Pool Boiling Heat Transfer Enhancement with Porous Pin Fin Arrays

• Main Authors: Yu-Lun Shih, 施毓倫
• Other Authors: 陳瑤明
• Format: Others
• Language: zh-TW
• Published: 2009
• Online Access: http://ndltd.ncl.edu.tw/handle/00004475149515578552

碩士 === 國立臺灣大學 === 機械工程學研究所 === 97 === With the increasing usage of high-power components, the demand of heat dissipation keeps raising, thermal management of products become more important for the operation temperature limits of those components inside. The excellent performance of the enhanced boiling heat transfer technology by porous structure surface in the industrial community has been sure. How to further improve the performance limitations caused by the vapor-liquid flow resistance in the high-wattage, for the creation of the boiling surface which under low superheat has a wider operating range will be an important topic. The purpose of this research was to modulate the porous pin-fin arrays on the porous surface sintered with copper dendritic powder in a fixed process of sintering, and the heat transfer performance for pool boiling of saturated R-134a on horizontal finned surface was discussed. The study was conducted following a statistical method with a two-level factorial plan involving four variables: the particle diameter (d=32~63μm), the bottom thickness (t=200~350μm), the fin length (L=400~600μm), the spacing (S=350~500μm). Finally, the performance of the porous surface which with and without porous pin-fin were compared to further understand the influence of porous pin-fin arrays. Statistical analysis showed that for average heat transfer coefficient, the particle diameter is a primary effect (percent contribution is 59%). Bottom thickness and Spacing are minor effects (percent contribution is 31% and 6%). Fin length has a little effect (percent contribution is 0.3%). This should due to the variation of particle diameter and bottom thickness will change the wetting surface area and internal gas-liquid flow resistance, by the way, the particle diameter impacts pore size and capillary force, and therefore leads to the most significant effect. The better parameters tend to have smaller particle diameter、spacing and higher bottom thickness；for the Critical Heat Flux, the fin length and spacing are main parameters (percent contribution is 58% and 23%). Particle diameter and bottom thickness have little effects (percent contribution is 2% and 0.7%). It’s found that the when the ratio of fin length and spacing (L/S) is greater than 1.2, the vapor-liquid separator could effectively lead to further enhance the CHF. The variation of spacing impacts the instability of vapor-liquid influence thus causing the CHF inversely proportional to the square root of the sum of fin width and spacing (W+S)1/2. Experimental results showed that it can be found though combining bottom thickness and particle diameter, the average heat transfer coefficient of porous pin-fin surface and porous surface both enhanced with increasing t/d, and have best performance with 11 in the range of parameters studied in present research, was different from the best ratio of 4-6 in previous literature using spherical powder. And follow-up experiment found that as t/d further increased to 16, the performance of porous pin-fin surface showed a downward trend. In addition, the heat transfer coefficient of porous pin-fin surface with S=500μm, was similar to porous surface with the same particle diameter and bottom thickness, but as the spacing shorten to 350μm, it showed a significantly enhancement. In the heat flux over 150kw/m2, the heat transfer enhancement ratios of best porous pin-fin surface and porous surface relatively smooth plane improved by 7~9 and 5~7times; the CHF was about 2.5 and 1.5 times over the smooth plane.