scholarly journals NUMERICAL STIMULATION OF RAYLEIGH BERNARD CONVECTION IN WAVY ENCLOSURES

2012 ◽  
pp. 274-277
Author(s):  
S. SUBHA
Keyword(s):  
Heat Transfer ◽  
Rayleigh Number ◽  
Flow Characteristics ◽  
Practical Interest ◽  
Nusselt Numbers ◽  
Numerical Stimulation ◽  
Vertical Walls ◽  
Finite Volume Approach ◽  
Fluid Flow Characteristics ◽  
Enclosed Space

Enclosures are frequently encountered in practice, and heat transfer through them is of practical interest. Heat transfer in enclosed space is complicated by the fact that fluid in the enclosure, in general, does not remain constant. The fluid adjacent to the hotter surface rises and the fluid adjacent to the cooler one falls, setting a rotionary motion within the enclosure that enhances the heat transfer through the enclosure. This paper describes a numerical predication of heat transfer and fluid flow characteristics inside an enclosure bounded by horizontal wavy walls and two periodic straight vertical walls. Governing equation were discretized using an implicit finite difference method, based on finite volume approach. Simulation was carried out for a range of Rayleigh number (104-106) and Aspect ratio (0.35-0.75) for the fluid having Prandtl number 0.71. Results are presented by streamlines, isotherms and local Nusselt numbers. It is observed that flow and thermal field inside the enclosure are affected by the shape of enclosure and heat transfer rate increases as Rayleigh number increase.

scholarly journals Numerical Investigation on Turbulent Flow and Heat Transfer of Rectangular Channels With Elliptic Scale-Roughened Walls

2012 ◽  
Author(s):  
Feng Zhou ◽  
Ivan Catton
Keyword(s):  
Heat Transfer ◽  
Flow Direction ◽  
Flow Characteristics ◽  
Spanwise Direction ◽  
Pressure Drops ◽  
Nusselt Numbers ◽  
Flow Mixing ◽  
Rectangular Channels ◽  
Smooth Channel ◽  
Fluid Flow Characteristics

In the present paper, six new types of rectangular channels with elliptic scale-roughened walls for heat transfer enhancement, which include elongated scale cases (Pt/Pl = 0.3, 0.5, 0.7) and squeezed scale cases (Pt/Pl = 1.43, 2, 3.33), are proposed. Heat transfer and fluid flow characteristics for sixteen different scale-roughened models (with the scale height varying in the range from 1mm to 2.5mm) are predicted numerically using commercial CFD code, Ansys CFX, with the Reynolds number ranging from 5000 to 15000. The turbulent model employed is the k-ω based Shear-Stress-Transport (SST) model with automatic wall function treatment. It is found that the elliptic scales with their long axis oriented perpendicular to the flow direction enhance the heat transfer performance considerably, while the scales elongated in the flow direction have lower Nusselt numbers and pressure drops compared to the circular scale-roughened channels. It is also found that the scale-shaped roughness strongly spins the flow in the spanwise direction, which breaks the near wall boundary layers continuously and enhances the bulk flow mixing. With the flow marching in a spiral pattern, Nusselt number ratios between the squeezed scale-roughened and smooth channel flows (Nu/Nu∞) could be augmented to be within the range of 6.1 to 8.1, which is a 50% improvement over the circular scale-roughened channels.

