scholarly journals The Natural Convective Heat Transfer in a Partially Divided Enclosure: A Study on the Influence of the Source Position

2009 ◽  
Vol 2009 ◽  
pp. 1-10 ◽  
Author(s):  
Francesco Corvaro ◽  
Massimo Paroncini
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Dynamic Behaviour ◽  
Velocity Fields ◽  
Source Position ◽  
Square Enclosure ◽  
Nusselt Numbers ◽  
First Case ◽  
Rayleigh Numbers

The aim of this paper is to analyse the natural convective heat transfer generated by a source with a height of located in two different positions inside a square enclosure of side . In the first case, is 0.5 of while in the second case it is 0.4. The comparison is based both on the evaluation of the local and average Nusselt numbers at different Rayleigh numbers and on the study of the velocity fields at the same Rayleigh numbers in the two different configurations. The experimental analysis was carried out through a holographic interferometry, to study the heat transfer, and through a 2D-PIV system, to analyse the dynamic behaviour of the phenomenon. Finally, for = 0.5 we compared the experimental results with those obtained through the volume finite software Fluent 6.3.26. In the analysis, it is possible to see that the position of the source influences both the average Nusselt numbers on the hot surfaces and the development of a small bubble on the upper surface.

scholarly journals Effect of Rayleigh Number on Internal Eccentricity in a Heated Horizontal Elliptical Cylinder to its Coaxial Square Enclosure

2020 ◽  
Vol 25 (3) ◽  
pp. 17-29
Author(s):  
Abdelkrim Bouras ◽  
Djedid Taloub ◽  
Zied Driss
Keyword(s):  
Heat Transfer ◽  
Rayleigh Number ◽  
Outer Cylinder ◽  
Boussinesq Approximation ◽  
Square Enclosure ◽  
Nusselt Numbers ◽  
Flow And Heat Transfer ◽  
Commercial Code ◽  
Volume Method ◽  
Rayleigh Numbers

AbstractThis paper deals with numerical investigation of a natural convective flow in a horizontal annular space between a heated square inner cylinder and a cold elliptical outer cylinder with a Newtonian fluid. Uniform temperatures are imposed along walls of the enclosure. The governing equations of the problem were solved numerically by the commercial code Fluent, based on the finite volume method and the Boussinesq approximation. The effects of Geometry Ratio GR and Rayleigh numbers on fluid flow and heat transfer performance are investigated. The Rayleigh number is varied from 103 to 106. Throughout the study the relevant results are presented in terms of isotherms, and streamlines. From the results, we found that the increase in the Geometry Ratio B leads to an increase of the heat transfer coefficient. The heat transfer rate in the annulus is translated in terms of the average Nusselt numbers along the enclosure’s sides. Tecplot 7 program was used to plot the curves which cleared these relations and isotherms and streamlines which illustrate the behavior of air through the channel and its variation with other parameters. The results for the streamlines, isotherms, local and average Nusselt numbers average Nusselt numbers are compared with previous works and show good agreement.

Simulation of electrically conductive liquid convection in a spherical layer when heat is applied to the inner sphere

2019 ◽  
Author(s):  
С.В. Соловьев
Keyword(s):  
Heat Transfer ◽  
Heat Exchange ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Magnetic Induction ◽  
Spherical Layer ◽  
Gravity Vector ◽  
Joule Dissipation ◽  
Conductive Liquid ◽  
Nusselt Numbers

Представлены результаты численного моделирования конвективного теплообмена электропроводящей жидкости между концентрическими сферами при подводе тепла к внутренней сфере. Исследовано влияние числа Грасгофа и джоулевой диссипации на структуру течения жидкости, поля температуры, магнитной индукции и распределение локальных чисел Нуссельта. Получено уравнение подобия теплообмена, когда ускорение свободного падения направлено к центру сферического слоя. The Boussinesq approximation is used for modelling a large class of problems of convective heat transfer in spherical concentric layers in which the gravity vector is directed vertically downwards. But for problems of geophysics and astrophysics there is a fundamental difference, the gravity vector is directed along the radius to the center of the spherical layer. Therefore, the study of convective heat transfer in spherical layers, when the vector of gravitational acceleration is directed along the radius to the center of the spherical layer, is of independent interest. In this paper, the influence of the Grashof number, the Joule dissipation heat on the fluid flow structure, temperature field, magnetic induction, and the distribution of Nusselt numbers when heat is applied from below are studied. To solve the problem, the finite element method is used. In a dimensionless formulation, the problem is solved taking into account both the heat of the Joule dissipation, magnetic, inertial, viscous and lifting forces in a spherical coordinate system and the symmetry in longitude. The stationary fields of temperature, stream functions, vortex strength, radial and meridional components of magnetic induction and the distribution of local Nusselt numbers of electro conductive liquid in a concentric spherical layer for different Grashof numbers with and without accounting for the heat of Joule dissipation are obtained when heat is applied to the inner sphere. Two critical values of the Grashof number are numerically determined. The equation of heat exchange similarity is obtained, when the acceleration of gravity is directed to the center of the spherical layer. The mathematical model and the presented results may be useful for the study of convective heat exchange of electrically conducting fluid in space technologies and in the geophysical and astrophysical problems.

