP due to their superior thermal conductivity properties. The analysis, focusing on thermal resistance as a performance metric, confirmed that a 50% fill ratio is optimal for the CLPHP’s performance. However, at a 60% fill ratio, superior performance was observed when lower heat inputs were applied. The experimental results demonstrated that the lowest overall thermal resistance was achieved when a 1% concentration of nanofluid was added to the base fluid. This result was found to be even better than the thermal resistance achieved with pure water.

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