Investigation of Nusselt numbers in the convection of thermally viscous liquids

2008 ◽  
Vol 6 ◽  
pp. 127-131
Author(s):  
K.V. Moiseyev ◽  
A.M. Ilyasov
Keyword(s):  
Nusselt Number ◽  
Free Convection ◽  
Viscous Liquids ◽  
Nusselt Numbers ◽  
Viscosity Function ◽  
Rayleigh Numbers ◽  
Square Cell

In the paper, free convection of thermally viscous liquids in a square cell is numerically investigated. Quadratic and exponential viscosity versus temperature is considered. The influence of these dependences on the Nusselt number is studied. It is established that the dependence of the Nusselt number on the Rayleigh numbers is characterized by the average viscosity, monotonicity, and convexity of the viscosity function of temperature.

An Interferometric Study of Combined Free and Forced Convection in a Horizontal Isothermal Tube

1981 ◽  
Vol 103 (2) ◽  
pp. 249-256 ◽  
Author(s):  
W. W. Yousef ◽  
J. D. Tarasuk
Keyword(s):  
Nusselt Number ◽  
Free Convection ◽  
Forced Convection ◽  
Average Nusselt Number ◽  
Three Dimensional ◽  
Convection Heat Transfer ◽  
Horizontal Tube ◽  
Reynolds Numbers ◽  
Nusselt Numbers ◽  
Free And Forced Convection

A Mach-Zehnder interferometer was employed to determine the three-dimensional temperature field, and the circumferential and average Nusselt numbers for laminar flow of air in the entrance region of an isothermal horizontal tube where the velocity and the temperature profiles were developing simultaneously. The influence of free convection due to buoyancy on forced convection heat transfer was investigated. 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 to 46. The free convection increases, substantially, the average Nusselt number, by up to a factor of 2.0 from the analytical predictions, which account for forced convection only, near the tube inlet. Far from the tube inlet the free convection tends to decrease the average Nusselt number below the analytical predictions.

Experimental Investigation of Free Convection in a Vertical Rod Bundle—A General Correlation for Nusselt Numbers

1985 ◽  
Vol 107 (3) ◽  
pp. 611-623 ◽  
Author(s):  
M. Keyhani ◽  
F. A. Kulacki ◽  
R. N. Christensen
Keyword(s):  
Nusselt Number ◽  
Rayleigh Number ◽  
Free Convection ◽  
Power Dissipation ◽  
Unit Length ◽  
Outer Cylinder ◽  
Working Fluid ◽  
Curvature Effects ◽  
Nusselt Numbers ◽  
Wide Range

Free convection in two vertical, enclosed rod bundles has been experimentally investigated for a wide range of Rayleigh numbers. A uniform power dissipation per unit length is supplied to each rod, and the enclosing outer cylinder is maintained at constant temperature. Nusselt numbers for each rod, as well as an overall value for each bundle, have been obtained as a function of Rayleigh number. Comparison of the results for air and water as the working fluid indicate that, for a fixed Rayleigh number, an increase in the Prandtl number produces a reduction in the Nusselt number. This is contrary to what has been reported for vertical cavities and is attributed to curvature effects. Furthermore, the data reveal the interesting fact that it is quite possible for the individual rods in the bundle to exchange energy with the working fluid via different but coexisting regimes at a given power dissipation. Also, as the Rayleigh number is increased, the rods each tend to assume nearly the same heat transfer coefficient. Finally, a correlation for the overall convective Nusselt number is developed in terms of Rayleigh number and geometric parameters.

