An experimental and numerical study of turbulent heat transfer enhancement for graphene nanofluids produced by pulsed discharge

Abstract

Developing production methods for graphene nanofluids that can produce them in large quantities at once in a short time and at a low cost will contribute to the development of a wide range of industries that use nanofluids, and understanding their properties through mathematical modeling and experiments will lead to the development of new nanofluids. In this study, the new production method of graphene nanofluids is proposed and experimental and numerical investigations of the turbulent heat transfer performance of graphene nanofluids in a horizontal circular tube subjected to constant heat flux are conducted. The experimental investigation is conducted to evaluate the turbulent heat transfer performance of graphene nanofluids which are made by a new method using pulsed discharge and to compare them with numerical results. In the numerical investigation, the finite volume method with a Realizable k-ε model and Two-layer model is employed to solve the continuity, momentum, and energy conservation in two-dimensional domains. The Lagrangian two-phase model is applied to consider the physical interaction between the dispersed phase and continuous phase. In this model, the particles are tracked in a Lagrangian manner and coupled with the Eulerian flow description. Since the computational burden would be tremendous if individual nanoparticles were tracked in a Lagrangian manner, we defined a cluster of particles, called a parcel and treated it statistically. This concept of parcels allowed the average behavior of nanoparticles to be established as an analytical parameter. As a result, graphene nanofluids are not produced by pulsed discharge alone but are successfully produced by applying ultrasonic. Experimental investigations show a 33% increase in the Nu number of graphene nanofluid produced by pulsed discharge compared to water as the flow velocity increased. Numerical investigations confirm changes in the properties (Turbulent kinetic energy, Velocity distribution, Temperature distribution) of the continuous phase due to physical interactions between the dispersed and continuous phases. It is also shown that these changes contribute to the improved turbulent heat transfer performance of the nanofluid and that the aggregation of particles into the center of the tube is responsible for these changes.

Keywords

• Nanofluid
• Pulsed discharge
• Two-phase model
• Convective heat transfer
• Graphene