scholarly journals Natural convection of Nanoliquid from a Cylinder in Square Porous Enclosure using Buongiorno’s Two-phase Model

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Abeer Alhashash
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Heated Surface ◽  
Active Surface ◽  
Darcy Number ◽  
Cylinder Surface ◽  
Two Phase ◽  
Porous Enclosure

AbstractNatural convection of nanoliquid in a square porous enclosure has been studied using non homogeneous two-phase Buongiorno’s model. The outer of enclosure has cold temperature and a circular cylinder is put at the center. A finite heated segment is located on the top cylinder surface which is otherwise insulated. The momentum in the porous layer is modeled applying the Brinkman-Forchheimer equations. The analysis are conducted in the following interval of the associated groups: the portion of heated surface (5% ≤ H ≤ 100%), the concentration (0.0 ≤ ϕ ≤ 0.04), the Darcy number, 10−5 ≤ Da ≤ 10−2 and the cylinder size, (0.15 ≤ R ≤ 0.25). The minimum heat transfer rate of the active surface were obtained at location ξ = 90°. In general, the ratio of the heat transfer per unit area of the heat source decreases as the length of the heated surface increases. The heat transfer rate is intensified for the half thermally active surface and high value of Darcy number at higher nanoparticles concentration.

Natural Convection in an Anisotropic Porous Enclosure Due to Nonuniform Heating From the Bottom Wall

2009 ◽  
Vol 131 (7) ◽  
Author(s):  
Ashok Kumar ◽  
P. Bera
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Principal Direction ◽  
Orientation Angle ◽  
Bottom Wall ◽  
Nonuniform Heating ◽  
Material Derivative ◽  
Porous Enclosure

A comprehensive numerical investigation on the natural convection in a hydrodynamically anisotropic porous enclosure is presented. The flow is due to nonuniformly heated bottom wall and maintenance of constant temperature at cold vertical walls along with adiabatic top wall. Brinkman-extended non-Darcy model, including material derivative, is considered. The principal direction of the permeability tensor has been taken oblique to the gravity vector. The spectral element method has been adopted to solve numerically the governing conservative equations of mass, momentum, and energy by using a stream-function vorticity formulation. Special attention is given to understand the effect of anisotropic parameters on the heat transfer rate as well as flow configurations. The numerical experiments show that in the case of isotropic porous enclosure, the maximum rates of bottom as well as side heat transfers (Nub and Nus) take place at the aspect ratio, A, of the enclosure equal to 1, which is, in general, not true in the case of anisotropic porous enclosures. The flow in the enclosure is governed by two different types of convective cells: rotating (i) clockwise and (ii) anticlockwise. Based on the value of media permeability as well as orientation angle, in the anisotropic case, one of the cells will dominate the other. In contrast to isotropic porous media, enhancement of flow convection in the anisotropic porous enclosure does not mean increasing the side heat transfer rate always. Furthermore, the results show that anisotropy causes significant changes in the bottom as well as side average Nusselt numbers. In particular, the present analysis shows that permeability orientation angle has a significant effect on the flow dynamics and temperature profile and consequently on the heat transfer rates.

scholarly journals Effect of Prandtl Number on Mixed Convective Heat Transfer from a Porous Cylinder in the Steady Flow Regime

Entropy ◽  
2020 ◽  
Vol 22 (2) ◽  
pp. 184 ◽  
Author(s):  
Shimin Yu ◽  
Tingting Tang ◽  
Jianhui Li ◽  
Peng Yu
Keyword(s):  
Heat Transfer ◽  
Prandtl Number ◽  
Steady Flow ◽  
Flow Regime ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Thermal Characteristics ◽  
Internal Heat ◽  
Darcy Number ◽  
Cylinder Surface

