Showing papers on "Natural convection published in 2021"

Investigation of mixture fluid suspended by hybrid nanoparticles over vertical cylinder by considering shape factor effect

Abstract: In this study, flow of a mixture of water and ethylene glycol (50–50%) with hybrid nanoparticles (MWCNT–Ag) over a vertical stretching cylinder has been investigated. In this research, the fluid passes through a porous media, while a magnetic field has been applied to the system. Furthermore, the effects of thermal radiation, viscous dissipation, and natural convection have been studied. As a novelty, the effects of different shape factors have been investigated. In the first step, the governing equations are extracted from partial differential equations and then converted to ordinary differential equations (ODE) using the similarity solution. In the next step, the fifth-order Runge–Kutta method has been used to solve the related ODEs. The effects of parameters such as magnetic field, radiation parameter, porosity parameter, nanofluid volume fraction, and nanofluid shape factor on dimensionless velocity and temperature profile have been presented for single and hybrid nanofluid. The results showed that at $$\eta$$ = 2.5 for hybrid nanoparticles the shape factors lamina and spherical have the largest difference; lamina is smaller by 6%, also the results demonstrated that at $$\eta$$ = 2 with increasing Ha, the radial velocity reduced 9.68% for hybrid nanoparticles.

A review of magnetic field influence on natural convection heat transfer performance of nanofluids in square cavities

Abstract: The emergence of nanofluids as high-performance thermal transport media has drawn great research attention in the field of heat transfer. Owning to the huge importance of natural convection applications in environmental, agricultural, manufacturing, electronics, aviation, power plants, and industrial processes, heat transfer and flow characteristics of these special fluids in various cavities have been extensively researched. This review paper has paid serious attention to the benefits of controlling the natural convection heat transfer and flow performance of nanofluids in square cavities using magnetic field sources in addition to the aspect ratio, porous media, cavity and magnetic field inclination, hybrid nanofluids, etc. The influence of several variables such as heat distribution methods, thermal and concentration boundary conditions, governing parameters, magnetic field types, numerical schemes, thermophysical correlation types, nanofluid types, slip conditions, Brownian motion, and thermophoresis on the magnetohydrodynamic (MHD) natural convection behaviours of nanofluids in square cavities has been reviewed. The paper focused on the application of numerical and experimental methods to hydromagnetic behaviours of nanofluids in square-shaped enclosures. The concept of bioconvection, bio-nanofluid (green nanofluid), ionic nanofluid, and hybrid nanofluid has also been reviewed in relation to natural convection for the first time. Special cases of MHD natural convection in cavities involving micropolar and hybrid nanofluids are also presented herein. Convective heat transfer in square cavities has been demonstrated to be altered due to the presence of magnetic fields.

Magneto-hydrodynamic thermal convection of Cu–Al 2 O 3 /water hybrid nanofluid saturated with porous media subjected to half-sinusoidal nonuniform heating

Abstract: The present work aims to examine the thermal efficacy of half-sinusoidal nonuniform heating at different spatial frequencies for a porous natural convection system using Cu–Al2O3/water hybrid nanofluid and magnetic field. The system is presented utilizing a classical square enclosure heated nonuniformly at the bottom wall, and the sidewalls are allowed to exchange heat with the surroundings. The Brinkman–Forchheimer–Darcy model is adopted catering other additional terms for buoyant force and magnetic field. The governing equations are transformed into nondimensional forms and then solved numerically using a finite volume-based computing code. The importance and fundamental flow physics are explored in terms of the pertinent parameters such as the amplitude (I) and spatial frequency (f) of half-sinusoidal heating, Darcy–Rayleigh number (Ram), volume fraction of hybrid nanoparticles ( $$ \phi $$ ), and Hartmann number (Ha). The flow structure and heat transfer characteristics are analyzed and presented utilizing heatlines, streamlines and isotherms and average Nusselt number. The results show that the use of half-sinusoidal nonuniform heating along with hybrid nanofluid can be a viable method for enhancement and control of the overall thermal performance. The study indicates that half-sinusoidal heating could be a promising technique for better heat transfer even in the presence of flow dampening effects like porous media and magnetic fields.

Numerical Investigation of Natural Convection and Irreversibilities between Two Inclined Concentric Cylinders in Presence of Uniform Magnetic Field and Radiation

Abstract: In this study, the free convection with volumetric radiation in a water–alumina nanofluid flowing between two inclined concentric cylinders was simulated. The enclosure, or the cavity between the t...

