scholarly journals Effects of Natural Convection from an Open Square Cavity Containing a Heated Circular Cylinder

2012 ◽  
Vol 47 (1) ◽  
pp. 19-28 ◽  
Author(s):  
Sheikh Anwar Hossain ◽  
MA Alim
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Circular Cylinder ◽  
Flow Field ◽  
Vertical Wall ◽  
Convection Heat Transfer ◽  
Constant Heat Flux ◽  
Bottom Wall ◽  
Coupled Equations ◽  
Inclination Angles

The problem of natural convection heat transfer in a square open cavity containing a heated and conducting circular cylinder at the centre is analyzed in this paper. As boundary conditions of the cavity, the left vertical wall is kept at a constant heat flux, bottom and top wall are kept at different high and low temperature respectively. The remaining side is open. Two dimensional laminar steady state natural convection is considered. This configuration is related in the design of electronic devices, solar energy receivers, uncovered flat plate solar collectors geothermal reservoirs etc. The fluid is concerned with different Prandtl numbers, Grashof numbers and the properties of the fluid are assumed to be constant. The development of Mathematical model is governed by the coupled equations of continuity, momentum and energy and is solved by employing Galerkin weighted finite element method. Flow field and heat transfer were predicted for fluid with Pr = 0.72 , 1.0 ,7.0; Gr = 103, 104, 105 ,106; inclination angles of the cavity are ? = 0°, 15°, 30°, 45° and diameter ratio dr = 0.2.The average Nusselt number increases as the increases of inclination angle of the cavity for lower Pr and lower temperature at bottom wall. The average Nu increases mainly for higher inclinations and for higher Gr. Various vortices and recirculations are formed into the flow field for higher Pr and higher temperature at the bottom wall. DOI: http://dx.doi.org/10.3329/bjsir.v47i1.10718Bangladesh J. Sci. Ind. Res. 47(1), 19-28, 2012

An Investigation of Natural Convection Heat Transfer in A Cubic Enclosure with Oriented Partial Partitions at Different Angles

2014 ◽  
Vol 2 (2) ◽  
pp. 28-46
Author(s):  
Dhia Al-Deen H. Alwan
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Flow Field ◽  
Inclination Angle ◽  
Convection Heat Transfer ◽  
Natural Convection Heat Transfer ◽  
Convection Heat ◽  
Worst Case ◽  
Fluid Layers ◽  
Inclination Angles

Natural convection heat transfer in an enclosure provided with inclined partitions to the two adiabatic sides, heated from the bottom with uniform heat flux and cooled from the top at constant temperature is studied experimentally and numerically in this work. The inclined partitions is well covered with an insulated material, so that, it can be assumed as parts of the adiabatic walls that places on. The governing parameter, Rayleigh number, is fixed in this work within 2.6x1011, so that the effect of inclination angles of the two side’s partitions can be investigated. The inclination angles of the two baffles range as (0o ≤ and ≥ 150o). In numerical solution the effect of turbulence is modelled using (k-ε) model. Some applications need to use the enclosed fluid layers as insulation, so that one purpose of this work deals with improve the insulating properties of fluid layers. The experimental and numerical works are done in 36 runs, grouped into 6 collections. Each collection with 6 runs done under a fixed inclination angle of one baffle and change the second baffle inclination angle to investigate the enclosure flow field and heat transfer. The result shows that a multi cells forms when the two baffles aboard to each other’s, which is a reason to make a separation between a cold, and hot circulation cells that forms in the enclosure and act as insulator. It is also conclude that for all cases, the long insulated baffle of any inclination angle causes a reduction to the heat exchange inside the enclosure due to the damping cause to the flow field. The less average Nusselt number occurs when the two angles are equals, and the worst case is (θ=β=90o). 

scholarly journals Natural convection in tilted square cavities with triangular shaped top cold wall

1970 ◽  
Vol 39 (1) ◽  
pp. 30-39 ◽  
Author(s):  
Tamanna Sultana ◽  
Sumon Saha ◽  
Goutam Saha ◽  
Md Quamrul Islam
Keyword(s):  
Heat Transfer ◽  
Finite Element ◽  
Nusselt Number ◽  
Natural Convection ◽  
Numerical Study ◽  
Constant Heat Flux ◽  
Heat Transfer Process ◽  
Bottom Wall ◽  
Grashof Number ◽  
Inclination Angles

A numerical study of natural convection in a tilted square cavity with heated horizontal base and cold upper wall is presented. The present study is based in such a configuration where the top triangular wall of two different shapes is maintained at a constant low temperature. A constant heat flux source whose length is 20% of the total length of the cavity is discretely embedded at the left corner of the bottom wall. The remaining part of the bottom wall and the two sidewalls are considered to be adiabatic. The study includes computations for inclination angles of the cavity from 0° to 45°, where the Grashof number, Gr varies from 103 to 106. The Penalty finite element method has been used to see the effects of inclination angles and Grashof number on heat transfer process in the cavity. Results are presented in the form of streamline and isotherm plots as well as the variation of the average Nusselt number. Observation shows the significant effect of different triangular top surface on the heat transfer characteristics at the higher Grashof number and inclination angle. Keywords: Natural convection, Penalty finite element, Nusselt number, Isoflux heating. doi:10.3329/jme.v39i1.1831 Journal of Mechanical Engineering, vol. ME39, No. 1, June 2008 30-39  

scholarly journals Natural convection heat transfer around a horizontal circular cylinder near an isothermal vertical wall

