Abstract
To improve the heat transfer characteristics of lubricant, graphene-based lubricants were prepared by adding graphene particles, due to its advantages of excellent thermal conductivity and two-dimensional sheet structure. In the present study, its physical properties were measured. A flow heat transfer experiment platform was built to study the flow and heat transfer characteristics of the graphene lubricating oil in a horizontal circular tube. The results show that the graphene lubricant prepared using a two-step approach had good stability, and the dispersibility was good without the agglomeration phenomenon, according to measurements undertaken using an electron microscope and centrifuge. The thermal conductivity and viscosity of graphene lubricant increased with the increase of the graphene concentration, and the thermal conductivity of graphene lubricant with the same concentration decreased with the increase of temperature. When the concentration was equal, the convective heat transfer Nusselt number (Nu) of graphene lubricant increased with the increase of Reynolds number (Re). When Re was equal, the convective heat transfer Nu increased with the increase of graphene particle concentration, and the maximum Nu increased by 40%.
Highlights
The internal combustion engine is a power source of vehicles
When graphene nanofluids were added to the lubricant, the thermal conductivity decreased the thermal conductivity decreased with the increase of temperature, and with the increase of mass with the increase of temperature, and with the increase of mass concentration, the decline increased
Because the fluid inlet temperature fluctuates slightly, the measured wall temperature was used to subtract the fluid inlet temperature as the excess wall temperature after normalization treatment. It can be seen in the figure that the excess wall temperature of lubricant with mass fractions of 0.5%, 1%, 2%, and 3% increased with the increase in tube length under the same flow rate, and when the velocity and position were fluctuates slightly, the measured wall temperature was used to subtract the fluid inlet temperature as the excess wall temperature after normalization treatment. It can be seen in the figure that the excess wall temperature of lubricant with mass fractions of 0.5%, 1%, 2%, and 3% increased with the increase in tube length under the same flow rate, and when the velocity and position were constant, excess wall temperature decreased with the increase in graphene nanofluid concentration
Summary
The internal combustion engine is a power source of vehicles. It converts the thermal energy released from the combustion of fuels into mechanical energy that drives the vehicles. As an important friction pair, the thermal load and lubrication friction status of the piston set–cylinder liner directly influence the reliability and durability of the internal combustion engine. The research of Heris et al [11] found that the convective heat transfer coefficient of nanofluid increased with the increase of volume concentration of nanoparticles. Regardless of the nanoparticles added to the lubricant, they can increase thermal conductivity and the convective heat transfer coefficient from the perspective of heat transfer Researchers believe this is caused by Brownian motion, the boundary layer between the surface of nanoparticles and the solution, and the particle aggregation in the solution and phonon transfer [22]. Graphene nanoparticles have become potential high-performance lubricating materials with excellent thermal conductivity, antifriction, and anti-wear properties, in addition to chemical inertness, which can obviously improve the heat transfer characteristics of lubricants. An experimental platform was built to study the flow and heat transfer characteristics in a horizontal round tube
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