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Augmentation of natural convection heat sink via using displacement design
(2020-06-01)
Abbas, Ali
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Wang, Chi-Chuan
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機械工程學系
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Department of Mechanical Engineering
Miniaturization of electronic devices demands an effective thermal management system for efficient cooling. Still, many electronic industries use natural convection cooling techniques like plate-fin heat sinks as far as no moving part (noise) and reliability is concerned. In this study, the widely-used plate fin heat sink is augmented by a novel fin displacement amid fin array. Yet the effect of fin displacement between alternate fins is experimentally and numerically investigated under natural convection condition. In the meantime, the effects of fin spacing, length, height, and heat flux on the heat sink performance subject to fin displacement is also studied. For the smaller fin pacing, introducing the fin displacement will delay the merging of boundary layers, and reduce the length of fully developed region accordingly. Smaller fin spacing can also entrain the outside air into the fin array at the upper portion of heat sink for offering additional enhancement. The fin displacement is especially effective for a smaller fin spacing. This is because fully developed flow prevails at a smaller fin spacing. On the other hand, the fin displacement may impair the performance when a very wide fin spacing is used. Similarly, the increase in the fin length also enhances the heat transfer performance under the fin displacement conditions. It is also found that the effect of fin height on the thermal performance is small and the effect of heat flux is negligible. The maximum reduction in the thermal resistance is 56% by adopting the displacement design. A drop in fin temperature at the upper portion with the displacement design may lead to a reduction in heat transfer coefficient. For the comparison containing the fixed volume, the heat sink with fin displacement offers a 30% heat transfer enhancement ratio, 28.7% reduction in total mass, and 27.4 % reduction in surface area when compared to the conventional heat sinks. (C) 2020 Elsevier Ltd. All rights reserved.
Experimental and numerical study on the performance of passive heat sink having alternating layout
(2019-06-01)
Chu, Wen-Xiao
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Lin, Yu-Chieh
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Chen, Ching-Yao
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Wang, Chi-Chuan
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機械工程學系
In this study, a novel passive heat sink with triangular fins having alternating layout to promote heat transfer performance of a passive heat sink is proposed and verified by experimental and numerical examinations. The heat sinks with rectangular fins (case A), triangular fins with right angle, 90 degrees (case B), triangular fins with right angle having alternating layout (case C), triangular fins with obtuse angle of 120 degrees (case D) and triangular fins with obtuse angle of 120 degrees having alternating layout (case E) are tested with vacuum pressure ranging from 400 Pa to atmosphere pressure. It is indicated that the triangular fin having alternating layout offer some benefits like entraining more airflow into the heat sink and a higher effective view factor, thereby showing an appreciable increase of effective heat transfer coefficient (HTC). Results obtained in low vacuum pressure show that the effective HTC of cases B, C, D and E can be improved by 1.5%, 5.5%, 3.0% and 12.1%, respectively as compared to the reference case A. Yet the effective HTC can be improved by 3.2%, 6.1%, 4.6% and 13.0%, respectively in atmosphere pressure. The numerical study is in line with the experimental results and the simulations suggest that the optimum angle of the proposed triangular fins having alternating layout can improve the effective HTC by up to 14.6% and 16.0% with obtuse angles of 150 degrees and 140 degrees when fin area is 2000 mm(2) and 3000 mm(2) , respectively. The benefits of triangular fins having alternating layout show even more superior performance when the heat sink is placed vertically and the effective heat transfer coefficient for triangular fins having alternating layout with 150 degrees is improved by up to 20.3%. (C) 2019 Elsevier Ltd. All rights reserved.
Analytical and Experimental Verification of Interleaved Trapezoidal Heat Sink
(2017-01-01)
Chen, Hong-Long
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Wang, Chi-Chuan
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機械工程學系
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Department of Mechanical Engineering
The objective of this paper is to explore the technique for lowering the contraction and hydraulic developing region pressure drop, in order to gain more airflow for electronic cooling heat sink for the same footprint and fin number. By combining two different geometrical perimeter shapes of fins, odd number is rectangular shape, and even number is trapezoidal shape, this new fin module design gains extra 10% airflow with little loss or equivalent thermal performance. Current data center server is suffering from too little airflow to cool essential chips due to enormous flow impedance for packing too many components inside. This technology is the solution to resolve this bottleneck. The precious extra 10% more airflow not only cools CPU chip itself; but also quite beneficial to cool other heating components inside servers. Also, this new design excels in low velocity of 2 m/s for thermal performance compared to original design. Lower velocity is equal to lower RPM of fan that leads to the advantage of energy saving.