Natural convection of CuO-water nanofluid in a conventional oil/water separator cavity: Application to combined-cycle power plants

Abstract: The oily water from various sources in combined cycle power plants is collected in oil/water separator in which the oil separates from water due to the density difference. The idea of the presented geometry is taken from conventional oil/water separators. This paper studies the natural convection of the CuO-water nanoliquid in a rectangular cavity with fins attached to the insulated wall and porous media. Discretion of Navier-Stokes equations is done by Finite Element Method and assumptions are laminar, steady and incompressible flow. Heat transfer performance and entropy generation are investigated for distinct Rayleigh numbers (103–105), Darcy numbers (10−2–10−4), and Hartmann numbers (0, 10, 20). Different sizes of the fins are also studied to show consequences of fin size on heat transfer in cavity. This is the first time that these parameters and their impacts on Nusselt number and entropy generation are studied for a conventional oil/water separator cavity. Corollaries demonstrate that increasing Rayleigh number and Darcy number improves heat transfer performance and average Nusselt number. Nevertheless, Hartmann number has a reverse effect with average Nusselt number. Finally, a new equation for average Nusselt number is developed with regard to Rayleigh number, Hartmann number, and Darcy number.

Characteristics of melting heat transport of blood with time-dependent cross-nanofluid model using Keller–Box and BVP4C method

Abstract: The blood flow with heat transportation has prominent clinical importance during the levels where the blood flow needs to be checked (surgery) and the heat transportation rate must be controlled (therapy). This work presents an analysis of the melting heat transport of blood, which consists of iron nanoparticles along free convection with cross-model and solution of the partial differential equation (PDEs) are emerged by the mathematical model. Being the importance of iron oxide nanoparticles in applications of the biomedical field due to their intrinsic properties such as colloidal stability, surface engineering capability and low toxicity, this study has been launched. Furthermore, PDEs of the problem are converted into a set of nonlinear ordinary differential equations (ODEs) by proper transformations. The solution of this system of ODEs is calculated through RK 4 method and Keller–Box scheme. Some leading points and numerical results of this study of both types of presence and absence of meting effects are tabulated.

Heat transfer hybrid nanofluid (1-Butanol/MoS2–Fe3O4) through a wavy porous cavity and its optimization

Abstract: The purpose of this paper is to investigate natural convection in a porous wavy-walled enclosure that is including a cylinder cavity in the middle of it and filled with a hybrid nanofluid contains 1-Butanol as the base fluid and MoS2–Fe3O4 hybrid nanoparticles.,The domain of interest is bounded by constant temperature horizontal corrugated surfaces and isothermal vertical flat surfaces. The numerical outputs are explained in the type of isotherms, streamline and average Nusselt number with variations of the Rayleigh number, Hartmann number, nanoparticle shape factor and porosity of the porous medium. For solving the governing equations, the finite element method has been used.,The results show that Nuave is proportional to Rayleigh and nanoparticle shape factor directly as well as it has an inverse relation with Hartmann and porosity. The obtained results reveal that the shape factor parameter has a significant effect on the heat transfer performance, which shows a 55.44% contribution on the average Nusselt number.,As a novelty, to maximize the heat transfer performance in a corrugated walls enclosure, the optimal parameters have intended by using the response surface and Taguchi methods. Additionally, an accurate correlation for the average Nusselt number is developed with sensibly great precision.

Hydrothermal and Entropy Investigation of Ag/MgO/H 2 O Hybrid Nanofluid Natural Convection in a Novel Shape of Porous Cavity

Abstract: In this study, a new cavity form filled under a constant magnetic field by Ag/MgO/H2O nanofluids and porous media consistent with natural convection and total entropy is examined. The nanofluid flow is considered to be laminar and incompressible, while the advection inertia effect in the porous layer is taken into account by adopting the Darcy–Forchheimer model. The problem is explained in the dimensionless form of the governing equations and solved by the finite element method. The results of the values of Darcy (Da), Hartmann (Ha) and Rayleigh (Ra) numbers, porosity ( e p ), and the properties of solid volume fraction (ϕ) and flow fields were studied. The findings show that with each improvement in the Ha number, the heat transfer rate becomes more limited, and thus the magnetic field can be used as an outstanding heat transfer controller.

