International Journal of Numerical Methods for Heat & Fluid Flow最新文献

Purpose

This study aims to extend the application of the lattice Boltzmann method (LBM) to solve solid-to-liquid phase transition problems involving low Prandtl number (Pr) materials. It provides insight about the flow instability in a cavity undergoing melting. This work further report interface development and thermal transport against the Boussinesq number.

Design/methodology/approach

This study modifies the lattice Bhatnagar–Gross–Krook model by including correction components in the energy and density distribution functions. To prevent numerical instability, a tuning parameter in the flow domain is set in the range of 0.15–0.7 for the range of Rayleigh number and Prandtl number. To the best of the authors’ knowledge, the modified LBM is being used for the first time to examine the low Pr domain melting behavior of liquid metals.

Findings

The interaction with complicated flow structure with natural convection, studied in a square enclosure, has a significant impact on the melting of metals in the low Pr range. Results show that the melting rate and the length of the interface between two phases are significantly influenced by the Boussinesq number (Bo), the product of Pr and Rayleigh number (Ra). For changing Ra, the maximum interface length is almost constant in the in the Boussinesq number range up to 100 and beyond this range the interface length increases with Bo.

Originality/value

The effects of Pr on melting rate, Ra and Pr together on the length of the solid–liquid interface and the thermofluidic behavior in the melt zone are explained. This work also includes mapping the maximum melt interface size with Bo.

Purpose

This study aims to perform a comprehensive comparative analysis of the performance of microchannel heat sinks (MCHS) across a wide range of operating conditions. It investigates the interplay between heat transfer efficiency, frictional effects and flow dynamics in different channel configurations and fluid types.

Design/methodology/approach

The analysis is conducted through numerical simulations, solving the governing equations for mass, momentum and energy conservation. Multiple channel geometries are evaluated, each incorporating specific strategies to disrupt the thermal boundary layer along the heated channel surface. The study also considers the influence of transverse vorticity effects arising from abrupt or smooth geometric variations. The performance is assessed for three distinct fluids – mercury, helium and water – to examine the complex interplay between fluid properties (e.g. viscosity and thermal diffusivity), momentum losses and heat transfer gains. Key parameters, including the Reynolds number and Prandtl number, are systematically varied to uncover their impact on heat transfer coefficients, vorticity distribution and flow stability.

Findings

The study reveals that microchannels with wavy geometries and double internal bifurcations consistently deliver superior thermal performance compared to other configurations, regardless of the working fluid. The results highlight that variations in the Prandtl number significantly influence the dimensional convective heat transfer coefficient, vorticity patterns and the onset of fluid-dynamic instabilities for a fixed Reynolds number and geometry. The authors introduce a correlation for the Nusselt number with the exponents for the Reynolds and Prandtl numbers being ½ and ¼, respectively; the authors also show that, in agreement with existing literature, the friction factor is primarily affected by the Reynolds number and channel shape, demonstrating no dependence on the Prandtl number.

Originality/value

This research provides novel insights into the non-linear scaling of heat transfer and momentum loss with fluid properties in MCHS. The systematic exploration of fluid and geometric interactions enriches the current understanding of microchannel heat transfer mechanisms, presenting actionable recommendations for real-world applications.

Purpose

The complex behavior of viscoelastic fluids and its flow analysis under the impact of transverse magnetic field are becoming increasingly important in numerous emerging applications including biomedical engineering, aerospace engineering, geophysics and industrial applications. Additionally, the thermal analysis and fluid flow driven by propagating membranes will aid significant applications for microscale transport in bio-thermal systems. This study aims to investigate the thermal effects of viscoelastic fluids driven by membrane-induced propagation and transverse magnetic field.

Design/methodology/approach

The propagation of the membranes will work as pump which pushes the fluids from bottom to top against the gravitation force; however, there is backflow due to compression and expansion phases of membrane propagation. The Jeffrey fluid model is employed to analyze the viscoelastic fluid flow, with entropy generation examined and equations solved analytically under low Reynolds number and long-wavelength assumptions.

Findings

The findings reveal that an increase in magnetic field strength impedes fluid flow, while higher values of the Grashof number, heat source parameter and Jeffrey fluid parameter enhance fluid motion. The study’s findings have significant implications for optimizing magnetohydrodynamic systems in various emerging applications, including biomedical engineering, aerospace, geophysics and industrial processes.