Numerical Study of Convective Heat Transfer of Multiple Internal Isolated Blocks in an Enclosure

Solar Energy ◽  
2005 ◽  
Author(s):  
Xutao Zhang ◽  
Jianing Zhao ◽  
Fusheng Gao ◽  
Jun Gao ◽  
Songling Wang
Keyword(s):  
Heat Transfer ◽  
Mixed Convection ◽  
Convective Heat Transfer ◽  
Forced Convection ◽  
Convective Heat ◽  
Numerical Study ◽  
Thermal Design ◽  
Square Enclosure ◽  
Forced Convective Heat Transfer ◽  
Low Reynolds

The treatment of Convective Heat Transfer Coefficients (CHTCs) in an enclosure has a significant impact on the thermal design of electronic appliance, especially the CHTCs in an enclosure with internal isolated blocks. The CHTCs of the isolated blocks for pure natural convection are usually used, while it may not be applicable to any practice. Combined convective heat transfer, even forced convective heat transfer, is sometime more applicable in reality. In our present work, first of all, validation of the turbulence model for CFD simulation of natural convective flows in a square enclosure is performed. The values of CHTCs for vertical walls obtained by using a low Reynolds k-ε model agree well with the existed correlations. The simulation also indicates that the distance from the first grid to the wall has a significant impact on the CHTCs. Using this low Reynolds k-ε model, computer simulations of natural and forced convective heat transfer within a square enclosure containing ten isolated blocks are performed. For both the natural and forced convection, the dimensionless Nusselt numbers are derived by the obtained results. For the case of mixed convection, the CHTCs are established by blending those for natural and forced convection using the Churchill-Usagi approach, which is a general expression combines the asymptotic solutions of independent CHTCs into the mixed convection by using a Churchill-Usagi blending coefficient.

Study on Forced Convective Heat Transfer of FC-72 in Vertical Small Tubes

2019 ◽  
Author(s):  
Yantao Li ◽  
Yulong Ji ◽  
Katsuya Fukuda ◽  
Qiusheng Liu ◽  
Hongbin Ma
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Convection Heat Transfer ◽  
Inlet Temperature ◽  
Experiment Data ◽  
Forced Convective Heat Transfer ◽  
Nusselt Numbers ◽  
Mini Channels ◽  
Heat Transfer Correlations

Abstract In this paper, the forced convective heat transfer of FC-72 was experimentally investigated for various of parameters like velocity, inlet temperature, tube size, and exponential period of heat generation rate. Circular tubes with different inner diameters (1, 1.8 and 2.8 mm) and heated lengths (30–50 mm) were used in this study. The experiment data suggest that the single-phase heat transfer coefficient increases with increasing flow velocity as well as decreasing tube diameter and ratio of heated length to inner diameter. The experiment data were nondimensionalized to study the effect of Reynolds number (Red) on forced convection heat transfer. The results indicate that the relation between Nusselt numbers (Nud) and Red for d = 2.8 mm show the same trend as the conventional correlations. However, the Nud for d = 1 and 1. 8 mm depend on Red in a different manner. The conventional heat transfer correlations are not adequate for prediction of forced convective heat transfer in mini channels. The heat transfer correlations for FC-72 in vertical small tubes with diameters of 1, 1.8 and 2.8 mm were developed separately based on the experiment data. The differences between experimental and predicted Nud are within ±15%.

