Abstract
In this work, we perform an extensive numerical investigation of the heat transfer behavior of nanofluid laminar flows, in wavy-wall channels. The adopted computational approach is based on a finite-volume formulation of the lattice Boltzmann method constructed on a fully-unstructured mesh. We show the validity and effectiveness of this numerical approach to deal with realistic problems involving nanofluid flows, and we employ it to analyze the effects of the wavy-wall channel geometry on the rate of heat transfer, thus providing useful information to the design of efficient heat transfer devices. Results show that an increasing of the wavy surface amplitude has a positive effect on the heat transfer rate, while a phase shift between the wavy walls leads to a decreasing of the mean Nusselt number along the channel. The addition of solid nanoparticles within a base liquid significantly contributes to increase the rate of heat transfer, especially when a relatively high value of nanoparticles volume fraction is employed. The present analysis then suggests that the use of nanofluids within an axis-symmetric configuration of the wavy-wall channel, with high wavy surface amplitude, may represent an optimal solution to enhance the thermal performances of heat transfer devices.
Highlights
The low thermal conductivity of common heat transfer fluids such as water, oil and ethylene glycol represents a major limitation to the development of high-efficient heat exchangers, that are required in many industrial applications
In this paper, we extend a fully-unstructured method based on a finite-volume lattice Boltzmann formulation, originally developed by the the authors in [51], to account for the thermo-fluid dynamics phenomena occurring within nanofluid flows
The results show that our method has significant potential for the accurate calculation of nanofluid flows in complex geometries domain
Summary
The low thermal conductivity of common heat transfer fluids such as water, oil and ethylene glycol represents a major limitation to the development of high-efficient heat exchangers, that are required in many industrial applications. Different LBM realizations have been applied to study the thermal behavior of nanofluids, either by using the single phase or the multiphase approach [43,44,45,46,47,48] The majority of these works adopt the original formulation of LBMs, which is based on a uniform space discretization. The fully-unstructured mesh allows for a more efficient geometrical representation of complex boundaries, with respect to the original Cartesian formulation of LBM, while keeping the computational burden at a relatively low level In this sense, the inherent geometrical complexity of the wavy-wall channel does represent an interesting benchmark problem to evaluate the capability of the proposed approach of capturing the relevant physics behind heat transfer in nanofluids.
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