Effect of velocity and rheology of nanofluid on heat transfer of laminar vibrational flow through a pipe under constant heat flux

Transverse vibration creates strong vorticity to the plane perpendicular to flow direction which leads to the radial mixing of fluid and, therefore, the results of heat transfer are significantly improved. Comparative studies of effects on heat transfer were investigated through a well-valid CFD model. Water and water-based nanofluid were selected as working substances, flowing through a pipe subjected to superimposed vibration applied to the wall. To capture the vibration effect in all aspects; simulations were performed for various parameters such as Reynolds number, solid particle diameter, volume fraction of nanofluid, vibration frequency, and amplitude. Temperature, solid particle diameter and volume fractiondependent viscosity have been considered; whereas, the thermal conductivity of nanofluid has been defined to the function of temperature, particle diameter and Brownian motion. Due to transverse vibrations, the thermal boundary layer is rapidly ruined. It increases the temperature in the axial direction for low Reynolds number flow that results in high heat transfer. As the Reynolds number increases, vibration effect is reduced for pure liquid, while there is noticeable increase for nanofluid. The rate of increment of heat transfer by varying volume fraction and particle diameter shows the usual feature as nanofluid under steady-state flow, but when subjected to vibration is much higher than pure liquid. As the frequency increases, the vibration effects are significantly reduced, and in amplitude they are profounder than frequency. The largest increase of about 540% was observed under the condition of vibrational flow compared to a steady-state flow.