Heat Transfer and Flow Phenomena in a Swirl Chamber Simulating Turbine Blade Internal Cooling

1998 ◽  
Author(s):  
C. R. Hedlund ◽  
P. M. Ligrani ◽  
H.-K. Moon ◽  
B. Glezer
Keyword(s):  
Heat Transfer ◽  
Turbine Blade ◽  
Flow Characteristics ◽  
Leading Edge ◽  
Internal Cooling ◽  
Vortex Pairs ◽  
Nusselt Numbers ◽  
Swirl Chamber ◽  
Flow Phenomena ◽  
Energy Balances

Heat transfer and fluid mechanics results are given for a swirl chamber whose geometry models an internal passage used to cool the leading edge of a turbine blade. The Reynolds numbers investigated, based on inlet duct characteristics, include values which are the same as in the application (18000–19400). The ratio of absolute air temperature between the inlet and wall of the swirl chamber ranges from 0.62 to 0.86 for the heat transfer measurements. Spatial variations of surface Nusselt numbers along swirl chamber surfaces are measured using infrared thermography in conjunction with thermocouples, energy balances, digital image processing, and in situ calibration procedures. The structure and streamwise development of arrays of Görtler vortex pairs, which develop along concave surfaces, are apparent from flow visualizations. Overall swirl chamber structure is also described from time-averaged surveys of the circumferential component of velocity, total pressure, static pressure, and the circumferential component of vorticity. Important variations of surface Nusselt numbers and time-averaged flow characteristics are present due to arrays of Görtler vortex pairs, especially near each of the two inlets, where Nusselt numbers are highest. Nusselt numbers then decrease and become more spatially uniform along the interior surface of the chamber as the flows advect away from each inlet.

Laminar Natural Convection in a Discretely Heated Cavity: II—Comparisons of Experimental and Theoretical Results

1995 ◽  
Vol 117 (4) ◽  
pp. 910-917 ◽  
Author(s):  
T. J. Heindel ◽  
F. P. Incropera ◽  
S. Ramadhyani
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Rayleigh Number ◽  
Vertical Wall ◽  
Three Dimensional ◽  
Companion Paper ◽  
Nusselt Numbers ◽  
Numerical Predictions ◽  
Number Flow ◽  
Experimental Geometry

Three-dimensional numerical predictions and experimental data have been obtained for natural convection from a 3 × 3 array of discrete heat sources flush-mounted on one vertical wall of a rectangular cavity and cooled by the opposing wall. Predictions performed in a companion paper (Heindel et al., 1995a) revealed that three-dimensional edge effects are significant and that, with increasing Rayleigh number, flow and heat transfer become more uniform across each heater face. The three-dimensional predictions are in excellent agreement with the data of this study, whereas a two-dimensional model of the experimental geometry underpredicts average heat transfer by as much as 20 percent. Experimental row-averaged Nusselt numbers are well correlated with a Rayleigh number exponent of 0.25 for RaLz ≲ 1.2 × 108.

3D Computational Analysis of Thermal and Hydraulic Performance of Louvered Fin Heat Exchanger With Variable Louver Angle and Louver Pitch

2016 ◽  
Author(s):  
Abdulkerim Okbaz ◽  
Ali Pınarbaşı ◽  
Ali Bahadır Olcay
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Pressure Drop ◽  
Flow Characteristics ◽  
Hydraulic Performance ◽  
Double Row ◽  
Louvered Fin ◽  
Goodness Factor ◽  
Fluid Flow Characteristics ◽  
Louvered Fins

In the present study, 3-D numerical simulations on heat and fluid flow characteristics of double-row multi-louvered fins heat exchanger are carried out. The heat transfer improvement and the corresponding pressure drop amounts were investigated depending on louver angles in the range of 20° ≤θ≤ 30°, louver pitches of Lp = 2,7mm, 3,5mm and 3,8mm and frontal velocities of Uin between 1.22 m/s and 3 m/s. The results are reported in terms of Colburn j-factor, Fanning friction factor f and area goodness factor j/f based on louver angle, louver pitch and Reynolds number. To understand local behavior of flow around louvered fins and heat exchanger tubes, flow visualization results of velocity vectors and stream-lines with temperature counters are presented. It is investigated that increasing louver angle enhances convective heat transfer while hydraulic performance decreases due to increased pressure drop. The flow noticeably behaves louver directed for all louver angles The flow can easily travel between different fins. This case study has been done to design and manufacture an industrial louver fin heat exchanger.

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.

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