Local Heat Transfer Distribution in a Rotating Serpentine Rib-Roughened Flow Passage

1993 ◽  
Vol 115 (3) ◽  
pp. 560-567 ◽  
Author(s):  
N. Zhang ◽  
J. Chiou ◽  
S. Fann ◽  
W.-J. Yang
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Performance ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Transfer Performance ◽  
Height Ratio ◽  
Nusselt Numbers ◽  
Rayleigh Numbers ◽  
Rib Roughened

Experiments are performed to determine the local heat transfer performance in a rotating serpentine passage with rib-roughened surfaces. The ribs are placed on the trailing and leading walls in a corresponding posited arrangement with an angle of attack of 90 deg. The rib height-to-hydraulic diameter ratio, e/Dh, is 0.0787 and the rib pitch-to-height ratio, s/e, is 11. The throughflow Reynolds number is varied, typically at 23,000, 47,000, and 70,000 in the passage both at rest and in rotation. In the rotation cases, the rotation number is varied from 0.023 to 0.0594. Results for the rib-roughened serpentine passages are compared with those of smooth ones in the literature. Comparison is also made on results for the rib-roughened passages between the stationary and rotating cases. It is disclosed that a significant enhancement is achieved in the heat transfer in both the stationary and rotating cases resulting from an installation of the ribs. Both the rotation and Rayleigh numbers play important roles in the heat transfer performance on both the trailing and leading walls. Although the Reynolds number strongly influences the Nusselt numbers in the rib-roughened passage of both the stationary and rotating cases, Nuo and Nu, respectively, it has little effect on their ratio Nu/Nuo.

scholarly journals Numerical investigation of molten salt-based nanofluid laminar heat transfer in a circular tube using Eulerian-Lagrangian method

2020 ◽  
pp. 199-199
Author(s):  
Boshu He ◽  
Zhaoping Ying
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Molten Salt ◽  
Heat Transfer Performance ◽  
Circular Tube ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Lagrangian Method ◽  
Transfer Performance ◽  
Discrete Phase Model

Molten salt-based nanofluid in a laminar region of a circular tube with constant wall heat flux was numerically investigated. An Eulerian- Lagrangian method, discrete phase model, was used to predict the heat transfer performance of nanofluid, considering the factors of inlet Reynolds number, the mass concentration of the nanoparticles and nanoparticle diameter. Validation results were found in a good match with experimental results obtained from the literature. Numerical results showed that the heat transfer performance of nanofluid was considerably better than that of pure molten salt. The local heat transfer coefficient and Nusselt number of nanofluid are about 30% higher than these of pure molten salt and increase with an increase of Reynolds number and nanoparticle concentration. Moreover, the heat transfer performance of nanofluid with the small size of the nanoparticles (10~100 nm) is improved significantly.

Heat Transfer in Serpentine Flow Passages With Rotation

1994 ◽  
Vol 116 (1) ◽  
pp. 133-140 ◽  
Author(s):  
S. Mochizuki ◽  
J. Takamura ◽  
S. Yamawaki ◽  
Wen-Jei Yang
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Heat Transfer Performance ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Transfer Performance ◽  
Flow Passage ◽  
Rotation Numbers ◽  
Straight Flow

Heat transfer characteristics of a three-pass serpentine flow passage with rotation are experimentally studied. The walls of the square flow passage are plated with thin stainless-steel foils through which electrical current is applied to generate heat. The local heat transfer performance on the four side walls of the three straight flow passages and two turning elbows are determined for both stationary and rotating cases. The throughflow Reynolds, Rayleigh (centrifugal type), and rotation numbers are varied. It is revealed that three-dimensional flow structures cause the heat transfer rate at the bends to be substantially higher than at the straight flow passages. This mechanism is revealed by means of a flow visualization experiment for a nonrotating case. Along the first straight flow passage, the heat transfer rate is increased on the trailing surface but is reduced on the leading surface, due to the action of secondary streams induced by the Coriolis force. At low Reynolds numbers, the local heat transfer performance is primarily a function of buoyancy force. In the higher Reynolds number range, however, the circumferentially averaged Nusselt number is only a weak function of the Rayleigh and rotation numbers.

