scholarly journals Laminar air flow free convective heat transfer inside a vertical circular pipe with different inlet configurations

2007 ◽  
Vol 11 (1) ◽  
pp. 43-63 ◽  
Author(s):  
Hussein Mohammed ◽  
Yasin Salman
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Nusselt Number ◽  
Convection Heat Transfer ◽  
Circular Pipe ◽  
Convection Heat ◽  
Inlet Condition ◽  
Bell Mouth ◽  
Free Convection Heat ◽  
Laminar Air Flow

Free convection heat transfer has been experimentally investigated for laminar air flow in a vertical circular pipe by using the boundary condition of constant wall heat flux in the ranges of local Rayleight number (RaL) from 1.1?109 to 4.7?109. The experimental setup was designed for determining the effect of different configurations placed at the inlet of a vertical heated pipe, on the surface temperature, the local and average heat transfer coefficients. The apparatus was made with an electrically heated aluminum pipe with length of 900 mm and inside diameter 30 mm. The inlet configurations included two circular pipes having the same diameter as the heated pipe but with lengths of 600 and 1200 mm, sharp-edge and bell-mouth. It was found that the surface temperature along the pipe surface for same heat flux would be higher values for inlet condition with length of 1200 mm and would be lower values for bell-mouth inlet condition. The results show that the local Nusselt number Nux and average Nusselt number (NuL) values would be higher for bell-mouth inlet condition and lower values for 1200 mm inlet condition. For all inlet configurations, the results reveal that the Nu increases as the heat flux increases. Empirical correlations have been proposed in a form of log NuL vs. log RaL for each case investigated and a general correlation for all cases has been obtained which reveals the effect of inlet conditions existence on the free convection heat transfer process in a vertical circular pipe. .

scholarly journals Numerical study of combined convection heat transfer for thermally developing upward flow in a vertical cylinder

2008 ◽  
Vol 12 (2) ◽  
pp. 89-102 ◽  
Author(s):  
Hussein Mohammed ◽  
Yasin Salman
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Nusselt Number ◽  
Temperature Profile ◽  
Local Nusselt Number ◽  
Convection Heat Transfer ◽  
Convection Heat ◽  
Flux Boundary Condition ◽  
Number Range ◽  
Dimensionless Velocity

The problem of the laminar upward mixed convection heat transfer for thermally developing air flow in the entrance region of a vertical circular cylinder under buoyancy effect and wall heat flux boundary condition has been numerically investigated. An implicit finite difference method and the Gauss elimination technique have been used to solve the governing partial differential equations of motion (Navier Stocks equations) for two-dimensional model. This investigation covers Reynolds number range from 400 to 1600, heat flux is varied from 70 W/m2 to 400 W/m2. The results present the dimensionless temperature profile, dimensionless velocity profile, dimensionless surface temperature along the cylinder, and the local Nusselt number variation with the dimensionless axial distance Z+. The dimensionless velocity and temperature profile results have revealed that the secondary flow created by natural convection have a significant effect on the heat transfer process. The results have also shown an increase in the Nusselt number values as the heat flux increases. The results have been compared with the available experimental study and with the available analytical solution for pure forced convection in terms of the local Nusselt number. The comparison has shown satisfactory agreement. .

An Experimental Study on the Effect of Partition Angle on Free Convection Heat Transfer in a Partition Cavity by Laser Interferometry Method

2010 ◽  
Author(s):  
Tooraj Yousefi ◽  
Sajjad Mahmoodi Nezhad ◽  
Masood Bigharaz ◽  
Saeed Ebrahimi
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Rayleigh Number ◽  
Free Convection ◽  
Average Nusselt Number ◽  
Convection Heat Transfer ◽  
Laser Interferometry ◽  
Heated Wall ◽  
Convection Heat ◽  
Free Convection Heat

Steady state two-dimensional free convection heat transfer in a partitioned cavity with adiabatic horizontal and isothermally vertical walls and an adiabatic partition has been investigated experimentally. The experiments have been carried out using a Mach-Zehnder interferometer. The effects of the angel of the adiabatic partition and Rayleigh number on the heat transfer from the heated wall are investigated. Experiments are performed for the values of Rayleigh number based on the cavity side length in the range between 1.5×105 to 4.5×105 and various angle of the partition with respect to horizon from 0° to 90°. The results indicate that at each angle of the adiabatic partition, by increasing the Rayleigh number, the average Nusselt number and heat transfer increase and at each Rayleigh number, the maximum and the minimum heat transfer occur at θ=45° and θ=90°, respectively. A correlation based on the experimental data for the average Nusselt number of the heated wall as a function of Rayleigh number and the angel of the adiabatic partition is presented in the aforementioned ranges.

