Natural Convective Heat Transfer in a Divided Vertical Channel: Part I—Numerical Study

1993 ◽  
Vol 115 (2) ◽  
pp. 377-387 ◽  
Author(s):  
D. Naylor ◽  
J. D. Tarasuk
Keyword(s):  
Heat Transfer ◽  
Numerical Study ◽  
Plate Thickness ◽  
Convection Heat Transfer ◽  
Vertical Channel ◽  
Channel Length ◽  
Navier Stokes ◽  
Nusselt Numbers ◽  
Data Correlations ◽  
Energy Equations

This is a two-part study of two-dimensional laminar natural convection heat transfer in a divided vertical channel. The divided channel consists of an isothermal dividing plate located on the center line of a vertical channel formed by two isothermal walls. The study examines the effect of Rayleigh number, plate-to-channel length ratio, vertical plate position, and plate thickness on the heat transfer rate from the channel walls, the dividing plate, and the channel as a whole. In Part I, solutions to both the full elliptic and parabolic forms of the Navier–Stokes and energy equations are obtained for Prandtl number Pr = 0.7 (air). Positioning the plate at the bottom of the channel was found to give the highest average Nusselt numbers for the plate and channel. Dividing plate average Nusselt numbers as much as two times higher than the isolated plate Nusselt number were predicted numerically. Experimental measurements and data correlations for the divided channel are presented in Part II of this paper.

Investigation of Natural Convection Heat Transfer in Converging Channel Flows Using a Specklegram Technique

1993 ◽  
Vol 115 (1) ◽  
pp. 140-148 ◽  
Author(s):  
K. D. Kihm ◽  
J. H. Kim ◽  
L. S. Fletcher
Keyword(s):  
Heat Transfer ◽  
Convection Heat Transfer ◽  
Vertical Channel ◽  
Channel Length ◽  
Heat Transfer Characteristics ◽  
Grashof Number ◽  
Nusselt Numbers ◽  
Single Plate ◽  
Converging Channel ◽  
Inclination Angles

Natural convection heat transfer characteristics in converging vertical channel flows were studied by nonintrusively measuring the wall temperature gradients using a laser specklegram technique. Local and average heat transfer coefficients were obtained for forty different configurations, including five different inclination angles from the vertical, γ = 0, 15, 30, 45 and 60 deg, with eight different channel exit openings for each inclination angle. Correlations for both local and average Nusselt numbers, based on the channel length L, were determined as functions of Grashof number, where the local Grashof number, based on the channel length L, ranged up to 7.16×106 and the overall Grashof number varied from 3.58×106 (γ = 60 deg) to 7.16×106 (γ = 0), depending upon the inclination angle. As the top opening was decreased, both local and average Nusselt numbers deviated from the single inclined plate theory and significant reductions in heat transfer resulted. The minimum opening ratio, at which the average Nusselt number started decreasing from that for the single plate, was determined as (b/L)min = 0.07, 0.1, 0.3, 0.35, and 0.4 for inclination angles of 0, 15, 30, 45 and 60 deg, respectively. For Ra* larger than 105, average Nusselt numbers, based on the channel opening b, approached the single-plate limit of the vertical channel flow theory, which was modified to incorporate the reduced gravity due to the inclination. When Ra* was smaller than 105, however, neither the single-plate limit nor the fully developed limit properly described the heat transfer characteristics in the converging channel.

