Thermal Performance of Sierpinski Carpet Fractal Fins in a Forced Convection Environment

2016 ◽  
Author(s):  
David Calamas ◽  
Daniel Dannelley ◽  
Gyunay Keten
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Forced Convection ◽  
Thermal Performance ◽  
Reynolds Numbers ◽  
Unit Mass ◽  
Thermal Testing ◽  
Sierpinski Carpet ◽  
Fractal Pattern ◽  
Sierpiński Carpet

When certain fractal geometries are used in the design of fins or heat sinks the surface area available for heat transfer can be increased while system mass can be simultaneously decreased. The Sierpinski carpet fractal pattern, when utilized in the design of an extended surface, can provide more effective heat dissipation while simultaneously reducing mass. In order to assess the thermal performance of fractal fins for application in the thermal management of electronic devices an experimental investigation was performed. The first four fractal iterations of the Sierpinski carpet pattern, used in the design of extended surfaces, were examined in a forced convection environment. The thermal performance of the Sierpinski carpet fractal fins was quantified by the following performance metrics: efficiency, effectiveness, and effectiveness per unit mass. The fractal fins were experimentally examined in a thermal testing tunnel for a range of Reynolds numbers. As the Reynolds number increased, the fin efficiency, effectiveness and effectiveness per unit mass were found to decrease. However, as the Reynolds number increased the Nusselt number was found to similarly increase due to higher average heat transfer coefficients. The fourth iteration of the fractal pattern resulted in a 6.73% and 70.97% increase in fin effectiveness and fin effectiveness per unit mass when compared with the zeroth iteration for a Reynolds number of 6.5E3. However, the fourth iteration of the fractal pattern resulted in a 1.93% decrease in fin effectiveness and 57.09% increase in fin effectiveness per unit mass when compared with the zeroth iteration for a Reynolds number of 1.3E4. The contribution of thermal radiation to the rate of heat transfer was as high as 62.90% and 33.69% for Reynolds numbers of 6.5E3 and 1.3E4 respectively.

Thermal Performance of Sierpinski Carpet Fractal Fins in a Natural Convection Environment

2015 ◽  
Author(s):  
David Calamas ◽  
Daniel Dannelley ◽  
Gyunay Keten ◽  
Philip Hines
Keyword(s):  
Heat Transfer ◽  
Experimental Investigation ◽  
Thermal Radiation ◽  
Thermal Performance ◽  
Total Heat ◽  
Unit Mass ◽  
Sierpinski Carpet ◽  
Total Heat Transfer ◽  
Fractal Pattern ◽  
Sierpiński Carpet

When certain fractal geometries are used in the design of fins or heat sinks the surface area available for heat transfer can be increased while system mass can be simultaneously decreased. In order to assess the thermal performance of fractal fins for application in the thermal management of electronic devices an experimental investigation was performed. The experimental investigation assessed the efficiency, effectiveness, and effectiveness per unit mass of straight rectangular fins inspired by the first four iterations of the Sierpinski carpet fractal pattern. The thermal performance of the fractal fins was investigated in a natural convection environment. While fin efficiency was found to decrease with fractal iteration fin effectiveness per unit mass increased with fractal iteration. In addition, a fractal fin inspired by the fourth iteration of the Sierpinski carpet fractal pattern was found to be more effective than a traditional straight rectangular fin of equal width, height, and thickness. When compared to a traditional straight rectangular fin, or the zeroth fractal iteration, a fin inspired by the fourth fractal iteration of the Sierpinski carpet fractal pattern was found to be 4.87% more effective, 15.19% less efficient, and 67.98% more effective per unit mass. The amount of the total heat transfer attributed to thermal radiation was also dependent on fractal iteration. Thermal radiation accounted for 45.52% of the total heat transfer for the baseline case, or zeroth fractal iteration. Thermal radiation accounted for 51.94%, 50.17%, 52.77%, and 66.62% of the total heat transfer for the first, second, third, and fourth fractal iteration respectively.