Influence of fin orientation on the natural convection of aqueous-based nano-encapsulated PCMs in a heat exchanger equipped with wing-like fins

Abstract: The heat transfer enhancement in pin-fin heat exchangers is achieved by fluid mixing, disruption of the thermal-viscous boundary and the extension of the effective surface area for maximum heat exchange. The orientation and configuration of the fins are among the prime factors influencing the performance of these heat exchangers. Therefore, the present study investigates the combined influences of fin angle ( 0 ≤ ζ ≤ 270 ), arrangement and position of the wing-like fins on the natural convection of aqueous-based nano-encapsulated phase change material (PCM) in a fin heat exchanger. The analysis is performed for Rayleigh and Stefan numbers of 1e3-1e5 and 0.2 respectively by considering the PCM concentration of 0.05. The flow is assumed to be laminar, incompressible and Newtonian. The results demonstrate that the vertical alignment of the fins contributes to the augmentation of the thermal performance compared to the horizontally arranged fins. At the larger Rayleigh number, the mode of heat transfer is predominantly convective and thermal performance slightly deteriorates due to the blockage caused by adjacent fins. For low Rayleigh number, the conduction is the primary mode of heat transfer between the source and sink fins. This phenomenon is crucial to determine the heat exchanger thermal performance.

Dissection of entropy production for the free convection of NEPCMs-filled porous wavy enclosure subject to volumetric heat source/sink

Abstract: Background The exploration of natural convection which is one the substantial types of convective heat transmission in various applications for instance heat exchangers and geothermal systems along with nanofluids (Nanofluids have greater thermal conductivity in comparison to the conventional fluids) engrossed all researchers’ attention. Methods This study is dedicated to the inspection of the free convection of nanofluid as well as entropy generation inside a porous cavity loaded with nano-encapsulated phase change materials (NEPCMs). The wavy bottom section of the enclosure may be subject to a constant heat flux due to the transmitted sunlight comes from a parabolic trough solar collector. The volumetric heat source/sink is comprised in the governing equation. The robust finite element method (FEM) is deployed to handle the transformed governing equations. Findings The numerical simulation of the streamlines and isotherms associated with velocity distribution for diverse factors are displayed. Further, the significant behavior of the contributing parameters on the Nusselt and Bejan numbers are represented. The results demonstrate that the various profiles of wavy bottom section could affect the heat transmission features as well as fluid flow remarkably. Furthermore, it is noteworthy that all the profiles of entropy enhance with increasing the amplitude with respect to the increasing undulation number for the existence of various Rayleigh number.

Non-Newtonian fluid flow around a Y-shaped fin embedded in a square cavity

Abstract: This study investigates the free convection of Casson fluid inside a square cavity with intruded Y-shaped fin at the bottom surface. The Casson fluid is a non-Newtonian fluid and has an infinite viscosity at zero rates of shear. This is the first time that this fluid is used in the square cavity containing Y-shaped fin at the bottom surface. The Y-shaped fin helps in understanding the constructal theory and enhancing the heat transfer rate from the fin. The main objective of using this fin is to increase the convective heat transfer surface area. The sidewalls of the cavity are kept at cold temperature, the bottom surface at a hot temperature, and the top surface as adiabatic. The tips of the Y-shaped fin are considered as hot, cold, and adiabatic. The effects of the magnetic field and radiation are included in the momentum and energy equations. The influence of viscous heating is neglected. The buoyancy term is included in the momentum equation using Boussinesq approximation. The dimensionless governing equations are solved numerically using a Galerkin weighted residual technique of the finite element method. The effects of Rayleigh number (Ra = 104–106), radiation parameter (Rd = 0–103), Hartmann number (Ha = 0–103), and Casson parameter (γ = 0.1–1) on streamlines, isotherms, dimensionless velocity components, temperature, and local Nusselt numbers along the fin and the bottom heated wall are investigated and presented graphically. It is demonstrated that, in the presence of Y-shaped fin, all the pertinent parameters and dimensionless numbers help in enhancing the heat transfer rate along the bottom surface.

Thermal-natural convection and entropy production behavior of hybrid nanoliquid flow under the effects of magnetic field through a porous wavy cavity embodies three circular cylinders

Abstract: In this numerical contribution, hybrid nanofluid flow behavior, thermal characteristics, and entropy generation analysis through a porous enclosure containing three circular cylinders with magnetic field effects were investigated using finite element approach. The cylinders are arranged in horizontal arrangement in the middle of cavity height, and the active hot central cylinder can move along the vertical central axis while other cold cylinders are considered fixed. The cylinders are enclosed by an adiabatic wavy cavity loaded with Cu-Al2O3-water. The results are discussed for the scrutinized parameters e.g., Rayleigh number (Ra), Darcy number (Da), Hartmann number (Ha), relative position of the hot cylinder (δ), and concentration in volume of nanoparticles (ϕ). It was inferred that the thermal-natural convective flow and overall heat transmission were reinforced by boosting Ra and Da, and lowering Ha. Changing the relative position of the hot cylinder has a remarkable effect on nanoliquid flow patterns, convective heat transfer and entropy generation characteristics.