Natural Convective Heat Transfer in a Divided Vertical Channel: Part II—Experimental Study

1993 ◽  
Vol 115 (2) ◽  
pp. 388-394 ◽  
Author(s):  
D. Naylor ◽  
J. D. Tarasuk
Keyword(s):  
Heat Transfer ◽  
Convection Heat Transfer ◽  
Vertical Channel ◽  
Channel Length ◽  
Nusselt Numbers ◽  
Numerical Predictions ◽  
Interferometric Study ◽  
Laminar Natural Convection ◽  
Nusselt Number Correlation ◽  
Good Agreement

An interferometric study has been conducted on two-dimensional laminar natural convection heat transfer in an isothermal vertical divided channel. Interferograms were obtained for air and a plate-to-channel length ratio of Lp/Lc= 1/3. Data are presented for the dividing plate located at the bottom (Li/Lc = 0) and top of the channel (Li/Lc=2/3). Comparisons of local and average Nusselt numbers are made with the numerical predictions from Part I. Although the experimental average Nusselt numbers are typically about 10 percent lower than the numerical results, the general trends of the data are in good agreement. Average Nusselt number correlation equations are presented.

Flow Characteristics in a Three-Dimensional Rectangular Channel With a Pair of Ribs Placed Symmetrically at the Channel Walls

2000 ◽  
Author(s):  
M. Singh ◽  
P. K. Panigrahi ◽  
G. Biswas
Keyword(s):  
Heat Transfer ◽  
Large Scale ◽  
Numerical Study ◽  
Rectangular Channel ◽  
Turbine Blades ◽  
Three Dimensional ◽  
Flow Characteristics ◽  
Navier Stokes ◽  
Complex Flow ◽  
Energy Equations

Abstract A numerical study of rib augmented cooling of turbine blades is reported in this paper. The time-dependent velocity field around a pair of symmetrically placed ribs on the walls of a three-dimensional rectangular channel was studied by use of a modified version of Marker-And-Cell algorithm to solve the unsteady incompressible Navier-Stokes and energy equations. The flow structures are presented with the help of instantaneous velocity vector and vorticity fields, FFT and time averaged and rms values of components of velocity. The spanwise averaged Nusselt number is found to increase at the locations of reattachment. The numerical results are compared with available numerical and experimental results. The presence of ribs leads to complex flow fields with regions of flow separation before and after the ribs. Each interruption in the flow field due to the surface mounted rib enables the velocity distribution to be more homogeneous and a new boundary layer starts developing downstream of the rib. The heat transfer is primarily enhanced due to the decrease in the thermal resistance owing to the thinner boundary layers on the interrupted surfaces. Another reason for heat transfer enhancement can be attributed to the mixing induced by large-scale structures present downstream of the separation point.

scholarly journals Convection Heat Transfer Analysis in a Channel with an Open Trapezoidal Cavity: Heat Source Locations effect

2020 ◽  
Vol 330 ◽  
pp. 01006
Author(s):  
F. Mebarek-Oudina ◽  
H. Laouira ◽  
A. Aissa ◽  
A. K. Hussein ◽  
M. El Ganaoui
Keyword(s):  
Heat Transfer ◽  
Heat Source ◽  
Numerical Study ◽  
Convection Heat Transfer ◽  
The Other ◽  
Heat Transfer Analysis ◽  
Convection Heat ◽  
Nusselt Numbers ◽  
Discrete Heat Source ◽  
Trapezoidal Enclosure

In this work, a numerical study of mixed convection inside a horizontal channel with an open trapezoidal enclosure subjected to a discrete heat source in different locations is carried out. The heat source with the length of ε = 0.75, is maintained at a constant temperature. The air flow with a fixed velocity and a cold temperature enters the channel horizontally. The other walls of the enclosure and the channel are adiabatic. The results are presented in the form of the contours of velocity, isotherms and Nusselt numbers profiles for various heat source locations, Prandtl number (Pr = 0.71) and Reynolds number (Re = 100) respectively. The distribution of the isotherms depends significantly on the position of the heat source. We noted that the best heat transfer is detected where the heat source is placed in the top of the left .

