Numerical Simulation of Oscillatory MHD Natural Convection in Cylindrical Annulus: Prandtl Number Effect

2018 ◽  
Vol 387 ◽  
pp. 417-427 ◽  
Author(s):  
Fateh Mebarek-Oudina ◽  
Oluwole Daniel Makinde
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Prandtl Number ◽  
Numerical Solutions ◽  
Physical Parameters ◽  
Magnetic Field Effects ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics ◽  
Flow And Heat Transfer ◽  
Cylindrical Annulus

The oscillatory natural convection between two concentric cylinders is numerically investigated. The effect of Prandtl number on flow and heat transfer characteristics with considering the magnetic field effects is investigated. For different values of physical parameters, critical Rayleigh numbers are determined. For buoyancy term, the Boussinesq approximation is used, and the numerical solutions are obtained using the finite volume method. For this kind of Prandtl number, the flow and heat transfer characteristics are unique and independent of the Prandtl number. Stability diagram (RaCr-Pr) highlights the dependence of RaCr via Prandtl numbers and various Hartmann number. The importance of this modeling is its practical application for stabilizing or weakening the convective effects in the design of magnetic systems.

Three Dimensional Numerical Simulation of the Natural Convection in an Annulus With an Internal Slotted Cylinder

2011 ◽  
Author(s):  
Mo Yang ◽  
Jin Wang ◽  
Kun Zhang ◽  
Ling Li ◽  
Yuwen Zhang
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Numerical Solutions ◽  
Three Dimensional ◽  
Convection Heat Transfer ◽  
Natural Convection Heat Transfer ◽  
Dimensional Model ◽  
Heat Transfer Characteristics ◽  
Flow And Heat Transfer ◽  
Rayleigh Numbers

Detailed numerical analysis is presented for three-dimensional natural convection heat transfer in annulus with an internal concentric slotted cylinder. The internal slotted cylinder and the outer annulus are maintained at uniform but different temperatures. Governing equations are discretized using control volume technique based on staggered grid formulation and solved using SIMPLE algorithm with QUICK scheme. Flow and heat transfer characteristics are investigated for a Rayleigh number range of 10 to 106 while Prandtl number (Pr) is taken to be 0.7. The results indicate, at Rayleigh numbers below 105, the system shows two dimensional flow and heat transfer characteristics. On the other hand, the flow and heat transfer shows three dimensional characteristics while for Rayleigh numbers greater than 5×105. Comparison with experimental results indicated that the numerical solutions by three dimensional model can obtain more accuracy than the numerical solutions by two dimensional model. Besides, Numerical results show that the average equivalent conductivity coefficient of natural convection heat transfer of this problem can be enhanced by as much as 30% while relative slot width is more than 0.1.

The Effect of Temperature Dependent Electrical Conductivity on the MHD Natural Convection of Al2O3–Water Nanofluid in a Rectangular Enclosure

2014 ◽  
Author(s):  
Ali Mohammad Asadian ◽  
Omid Abouali ◽  
Mahmoud Yaghoubi ◽  
Goodarz Ahmadi
Keyword(s):  
Magnetic Field ◽  
Heat Transfer ◽  
Electrical Conductivity ◽  
Natural Convection ◽  
Effect Of Temperature ◽  
Fluid Viscosity ◽  
Heat Transfer Characteristics ◽  
Volume Fractions ◽  
Transfer Characteristics ◽  
Flow And Heat Transfer

The present paper is concerned with the study of flow and heat transfer characteristics in the steady state free convective flow of Al2O3-waternanofluids in a square enclosure in the presence of magnetic field. Attention is given to the temperature variation of the electrical conductivity and its effect on the electromagnetic force induced by the motion of the nanofluid. A new experimental correlation recently presented in the literature was used for this aim. In all the earlier studies in this area the electrical conductivity variation of nanofluid with temperature was neglected. The fluid viscosity and thermal conductivity are assumed to vary as a function of temperature and this variation is modeled using the available experimental correlations. The governing differential equations are solved numerically using finite element method. The features of fluid flow and heat transfer characteristics are analyzed for various strengths of the magnetic field and different nanoparticle volume fractions. The results show that when the inclusion of the variation of the electrical conductivity with temperature in the numerical model noticeably affects the natural convection heat transfer in the studied rectangular cavity. The variations of Nusselt number for natural convection of Al2O3-water nanofluid with nanoparticle volume fractions are presented at various Rayleigh and Hartmann numbers.

Numerical Investigation of Two Phase Flow and Heat Transfer Characteristics of Passive Containment Cooling System

2013 ◽  
Author(s):  
Jia-Jia Deng ◽  
Liang-Ming Pan ◽  
Mei-Qiang Kang
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Cooling System ◽  
Water Film ◽  
Phase Flow ◽  
Air Flow Rate ◽  
Heat Transfer Characteristics ◽  
Two Phase ◽  
Transfer Characteristics ◽  
Flow And Heat Transfer

The heat transfer characteristics of passive containment cooling system (PCS) are very important to protect the nuclear reactor from early release in some severe accident scenarios. In this paper, based on the natural convection and the VOF (Volume of Fluid) multiphase model, the two-phase flow and heat transfer characteristics of the water film of PCS at postulated accident was numerically investigated. To economize the calculation resource, a two dimensional axis symmetry cooling system was included in the simulation model owing to the symmetry of the system. The transportation of mass and energy during the phase change at film interface was established by adding source terms to the mass and energy equations with User Defined Function (UDF). Because of the lower heat capacity of the cooling gas, the air flow rate and flow pattern of natural convection were the governing factor of the heat transfer through containment. Generally, the heat transfer rate is very lower because the heat and flow attached layer at air baffle and water film are very thick due to the flat plate air baffle, but stronger vortex produced by air baffle will reduce the heat transfer because of damage of the water film. The dimensions and the shape of the air baffle have important effect on air flow rate and flow pattern of the natural convection, and the optimal option was chosen based on the simulation results.

Flow and Heat Transfer Characteristics of Heterogeneous Nanofluids in Pipes

2011 ◽  
Author(s):  
Khalid N. Alammar ◽  
Abdullah Mohammed
Keyword(s):  
Heat Transfer ◽  
Prandtl Number ◽  
Volume Concentration ◽  
Transfer Enhancement ◽  
Heat Transfer Characteristics ◽  
Nanofluid Flow ◽  
Nanoparticle Distribution ◽  
Heterogeneous Flow ◽  
Transfer Characteristics ◽  
Flow And Heat Transfer

Heterogeneous nanofluid flow in pipes is simulated. Assuming incompressible, axisymmetric, and laminar flow, effect of nanoparticle distribution and Prandtl number on flow and heat transfer characteristics is investigated. With nanoparticle overall volume concentration of 0.05, up to 20% heat transfer enhancement was predicted for fully developed heterogeneous flow compared to homogeneous nanofluid. At the entrance region, the enhancement is shown to increase with increasing Prandtl number.

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