scholarly journals The Effect of Periodic Ribs on the Local Aerodynamic and Heat Transfer Performance of a Straight Cooling Channel

1996 ◽  
Author(s):  
G. Rau ◽  
M. Çakan ◽  
D. Moeller ◽  
T. Arts
Keyword(s):  
Heat Transfer ◽  
Flow Field ◽  
Heat Transfer Performance ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Hydraulic Diameter ◽  
Transfer Performance ◽  
Local Pressure ◽  
Reynolds Analogy ◽  
Law Of The Wall

The local aerodynamic and heat transfer performance were measured in a rib-roughened square duct as a function of the rib pitch to beight ratio. The blockage ratio of these square obstacles was 10% or 20% depending on whether they were placed on one single (1s) or on two opposite walls (2s). The Reynolds number, based on the channel mean velocity and hydraulic diameter, was fixed at 30000. The aerodynamic description of the flow field was based on local pressure distributions along the ribbed and adjacent smooth walls as well as on 2D LDV explorations in the channel symmetry plane and in two planes parallel to the ribbed wall(s). Local heat transfer distributions were obtained on the floor, between the ribs, and on the adjacent smooth side wall. Averaged parameters, such as friction factor and averaged heat transfer enhancement factor, were calculated from the local results and compared to correlations given in literature. This contribution showed that simple correlations derived from the law of the wall similarity and from the Reynolds analogy could not be applied for the present rib height-to-channel hydraulic diameter ratio (e/Dh=0.1). The strong secondary flows resulted in a three-dimensional flow field with high gradients in the local heat transfer distributions on the smooth side walls.

scholarly journals The Effect of Periodic Ribs on the Local Aerodynamic and Heat Transfer Performance of a Straight Cooling Channel

1998 ◽  
Vol 120 (2) ◽  
pp. 368-375 ◽  
Author(s):  
G. Rau ◽  
M. C¸akan ◽  
D. Moeller ◽  
T. Arts
Keyword(s):  
Heat Transfer ◽  
Flow Field ◽  
Heat Transfer Performance ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Hydraulic Diameter ◽  
Transfer Performance ◽  
Local Pressure ◽  
Reynolds Analogy ◽  
Law Of The Wall

The local aerodynamic and heat transfer performance were measured in a rib-roughened square duct as a function of the rib pitch to height ratio. The blockage ratio of these square obstacles was 10 or 20 percent depending on whether they were placed on one single (1s) or on two opposite walls (2s). The Reynolds number, based on the channel mean velocity and hydraulic diameter, was fixed at 30,000. The aerodynamic description of the flow field was based on local pressure distributions along the ribbed and adjacent smooth walls as well as on two-dimensional LDV explorations in the channel symmetry plane and in two planes parallel to the ribbed wall(s). Local heat transfer distributions were obtained on the floor, between the ribs, and on the adjacent smooth side wall. Averaged parameters, such as friction factor and averaged heat transfer enhancement factor, were calculated from the local results and compared to correlations given in literature. This contribution showed that simple correlations derived from the law of the wall similarity and from the Reynolds analogy could not be applied for the present rib height-to-channel hydraulic diameter ratio (e/Dh = 0.1). The strong secondary flows resulted in a three-dimensional flow field with high gradients in the local heat transfer distributions on the smooth side walls.