Numerical study of the fin effect on mixed convection heat transfer in a lid-driven cavity

2010 ◽  
Vol 225 (2) ◽  
pp. 397-406 ◽  
Author(s):  
A A R Darzi ◽  
M Farhadi ◽  
K Sedighi
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Richardson Number ◽  
Numerical Study ◽  
Convection Heat Transfer ◽  
Thermal Conductivity Ratio ◽  
Driven Cavity ◽  
Ratio Change ◽  
Vertical Walls ◽  
Energy Equations

In this study, the mixed convective heat transfer in a lid-driven cavity was investigated numerically. The finite volume discritization method was used to solve the momentum and energy equations by using the classic Boussinesq incompressible approximation. The cavity vertical walls are insulated whereas the bottom (hot wall) and top (cold wall) surface are maintained at a uniform temperature and fins are located on bottom wall. The effect of fin numbers over the flow field and heat transfer was investigated at various Richardson numbers. Study was carried out for Richardson numbers ranging from 0.01 to 10, fin numbers between 1 and 7, fin height ratio change from 0.05 to 0.3, and thermal conductivity ratio (fin to fluid) from 10 to 104, respectively. The results are presented in the form of streamlines, temperature contours, and Nusselt number distributions. The results show that the Nusselt number increases when the number of fin and fin height decrease. In addition, in all cases an increasing Richardson number caused increasing the relative Nusselt number ( Nu / Nu0). The heat transfer enhancement was observed at low fin numbers (1 and 3) and high Richardson number in comparison with the cavity without fins.

scholarly journals Prandtl Number Effects on the Entropy Generation During the Transient Mixed Convection in a Square Cavity Heated from Below

2021 ◽  
Author(s):  
Nawal Ferroudj ◽  
Hasan Koten ◽  
Sacia Kachi ◽  
Saadoun Boudebous
Keyword(s):  
Heat Transfer ◽  
Prandtl Number ◽  
Mixed Convection ◽  
Entropy Generation ◽  
Numerical Study ◽  
Convection Heat Transfer ◽  
Working Fluid ◽  
Square Cavity ◽  
Nusselt Numbers ◽  
The Impact

This numerical study considers the mixed convection, heat transfer and the entropy generation within a square cavity partially heated from below with moving cooled vertical sidewalls. All the other horizontal sides of the cavity are assumed adiabatic. The governing equations, in stream function–vorticity form, are discretized and solved using the finite difference method. Numerical simulations are carried out, by varying the Richardson number, to show the impact of the Prandtl number on the thermal, flow fields, and more particularly on the entropy generation. Three working fluid, generally used in practice, namely mercury (Pr = 0.0251), air (Pr = 0.7296) and water (Pr = 6.263) are investigated and compared. Predicted streamlines, isotherms, entropy generation, as well as average Nusselt numbers are presented. The obtained results reveal that the impact of the Prandtl number is relatively significant both on the heat transfer performance and on the entropy generation. The average Nusselt number increase with increasing Prandtl number. Its value varies thereabouts from 3.7 to 3.8 for mercury, from 5.5 to 13 for air and, from 12.5 to 15 for water. In addition, it is found that the total average entropy generation is significantly higher in the case of mercury (Pr«1) and water (Pr»1) than in the case of air (Pr~1). Its value varies approximately from 700 to 1100 W/m3 K for mercury, from 200 to 500 W/m3 K for water and, from 0.03 to 5 W/m3 K for air.    

Experimental and Computational Analysis of Natural Convection Over Flat Plate

2008 ◽  
Author(s):  
Farhana Afroz ◽  
Chowdhury Md. Feroz
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Flat Plate ◽  
Convection Heat Transfer ◽  
Boussinesq Approximation ◽  
Heat Fluxes ◽  
Navier Stokes ◽  
Heated Plate ◽  
Wide Range ◽  
Energy Equations

Natural convection heat transfer over a flat plate with a heat source at bottom side of plate is studied experimentally and numerically. We consider the two-dimensional problem of both steady and unsteady natural convection over the flat plate at vertical, horizontal and inclined position. Experimental analysis is done for three different constant heat fluxes for each angle position. The Navier-Stokes and Energy equations with the Boussinesq approximation are written in Cartesian coordinate system. The problem is solved in the physical variables on the basis of a completely implicit Finite element Method order to examine the heat transfer characteristics. To see the effects of different angle position phenomena of natural convection over flat plate, the computational results presented in the form of streamlines for a wide range of Grashof number at different heat fluxes. The average Nusselt number of heated plate for different angle position has been observed.

