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

Abstract

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.

Stability analysis of multiple solutions in case of a stretched nanofluid flow obeying Corcione's correlation: An extended Darcy model

“…The trend is similar for the second and third solutions as well for each case. The effects of variations in porosity (𝜙), nanoparticle volume fraction (𝜑) and nanoparticle shape (𝑛) on 𝑉 ′ and 𝜃 for the triple solutions is displayed in Figures (10)- (15). In case of larger 𝜙, the medium gets larger pore space, which leads to augmentation of nanofluid flow.…”

“…Opposite effects in natural convection conditions were discussed by Wang et al [11] where the heat transfer enhancement ratio deteriorated with reducing the size of 𝐴𝑙 2 𝑂 3 nanoparticles in a water based colloid. Some recent studies have also been conducted utilizing the empirical Corcione's correlation [12][13][14][15]. With the incorporation of Corcione's model of effective dynamic viscosity, it will be interesting to explore the immediate influence of nanoparticle size on the dynamics of nanofluid flow occupying a porous space.…”

Thermal Performance Enhancement in Flat Plate Solar Collector Solar Water Heater: A Review

“…The vibration effect on natural convection heat transfer increased heat-transfer coefficient up to 104%. Santosh et al [65] studied the convective heat-transfer coefficient of steady-state and unsteady-state (vibration) laminar flow of Al 2 O 3 -water-based nanofluid and of pure water at frequency 50 to 100 Hz. The result showed heat-transfer rate for nanofluid flow was greatly influenced by the amplitude and frequency.…”

Theoretical study on the optimal thermal excitation of bimaterial cantilevers

“…This result can be qualitatively explained if the vibrationdependent heat transfer is considered. It has been shown that vibrating surfaces 27) or liquid 28) can greatly enhance heat transfer; for example, an increase by eight times for Ti films vibrating in water was observed at frequency of kHz in comparison to that for a static film. 27) Therefore, the forced convection can be increased several times and it can result in a different response of the cantilever.…”