Effects of Creep Flow and Viscous Dissipation in the Slip Regime for Isoflux Rectangular Microchannels

2007 ◽  
Author(s):  
Jennifer van Rij ◽  
Tim Ameel ◽  
Todd Harman
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Pressure Drop ◽  
Convective Heat Transfer ◽  
Viscous Dissipation ◽  
Convective Heat ◽  
Numerical Algorithm ◽  
Slip Flow ◽  
Creep Flow ◽  
Nusselt Numbers

The effects of rarefaction on convective heat transfer and pressure drop characteristics are numerically evaluated for uniform wall heat flux rectangular microchannels. Results are obtained by numerically solving the momentum and energy equations with both first- and second-order slip velocity and temperature jump boundary conditions. The resulting velocity and temperature fields are then evaluated to obtain the microchannel Poiseuille and Nusselt numbers. In addition to the effects of rarefaction, the effects of aspect ratio, thermal creep flow, and viscous dissipation are investigated for locally fully developed Poiseuille and Nusselt numbers. The constant wall heat flux results obtained in this study are compared to constant wall temperature results obtained previously, using the same numerical algorithm, at various aspect ratios including the limiting case of parallel plate microchannels. In addition to supplying previously unreported data on slip flow convective heat transfer and pressure drop characteristics, these results verify the numerical algorithm for more complex future slip flow analyses.

Free Convection Effects on Laminar Forced Convective Heat Transfer in a Horizontal Isothermal Tube

1982 ◽  
Vol 104 (1) ◽  
pp. 145-152 ◽  
Author(s):  
W. W. Yousef ◽  
J. D. Tarasuk
Keyword(s):  
Heat Transfer ◽  
Laminar Flow ◽  
Free Convection ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Temperature Difference ◽  
Reynolds Numbers ◽  
Transfer Data ◽  
Forced Convective Heat Transfer ◽  
Nusselt Numbers

The influence of free convection due to buoyancy on forced laminar flow of air in the entrance region of a horizontal isothermal tube was investigated. The Graetz numbers ranged form 2.5 to 110.0, the Reynolds numbers ranged from 120 to 1200, the Grashof numbers ranged from 0.8 × 104 to 8.7 × 104, and the ratio L/D was varied from 6 up to 46. The average Nusselt numbers based on the log-mean temperature difference, ranged from 2.0 to 25.9. The heat transfer data were correlated according to the influence of free convection which was found to have a significant effect at points close to the entrance to the tube.

Natural Convective Heat Transfer Through a Liquid Between a Heated Horizontal Surface and a Vertical Fin Attached to a Cooled Surface

1999 ◽  
Author(s):  
Patrick H. Oosthuizen
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Prandtl Number ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Lower Surface ◽  
Horizontal Surface ◽  
Finite Element Procedure ◽  
Liquid Depth ◽  
Rayleigh Numbers

Abstract Natural convective heat transfer from a heated horizontal surface directly exposed to a liquid into which vertical fins, attached to a cooled horizontal surface, project vertically downwards has been numerically studied. It has been assumed that the flow is steady, laminar and two-dimensional. The governing equations have been written in terms of dimensionless variables and have been solved using the finite element procedure. The solution has the following parameters: the Rayleigh number, the Prandtl number, the dimensionless half-width i.e. the ratio of the half-distance between the fins to the liquid depth, the dimensionless gap between the bottom of the fin and the lower surface, and the ratio of the thermal conductivity of the fin material to that of the liquid. Because of the application being considered, the Prandtl number has been taken as 5. Solutions have been obtained for Rayleigh numbers of between 10 and 1,000,000 for dimensionless half-widths of between 1 and 0.2 for thermal conductivity ratios of 20, 10 and 4 for a range of dimensionless fin gaps and widths.

Experimental Investigation of Dynamically Forced Impingement Cooling

2017 ◽  
Author(s):  
Arne Berthold ◽  
Frank Haucke
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Cross Flow ◽  
Side Wall ◽  
Cooling Efficiency ◽  
Liquid Crystal Thermography ◽  
Nusselt Numbers ◽  
Dynamic Forcing ◽  
The Individual

The influence of dynamic forcing of a 7 by 7 impinging jet array on the cooling efficiency is investigated experimentally. Thereby, this work focused on determining the influence side wall induced cross flow has on the local convective heat transfer on an electrically heated target plate and on enhancing the local convective heat transfer. For the enhancement the main focus is on the influence of the impingement distance, the impingement frequency and the phaseshift between the individual rows of nozzles. Liquid crystal thermography is employed for measuring the local wall temperatures, which are used to calculate the local Nusselt numbers. The cooling efficiency of this dynamic approach is determined by comparing local Nusselt numbers with steady blowing conditions.

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