Numerical Study of the Free Convection Heat Transfer From an I-Beam Support Structure

2014 ◽  
Author(s):  
Ayoola T. Brimmo ◽  
Youssef Shatilla ◽  
Mohamed I. Hassan
Keyword(s):  
Heat Transfer ◽  
Free Convection ◽  
Numerical Study ◽  
Convection Heat Transfer ◽  
Convection Flow ◽  
Support Structure ◽  
Ansys Fluent ◽  
Aluminum Reduction ◽  
Nusselt Numbers ◽  
Convection Cooling

In this study, a computational fluid dynamics (CFD) model is used to numerically characterize the heat transfer from an I-beam support structure of an aluminum reduction pot, during the free convection cooling process. A slice of the I-beam structure is modeled on two different finite element commercial platforms, ANSYS (FLUENT) and StarCCM+, in a suitable domain of air. The K-epsilon Reynolds averaging technique is used to model the turbulence in both platforms. Validation of the modeling technique and parameters adapted is appropriately performed. The structure is segmented and space mean Nusselt numbers (Nu) characterizing the flow are calculated for each section, for Rayleigh number (Ra) ranges typically experienced by the respective section. Expressions correlating the free convection flow over this structure are deduced based on a regression analysis. To conclude, an application of the deduced correlation in modeling the free convection cooling of an aluminum reduction pot is presented.

ANALYSIS OF NATURAL CONVECTION HEAT TRANSFER BETWEEN TWO HORIZONTAL CYLINDERS AND THEIR ENCLOSURE

1992 ◽  
Vol 16 (1) ◽  
pp. 17-32 ◽  
Author(s):  
M. Lacroix
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Natural Convection ◽  
Numerical Study ◽  
Convection Heat Transfer ◽  
Natural Convection Heat Transfer ◽  
Convection Heat ◽  
Nusselt Numbers ◽  
Horizontal Cylinders ◽  
Rayleigh Numbers

A numerical study has been conducted for natural convection heat transfer for air around two horizontal heated cylinders placed inside a rectangular enclosure cooled from the side. Three cylinder spacings were investigated. The local and overall Nusselt numbers were determined over the range of Rayleigh numbers from 104 to 106. It is found that the thermal performance of the unit is strongly influenced by the Rayleigh number and, to a lesser extent, by the cylinder spacing. A correlation is suggested for the overall Nusselt number.

Forced Convection Heat Transfer in a Finitely Conducting Externally Finned Pipe

1988 ◽  
Vol 110 (3) ◽  
pp. 571-576 ◽  
Author(s):  
F. Moukalled ◽  
S. Acharya
Keyword(s):  
Heat Transfer ◽  
Forced Convection ◽  
Numerical Study ◽  
Convection Heat Transfer ◽  
Axial Direction ◽  
Bulk Temperature ◽  
Convection Heat ◽  
Forced Convection Heat Transfer ◽  
Nusselt Numbers ◽  
Wall Conductivity

A numerical study to determine the influence of axial wall conduction on forced convection heat transfer in an externally finned pipe has been made. The effects of wall conductivity, interfin spacing, and external heat transfer coefficient are examined by comparing the results with the corresponding solutions obtained assuming negligible wall conduction. Results indicate that the axial conduction in the pipe walls has a significant influence on the heat transfer behavior. The bulk temperature or the heat transferred to the fluid is underestimated when wall conduction is ignored. At high wall conductivity values, the wall temperatures and Nusselt numbers exhibit a monotonic variation in the axial direction, with the behavior becoming increasingly nonmonotonic as the wall conductivity value is decreased.

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