2018 ◽  
Vol 180 ◽  
pp. 02077
Author(s):  
Marcel Novomestský ◽  
Richard Lenhard ◽  
Ján Siažik
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Circular Cylinder ◽  
Vertical Wall ◽  
Convection Heat Transfer ◽  
Side Wall ◽  
Horizontal Cylinder ◽  
Natural Convection Heat Transfer ◽  
Convection Heat ◽  
Heated Cylinder

Natural convection heat transfer from a single horizontal cylinder near an isothermal wall is experimentally investigated in the environmental chamber. When cylinder is heated the plume rising from the heated cylinder interacts with the wall and significantly affects the surface heat transfer distribution. Thus, the distance between horizontal cylinder and side wall can influence the heat transfer. The heat transfer from heated cylinder with different distances was compared. It was found that the influence of the wall on the convection heat transfer from the circular cylinder began when the distance between the wall and cylinder is less than 80 mm.

scholarly journals Electrical Resistance and Natural Convection Heat Transfer Modeling of Shape Memory Alloy Wires

2014 ◽  
Author(s):  
Anita Eisakhani ◽  
Xiujie Gao ◽  
Rob Gorbet ◽  
J. Richard Culham
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Electrical Resistance ◽  
Ambient Pressure ◽  
Convection Heat Transfer ◽  
Natural Convection Heat Transfer ◽  
Convection Heat ◽  
Heat Transfer Correlation ◽  
Niti Sma ◽  
Inclination Angles

Shape memory alloy (SMA) actuators are becoming increasingly popular in recent years due to their properties such as large recovery strain, silent actuation and low weight. Actuation in SMA wires depends strongly on temperature which is difficult to measure directly. Therefore, a reliable model is required to predict wire temperature, in order to control the transformation, and hence the actuation, and to avoid potential degradation due to overheating. The purpose of this investigation is to develop resistance and natural convection heat transfer models to predict temperature of current-carrying SMA wires using indirect temperature measurement methods. Experiments are performed on electrically heated 0.5 mm diameter NiTi SMA wire during phase transformation. Convection heat transfer experiments are performed in an environment of air that allows for control of the ambient pressure and in turn the thermofluid properties, such as density and viscosity. By measuring convective heat loss at a range of pressures, an empirical natural convection heat transfer correlation is determined for inclination angles from horizontal to vertical, in the Rayleigh number range of 2.6 × 10−8 ≤ RaD ≤ 6.0 × 10−1. Later, effect of temperature changes on electrical resistance and other control parameters such as applied external stress, wire inclination angle, wire length and ambient pressure is investigated. Based on experimental results a resistance model is developed for SMA wires that combined with the heat transfer correlation previously derived can be used to predict temperature and natural convection heat transfer coefficient of NiTi SMA wires during phase transformation for different wire lengths and inclination angles under various applied external stresses.

Numerical analysis of natural convection heat transfer and entropy generation in a porous quadrantal cavity

2019 ◽  
Vol 29 (12) ◽  
pp. 4826-4849 ◽  
Author(s):  
Shantanu Dutta ◽  
Arup Kumar Biswas ◽  
Sukumar Pati
Keyword(s):  
Heat Transfer ◽  
Porous Medium ◽  
Natural Convection ◽  
Convection Heat Transfer ◽  
Bottom Wall ◽  
Natural Convection Heat Transfer ◽  
Convection Heat ◽  
Uniform Temperature ◽  
Content Type ◽  
Temperature Heating

Purpose The purpose of this paper is to analyze the natural convection heat transfer and irreversibility characteristics in a quadrantal porous cavity subjected to uniform temperature heating from the bottom wall. Design/methodology/approach Brinkmann-extended Darcy model is used to simulate the momentum transfer in the porous medium. The Boussinesq approximation is invoked to account for the variation in density arising out of the temperature differential for the porous quadrantal enclosure subjected to uniform heating on the bottom wall. The governing transport equations are solved using the finite element method. A parametric study is carried out for the Rayleigh number (Ra) in the range of 103 to 106 and Darcy number (Da) in the range of 10−5-10−2. Findings A complex interaction between the buoyant and viscous forces that govern the transport of heat and entropy generation and the permeability of the porous medium plays a significant role on the same. The effect of Da is almost insignificant in dictating the heat transfer for low values of Ra (103, 104), while there is a significant alteration in Nusselt number for Ra ≥105 and moreover, the change is more intense for larger values of Da. For lower values of Ra (≤104), the main contributor of irreversibility is the thermal irreversibility irrespective of all values of Da. However, the fluid friction irreversibility is the dominant player at higher values of Ra (=106) and Da (=10−2). Practical implications From an industrial point of view, the present study will have applications in micro-electronic devices, building systems with complex geometries, solar collectors, electric machinery and lubrication systems. Originality/value This research examines numerically the buoyancy driven heat transfer irreversibility in a quadrantal porous enclosure that is subjected to uniform temperature heating from the bottom wall, that was not investigated in the literature before.

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