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Now showing 1 - 9 of 9

CFD analysis and experimental verification on a new type of air-cooled heat sink for reducing maximum junction temperature
(2020-02-01)
Chu, Wen-Xiao
;
Tsai, Ming-Kun
;
Jan, Shun-Yuan
;
Huang, Hsiang-Ho
;
Wang, Chi-Chuan
This paper investigates a new type of plate-fin heat sink having a rectangular fin-cut at the entrance while containing a fin-protrusion part at the rear of the heat sink. The design not only offers appreciable heat transfer enhancement without pressure drop penalty, but also pronouncedly reduces the maximum junction temperature (T-max). It is experimentally validated that the effective thermal resistance can be reduced by 5.5-7.2% under the heating load of 250 W, and the temperature at the rear heat source can be reduced by about 2.5 K under same pumping power compared to the original plate-fin heat sink. Triangular fin-protrusion applying at the rear part shows more pronounced improvement on thermal performance compared to a rectangular one because of better heat spreading. Meanwhile, by placing a partition baffle below the rectangular fin-cut can further reduce the T-max to reach as low as 354.5 K under the pumping power of 0.3 W. The effect of partition baffle and fin angle (theta) is quantitatively studied in more details. When theta is increased over 45 degrees, the partition baffle shows further improvement on T-max at fixed pumping power. The lowest T-max is obtained when the fin angle (theta) of the fin-protrusion area reaches 65 degrees It is also observed that the rectangular fin-cut is superior to a triangular one, suggesting a "Coanda-like" effect. In addition, a correlation is developed to predict the T-max of the new air-cooled heat sink. The predictive deviations of the correlation against numerical results are within +/- 12.0 K, showing a reasonably predictive ability. (C) 2019 Elsevier Ltd. All rights reserved.
The numerical simulation with staggered alternation locations and multi-flow directions on the thermal performance of double-layer microchannel heat sinks
(2019-12-25)
Shen, Han
;
Xie, Gongnan
;
Wang, Chi-Chuan
;
機械工程學系
;
Department of Mechanical Engineering
The novel staggered flow alternation structure (SFAS) proposed in prior study has proved to be an efficient way in improving the overall thermal performance with acceptable pressure drop penalty in Double-layer Microchannel Heat Sinks (DMHSs). Based on the prior design, a further numerical investigation concerning the optimum location of SFAS in DMHSs is presented. The corresponding temperature fields, Nusselt number, flow fields, pressure drop and thermal characteristics are presented through verified computational mode. In addition, the effect of flow arrangements such as concurrent, upper-inlet/lower-inlet countercurrent arrangement on the thermal performance are studied in more details. The best thermal location of SFAS in the DMHSs is found to be based on the alterable locations and multi-flow directions. Yet, changing the location of staggered alternation structure does not lead to an appreciable rise of pressure drop penalty in DMHSs. However, the improvement in thermal performance for upper-inlet countercurrent arrangement is significant. Placing the SFAS in the middle of the DMHSs ensures the best overall thermal performance.
Heat transfer and thermodynamic analysis by introducing multiple alternation structures into double-layer microchannel heat sinks
(2019-11-01)
Shen, Han
;
Xie, Gongnan
;
Wang, Chi-Chuan
;
機械工程學系
;
Department of Mechanical Engineering
The study examined the performance of a novel staggered flow alternation structure in the Double-layer Microchannel Heat Sink (DMHS) based on authors' prior work and further detailed and quantitatively influences regarding the effects of the numbers of multiple staggered flow alternation structures are thoroughly investigated. Yet the analysis also contains more in-depth description about the entropy generation caused by heat transfer and liquid flow based on the second-law perspective. The major influential factors combining thermal performance and pressure drop penalty such as Nusselt number, Reynolds number, pumping power and thermal performance factor have been numerically studied. Moreover, the flow directions with parallel/counter stream were also compared in the present work. Through these detailed analysis, the propose multiple novel design offers much superior performance with better thermal uniformity and augment entropy generation number. The results show that the temperature difference of the substrate can be made quite uniformly by adding the number of multiple staggered flow alternation structure, and superior performance of the proposed DMHS can be achieved with affordable pressure drop penalty, while the DMHS with single alternation structure shows higher thermal performance.
Investigation of the evacuation pressure on the performance of pulsating heat pipe
(2017-07-01)
Sun, Chien-Hung
;
Tseng, Chih-Yung
;
Yang, Kai-Shing
;
Wu, Shih-Kuo
;
Wang, Chi-Chuan
This study examines the influence of evacuation pressure on the startup and overall performance of pulsating heat pipes (PHP). The outer diameter of the copper tube is 3 mm and 2 mm (double tube design) having a wall thickness of 0.3 mm and 0.2 mm, respectively. The working fluids in this study include water and HFE-7000 with filling ratios around 50%, and the evacuation pressure ranging from 0.01 Torr to atmosphere pressure. For an evacuation pressure of 0.01 Torr at a supplied power of 80 W, the thermal resistance of the PHP filling with water is 0.928 K/W while it is 1.161 K/W for HFE-7000. However, the trend is reversed and the thermal resistance for HFE-7000 is lower than water when the evacuation pressure is increased over 100 Torr. The corresponding effective thermal conductivity of waterfilling PHP reaches 51,448 W/m K in comparison with 12,692 W/m K for HFE-7000. However, the effective thermal conductivity for waterfilling PHP drops appreciably with rising evacuation pressure, and the PHP is not functional at the atmosphere pressure. Conversely, although the effective thermal conductivity for HFE-7000 PHP still drops with the rise of evacuation pressure, the HFE-7000 PHP is still in operation even without any evacuation. The gigantic difference in the startup and performance of PHP is related to the solubility of noncondensable gas amid water and HFE-7000.