The effect of the Prandtl number (Pr) on the flow and heat transfer from a porous circular cylinder with internal heat generation in the mixed convection regime is numerically investigated. The steady flow regime is considered over the ranges of the Reynolds number (Re), Darcy number (Da), and Richardson number (Ri), varying from 5 to 40, 10−6 to 10−2, and 0 to 2, respectively. The wake structure, the temperature distribution, and the heat transfer rate are discussed. Besides precipitating the growth of the recirculating wake, the Prandtl number is found to have a significant impact on the thermal characteristics. The concave isotherms, resembling a saddle-shaped structure, occur behind the cylinder at larger Pr, resulting in swells of the isotherms pairing off at the lateral sides. These swells are found to have a negative effect on heat transfer owing to a relatively smaller temperature gradient there. Then, the heat transfer rate in terms of the local Nusselt number (Nu) and enhancement ratio (Er) is calculated, which is closely related to Pr, Re, Da, and Ri. The local minimum heat transfer rate along the cylinder surface is found at the position where the swells of the isotherms form.

Conjugate Natural Convection in Porous Medium With a Thick Square-Wave Partition

2020 ◽  
Vol 13 (1) ◽  
Author(s):  
Jayesh Subhash Chordiya ◽  
Ram Vinoy Sharma
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Natural Convection ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Convection Heat Transfer ◽  
Thermal Conductivity Ratio ◽  
Convection Heat ◽  
Square Wave ◽  
Porous Enclosure

Abstract Natural convection within a differentially heated porous enclosure is substantially affected by the presence of partition, fins, or baffles within it. However, not much is known about the effect of partition shape and size. Thus, a solid thick partition in a square-wave shape embedded within a differentially heated porous enclosure has been investigated in this numerical analysis. Through this study, it is sought to contemplate the reduction in the convection heat transfer rate that could be achieved across a differentially heated porous enclosure. The influence of partition thickness, partition amplitude, thermal conductivity ratio, and partition position has been studied. Darcy’s flow model has been solved using the successive accelerated replacement scheme by the finite difference method. One of the findings of this study suggests that lower thermal conductivity of partition, lower partition amplitude, and higher thickness results in a greater reduction in the convection heat transfer rate.

scholarly journals Control temperature fluctuations in two-phase CuO-water nanofluid by transfiguration of the enclosures

2020 ◽  
pp. 334-334
Author(s):  
Hadi Pourziaei Araban ◽  
Javad Alinejad ◽  
Ganji Domiri
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Natural Convection ◽  
Heat Transfer Rate ◽  
Wall Temperature ◽  
Transfer Rate ◽  
Volume Fraction ◽  
Temperature Fields ◽  
Two Phase ◽  
Flux Boundary Condition

The innovation of this paper is to simulate two-phase nanofluid natural convection inside the transformable enclosure to control the heat transfer rate under different heat flux. Heat transfer of a two-phase CuO-water nanofluid in an enclosure under different heat flux has many industrial applications including energy storage systems, thermal control of electronic devices and cooling of radioactive waste containers. The Lattice Boltzmann Method based on the D2Q9 method has been utilized for modeling velocity and temperature fields. Streamlines, isotherms and nanoparticle volume fraction, have been investigated for control the heat transfer rate for several cases. The purpose of this feasibility study is to achieve uniform temperature profiles and Tmax < 50?C under different heat flux. Natural convection heat transfer in the rectangular and parallelogram enclosures with positive and negative angular adiabatic walls were simulated. The average wall temperature under heat flux boundary condition has been studied to predict optimal levels of effective factors to control the maximum wall temperature. The results illustrated parallelogram enclosures with positive angle of case 1 and case 3 and 4 with rectangular enclosures were best cases for considering physical conditions. Average of temperature for these cases were 37.9, 29.7 and 38.2, respectively.

