Enhancing Heat Transfer with Nanofluids: A New Frontier in Cooling Systems

Efficient heat transfer is vital for numerous industrial applications, from cooling electronics to optimizing renewable energy systems. The latest research led by a team led by Dr. Samarshi Chakraborty from BITS- K K Birla Goa Campus, in collaboration with other National & International institutes, explores the potential of nanofluids—fluids infused with nanoparticles—as superior coolants. This study investigates the thermal properties and flow behaviour of 45 different nanofluids, focusing on optimizing their use in heat transfer systems. By examining factors such as the heat transfer coefficient and pumping power, the research aims to rank the most efficient nanofluids for practical applications.

Nanofluids are a blend of a base fluid, like water or oil, and nanoparticles- ultrafine particles typically less than 100 nanometres in size. They enhance the fluid’s thermal conductivity and heat transfer performance. Unlike conventional coolants, nanofluids offer improved efficiency even with small concentrations of nanoparticles. Various types of nanofluids, including metal-based (e.g., silver, copper), metal-oxide-based (e.g., Al2O3, TiO₂), non-metal-based (e.g., graphene, CNT), and hybrid combinations (e.g., Ag/HEG, CNT/Al2O3) were analysed.

The research focused on developing a comprehensive dataset on the thermo-physical properties of different mono and hybrid nanofluids. By employing the figure of merit analysis, the study aimed to determine the suitable operational flow regimes and overall thermal effectiveness of these nanofluids. It evaluated factors like heat transfer performance, friction factor, and pumping power, ranking the nanofluids by heat transfer coefficients. The study also analyzed how various design and process parameters, such as pressure drop and flow velocity, affect the thermal performance of nanofluids. Overall, the research offers insights into maximizing heat transfer efficiency while minimizing energy costs. The team analyzed several thermo-physical properties, heat transfer performance indicators, and operational factors, such as:

• Thermo-physical properties: Density, thermal conductivity, specific heat, and viscosity of the nanofluids.

• Heat transfer coefficient: A measure of how effectively the fluid transfers heat.

• Friction factor: This influences the pumping power required to move the nanofluid through a system.

Figure of merit (FOM) analysis determines the optimal flow regime for a nanofluid using the Mouromtseff number (Mo), which indicates the thermal effectiveness of heat transfer fluids. It's calculated by comparing the Mo of the nanofluid to that of the base fluid. For nanofluids to be practical, their improved thermal properties must compensate for any increase in viscosity due to nanoparticle addition. This balance is assessed through FOM analysis. A higher Mo value (Mo > 1) indicates more efficient heat transfer with minimized energy costs. This study tested nanofluids in both laminar and turbulent flow regimes to identify the best-performing fluids under each condition. 

The study examined 45 nanofluids, focusing on 20 popular ones to analyze nanoparticle loading effects on operational feasibility across various flow regimes. Out of these, 9 nanofluids were selected for detailed sensitivity analysis on parameters like pressure drop, flow velocity, mass flow rate, channel diameter, and temperature gradients. Key findings from the work include:

• Among 45 tested nanofluids, 13 nanofluids are suitable for laminar flow, 1 for turbulent flow, and 26 for both.

• Nanofluids' heat transfer coefficient, friction factor, and pumping power were evaluated, showing CNT/Al2O3 (at 0.01 vol% loading), Cu (at 0.05 vol% loading), and CNT (at 1 vol% loading) nanofluid, as the top performers based on heat transfer coefficient value.

• Optimal nanofluid concentration is crucial for desired heat transfer performance.

• Pressure drop and flow velocity significantly affect friction factor and pumping power.

• Heat transfer coefficient varies with mass flow rate, internal diameter, and fluid temperature gradient.

Overall, the study provides insights into maximizing heat transfer efficiency and minimizing energy costs using nanofluids under different operational conditions. The insights gained from this study could pave the way for more efficient cooling systems across industries. The superior heat transfer properties of nanofluids, especially those with copper, CNT, and hybrid compositions, make them promising candidates for use in high-performance cooling systems, such as those used in electronic devices, automotive systems, and even renewable energy technologies like solar thermal systems.

This research highlights the interdisciplinary collaboration between multiple institutions. Researchers from BITS- K K Birla Goa Campus collaborated with experts from the Vellore Institute of Technology (India), University of Sharjah (UAE), Lebanese American University (Lebanon), Instituto Superior Técnico (Portugal), and Western Sydney University (Australia), combining expertise in chemical engineering, mechanical engineering, and renewable energy to push the boundaries of nanofluid applications.