Free Convection Heat Transfer From Sierpinski Carpet Fractal Fins of Varying Size

2017 ◽  
Author(s):  
David Calamas ◽  
Daniel Dannelley ◽  
Jennifer Shaffer ◽  
Valentin Soloiu
Keyword(s):  
Heat Transfer ◽  
Free Convection ◽  
Thermal Radiation ◽  
Thermal Performance ◽  
Unit Mass ◽  
Sierpinski Carpet ◽  
Fractal Pattern ◽  
Sierpiński Carpet ◽  
The Impact ◽  
Equal Height

This works experimentally investigates the thermal performance of extended surfaces inspired by the first four fractal iterations of the Sierpinski carpet fractal pattern in a free convection environment. Fractal fins inspired by the Sierpinski carpet fractal pattern can result in an increase in surface area for convective heat transfer coupled with a simultaneous decrease in mass and are thus desirable in aerospace applications. The thermal performance of the Sierpinski carpet fractal fins was quantified based on fin efficiency, fin effectiveness, and perforated fin effectiveness. When compared with a solid rectangular fin, without perforations, and of an equal base area and package volume a fin inspired by the fourth iteration of the Sierpinski carpet fractal pattern was found to be more effective at dissipating heat by convection. The impact of fin size on the thermal performance of the fractal fins was investigated for a range of power inputs applied at the base (2.5 W, 5 W, and 10 W). A 5.08 cm × 5.08 cm (2 in × 2 in × 1/16 in) fractal fin inspired by the fourth iteration of the Sierpinski carpet fractal was found to have a convective effectiveness, convective efficiency, and convective effectiveness per unit mass, 10.91% more, 10.31% less, and 77.65% more, than a traditional solid (non-perforated) rectangular fin of equal height, width, and thickness. Similarly, a 10.16 cm × 10.16 cm (4 in × 4 in × 1/8 in) fin inspired by the fourth fractal iteration was found to have a convective effectiveness, convective efficiency, and convective effectiveness per unit mass, 3.97% more, 15.91% less, and 66.54% more, than a traditional solid (non-perforated) rectangular fin of equal height, width, and thickness. Thus, the thermal performance of the fractal fins increased as the size of the fins decreased. Regardless of size, the contribution of thermal radiation was significant (often greater than 50%) and should not be neglected. In general, for a fin with a uniform cross-section, intersurface thermal radiation accounts for a significant percentage of thermal radiation heat transfer, particularly as the size of the perforations decreases.

Experimental Effectiveness of Sierpinski Carpet Fractal Fins in a Natural Convection Environment

2017 ◽  
Vol 139 (9) ◽  
Author(s):  
David M. Calamas ◽  
Daniel G. Dannelley ◽  
Gyunay H. Keten
Keyword(s):  
Heat Transfer ◽  
Experimental Investigation ◽  
Natural Convection ◽  
Thermal Radiation ◽  
Total Heat ◽  
Unit Mass ◽  
Sierpinski Carpet ◽  
Total Heat Transfer ◽  
Fractal Pattern ◽  
Sierpiński Carpet

When certain fractal geometries are used in the design of fins or heat sinks, the surface area available for heat transfer can be increased while system mass can be simultaneously decreased. In order to assess the thermal performance of fractal fins for application in the thermal management of electronic devices, an experimental investigation was performed. The experimental investigation assessed the efficiency, effectiveness, and effectiveness per unit mass of straight rectangular fins inspired by the first four iterations of the Sierpinski carpet fractal pattern. The thermal performance of the fractal fins was investigated in a natural convection environment with thermal radiation accounted for. Fin performance was analyzed under power inputs of 2.5, 5, 10, and 20 W. While fin efficiency was found to decrease with fractal iteration, fin effectiveness per unit mass increased with fractal iteration. In addition, a fractal fin inspired by the fourth iteration of the Sierpinski carpet fractal pattern was found to be more effective than a traditional straight rectangular fin of equal width, height, and thickness. When compared to a traditional straight rectangular fin, or the zeroth fractal iteration, a fin inspired by the fourth fractal iteration of the Sierpinski carpet fractal pattern was found to be on average 3.63% more effective, 16.19% less efficient, and 65.99% more effective per unit mass. The amount of the total heat transfer attributed to thermal radiation was also dependent on fractal iteration. Thermal radiation accounted for, on average, 57.00% of the total heat transfer for the baseline case, or zeroth fractal iteration. Thermal radiation accounted for 53.67%, 50.33%, 48.84%, and 45.84% of the total heat transfer for the first, second, third, and fourth fractal iterations, respectively.