Heat Transfer Investigation of a Tube Partially Wrapped by Metal Porous Layer as a Potential Novel Tube for Air Cooled Heat Exchangers

2018 ◽  
Vol 141 (1) ◽  
Author(s):  
M. Mohammadpour-Ghadikolaie ◽  
M. Saffar-Avval ◽  
Z. Mansoori ◽  
N. Alvandifar ◽  
N. Rahmati
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Heat Transfer Rate ◽  
Porous Layer ◽  
Transfer Rate ◽  
Metal Foam ◽  
Convection Heat Transfer ◽  
Darcy Number ◽  
High Heat Transfer

Laminar forced convection heat transfer from a constant temperature tube wrapped fully or partially by a metal porous layer and subjected to a uniform air cross-flow is studied numerically. The main aim of this study is to consider the thermal performance of some innovative arrangements in which only certain parts of the tube are covered by metal foam. The combination of Navier–Stokes and Darcy–Brinkman–Forchheimer equations is applied to evaluate the flow field. Governing equations are solved using the finite volume SIMPLEC algorithm and the effects of key parameters such as Reynolds number, metal foam thermophysical properties, and porous layer thickness on the Nusselt number are investigated. The results show that using a tube which is fully wrapped by an external porous layer with high thermal conductivity, high Darcy number, and low drag coefficient, can provide a high heat transfer rate in the high Reynolds number laminar flow, increasing the Nusselt number almost as high as 16 times compared to a bare tube. The most important result of thisstudy is that by using some novel arrangements in which the tube is partially covered by the foam layer, the heat transfer rate can be increased at least 20% in comparison to the fully wrapped tube, while the weight and material usage can be considerably reduced.

scholarly journals A RANS K-? SIMULATION OF 2D TURBULENT NATURAL CONVECTION IN AN ENCLOSURE WITH HEATING SOURCES

2019 ◽  
Vol 20 (1) ◽  
pp. 229-244
Author(s):  
Mehdi Ahmadi ◽  
Seyed Ali Agha Mirjalily ◽  
Seyed Amir Abbas Oloomi
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Rayleigh Number ◽  
Kinetic Energy ◽  
Aspect Ratio ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Turbulent Natural Convection ◽  
Cold Source ◽  
Thermal Sources

ABSTRACT: This study is conducted to investigate turbulent natural convection flow in an enclosure with thermal sources using the low-Reynolds number (LRN) k-? model. This enclosure has a cold source with temperature Tc and a hot source with temperature Th as thermal sources, other walls of the enclosure are adiabatic. The aim of this study is to predict the effect of change in Rayleigh number, repositioning of cold and hot sources, and thermal sources aspect ratio on the flow field, temperature, and rate of heat transfer. To achieve this aim, the equations of continuity, momentum, energy, turbulent kinetic energy, and kinetic energy dissipation are employed in the case of 2D turbulence with constant thermo-physical properties except the density in the buoyancy term (Boussinesq approximation). To numerically solve these equations, the finite volume method and SIMPLE algorithm are used. According to the modeling results, the most optimal temperature distribution in the enclosure is seen when the hot source is below the cold source. With decreasing distance between hot and cold sources, heat transfer rate increases. The maximal heat transfer rate is derived via study of the heating sources aspect ratio. In constant positions of cold and hot sources on a wall, the heat transfer rate increases with increasing Rayleigh number (Ra=109-1011). ABSTAK: Kajian ini dijalankan bagi mengkaji perubahan semula jadi aliran perolakan dalam tempat tertutup dengan sumber haba menggunakan model k-? nombor Reynolds-rendah (LRN). Bekas tertutup ini mempunyai dua sumber haba iaitu sumber sejuk dengan suhu Tc dan sumber panas dengan suhu Th, manakala dinding lain bekas ini adalah adiabatik. Tujuan kajian ini adalah bagi mengesan perubahan nombor Rayleigh, mengubah sumber sejuk dan panas dan nisbah sumber haba kepada kawasan aliran, suhu dan halaju perubahan haba. Bagi mencapai tujuan tersebut, persamaan sambungan, momentum, tenaga, tenaga kinetik perolakan, dan pengurangan tenaga kinetik telah dilaksanakan dalam kes perolakan 2D dengan sifat fizikal-haba berterusan (malar) kecuali isipadu terma keapungan (anggaran Boussinesq). Bagi menyelesaikan persamaan ini secara berangka, kaedah isipadu terhad dan algorithma MUDAH telah digunakan. Berdasarkan keputusan model, suhu distribusi optimal dalam bekas tertutup dilihat apabila sumber panas adalah kurang daripada sumber sejuk. Dengan pengurangan jarak antara sumber panas dan sejuk, kadar pertukaran haba meningkat. Kadar pertukaran haba maksima telah diperoleh melalui kajian nisbah  aspek sumber pemanasan. Kadar pertukaran haba bertambah dengan bertambahnya nombor Rayleigh  (Ra=109-1011), pada posisi tetap sumber sejuk dan panas pada dinding bekas.

