Magnetic Field Effect on the Double Diffusive Natural Convection in Three-Dimensional Cavity Filled with Micropolar Nanofluid

This article presents a three-dimensional numerical investigation of heat and mass transfers and fluid flow in a cavity filled with an Al2O3/water micropolar fluid under uniform magnetic field. To solve the governing non-dimensional equations, Finite Volume Method (FVM) based on 3-D vorticity-vector potential formulation has been employed. The effects of various parameters such as buoyancy ratio (−2 ≤ N ≤ 0), Rayleigh number (103 ≤ Ra ≤ 105), Hartmann number (0≤ Ha≤ 60), nanoparticles volume fraction (0 ≤ φ ≤ 0.06) and micropolar material parameter (0≤ K≤ 5) on flow structure and on heat and mass transfers are presented. The results illustrate that for the micropolar nanofluid model, both heat and mass transfer rates and three-dimensional character of the flow are smaller when compared with the pure nanofluid model. It is also observed that increase and decrease in heat and mass transfer rates is experienced due to increase in Rayleigh number and Hartmann number, respectively. It is also noted that increase in vortex viscosity parameter reduces the average heat and mass transfer rates and is more evident when the magnetic field is imposed. Combined effects of magnetic field and nanoparticles volume fraction on heat and mass transfers are also explored

Numerical simulation of three-dimensional thermo-solutal convection of micropolar multi-walled carbon nanotubes water nanofluid stabilized by lignin and sodium polycarboxylate

International audienceA computational analysis has been performed in this study to solve three-dimensional thermo-solutal natural convection in a differentially heated cubical enclosure filled with micropolar CNT/water nanofluid stabilized by two types of surfactants lignin and sodium polycarboxylate. The work is carried out for different pertinent parameters as Rayleigh number (104 ≤ Ra ≤ 106), micropolar parameter (0 ≤ K ≤ 10), buoyancy ratio (−1 ≤ N ≤ 0) and nanoparticles’s volume fraction (0.0055% ≤φ≤ 0.557%). It is observed that the heat and mass transfer rates are lower for a micropolar nanofluid model when compared to the pure nanofluid model. In fact, the enhancement of micropolar parameter results a decrease in average Nusselt and Sherwood numbers. The use of lignin as a surfactant ameliorates heat and mass transfer rate and nanofluid flow better than the use of sodium polycarboxylate as a surfactant. The nanoparticles volume fraction can be used as a control element for heat rate and fluid flow. Thus, for a nanoparticles volume concentration less than the critical value, the flow intensity is ameliorated and is deteriorated when it exceeds this value

Effect of Surfactants on double diffusive natural convection of CNT water-based micropolar nanofluids

International audienc

Three-dimensional analysis of combined thermal-solutal buoyancy and capillary convection of water-based micropolar multi-walled carbon nanotubes nanofluids

International audienceA parametric numerical investigation has been performed of three-dimensional combined thermal-solutal capillary and buoyancy convection performances of micropolar multi-walled carbon nanotubes-water nanofluid. The governing equations are given based on vorticity-vector potential formulation and numerically resolved with finite volume method. The effects of Rayleigh number (10(4) <= Ra <= 10(6)), micropolar parameter (0 <= K <= 5), buoyancy ratio (- 2 <= N <= 0), Marangoni number (0 <= Ma <= 1000), and nanofluid concentration (0.0055% <= phi <= 0.557%) on Sherwood/averaged Nusselt number are examined along with their impact on the streamlines, isotherms, and isoconcentrations. The results imply the significant impact of surface tension on the heat/mass transfer rate, in low Rayleigh number in particular Besides, the averaged Nusselt and Sherwood numbers are improved significantly due to arise in the Marangoni number originated from unidirectional effects of surface tension and buoyancy for the thermal-dominated regime. Within solutal-buoyancy governed zone, however, an opposite trend is evidenced. Heat/mass transfer rate is overestimated when the micropolar theory is not taken into consideration. Also, the performance of multi-walled carbon nanotubes/water nanofluid depends on the nanoparticles volume concentration. Hence, there is a critical nanofluid concentration beyond which the intensity of flow increases and then declines

Improvement of the energy and exergy efficiencies of the parabolic solar collector equipped with a twisted turbulator using SWCNT-Cu/water two-phase hybrid nanofluid

Please read abstract in the article.The Deanship of Scientific Research at King Khalid University, Abha, Saudi Arabia.http://www.elsevier.com/locate/seta2023-11-17hj2023Mechanical and Aeronautical Engineerin

Estimating Relaxation Time and Fractionality Order Parameters in Fractional Non-Fourier Heat Conduction Using Conjugate Gradient Inverse Approach in Single and Three-Layer Skin Tissues

In this work, the relaxation parameter (τ) and fractionality order (α) in the fractional single phase lag (FSPL) non-Fourier heat conduction model are estimated by employing the conjugate gradient inverse method (CGIM). Two different physics of skin tissue are chosen as the studied cases; single and three-layer skin tissues. Single-layer skin is exposed to laser radiation having the constant heat flux of Qin. However, a heat pulse with constant temperature is imposed on the three-layer skin. The required inputs for the inverse problem in the fractional diffusion equation are chosen from the outcomes of the dual phase lag (DPL) theory. The governing equations are solved numerically by utilizing implicit approaches. The results of this study showed the efficiency of the CGIM to estimate the unknown parameters in the FSPL model. In fact, obtained numerical results of the CGIM are in excellent compatibility with the FSPL model