A parametric study on thermal performance of microchannel heat sinks with internally vertical bifurcations in laminar liquid flow
(2018-02-01)
Shen, Han
;
Wang, Chi-Chuan
;
Xie, Gongnan
;
機械工程學系
;
Department of Mechanical Engineering
The optimal position of internal vertical bifurcation integrated with a microchannel heat sink (MHS) is investigated numerically in the present research. The corresponding rectangular smooth microchannel is compared with those with internal vertical bifurcation. The optimal position along the streamwise direction for interval distances is studied in detail. The corresponding temperature fields, flow fields, pressure drop and thermal characteristics are presented through verified computational model. The numerical simulation indicates that a clear inflection point of pressure gradient may prevail with the presence of internal vertical bifurcation. It is also found that the microchannel heat sink with a small distance between the tail end of internal vertical bifurcation and the outlet of microchannel shows the best thermal performance instead of those with setting the tail end of internal bifurcation at the outlet of microchannel. The proposed optimal design of internal vertical bifurcation shows improved thermal performance without any pressure drop penalty. (C) 2017 Elsevier Ltd. All rights reserved.
Analytical analysis and experimental verification of interleaved parallelogram heat sink
(2017-02-05)
Chen, Hong-Long
;
Wang, Chi-Chuan
;
機械工程學系
;
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.
Evaluation of thermal performance of packaged GaN HEMT cascode power switch by transient thermal testing
(2016-04-05)
Chen, Szu-Hao
;
Chou, Po-Chien
;
Cheng, Stone
;
機械工程學系
;
Department of Mechanical Engineering
In this investigation, thermal transient measurements and analyses are used to study the thermal performance of a cascoded GaN power device. The method is based on the thermal characterization of the on-resistance (R-on) of the device and the synchronized current-voltage characteristics under continuous operation. The changes in R-on with temperature (25 degrees C-180 degrees C) are measured, statistically studied, and correlations investigated. The proposed method for estimating transient thermal impedance has the following characteristics: (1) it is robust and reproducible; (2) it yields a heating curve to prevent overheating for the device under test (DUT); (3) it provides in-situ current-voltage characterization; (4) it includes a transient offset correction for initial transient electrical disturbances (such as current collapse); (5) it optimizes a compact thermal model; (6) it is sensitive to package structure and design variables. This monitoring of thermal impedance variation provides a simple and fast non-destructive method for analyzing power switching devices during thermal testing. Satisfactory experimental results confirm the feasibility of in-situ current-voltage characterization and the real power varies with the thermal impedance. (C) 2015 Elsevier Ltd. All rights reserved.
A novel double pipe pulsating heat pipe design to tackle inverted heat source arrangement
(2016-08-05)
Tseng, Chih-Yung
;
Yang, Kai-Shing
;
Chien, Kuo-Hsiang
;
Wu, Shih-Kuo
;
Wang, Chi-Chuan
Traditional pulsating heat pipe with fewer turns is functional only when the heat source is placed at the bottom while the heat sink is on top. This study proposes a novel design having alternative double-pipe tube diameter with some extra open connections of these double-pipes. By introducing extra un-balanced pressure force, capillary force and gravity force, the PHP can be easily starting up even for an opposite heat source/sink arrangement while the conventional single tube design fails to start up with this opposite arrangement. The thermal resistance of double pipe PHP can be lowered to 0.0729 W/K with an effective thermal conductivity of 12,603 W/m.K when the heat source is placed on top. Yet the thermal resistance for the proposed double pipe design is only half of the single tube design. (C) 2016 Elsevier Ltd. All rights reserved.
Parametric study on thermal performance of microchannel heat sinks with internal vertical Y-shaped bifurcations
(2015-11-01)
Xie, Gongnan
;
Shen, Han
;
Wang, Chi-Chuan
;
機械工程學系
;
Department of Mechanical Engineering
In this paper, internal vertical Y-shaped bifurcation plates are integrated with the microchannel heat sink (MHS), and its corresponding thermal and fluid flow characteristics are investigated numerically. The effect of the length of Y-shaped bifurcation and the angles of the arms on the overall performance are examined. A best Y-shaped plate length are firstly screened out from three designs and are compared with the corresponding rectangular smooth microchannel. Based on the best thermal performance with a specific length, the effect of arm angles in terms of five different configurations of Y-shaped plates are further investigated. Through the calculations, the corresponding flow field, temperature field and pressure drop characteristics are reported. It is found that the thermal performance of MHSs with internal Y-shaped bifurcations is much better than that of the traditional rectangular microchannel. The longest internal Y-shaped bifurcation microchannel results in best thermal performance. On the other hand, a larger arm angle leads to a better thermal performance of the internal Y-shaped bifurcation microchannel. (C) 2015 Elsevier Ltd. All rights reserved.

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