Unsteady stagnation-point flow of upper-convected Oldroyd-B nanofluid with variable thermal conductivity and relaxation-retardation double-diffusion model
International Journal of Numerical Methods for Heat & Fluid Flow
ISSN: 0961-5539
Article publication date: 21 August 2021
Issue publication date: 1 November 2021
Abstract
Purpose
This paper aims to examine the unsteady stagnation-point flow, heat and mass transfer of upper-convected Oldroyd-B nanofluid along a stretching sheet. The thermal conductivity is taken in a temperature-dependent fashion. With the aid of Cattaneo–Christov double-diffusion theory, relaxation-retardation double-diffusion model is advanced, which considers not only the effect of relaxation time but also the influence of retardation time. Convective heat transfer is not ignored. Additionally, experiments verify that with sodium carboxymethylcellulose (CMC) solutions as base fluid, not only the flow curve conforms to Oldroyd-B model but also thermal conductivity decreases linearly with the increase of temperature.
Design/methodology/approach
The suitable pseudo similarity transformations are adopted to address partial differential equations to ordinary differential equations, which are computed analytically through homotopy analysis method (HAM).
Findings
It is worth noting that the increase of stagnation-point parameter diminishes momentum loss, so that the velocity enlarges, which makes boundary layer thickness thinner. With the increase of thermal retardation time parameter, the nanofluid temperature rises that implies heat penetration depth boosts up and the additional time required for nanofluid to heat transfer to surrounding nanoparticles is less, which is similar to the effects of concentration retardation time parameter on concentration field.
Originality/value
This paper aims to explore the unsteady stagnation-point flow, heat and mass transfer of upper-convected Oldroyd-B nanofluid with variable thermal conductivity and relaxation-retardation double-diffusion model.
Keywords
Acknowledgements
This work is supported by the National Key Research Program of China (No. 2016YFC0700601), the National Natural Science Foundation of China (No. 21878018), the Joint Funding Project of Beijing Municipal Natural Science Foundation and Beijing Municipal Education Commission (No. KZ201810016018) and the Fundamental Research Funds for Beijing University of Civil Engineering and Architecture (X20142). The authors sincerely thank the editor and referees for their helpful comments and suggestions.
Citation
Bai, Y., Wang, Q. and Zhang, Y. (2021), "Unsteady stagnation-point flow of upper-convected Oldroyd-B nanofluid with variable thermal conductivity and relaxation-retardation double-diffusion model", International Journal of Numerical Methods for Heat & Fluid Flow, Vol. 31 No. 11, pp. 3373-3393. https://doi.org/10.1108/HFF-10-2020-0664
Publisher
:Emerald Publishing Limited
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