On Gaseous Free-Convection Heat Transfer With Well-Defined Boundary Conditions

2000 ◽  
Vol 122 (4) ◽  
pp. 661-668 ◽  
Author(s):  
M. R. D. Davies ◽  
D. T. Newport ◽  
T. M. Dalton
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Free Convection ◽  
Boundary Conditions ◽  
Convection Heat Transfer ◽  
Boussinesq Approximation ◽  
Horizontal Cylinder ◽  
Convection Heat ◽  
Variable Property ◽  
Free Convection Heat

The scaling of free convection heat transfer is investigated. The nondimensional groups for Boussinesq and fully compressible variable property free convection, driven by isothermal surfaces, are derived using a previously published novel method of dimensional analysis. Both flows are described by a different set of groups. The applicability of each flow description is experimentally investigated for the case of the isothermal horizontal cylinder in an air-filled isothermal enclosure. The approach taken to the boundary conditions differs from that of previous investigations. Here, it is argued that the best definition of the boundary conditions is achieved for heat exchange between the cylinder and the enclosure rather than the cylinder and an arbitrarily chosen fluid region. The enclosure temperature is shown both analytically and experimentally to affect the Nusselt number. The previously published view that the Boussinesq approximation has only a limited range of application is confirmed, and the groups derived for variable property compressible free convection are demonstrated to be correct experimentally. A new correlation for horizontal cylinder Nusselt number prediction is presented. [S0022-1481(00)01604-2]

Free Convection Heat Transfer Across Inclined Honeycomb Panels

1977 ◽  
Vol 99 (1) ◽  
pp. 86-91 ◽  
Author(s):  
R. L. D. Cane ◽  
K. G. T. Hollands ◽  
G. D. Raithby ◽  
T. E. Unny
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Free Convection ◽  
Convection Heat Transfer ◽  
Correlation Equation ◽  
Base Flow ◽  
Convection Heat ◽  
Radiative Coupling ◽  
Aspect Ratios ◽  
Free Convection Heat

Experimentally obtained Nusselt number-Rayleigh number plots are presented for free convective heat transfer across honeycomb panels, heated from below, and inclined with respect to the horizontal at angles of 0, 30, 45, 60, and 90 deg. Aspect ratios of honeycomb cells of 2, 3, 4, and 5 are included; the fluid contained in the cells is air. Substantial suppression of free convection is observed when compared with an air layer of the same depth but not containing a honeycomb. Heat transfer associated with the base flow is found to be of only moderate importance at angles near horizontal, but of considerable consequence for angles near the vertical. The honeycomb walls used were partly transparent to thermal radiation, and a strong radiative coupling is indicated. A correlation equation for the Nusselt number, valid over part of the experimental range, is presented.

Natural Convection Heat Transfer of Concentric/Eccentric Annulus Subjected to Inner Tube of Constant Heat Flux

2011 ◽  
Author(s):  
R. Hosseini ◽  
M. Alipour ◽  
A. Gholaminejad
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Nusselt Number ◽  
Natural Convection ◽  
Rayleigh Number ◽  
Surface Temperature ◽  
Convection Heat Transfer ◽  
Natural Convection Heat Transfer ◽  
Convection Heat ◽  
Eccentric Annulus

This paper describes the experimental results of natural convection heat transfer from vertical, electrically heated cylinder in a concentric/eccentric annulus and develops correlations for the dependence of the average annulus Nusselt number upon the Rayleigh number. Wall surface temperature have been recorded for diameter ratio of d/D = 0.4, with the apparatus immersed in stagnant air with uniform temperature. Measurements have been carried out for eccentric ratios of E = 0, 0.19, 0.34, 0.62 and 0.89 in the range of heat flux of 45 to 430 W/m2. The surface temperature of the heater was found to increase upwards and reach a maximum at some position, beyond which it decreases again. It is observed, that this maximum temperature occurs near h/l = 0.8 for 0 ≤ E ≤ 0.62 at almost all power levels, but shifts downwards for E = 0.89. Moreover, empirical correlations between the average Nusselt number and the Rayleigh number are derived for concentric and eccentric annuli.

scholarly journals Free convection limit to heat transfer from heatsinks with square fins on a horizontal base: Comparison with cylindrical fins

2015 ◽  
Vol 19 (5) ◽  
pp. 1565-1574
Author(s):  
S.C. Haldar ◽  
S. Manna
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Heat Flux ◽  
Free Convection ◽  
Convection Heat Transfer ◽  
Far Field ◽  
Convection Heat ◽  
Horizontal Plate ◽  
Controlling Mechanism ◽  
Free Convection Heat

Free convection about a single vertically orientated square fin on a horizontal plate has been investigated numerically. Fluid is drawn towards the fin from the far field which cools the fin and finally leaves through the top. For short fins, convection rather than the conduction is the controlling mechanism and this renders the fin thermal conductivity a parameter of little importance for such fins. Heat flux at the base of the fin decreases with increasing width of the fin confirming the benefits of large number of slender fins. A correlation has been developed to evaluate the heat flux at fin base which may be used to predict the upper bound of free convection heat transfer from any heat sink with square fins on a horizontal base. Rate of heat transfer so calculated has been compared with experimental data published recently. The study also reveals the advantage of the cylindrical fins over square fins.

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