Heat Transfer Analysis in Mixed Convection

2010 ◽  
Author(s):  
Shan-Fang Huang ◽  
Tai-Yi Ma ◽  
Han-Yang Gu ◽  
Yan-Hua Yang ◽  
Xiao Yan
Keyword(s):  
Heat Transfer ◽  
Mixed Convection ◽  
Heat Resistance ◽  
Heat Transfer Performance ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Resistance Coefficient ◽  
Heat Transfer Analysis ◽  
Transfer Performance ◽  
Transfer Resistance

Heat transfer is analyzed from a different view in mixed convection in this paper. A concept, namely averaged heat transfer resistance coefficient, is used to describe heat transfer performance. For local position, heat transfer defined by generalized Fourier law is determined by fluid conductance and turbulence heat transfer. On the other hand, heat resistance over the cross section is the integer of the local resistance, where the weight, a function of spatial position, can be expressed by product of local heat transfer and temperature. To enhance heat transfer, it is crucial to reduce the heat resistance where the weight is big, namely near the wall. Heat transfer performance under different buoyancy effect is analyzed by the new. The results show that flow structure and heat transfer are closely connected by a straightforward expression. Heat transfer mechanism of enhancement and deterioration under different stages can be perfectly explained, which can predict heat transfer qualitatively.

Average Nusselt Number for Pressure and Suction Sides of Squealer Turbine Blade Tip

2011 ◽  
Author(s):  
Chaouki Ghenai
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Turbine Blade ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Transfer Coefficients ◽  
Cavity Depth ◽  
Heat Transfer Coefficients ◽  
Nusselt Numbers ◽  
Blade Tip

Numerical simulations of the flow field and heat transfer of squealer blade tip are performed in this study. The effect of Reynolds number (Re = 10000–40000), the clearance gap to width ratios (C/W = 5%–15%) and the cavity depth to width ratios (D/W = 10%, 20% and 50%) on fluid flow and heat transfer characteristics are obtained. The temperature and velocity distributions inside the cavity, the local heat transfer coefficients, and the average Nusselt numbers for the pressure and suction sides of the turbine blade tip are determined. This paper presents the results of the effects of Reynolds number, clearance gap and width ratios on the Nusslet number for the pressure and suction sides of squealer turbine blade tip. The results show a good agreement with the experimental data obtained by Metzger and Bunker. New correlations for the average Nusselt numbers for turbine blade tip pressure and suction sides are presented.

The Optimum Height of Winglet Vortex Generators Mounted on Three-Row Flat Tube Bank Fin

2003 ◽  
Vol 125 (6) ◽  
pp. 1007-1016 ◽  
Author(s):  
S. D. Gao ◽  
L. B. Wang ◽  
Y. H. Zhang ◽  
F. Ke
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Performance ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Vortex Generators ◽  
Local Characteristic ◽  
Transfer Performance ◽  
Tube Bank ◽  
Flat Tube ◽  
Optimum Height

Winglet vortex generators can be used to enhance the heat transfer performance of finned flat tube bank fin. The effects of the height of vortex generators (VG) on local heat transfer were studied using the naphthalene sublimation method and the optimum height of winglet VG are screened by using JF, a dimensionless factor of the larger the better characteristics. In order to get JF, the local heat transfer coefficient obtained in experiments and a numerical method were used to get the heat transferred from the fin. For the configurations studied in this paper: for local characteristic, as increasing height of VG, heat transfer is enhanced, but the mostly enhanced region moves away from the tube wall; with increasing height of VG to certain degree, the width of enhanced region does not increase significantly; the effects of VG’s height on span-average Nusselt number (Nu) are more mixed on fin surface mounted with VGs and its back surface, with increasing height of VG, in some region heat transfer is worsened, and in other region heat transfer is enhanced; in real working condition, the heat transferred from fin surface mounted with VGs is larger than the heat transferred from the other surface of the fin; increasing the height of VG (H) increases average Nu and friction factor (f ), but with considering the fin efficiency, there is an optimum H to get best heat transfer performance; the optimum height of VG is dependent on the thickness of fin and its heat conductivity, for mostly used fin thickness and material, the optimum height of VG is 0.8 times of net fin spacing.

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