Graphene based Efficient Heat Transfer Nanofluids for IC Engine Applications

Introduction: Nowadays, the need for specialty thermal fluids for critical applications are fulfilled by specifically formulated functional fluids. In daily used vehicles e.g. cars the ~ 80% energy get wasted as system energy loss (1). The rapidly increasing demand for high performance fluids for fast growing automotive sectors propel the newer research for development of functional fluids leading to enhancement in engine efficiency (2-4). The enhancement in engine efficiency can be achieved by increasing engine performance parameters e.g., improving design parameters, using efficient lubricants and coolants. The important area which largely affects the economic performance of engines and efficiency is engine cooling system and this has got little attention as compared to engine design. Therefore, an emerging area of research is to improve heat transfer efficiency of conventional heat transfer fluids. Development of new method with cost-effective route, scalable process to produce stable nanofluid dispersions with improved performance in all type of cooling needs is a big challenge. In recent years, the carbon nanostructure based nanofluids for heat transfer application have attracted huge interest (5). Methods: In the present work, graphene-based hybrid material was synthesized as thermally conducting additive. In order to synthesize graphene-based hybrid material, first reduced graphene oxide was synthesized followed by this it was in-situ reduced with silver nitrate to get silver decorated reduced graphene oxide. The final product formed was having silver nanoparticles decorated over ultra-thin reduced graphene oxide. Finally, nanofluids were developed using this material and thermal conductivity were evaluated under varying measurement conditions and concentrations. Results and discussions:  The nanofluid developed was subjected to its thermal conduction property evaluation. The thermal conductivities of nanofluids and base fluid was evaluated with KD2 pro instrument. Significant enhancement was observed in the thermal conductivity of the nanofluid developed and highest enhancement in thermal conductivity observed was 32% with respect to base fluid at room temperature at 0.2% vol. concentration. The measurements were also done with varying vol. concentration ranging from 0.01% to 0.4%. The rise in concentration resulted into rise in thermal conductivities but going beyond 0.2% concentration resulted into nominal to no change in thermal conductivities. The thermal conductivity was also evaluated with varying temperatures, ranging from 30℃ to 60 ℃. The rise in temperature lead to rise in thermal conductivity. The maximum thermal conductivity enhancement (by 39%) was observed at 60℃. The results show remarkable enhancement in thermal conductivity of nanofluid developed. Furthermore, the developed nanofluid was applied in custom made IC engine to evaluate its performance. The use of nanofluid in place of conventional coolant in IC engine lead to significant enhancement in different engine performance parameters. The total fuel consumption was enhanced by 10-12% compared to base fluid. Conclusions: The silver nanoparticles decorated graphene based thermal conductivity enhancement additive was developed and employed for the development of highly efficient engine coolant. The room temperature thermal conductivity enhancement was 32% with significant enhancement in engine performance parameters, which is quite promising result for engine cooling applications. Keywords: Nanofluids, thermal conductivity, graphene References Holmberg, K. and Erdemir A. (2019) The impact of tribology on energy use and CO2 emission globally and in combustion engine and electric cars. Tribology International. 135: p. 389-396. Gupta, K., et al., (2017) Catalytic Aerial Oxidation of Biomass‐Derived Furans to Furan Carboxylic Acids in Water over Bimetallic Nickel–Palladium Alloy Nanoparticles. 9(14): p. 2760-2767. Tanvir, S. and Qiao, L. (2012) Surface tension of nanofluid-type fuels containing suspended nanomaterials. Nanoscale research letters. 7(1): p. 1-10. Zhang, G., et al. (2016) Excellent heat dissipation properties of the super-aligned carbon nanotube films. RSC Advances. 6(66): p. 61686-61694. Kibria, M., et al. (2015) A review on thermophysical properties of nanoparticle dispersed phase change materials. Energy conversion and management. 95: p. 69-89.