Originality/value

This study aims to investigate the impact of a transverse magnetic field on the flow and heat transfer characteristics of viscoelastic fluids driven by membrane propagation.

Purpose

The purpose of this study is to develop and evaluate a novel solar still system integrating external solar heating and condensation units, comparing its performance with traditional methods through experimental and numerical analyses to optimize clean water production and energy efficiency.

Design/methodology/approach

This study involved designing a novel solar still system with an external solar heating unit and a prism-type condensation chamber. Two configurations were tested experimentally: one with internal condensation inside the prism and another with an air pump extracting vapor for external condensation. computational fluid dynamics (CFD) simulations were conducted to analyze temperature distributions and airflow dynamics in the system. Energy and exergy analyses were performed to evaluate the thermal performance and efficiency of both configurations, comparing clean water production rates and system effectiveness.

Findings

This study found that the solar still system using an air pump with external condensation significantly enhanced water production, achieving approximately 144.7% more clean water compared to the internal condensation method. Scenario 2, with the external condensation configuration, demonstrated a slight improvement in thermal efficiency (12.84%) over Scenario 1 (12.36%) and higher exergy efficiency (5.86% compared to 4.83%). CFD simulations provided insights into the temperature and air velocity distributions, highlighting the effectiveness of the external heating and condensation setup. The results demonstrate the potential of the novel system to improve clean water production while maintaining energy efficiency.

Originality/value

This study introduces a novel solar still design that integrates an external solar heating unit and an air pump-driven external condensation system, demonstrating a significant improvement in clean water production. By combining experimental results, CFD simulations and energy-exergy analyses, it provides valuable insights for optimizing solar-powered desalination systems with enhanced efficiency and sustainability.

Purpose

This study aims to explore the influence of Fourier-feature enhanced physics-informed neural networks (PINNs) on effectively solving two-dimensional local time-fractional anomalous diffusion equations with nonlinear thermal diffusivity. By tackling the shortcomings of conventional numerical methods in managing fractional derivatives and nonlinearities, this research addresses a significant gap in the literature regarding efficient solution strategies for complex diffusion processes.

Design/methodology/approach

This study uses a quantitative methodology featuring a feed-forward neural network architecture combined with a Fourier feature layer. Automatic differentiation is implemented to ensure precise gradient calculations for fractional derivatives. The effectiveness of the proposed approach is showcased through numerical simulations across various sub-diffusion and super-diffusion scenarios, with fractal space parameters adjusted to examine behavior. In addition, the training process is assessed using the Fisher information matrix to analyze the loss landscape.

Findings

The results demonstrate that the Fourier-feature enhanced PINNs effectively capture the dynamics of the anomalous diffusion equation, achieving greater solution accuracy than traditional methods. The analysis using the Fisher information matrix underscores the importance of hyperparameter tuning in optimizing network performance. These findings support the hypothesis that Fourier features improve the model’s capacity to represent complex solution behaviors, providing the relationship between model architecture and diffusion dynamics.

Originality/value

This research presents a novel approach to solving fractional anomalous diffusion equations through Fourier-feature enhanced PINNs. The results contribute to the advancement of computational methods in areas such as thermal engineering, materials science and biological diffusion modeling, while also providing a foundation for future investigations into training dynamics within neural networks.

Purpose

This paper aims to present a topology optimization (TopO) method for designing heat exchangers (HEx) with two working fluids to be kept apart. The introduction of cut–cells gives rise to the cut-cell TopO method, which computes the optimal distribution of an artificial impermeability field and successfully overcomes the weaknesses of the standard density-based TopO (denTopO) by computing the fluid–solid interface (FSI) at each cycle. This allows to accurately solve the flow and conjugate heat transfer (CHT) problem by imposing exact boundary conditions on the computed FSI and results to correct performances computed without the need to re-evaluate the optimized solutions on a body-fitted grid.

