Using MWCNT and titanium oxide as boosters in passive heat transfer methods for clean and renewable energy applications

Passive heat transfer (PHT) methods provide an energy-efficient and environmentally friendly approach for transferring heat between systems, making them a promising solution for renewable and clean energy utilization across various applications. Changing the performance of heat transfer systems can be achieved by manipulating fluid flows. In this study, an investigation was conducted on the use of four blocks with different positions and sizes as obstacles embedded within a square enclosure, which affected the heat transfer through natural convection. Additionally, the study explored the effectiveness of a hybrid nanofluid created by injecting two types of nanoparticles, titanium oxide (TiO₂) and Multi-walled Carbon Nanotube (MWCNT), into the cooling fluid. Computational fluid dynamics (CFD) simulations were employed to examine the impact of the blocks, nanoparticle concentration, and Rayleigh number on heat transfer parameters. The findings revealed that the addition of a 6 % volume fraction of titanium oxide and MWCNT to the base fluid resulted in a notable increase of over 5 % but less than 30 % in the average Nusselt number. In contrast to expectations, embedding obstacles drooped off average Nusselt number by 9 to 30 % in Rayleigh numbers of 10,000 and 100,000, and had no effect in Rayleigh numbers of 100 and 1000.