Nonlinear thermal convection of a non-Fourier fluid

Abstract

Purpose

The purpose of this paper is to determine the thermo-gravitational convective state of a non-Fourier fluid layer of the single-phase-lagging type, heated from below. Unlike existing methodologies, the spectral modes are not imposed arbitrarily. They are systematically identified by expanding the spectral coefficients in terms of the relative departure in the post-critical Rayleigh number (perturbation parameter). The number and type of modes is determined to each order in the expansion. Non-Fourier effects become important whenever the relaxation time (delay in the response of the heat flux with respect to the temperature gradient) is of the same order of magnitude as process time.

Design/methodology/approach

In the spectral method the flow and temperature fields are expanded periodically along the layer and orthonormal shape functions are used in the transverse direction. A perturbation approach is developed to solve the nonlinear spectral system in the post-critical range.

Findings

The Nusselt number increases with non-Fourier effect as suggested in experiments in microscale and nanofluid convection.

Originality/value

Unlike existing nonlinear formulations for RB thermal convection, the present combined spectral-perturbation approach provides a systematic method for mode selection.

Citation

Khorasany, R.M., Khayat, R.E. and Niknami, M. (2016), "Nonlinear thermal convection of a non-Fourier fluid", International Journal of Numerical Methods for Heat & Fluid Flow, Vol. 26 No. 3/4, pp. 639-670. https://doi.org/10.1108/HFF-05-2015-0205