Analysis and experimental verification of weight saving with trapezoidal base heat sink
(2018-03-05)
Chen, Hong-Long
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Wang, Chi-Chuan
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機械工程學系
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Department of Mechanical Engineering
A quick weight saving methodology with trapezoidal base heat sink applicable for electronic cooling application is studied analytically, numerically, and experimentally. The conventional heat sink with rectangular base can be modified into trapezoidal base for material saving. A differential equation capable of describing the temperature distribution of the trapezoidal base is derived and its closed-form analytic expression is derived. It is found that three parameters r(A) (ratio of effective surface area to the base area), r(d) (ratio of chip lateral length to the base length) and h(+) (modified convection heat transfer coefficient) play pivotal roles in balancing the material saving and the performance loss. When r(d) = 0.1, the material saving for r(t) = 0.6 is about 18%; while the corresponding performance loss is 2.93%. When r(d) = 0.2, the material saving for r(t) = 0.6 is about 16%; while the corresponding performance loss is 2.47%. The analytical results are verified with experiments with good agreement. (C) 2017 Elsevier Ltd. All rights reserved.
Analytical analysis and experimental verification of interleaved parallelogram heat sink
(2017-02-05)
Chen, Hong-Long
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Wang, Chi-Chuan
;
機械工程學系
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Department of Mechanical Engineering
In this study, a novel air-cooled heat sink profile is proposed to compete with the conventional design. The new design is termed as IPFM (Interleaved Parallelogram Fin Module) which features two different geometrical perimeter shapes of fins. This new design not only gains the advantage of lower pressure drop for power saving; but also gains a material saving for less fin surface area. An assessment of flow impedance and performance between the conventional and IPFM heat sink is analytically investigated and experimentally verified. A new modified dimensionless friction factor for triangular region is proposed. The analytical predictions agree with experimental measurements for both conventional and IPFM design. In electronic cooling design, especially for cloud server air-cooled heat sink design, the flow pattern is usually laminar with Reynolds number being operated less than 2000. In this regime, the IPFM design shows 8-12% less of surface than conventional design when the flow rate is less than 10 CFM; yet the thermal performance is slightly inferior to the conventional design when the flowrate is raised towards 25 CFM. Yet in the test range of 5-25 CFM, a 10-15% lower flow impedance is observed. The smaller fin spacing, the more conspicuous reduction of flow impedance is observed. The optimization of cutting angle is around 35 degrees for 10 CFM, and it is reduced to 15 degrees at a larger flowrate of 20 CFM. (C) 2016 Elsevier Ltd. All rights reserved.
Performance improvement of high power liquid-cooled heat sink via non-uniform metal foam arrangement
(2015-08-05)
Chen, Kuan-Cheng
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Wang, Chi-Chuan
;
機械工程學系
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Department of Mechanical Engineering
The present study proposes a novel concept by employing non-uniform arrangements of metal foams alongside the heat sink applicable for liquid cooling. A total of 7 arrangements by varying PPI (pores per inch) of metal foam are made and additional 4 multiple channel designs are fabricated for comparison. Test results indicate that non-linearity term in Forchheimer equation rises significantly with increase of PPI (or with the decrease of permeability). The results suggest that the transition from the linear Darcy regime to the quadratic Forchheimer regime depends on the metal foam structure. It is also found that metal foam appreciably outperforms conventional multiple channel heat sink. The thermal resistance can be reduced by more than 62% as compared to that of empty plate design. For a given pumping power, the non-uniform arrangement of metal foam shows the best performance by employing a larger PPI metal foam at the inlet, followed by a smaller PPI metal foam, and the least PPI metal foam should be placed at the rear part of the heat sink. (C) 2015 Elsevier Ltd. All rights reserved.
A novel heat dissipation fin design applicable for natural convection augmentation
(2014-12-01)
Charles, Roody
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Wang, Chi-Chuan
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機械工程學系
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Department of Mechanical Engineering
In this study, a comparative study of heat sink having various fin assembly under natural convection is investigated. The fin pattern includes a rectangular, a trapezoidal and an inverted trapezoidal configuration. Tests were performed in a well controlled environmental chamber having a heat load ranging from 3 to 20 W. From the test results, the heat transfer coefficient of the conventional rectangular fins is higher than that of the trapezoidal fins while the heat transfer coefficient of the inverted trapezoidal fins is higher than the trapezoidal one by approximately 25%, and it exceeds that of convectional rectangular fin by about 10%. The heat transfer improvements of the inverted trapezoidal fin are mainly associated with a larger temperature difference and inducing more air flow into the heat sink. (C) 2014 Elsevier Ltd. All rights reserved.