Effect of departures from the Oberbeck-Boussinesq approximation on the heat transport of horizontal convecting fluid layers

1980 ◽  
Vol 98 (1) ◽  
pp. 137-148 ◽  
Author(s):  
Guenter Ahlers
Keyword(s):  
Nusselt Number ◽  
Rayleigh Number ◽  
Critical Rayleigh Number ◽  
Boussinesq Approximation ◽  
Initial Slope ◽  
Nusselt Numbers ◽  
Fluid Layers ◽  
Different Temperatures ◽  
Rayleigh Numbers ◽  
Experimental Scatter

Measurements are presented of the Nusselt numbers N and Rayleigh numbers R for shallow layers of 4He gas heated from below. By choosing different temperatures between 2·3 K and 5·1 K and different pressures between 0·07 bar and 1 bar, the extent Q of departures from the Oberbeck-Boussinesq approximation was varied. When R was evaluated at the static temperature at the midplane of the cell, both the critical Rayleigh number Rc and the initial slope N1 of the Nusselt number were found to be independent of Q within experimental scatter. This result agrees with the prediction of Busse (1967). When R was evaluated at the cold end temperature of the cell, both Rc and N1 depended strongly upon Q.

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.

scholarly journals Numerical Analysis of the Improving Thermal Energy Efficiency of Taylor-couette Flow

2021 ◽  
Vol 15 ◽  
pp. 236-247
Author(s):  
Khaoula Ben Abdelmlek ◽  
Fayçal Ben Nejma
Keyword(s):  
Energy Efficiency ◽  
Nusselt Number ◽  
Rayleigh Number ◽  
Numerical Study ◽  
Rotation Velocity ◽  
Radius Ratio ◽  
Nusselt Numbers ◽  
Cylindrical Annulus ◽  
The Mean ◽  
Rayleigh Numbers

This paper deals with adimensionnal analysis of natural convection in a horizontal cylindrical annulus. The inner cylinder is isothermally heated and rotates with an angular velocity Ω, however the outer one is kept cold and motionless. The gap between cylinders is defined by an adimensional radius ratio f. The numerical study was carried out using COMSOL Multiphysics. The effects of Rayleigh number ranging from 102 to 106, radius ratio and rotation velocity on the flow pattern and the thermal behavior in the annulus are then elaborated. Particular attention is paid to the effect of different parameters on the local Nusselt numbers on the inner and outer cylinders, the mean Nusselt number and the energy efficiency of the process. Results show that the mean Nusselt number increases with the increase of Rayleigh number. However, it decreases with the increase of the radius ratio f because of the narrowing of the annulus. The results prove also that the heat transfer rate drops with the rise of rotation velocity. Finally, it was found that the energy efficiency achieved its maximum for lower Rayleigh numbers Ra=103, and lower rotation velocities.

Free Convection in Antisymmetrically Heated Vertical Channels

2013 ◽  
Vol 136 (1) ◽  
Author(s):  
D. Roeleveld ◽  
D. Naylor ◽  
W. H. Leong
Keyword(s):  
Temperature Field ◽  
Free Convection ◽  
Vertical Channel ◽  
Laser Interferometry ◽  
Measured Temperature ◽  
Ansys Fluent ◽  
Nusselt Numbers ◽  
Numerical Predictions ◽  
Rayleigh Numbers ◽  
Special Case

Free convection in a vertical channel with antisymmetrical heating is a special case that has not received a great deal of attention in the literature. Antisymmetrical heating is where the hot wall is heated above the ambient temperature by the same amount that the cold wall is cooled below the ambient, giving equal but opposing buoyancy forces inside the channel. An experimental model was constructed to study antisymmetrical heating inside an isothermally heated vertical channel. Flow visualization was used to obtain the flow field and laser interferometry was used to obtain the temperature field. Based on the measured temperature field, the local and average Nusselt numbers were determined, which were compared with numerical predictions obtained using ansys fluent. A range of Rayleigh numbers were studied for air with a Prandtl number of 0.71. The results show that an open-ended channel with antisymmetrical heating has some similarities to a tall enclosure. The average convective heat transfer can be approximated using an existing correlation for a tall enclosure from the literature.

