Optimization of Fin Performance in a Laminar Channel Flow Through Dimpled Surfaces

2008 ◽  
Vol 131 (2) ◽  
Author(s):  
Carlos Silva ◽  
Doseo Park ◽  
Egidio (Ed) Marotta ◽  
Leroy (Skip) Fletcher
Keyword(s):  
Heat Transfer ◽  
Fluid Dynamics ◽  
Experimental Investigation ◽  
Channel Flow ◽  
Heat Load ◽  
Pressure Losses ◽  
Thermal Improvement ◽  
Laminar Channel Flow ◽  
Flow Through ◽  
The Heat Transfer Coefficient

The effect of the dimple shape and orientation on the heat transfer coefficient of a vertical fin surface was determined both numerically and experimentally. The investigation focused on the laminar channel flow between fins, with a Re=500 and 1000. Numerical simulations were performed using a commercial computational fluid dynamics code to analyze optimum configurations, and then an experimental investigation was conducted on flat and dimpled surfaces for comparison purposes. Numerical results indicated that oval dimples with their “long” axis oriented perpendicular to the direction of the flow offered the best thermal improvement, hence the overall Nusselt number increased up to 10.6% for the dimpled surface. Experimental work confirmed these results with a wall-averaged temperature reduction of up to 3.7K, which depended on the heat load and the Reynolds number. Pressure losses due to the dimple patterning were also briefly explored numerically in this work.

Experimental Investigation of Enhanced Heat Transfer and Pressure Drop in a Solar Air Heater Duct With Discretized Broken V-Rib Roughness

2014 ◽  
Vol 137 (2) ◽  
Author(s):  
Anil Kumar Patil ◽  
J. S. Saini ◽  
Krishna Kumar
Keyword(s):  
Heat Transfer ◽  
Experimental Investigation ◽  
Geometrical Parameters ◽  
Solar Air Heater ◽  
Enhanced Heat Transfer ◽  
Transfer Rates ◽  
Air Heater ◽  
Effective Efficiency ◽  
Flow Through ◽  
Considerable Enhancement

The present study examines the augmentation in heat transfer and friction in a flow through solar air heater duct with discretized broken V-rib roughness. The experimental outcomes pertaining to Reynolds number from 3000 to 17,000, relative gap position (s′/s) from 0.2 to 0.8, relative staggered rib position (p′/p) from 0.2 to 0.8 have been presented and discussed. Discretized broken V-rib roughness brought out considerable enhancement in heat transfer rates over V-rib roughness and smooth duct. Effective efficiency of discretized broken V-rib roughened solar air heater is estimated and geometrical parameters of roughness are optimized with regard to temperature rise parameter and insolation.

Experimental Investigation on Onset of Nucleate Boiling in Tube-Bundle Channels

2009 ◽  
Author(s):  
Guangyao Lu ◽  
Junsheng Ren ◽  
Guisheng Zhao ◽  
Wenyuan Xiang ◽  
Huaning Ai
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Experimental Investigation ◽  
Heat Transfer Coefficient ◽  
Tube Bundle ◽  
Nucleate Boiling ◽  
Visualization Experiment ◽  
Inclined Tube ◽  
Good Accordance ◽  
The Heat Transfer Coefficient

Experiments are carried out to investigate the Onset of Nucleate Boiling (ONB) of refrigerant R-113 through vertical and inclined tube-bundle channels. Several methods are adopted to ascertain ONB in the experiments, and their differences are analyzed. The experiments show that the results of ONB estimation from the visualization experiment, ONB estimation from the wall temperature and that from the heat transfer coefficient are uniform. The influences of heat flux, mass flow rate, the geometric dimensions and inclination angle of the tube-bundle channels on the ONB height are explored in detail. On the foundation of the comparisons and analyses, an equation is put forward for calculating the ONB height in tube-bundle channels, which has a good accordance with the experimental results.

scholarly journals An Experimental Investigation on the Flow Characteristics Over Dimple Arrays Pertinent to Internal Cooling of Turbine Blades

2014 ◽  
Author(s):  
Wenwu Zhou ◽  
Hui Hu ◽  
Yu Rao
Keyword(s):  
Heat Transfer ◽  
Experimental Investigation ◽  
Heat Transfer Enhancement ◽  
Channel Flow ◽  
Flat Surface ◽  
Reynolds Shear Stress ◽  
Turbine Blades ◽  
Flow Characteristics ◽  
Internal Cooling ◽  
Transfer Enhancement