An experimental investigation of air cooling thermal module using various enhancements at low Reynolds number region
(2010-12-01)
Yang, Kai-Shing
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Li, Shu-Lin
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Chen, Ing Youn
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Chien, Kuo-Hsiang
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Hu, Robert
This study examines the airside performance of heat sinks having fin patterns of plate fin (Type I), interrupted fill geometry (Type II), dense vortex generator (Type III), and loose vortex generator (Type IV). Test results indicate that the heat transfer performance is strongly related to the arrangement of enhancements. The interrupted and dense vortex generator configurations normally contribute more pressure drop penalty than improvements of heat transfer. This is especially pronounced when operated at a lower frontal velocity. Actually the plain fin geometry outperforms most of the enhanced fin patterns such as of Type II and Type Ill at the fully developed region. This is because a close spacing prevents the formation of vortex, and the presence of interrupted surface may also suffer from the degradation by constriction of conduction path. The results suggest that the vortex generators operated at a higher frontal velocity is more beneficial than that of plain fin geometry. In association with the VG-1 criteria (same pumping power and same heat transfer capacity), the results show that effective reduction of surface area can be achieved when the frontal velocities are at 3-5 m s(-1) and the fin patterns are triangular, triangular attack, or two-groups dimple. The result from the present experiment suggests that the asymmetric combination such as using loose vortex generator (Type IV) can be quite effective. The triangular attack vortex generator is regarded as the optimum enhancement design for it could reduce 12-15% surface area at a frontal velocity around 3-5 m s(-1). The asymmetric design is still applicable even when the fin pitch is reduced to 1 mm. (C) 2010 Elsevier Ltd. All rights reserved.
Effect of cannelure fin configuration on compact aircooling heat sink
(2011-07-01)
Wang, Chi-Chuan
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Yang, Kai-Shing
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Liu, Yang-Ping
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Chen, Ing Youn
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機械工程學系
The present study proposed a novel cannelure fin structure applicable to compact air-cooled heat sink under cross flow condition. A total of eight heat sinks were made and tested, including plain fin, oblique dimple type (I), oblique dimple type (II), straight cannelure, full oblique cannelure, half oblique cannelure with dimple/cavity type, half oblique cannelure with dimple/cavity type (II), and full oblique cannelure with dimple/cavity. Test results indicate that the proposed full cannelure fin along with the dimple/cavity structure can attain approximately 25% increase of heat transfer performance, and accompanies a friction reduction of about 20%. Moreover, converse to those interrupted fin or triangular vortex generator, it is found that the proposed fin structure still offers significant augmentation in fully developed region. The observed IR image of the temperature measurement of the test fin configurations also confirms the measurements. (C) 2011 Elsevier Ltd. All rights reserved.
Effect of non-uniform heating on the performance of the microchannel heat sinks
(2013-04-01)
Liu, Chun-Kai
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Yang, Shu-Jung
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Chao, Yu-Lin
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Liou, Kun Ying
;
Wang, Chi-Chuan
The present study experimentally investigates the performance of a 2-pass microchannel heat sink subject to non-uniform heating. The size of the microchannel heat sink is 132 mmx82 mmx6 mm with a rectangular channel of 1 mmx1 mm. Three independent heaters having identical size (96 mmx38.5 mm x 1 mm) is placed consecutively below the microchannel heat sink. Two kinds of manifolds are used for testing of the microchannel, one with a side entrance (type A) and the other with a front entrance (type B). Test results show that both maximum temperature and average temperature rise with the total input power, and this is applicable for both manifolds. For uniform heating condition, the maximum temperature for type B manifold is much lower than that for type A manifold due to a better flow distribution and heat transfer performance. The pressure drop is slightly reduced with the rise of supplied power. For non-uniform heating, the maximum temperature and the average temperature depend on the location of heaters. For the same supplied power with non-uniform heating, it is found that heater being placed at the inlet of the microchannel will give rise to a higher maximum temperature than that being placed at the rear of the heat sink. This phenomenon is especially pronounced when the inlet flowrate is comparatively small and becomes less noted as the inlet flowrate is increased to 0.7 L/min. (C) 2013 Elsevier Ltd. All rights reserved.

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