A Fully Resolved Computational Fluid Dynamics Study of the Boundary Layer Flow of an Aqueous Nanoliquid Comprising Gyrotactic Microorganisms over a Stretching Sheet: The Validity of Conventional Similarity Models

When materials are processed in the form of sheets that are stretched, cooling is often required. Coolants have been developed to maximize the rate of heat transfer away from the sheet, including by adding nanoparticles and microorganisms to control the physical properties of the fluid. Such coolants perform well, but the interaction between them and the sheet is not yet fully understood. Most of the articles found in the literature have used similarity models to solve the set of governing equations. In this method, the governing equations can be mapped into a set of 1-D equations and solved easily. However, care should be taken when using this method as the validity of this method is ensured only in the fully developed region, far away enough from the extrusion slit. The present study, therefore, aims to explore the reliability of a similarity model by comparing it with a full computational fluid dynamics (CFD) approach. In this work, the boundary layer flow of a nanoliquid comprising gyrotactic microorganisms in both the developed and undeveloped regions of a stretching sheet is studied using computational fluid dynamics with the finite difference approach, implemented using FORTRAN. The results of the CFD method are compared against the similarity analysis results for the length of the developed and undeveloped regions. This study, for the first time, distinguishes between the undeveloped and fully developed regions and finds the region in which the similarity analysis is valid. The numerical results show that the critical Reynolds numbers for the boundary layers of the concentration of the nano-additives and of density of the microorganisms are equal. To achieve an agreement between the CFD and the similarity model within 5%, the Grashof number for the hydrodynamic boundary layer must be <4 × 104. Increasing the bioconvection Rayleigh number leads to a decrease in the skin friction coefficient. The length of the region in which the microorganism’s density is not fully developed remains approximately constant for 103 < Gr < 105. Nonetheless, this length reduces significantly when the Grashof number increases from 105 to 106. The reduced Nusselt number, Nur, increases when the density difference of the microorganisms increases

Improving the thermal-hydraulic performance of parabolic solar collectors using absorber tubes equipped with perforated twisted tape containing nanofluid

The thermal and hydraulic efficiency of a parabolic trough solar collector is investigated in this study. The collector absorber tube is equipped with twisted tape with circular holes containing water-copper oxide nanofluid with three nanoparticles volume fractions of 1%, 2% and 4%. In three modes (d/W = 0.5, 0.7, 0.9), circular holes are constructed for the ratio of the circle's diameter to the twisted tape's breadth. All turbulent flow simulations were done using the SIMPLEC algorithm, FVM and RNG k-ε model in three Reynolds numbers as 10,000, 20,000 and 30,000. Studies have shown inserting twisted tape with a circular hole increases the pressure drop and the heat transfer rate compared to a pipe without twisted tape. The highest coefficient of thermal performance occurs in Reylond number of 10,000 and a nanoparticles volume fraction of 4%. The findings indicate that using nanoparticles improves the solar collector's energy and exergy efficiency. As a result, the best collector performance was obtained when using nanofluids with an nanoparticles volume fraction of 4%.The Deanship of Scientific Research at King Khalid University, Abha, Saudi Arabia.http://www.elsevier.com/locate/seta2024-04-11hj2023Mechanical and Aeronautical Engineerin

Numerical study and optimization of thermal efficiency for a pin fin heatsink with nanofluid flow by modifying heatsink geometry

This paper presents a numerical study on the thermal efficiency of a pin fin heatsink (HEK). The working fluid used is an alumina/water nanofluid, which enters the HEK in a laminar flow regime and exits from its surroundings. This study involves varying the distance between circular pin fins, their height, and their diameter. By altering these parameters, we determine the values of thermal resistance (THR) and temperature uniformity (Teta) on the HEK, along with the heat transfer coefficient (HTC). We further optimize the obtained results using artificial intelligence techniques to minimize the THR of the HEK, maximize the HTC, and achieve the best Teta on the HEK. This numerical investigation employs a two-phase approach to model nanofluid flow within the HEK. The optimization process yields predictions with an accuracy of less than 4%. The findings reveal that increasing the height of the pin fins reduces the HTC and the heat capacity of the HEK, while simultaneously improving the Teta on the HEK. Expanding the distance between pin fins enhances the HTC, decreases the THR of the HEK, and further improves the Teta on the HEK. Similarly, augmenting the diameter of the pin fins amplifies the HTC, reduces the THR, and enhances the Teta on the HEK

Unsteady radiative slip flow of MHD Casson fluid over a permeable stretched surface subject to a non-uniform heat source

The two-dimensional unsteady radiative stagnation point flow of a Casson fluid is considered across a permeable stretching surface subject to a non-uniform heat source. Furthermore, the association of wall suction and aligned magnetic field have been examined with the slip velocity. These condition leads to the mathematical model of the nonlinear partial differential equations (PDEs), which are initially changed to the dimensionless ordinary differential equations (ODEs) with the use of similarity transformations. The MATLAB function bvp4c was used to resolve the subsequent nonlinear ODEs and the solution has been estimated in terms of temperature, friction drag, Nusselt number and velocity of fluid which are determined under the influence of smallest suitable values of the relevant flow parameters. It appears that the friction drag escalates with the strength of suction, Casson parameter and magnetic field, while the Nusselt number decays with the escalation of Eckert number, however it improves with the higher values of the radiation and suction parameter. Additionally, the flow velocity decreases with the rising values of porosity parameter and inclination angle however it enhances with the boosting values of slip parameter. The temperature profile correspondingly enhances with the rising values of radiation parameter, Boit number, and Ecker number