Design/methodology/approach

The elements of an artificial impermeability distribution field defined on a background grid act as the design variables and allow topological changes to take place. Post-processing them yields two fields indicating the location of the two flow streams inside the HEx. At each TopO cycle, the FSIs computed based on these two fields are used as the cutting surfaces of the cut-cell grid. On the so-computed grid, the incompressible Navier–Stokes equations, coupled with the Spalart–Allmaras turbulence model, and the temperature equation are solved. The derivatives of the objective and constraint functions with respect to the design variables of TopO are computed by the continuous adjoint method, using consistent discretization schemes devised thanks to the “Think Discrete – Do Continuous” (TDDC) adjoint methodology.

Findings

The effectiveness of the cut-cell–based TopO method for designing HEx is demonstrated in 2D parallel/counter flow and 3D counter flow HEx operating under both laminar and turbulent flow conditions. Compared to the standard denTopO, its ability to compute FSIs along which accurate boundary conditions are imposed, increases the accuracy of the flow solver, which usually leads to optimal, rather than sub-optimal, solutions that truly satisfy the imposed constraints.

Originality/value

This work proposes a new/complete methodology for the TopO of two-fluid systems including CHT that relies on the cut-cell method. This successfully combines aspects from both TopO and Shape Optimization (ShpO) in a single framework thus overcoming the well-known downsides of standard denTopO regarding its accuracy or the need for a follow-up ShpO after TopO. Instead of adding the well-known Brinkman penalization terms into the flow equations, it computes the FSIs at each optimization cycle allowing the solution of the CHT problem on a cut-cell grid.

Purpose

This study aims to present an isogeometric boundary element formulation that stably and accurately models the motion of a droplet with arbitrary viscosity in free flows and microchannel confinements.

Design/methodology/approach

Like other numerical methods, isogeometric boundary element formulation also suffers from mesh distortion; therefore, volume correction and mesh relaxation are also required for efficient and stable simulations of deformable particles in Stokes flow with high accuracy. To improve the stability and accuracy of the proposed formulation, (i) volume correction and (ii) mesh relaxation algorithms to prevent mesh distortion are implemented.

Findings

Several test cases for a droplet in free-space shear flow are demonstrated for different Ca and viscosity ratio values which determine the deformability of a droplet. The results reveal that the drift of the enclosed volume inside a droplet and the mesh distortion becomes severe at low viscosity ratios and high Ca values, i.e. in the high deformability regime. The proposed numerical method integrating the stabilization algorithm enables the simulations at low spatiotemporal resolutions, even in extreme cases. The proposed method provides more than 10× speed-up compared to high-fidelity simulations without mesh relaxation. Efficient and accurate 3D simulations of droplets are also presented for simulations in microfluidic confinement.

Practical implications

The current formulation can be applied for many different microfluidic applications, and can be extended to tackle multiphysics simulations of multiple droplets in microchannel confinement.

Originality/value

The paper presents an isogeometric boundary element formulation with volume correction and mesh relaxation to model the motion of a droplet with arbitrary viscosity in free flows and microchannel confinements.

Purpose

Magnetohydrodynamics (MHD) in nanofluids is crucial in boundary layer flow as it enables the manipulation of fluid motion through magnetic fields, which leads to improved stability and efficiency. This study aims to introduce a model and solutions for the boundary layer flow of a ternary hybrid nanofluid past a permeable shrinking sheet, integrating both magnetohydrodynamic and slip effects.

Design/methodology/approach

The model is firstly expressed as partial differential equations and subsequently converted into ordinary differential equations (ODEs) through a similarity transformation technique. A finite difference scheme with the Lobatto IIIa formula in MATLAB is applied to numerically solve the ODEs, where the respective outcomes provide insights into the skin friction coefficient, Nusselt number, velocity profiles and temperature profiles.

Findings

The results highlight the significance of enhancing magnetohydrodynamic effects and first-order velocity slip to reduce skin friction, improve heat transfer, delay boundary layer separation, increase flow velocity and lower fluid temperature. In addition, the stable numerical solution is scrutinized using response surface methodology (RSM) to validate and optimize flow control. The RSM optimization confirms that higher suction, magnetohydrodynamic effects and first-order slip levels are essential for minimizing skin friction and maximizing heat transfer simultaneously.

Originality/value

The presented model together with the numerical and statistical results can be used as a guidance to control the flow and heat transfer that occur within a related practical application, especially in engineering and industrial activities such as cooling technologies, energy harvesting or fluid transport in nanotechnology, where precise control of heat transfer and fluid dynamics is essential for optimizing performance and reducing energy consumption.