Due to the dimple’s unique characteristics of comparatively low pressure loss penalty and good heat transfer enhancement performance, dimple provides a very desirable alternative internal cooling technique for gas turbine blades. In the present study, an experimental investigation was conducted to quantify the flow characteristics over staggered dimple arrays and to examine the vortex structures inside the dimples. In addition to the surface pressure measurements, a high-resolution digital Particle Image Velocimetry (PIV) system was also utilized to achieve detailed flow field measurements to quantify the characteristics of the turbulent channel flow over the dimple arrays in terms of the ensemble-averaged velocity, Reynolds shear stress and turbulence kinetic energy (TKE) distributions. The experimental measurement results show that the friction factor of the dimpled surface is much higher than that of a flat surface. The measured pressure distribution within a dimple reveals clearly that flow separation and attachment would occur inside each dimple. In comparison with those of a conventional channel flow with flat surface, the channel flow over the dimpled arrays was found to have much stronger Reynolds stress and higher TKE level. Such unique flow characteristics are believed to be the reasons why a dimpled surface would have a better heat transfer enhancement performance for internal cooling of turbine blades as reported in those previous studies.

Heat and Mass Transfer Caused by a Laminar Channel Flow Equipped With a Synthetic Jet Array

2010 ◽  
Author(s):  
Zdeneˇk Tra´vni´cˇek ◽  
Petra Dancˇova´ ◽  
Jozef Kordik ◽  
Toma´sˇ Vit ◽  
Miroslav Pavelka
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Reynolds Number ◽  
Heat Transfer Enhancement ◽  
Channel Flow ◽  
Heat Mass Transfer ◽  
Low Reynolds Number ◽  
Transfer Enhancement ◽  
Laminar Channel Flow ◽  
Low Reynolds

Low-Reynolds-number laminar channel flow is used in various heat/mass transfer applications, such as cooling and mixing. A low Reynolds number implies a low intensity of heat/mass transfer processes, since they rely only on the gradient diffusion. To enhance these processes, an active flow control by means of synthetic (zero-net-mass-flux) jets is proposed. This arrangement can be promising foremost in microscale. The present study is experimental in which a Reynolds number range of 200–500 is investigated. Measurement was performed mainly in air as the working fluid by means of hot-wire anemometry and the naphthalene sublimation technique. PIV experiments in water are also discussed. The experiments were performed in macroscale at the channel cross-section (20×100)mm and (40×200)mm in air and water, respectively. The results show that the low Reynolds number channel flow can be actuated by an array of synthetic jets, operating near the resonance frequency. The control effect of actuation and the heat transfer enhancement was quantified. The stagnation Nusselt number was enhanced by 10–30 times in comparison with the non-actuated channel flow. The results indicate that the present arrangement can be a useful tool for heat transfer enhancement in various applications, e.g., cooling and mixing.

scholarly journals An Experimental Investigation of Heat Transfer Coefficients in a Spanwise Rotating Channel With Two Opposite Rib-Roughened Walls

1989 ◽  
Author(s):  
M. E. Taslim ◽  
A. Rahman ◽  
S. D. Spring
Keyword(s):  
Heat Transfer ◽  
Experimental Investigation ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Reynolds Numbers ◽  
Blockage Ratio ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
The Heat Transfer Coefficient ◽  
Rotating Channel

Liquid crystals are used in this experimental investigation to measure the heat transfer coefficient in a spanwise rotating channel with two opposite rib-roughened walls. The ribs (also called turbulence promoters or turbulators) are configured in a staggered arrangement with an angle of attack to the mainstream flow, α, of 90° for all cases. Results are presented for three values of turbulator blockage ratio, e/Dh (0.1333, 0.25, 0.333) and for a range of Reynolds numbers from 15,000 to 50,000 while the test section is rotated at different speeds to give Rotational Reynolds numbers between 450 and 1800. The Rossby number range is 10 to 100 (Rotation number of 0.1 to 0.01). The effect of turbulator blockage ratios on heat transfer enhancement is also investigated. Comparisons are made between the results of geometrically identical stationary and rotating passages of otherwise similar operating conditions. The results indicate that a significant enhancement in heat transfer is achieved in both the stationary and rotating cases, when the surfaces are roughened with turbulators. For the rotating case, a maximum increase over that of the stationary case of about 45% in the heat transfer coefficient is seen for a blockage ratio of 0.133 on the trailing surface in the direction of rotation and the minimum is a decrease of about 6% for a blockage ratio of 0.333 on the leading surface, for the range of rotation numbers tested. The technique of using liquid crystals to determine heat transfer coefficients in this investigation proved to be an effective and accurate method especially for nonstationary test sections.

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