Influence of fin parameters on the melting behavior in a horizontal shell-and-tube latent heat storage unit with longitudinal fins

Abstract: Adding longitudinal fins is an efficient method to enhance the melting behavior of a horizontal heat-storage tube. Nevertheless, the inhomogeneous heat transfer intensity, which is brought by the natural convection of liquid phase change material, causes a hard-melting region in the bottom half of the tube. In this study, two-dimensional models considering natural convection have been established to investigate the melting of phase change material in the latent heat storage unit with longitudinal fins. Optimization of the structural parameters, including fin-thickness and fin-length, are conducted and numerically calculated to accelerate the melting process. To enhance the charging of the hard-melting region, four strategies are employed and compared with the conventional model 1, whose fin length and fin thickness are constant. It is observed that the intensity of heat transfer is higher in the top-half domain, and it is lower in the bottom half. Moreover, thickening the bottom fins and thinning the top fins can efficiently enhance the charging process. An 8.7% reduction in the complete melting time can be realized by model 6 with the thickest bottom fins as compared to model 1 with equal length and equal thickness fins. Meanwhile, model 9, who has the longest bottom fins, can reduce the complete melting time by 47.1% as compared to model 1, so that the method of lengthening the bottom fins and shortening the top fins is likewise useful in accelerating the melting process. Based on the two strategies, we proposed an optimal model 10, who has the thickest and longest bottom fins, is conducted, and the complete melting time can be reduced by 54.1% compared with the original model 1. Consequently, the key limitation of heat storage in the horizontal tube is located in the bottom half, which is defined as hard-melting region, and thickening and lengthening the bottom fins is conducive to enhance the heat storage in the horizontal tube.

Thermal analysis of a binary base fluid in pool boiling system of glycol–water alumina nano-suspension

Abstract: The main aim of the present research is to measure the nucleate boiling heat transfer coefficient (BHTC) of aqueous glycol nano-suspension as a coolant around a horizontal heater Alumina nanoparticles were added to the base fluid at a volumetric concentration of 1% to improve the thermal conductivity of the nano-suspension The pressure of the system was set to the atmospheric pressure, and the coolant was tested at different applied heat fluxes (HF) ranged from 0 to 90 kW m−2 and volumetric concentration of 0–40% of the heavier component Two zones of heat transfer were identified, including a natural convection zone and nucleate boiling one mixed with bubble formation and bubble interactions Results also showed that the HTC of the nano-suspension is smaller than those recorded for the pure water A rough comparison was made to examine the accuracy of the developed equations for estimating the BHTC value against the experimental data It was found that the developed equations are not accurate for the data measured in the free convection region Thus, the Churchill-Chu correlation was recommended for estimating the BHTC in the free convection area of heat transfer Also, the effect of operating parameters such as HF and volumetric concentration on the pool boiling HTC of the solution was studied

Investigation of the effect of adding nano-encapsulated phase change material to water in natural convection inside a rectangular cavity

Abstract: The present simulation aims to investigate adding NEPCM nanoparticles to water in the natural convection inside a cavity by using FVM method and SIMPLE algorithm Nano-encapsulated phase change material (NEPCM) consists of a shell and core with phase change property The NEPCM particles in base fluid have the ability to transfer heat by absorbing and dissipating heat in the liquid-solid phase change state In this study, the energy wall phenomenon due to the phase change of NEPCM core has appeared that the whose energy transfer strength is proportional to the latent heat of NEPCM core and the thickness of the energy wall Moreover, the relationship between the energy wall and the heat transfer rate is payed attention, and the effects of the energy wall parameters including strength, thickness, and event location of energy wall and volume fraction are studied on the energy wall and heat transfer rate According to the obtained results, adding NEPCM to the water enhances its heat transfer up to 48% in order to increase heat capacity of water-NEPCM mixture Also, best heat transfer rate happens when the energy wall is at the center of the cavity Moreover, a relation is presented for the thermal expansion coefficient of NEPCM, which considers the effects of the thermal expansion coefficient of the core and shell material