Experimental Study of Thermal Properties and Dynamic Viscosity of Graphene Oxide/Oil Nano-Lubricant

Ready-to-use graphene-related material-added multi-grade oils: characterization and performance in car engine working conditions

The need for energy efficiency is leading to the growing use of additives to enhance the performance of oil in automotive engines. Great interest is focused on nano-additives even if to date there is still no practical use in commercial liquid lubricants. Herein, the potential of industrially scalable and low-cost graphene-related materials (GRMs) as additives to enhance the performance of oil in automotive engines is explored. The use of polyalkylmethacrylate dispersants, the most common key additives to formulate "green technology" lubricant oils liquid-processed GRM, is explored, investigating the role of the lateral size and the chemical analysis in the stability of the lubricant GRM dispersions. Showing the maximum duration of stability and a production method that avoids the use of strong oxidants, rheological tests were then focused on multilayered graphene flakes with sub-micrometre lateral size mixed in two commercial oil grades (5W-30 and 5W-40) under conditions similar to those of engine operation. The addition of such a filler increases the viscosity without affecting the Newtonian fluid behavior, while four-ball tests show a reduction in wear, indicating improved lubrication performance. Finally, preliminary bench-test on a commercial car engine showed increased power output corresponding to enhanced engine efficiency. The results clearly indicate the effective improvement in lubricating commercial oils due to GRM additives.

Thermal performance analysis of a flat-plate solar heater with zigzag-shaped pipe using fly ash-Cu hybrid nanofluid: CFD approach

Regarding the detrimental impacts of using non-renewable energy resources on the environment and the importance of increasing heat transfer in heat exchangers, this research is aimed to increase the heat transfer surface of the collector pipe in contact with the absorber plate at the flat-plate solar collector by designing the pipe in a zigzag shape instead of conventional straight pipe. The 3D coupled investigation of fly ash-Cu/water hybrid nanofluids and analyzing the thermal performance of the proposed solar collector comprising zigzag pipe are the innovation of this research. Also, the effect of variations in mass flow rate, fluid inlet temperature, the volume fraction of nanoparticles on thermal efficiency, Nusselt number, pressure drop, Rayleigh number, and rate of heat transfer coefficient in three irradiations with two types of working fluids have been investigated. Results indicate that due to the enhancement in heat transfer surface in the case where the fluid path is zigzag, the thermal efficiency has improved compared to the straight pipe. In addition, with enhancing mass flow rate, temperature, and irradiation, the average Nusselt number increased. The heat transfer coefficient and pressure drop have the highest value by utilizing 0.5% and 3.5% nanoparticle concentration up to 10.84% and 7.603%, respectively, at a mass flow rate of 0.0089 kg/s, and irradiation of 800 W/m2. Finally, by calculating the efficiency index of the proposed flat-plate solar collector, the proper volume concentration for using copper-fly ash/water hybrid nanofluid is obtained at fraction of 0.5% and a mass flow rate of 0.0045 kg/s.

A Review on Thermophysical Properties for Heat Transfer Enhancement of Carbon‐Based Nanolubricant

In previous years, nanolubricants have gained attention in terms of their use as heat transfer fluids in applications such as engine cooling and air conditioning. Carbon‐based nanolubricants have attracted great interest due to their superior heat transfer performance. To date, the stability of a carbon‐based nanolubricant is crucial if the enhanced properties are to be retained after the fabrication process. In this context, the current research aims to review the stability and thermophysical properties of carbon‐based nanolubricants. Recent works on these nanolubricants are summarized herein, including the method of preparation and improvements in their properties. The factors that affect the thermal conductivity and viscosity are also discussed, and finally, the applications of nanolubricants are described. The recent studies of nanolubricants are summarized and opportunities for further improvements in their efficiency are suggested.