Heat Transfer Coefficient Distribution of W and Broken W Turbulators At High Reynolds Numbers

2021 ◽  
pp. 1-29
Author(s):  
Sam Ghazi-Hesami ◽  
Dylan Wise ◽  
Keith Taylor ◽  
Étienne Robert ◽  
Peter Ireland
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Thermal Performance ◽  
Reynolds Numbers ◽  
High Reynolds Numbers ◽  
Smooth Channel ◽  
Wide Range ◽  
High Reynolds

Abstract An experimental and numerical study of the convective heat transfer enhancement provided by two rib families (W and Broken W) is presented, covering Reynolds numbers (Re) between 300,000 to 900,000 in a straight channel with a rectangular cross section (AR=1.29). These high Reynolds numbers were selected for the current study since most data in the available literature typically pertain to investigations at lower Reynolds numbers. The objective of this study is to assess the local heat transfer coefficient (HTC) enhancement (compared with a smooth channel) and the overall thermal performance, taking into account the effect of increased roughness on the friction factor, of a group of W shaped turbulators over a wide range of Reynolds numbers. Furthermore, the effects of increasing the rib spacing on the thermal performance of the Broken W configuration are presented and discussed. The numerical results are compared against heat transfer measurements obtained using the Transient Liquid Crystal (TLC) method. The research shows that for the Broken W turbulators, increasing the Reynolds number is associated with an overall decrease of the thermal performance while the thermal performance of the W configuration is relatively insensitive to Reynolds number. Nevertheless, the Broken W configuration delivers higher thermal performance and heat transfer compared with the W configuration for the range of Re investigated. The Broken W configuration with a pitch spacing of 10 times the rib height was shown to provide the optimal thermal performance in the configurations investigated here.

Experimental Study of Forced Convection From Isothermal Circular and Square Cylinders and Toroids

1997 ◽  
Vol 119 (1) ◽  
pp. 70-79 ◽  
Author(s):  
G. Refai Ahmed ◽  
M. M. Yovanovich
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Forced Convection ◽  
Convection Heat Transfer ◽  
Reynolds Numbers ◽  
Empirical Models ◽  
Experimental Program ◽  
Convection Heat ◽  
Forced Convection Heat Transfer ◽  
Wide Range

Experimental studies of forced convection heat transfer from different body shapes were conducted to determine the effects of Reynolds number and different characteristic body lengths on the area-averaged Nusselt number. Although the bodies differed significantly in their shapes, they had approximately the same total surface area, A = 11,304 mm2 ± 5%. This ensured that for a given free stream velocity and total heat transfer rate all bodies had similar trends for the relationship of Nusselt and Reynolds numbers. The experimental program range was conducted in the Reynolds number range 104≤ReA≤105 and Prandtl number 0.71. Finally, the empirical models for forced convection heat transfer were developed. These empirical models were valid for a wide range of Reynolds numbers 0≤ReA≤105. The present experimental correlations were compared with available correlation equations and experimental data. These comparisons show very good agreement.

scholarly journals CFD Analysis on the Air-Side Thermal-Hydraulic Performance of Multi-Louvered Fin Heat Exchangers at Low Reynolds Numbers

2017 ◽  
Author(s):  
Arslan Saleem ◽  
Man-Hoe Kim
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Coefficient ◽  
Heat Exchanger ◽  
Pressure Drop ◽  
Transfer Coefficient ◽  
Thermal Performance ◽  
Heat Exchangers ◽  
Reynolds Numbers ◽  
Hydraulic Performance

The air side thermal hydraulic performance of multi-louvered aluminium fin heat exchangers is investigated. A detailed study was performed to analyse the thermal performance of air over a wide range of Reynolds number i.e. from 30 to 250. Air-side heat transfer coefficient and air pressure drop were calculated and validated over the mentioned band of Reynolds numbers. Critical Reynolds number was determined numerically and the variation in flow physics along with the thermal and hydraulic performance of microchannel heat exchanger associated with R_cri has been reported. Moreover, a parametric study of the multi-louvered aluminium fin heat exchangers was also performed for 36 heat exchanger configurations with the louver angles (19-31°), fin pitches (1.0, 1.2, 1.4 mm) and flow depths (16, 20, 24 mm); and the geometric configuration exhibiting the highest thermal performance was reported. The air-side heat transfer coefficient and pressure drop results for different geometrical configurations were presented in terms of Colburn j factor and Fanning friction factor f, as a function of Reynolds number based on louver pitch.

scholarly journals EXPERIMENTAL STUDY OF HEAT TRANSFER OF A SINGLE-ROW BUNDLE OF FINNED TUBES IN MIXED CONVECTION OF AIR

2017 ◽  
Vol 60 (4) ◽  
pp. 352-366 ◽  
Author(s):  
A. B. Sukhotskii ◽  
G. S. Sidorik
Keyword(s):  
Heat Transfer ◽  
Experimental Study ◽  
Reynolds Number ◽  
Free Convection ◽  
Mixed Convection ◽  
Forced Convection ◽  
Reynolds Numbers ◽  
Convection Flow ◽  
Single Bundle ◽  
Single Row