Effect of a Magnetic Field on the Heat Transfer Rate on Free Convection in a Rectangular Cavity

2005 ◽  
Author(s):  
Gustavo Gutierrez ◽  
Ezequiel Medici
Keyword(s):  
Magnetic Field ◽  
Heat Transfer ◽  
Natural Convection ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Stokes Equations ◽  
Rectangular Cavity ◽  
Convection Flow ◽  
Interesting Phenomenon ◽  
The Magnetic Field

The interaction between magnetic fields and convection is an interesting phenomenon because of its many important engineering applications. Due to natural convection motion the electric conductive fluid in a magnetic field experiences a Lorenz force and its effect is usually to reduce the flow velocities. A magnetic field can be used to control the flow field and increase or reduce the heat transfer rate. In this paper, the effect of a magnetic field in a natural convection flow of an electrically conducting fluid in a rectangular cavity is studied numerically. The two side walls of the cavity are maintained at two different constant temperatures while the upper wall and the lower wall are completely insulated. The coupling of the Navier-Stokes equations with the Maxwell equations is discussed with the assumptions and main simplifications assumed in typical problems of magnetohydrodynamics. The nonlinear Lorenz force generates a rich variety of flow patterns depending on the values of the Grashof and Hartmann numbers. Numerical simulations are carried out for different Grashof and Hartmann numbers. The effect of the magnetic field on the Nusselt number is discussed as well as how convection can be suppressed for certain values of the Hartmann number under appropriate direction of the magnetic field.

Numerical Research on Heat Transfer Characteristics Analysis of Two Particles in Supercritical Water

2021 ◽  
Author(s):  
Xiaoyu Li ◽  
Zhenqun Wu ◽  
Huibo Wang ◽  
Hui Jin
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Phase Flow ◽  
Heat Transfer Characteristics ◽  
Particle Cluster ◽  
Two Phase ◽  
Transfer Characteristics

Abstract In the supercritical water (SCW)-particle two-phase flow of fluidized bed, the particles that make up the particle cluster interact with each other through fluid, and it will affect the flow and heat transfer. However, due to the complex properties of SCW, the research on particle cluster is lacking, especially in terms of heat transfer. This research takes two particles as an example to study the heat transfer characteristics between SCW and another particle when one particle exists. This research uses the distance and angle between the two particles as the influencing factors to study the average heat transfer rate and local heat transfer rate. In this research, it is found that the effect is obvious when L/D = 1.1. When L = 1.1D, the temperature field and the flow field will partially overlap. The overlap of the temperature field will weaken the heat transfer between SCW and the particle. The overlap of the flow field has an enhanced effect on the heat transfer between SCW and the particle. The heat transfer between SCW and particles is simultaneously affected by these two effects, especially local heat transfer rate. In addition, this research also found that as the SCW temperature decreases, the thermal conductivity and specific heat of SCW increases, which enhances the heat transfer between SCW and the particles. This research is of great significance for studying the heat transfer characteristics of SCW-particle two-phase flow in fluidized bed.

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