Free Convection Heat Transfer From Upward-Facing Isothermal Horizontal Surfaces

1982 ◽  
Vol 104 (3) ◽  
pp. 493-500 ◽  
Author(s):  
W. W. Yousef ◽  
J. D. Tarasuk ◽  
W. J. McKeen
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Free Convection ◽  
Heated Surface ◽  
Convection Heat Transfer ◽  
Mean Value ◽  
Convection Flow ◽  
Transfer Coefficients ◽  
Mean Values ◽  
Nusselt Numbers

Heat transfer by free convection in air from isothermal horizontal surfaces heated and facing upward has been experimentally studied by using a Mach-Zehnder interferometer. The local and the average heat-transfer coefficients and the temperature distributions were determined in the range of Gr Pr from 1.9 × 106 to 1.7 × 108. Measurements were compared with available experimental and theoretical results. Periodical flow instabilities caused random changes, which could reach +45 and −35 percent of mean values in the local Nusselt number and +23 and −15 percent of mean value in the average Nusselt number. The nature of the free convection flow over the heated surface and the separation of the boundary layer were inferred from these random changes in the local and average Nusselt numbers.

scholarly journals Magnetic nanofluid behavior including an immersed rotating conductive cylinder: finite element analysis

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Hameed K. Hamzah ◽  
Farooq H. Ali ◽  
M. Hatami ◽  
D. Jing ◽  
Mohammed Y. Jabbar
Keyword(s):  
Magnetic Field ◽  
Finite Element ◽  
Nusselt Number ◽  
Average Nusselt Number ◽  
Volume Fraction ◽  
Element Analysis ◽  
Magnetic Nanofluid ◽  
Nusselt Numbers ◽  
Velocity Pressure ◽  
Rayleigh Numbers

AbstractIn this paper, numerical Galerkin Finite Element Method (GFEM) is applied for conjugate heat-transfer of a rotating cylinder immersed in Fe3O4-water nanofluid under the heat-flux and magnetic field. The outer boundaries of the cavity were maintained at low temperatures while beside the cylinder were insulated. It is assumed that the cylinder rotates in both clockwise and counter-clockwise directions. The dimensionless governing equations such as velocity, pressure, and temperature formulation were analyzed by the GFEM. The results were evaluated using the governing parameters such as nanoparticles (NPs) volume fraction, Hartmann and Rayleigh numbers, magnetic field angle and NPs shapes. As a main result, the average Nusselt number increases by increasing the NPs volume fraction, inclination angle and thermal conductivity ratios, while increasing the Hartmann number decreased the Nusselt number. Furthermore, platelet NPs had the maximum average Nusselt number and spherical NPs made the minimum values of Nusselt numbers among examined NPs shapes.

An Experimental Study of Free Corrective Heat Transfer in a Parallelogrammic Enclosure

1983 ◽  
Vol 105 (3) ◽  
pp. 433-439 ◽  
Author(s):  
N. Seki ◽  
S. Fukusako ◽  
A. Yamaguchi
Keyword(s):  
Heat Transfer ◽  
Experimental Study ◽  
Nusselt Number ◽  
Correlation Equation ◽  
Transformer Oil ◽  
Experimental Measurements ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Prandtl Numbers ◽  
Rayleigh Numbers

Experimental measurements are presented for free convective heat transfer across a parallelogrammic enclosure with the various tilt angles of parallel upper and lower walls insulated. The experiments covered a range of Rayleigh numbers between 3.4 × 104 and 8.6 × 107, and Prandtl numbers between 0.70 and 480. Those also covered the tilt angles of the parallel insulated walls with respect to the horizontal, φ, of 0, ±25, ±45, ±60, and ±70 deg under an aspect ratio of H/W = 1.44. The fluids used were air, transformer oil, and water. It was found that the heat transfer coefficients for φ = −70 deg were decreased to be about 1/18 times those for φ = 0 deg. Experimental results are given as plots of the Nusselt number versus the Rayleigh number. A correlation equation is given for the Nusselt number, Nu, as a function of φ, Pr, and Ra.

Free Convection Nusselt Number for Vertical U-Shaped Channels

1973 ◽  
Vol 95 (4) ◽  
pp. 542-543 ◽  
Author(s):  
D. W. Van de Pol ◽  
J. K. Tierney
Keyword(s):  
Nusselt Number ◽  
Free Convection
Sign in / Sign up

Export Citation Format

Share Document