The technique and results of experimental study of heat transfer of a single bundle consisting of bimetallic tubes with helically knurled edges, in natural and mixed convection of air are presented. Mixed convection, i.e. a heat transfer, when the contribution of free and forced convection is comparable, was created with the help of the exhaust shaft mounted above the heat exchanger bundle and forced air movement was created by the difference in density of the air in the shaft and the environment. The experimental dependence of the heat transfer of finned single row of bundles in the selected ranges of Grashof and Reynolds numbers has been determined. It is demonstrated that heat transfer in the mixed convection is 2.5−3 times higher than in free one and the growth rate of heat transfer with increasing Reynolds number is more than in the forced convection. Different forms of representation of results of experiments were analyzed and it was determined that the Nusselt number has a single power dependence on the Reynolds number at any height of the exhaust shafts. A linear dependence of the Reynolds number on the square root of the Grashof number was determined as well as the proportionality factors for different shaft heights. It is noted that the characteristics of the motion of air particles in the bundle in free convection is identical to the motion of particles in forced convection at small Reynolds numbers, i.e. a free convection flow smoothly flows into a forced convection one without the typical failures or surges if additional driving forces arise.

Comparison of Staggered and In-Line V-Shaped Dimple Arrays Using S-PIV

2015 ◽  
Author(s):  
Charles P. Brown ◽  
Lesley M. Wright ◽  
Stephen T. McClain
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Pressure Drop ◽  
Thermal Performance ◽  
Rectangular Channel ◽  
Reynolds Numbers ◽  
Secondary Flows ◽  
Spanwise Direction ◽  
Reduced Pressure ◽  
Line Array

As a result of the reduced pressure loss relative to ribs, recessed dimples have the potential to increase the thermal performance of internal cooling passages. In this experimental investigation, a Stereo-Particle Image Velocimetry (S-PIV) technique is used to characterize the three-dimensional, internal flow field over V-shaped dimple arrays. These flowfield measurements are combined with surface heat transfer measurements to fully characterize the performance of the proposed V-shaped dimples. This study compares the performance of two arrays. Both a staggered array and an in-line array of V-shaped dimples are considered. The layout of these V-shaped dimples is derived from a traditional, staggered hemispherical dimple array. The individual V-shaped dimples follow the same geometry, with depths of δ / D = 0.30. In the case of the in-line pattern, the spacing between the V-shaped dimples is 3.2D in both the streamwise and spanwise directions. For the staggered pattern, a spacing of 3.2D in the spanwise direction and 1.6D in the streamwise direction is examined. Each of these patterns was tested on one wide wall of a 3:1 rectangular channel. The Reynolds numbers examined range from 10000 to 37000. S-PIV results show that as the Reynolds numbers increase, the strength of the secondary flows induced by the in-line array increases, enhancing the heat transfer from the surface, without dramatically increasing the measured pressure drop. As a result of a minimal increase in pressure drop, the overall thermal performance of the channel increases as the Reynolds number increases (up to the maximum Reynolds number of 37000).

Heat Transfer and Pressure Drop Correlations for Square Channels With V-Shaped Ribs at High Reynolds Numbers

2011 ◽  
Vol 133 (11) ◽  
Author(s):  
Nawaf Y. Alkhamis ◽  
Akhilesh P. Rallabandi ◽  
Je-Chin Han
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Friction Factor ◽  
Thermal Performance ◽  
Reynolds Numbers ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
High Reynolds Numbers ◽  
High Reynolds ◽  
Rib Roughened

Heat transfer coefficients and friction factors are measured in a 45 deg V-shaped rib roughened square duct at high Reynolds numbers, pertaining to internal passages of land-based gas turbine engines. Reynolds numbers in this study range from 30,000 to 400,000, which is much higher than prior studies of V-shaped rib roughened channels. The dimensions of the channel are selected to ensure that the flow is in the incompressible regime. Blockage ratio e/D ranges from 0.1 to 0.18 and the spacing ratio P/e ranges from 5 to 10. Reported heat transfer coefficients are regionally averaged, measured by isothermal copper plates. Results show that the heat transfer enhancement decreases with increasing Reynolds number. The friction factor is found to be independent of the Reynolds number. The thermal performance decreases when the Reynolds number increases. 45 deg V-shaped ribs show a higher thermal performance than corresponding 45 deg angled ribs, consistent with the trend established in literature. Correlations for the Nusselt number and the friction factor as function of Re, e/D, and P/e are developed. Also developed are correlations for R and G (friction and heat transfer roughness functions, respectively) as a function of the roughness Reynolds number (e+).

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