奈米流體應用於池沸騰熱傳增強研究

Enhanced Pool Boiling Heat Transfer by Nanofluids

王仲愷(Chung-Kai Wang)

指導教授 ： 陳瑤明

國立臺灣大學/工學院/機械工程學研究所/碩士(2008年)

https://doi.org/10.6342/NTU.2008.00187

摘要

奈米流體為深具發展潛力之熱傳增強技術之ㄧ，而池沸騰亦是工業界重要應用模式。然而奈米流體於池沸騰熱傳增強之研究尚付闕如，且效能不彰。因此本文旨在探討使用不同於前人研究之新式奈米流體搭配，期能進一步提升奈米流體於池沸騰系統之熱傳增強性能。研究方法為使用二階段法將二氧化鈦（TiO2）奈米粒子分散於1,1,1,2-四氟乙烷冷媒（R-134a）中以製得奈米流體，並找出對流熱傳係數與熱傳導係數之關係，期望能初步探討奈米流體之沸騰熱傳增強性能。
研究結果顯示濃度0.005 (%vol.)粒徑20 ~ 25 (nm)之TiO2/R134a奈米流體其沸騰對流熱傳係數可達60 (kW/m2-K)，與純質R134a相比提升150 %。相同濃度下粒徑<50 (nm)之CuO/R134a與Al2O3/R134a亦有100 %與50 %之提升。由於本研究所使用之奈米流體其濃度低粒徑小，短期再分散性與數據重複性尚佳。由於沸騰溫度低故熱傳表面沉積層形成有限，致使臨界熱通量維持不變。本研究透過調控奈米流體熱傳導預測式以及池沸騰關係式中的參數，可初步定性分析池沸騰對流熱傳係數增強之現象。
總結而言，本實驗使用金屬氧化物與R134a搭配之奈米流體，並獲知其池沸騰熱傳增強性較水基者有更高的提升，可初步推論奈米粒子與工質之搭配將影響熱傳增強性能，本研究之經驗公式有待更精確的實驗與理論驗證。

關鍵字

熱傳增強 ； 池沸騰 ； 奈米流體 ； 二氧化鈦 ； 四氟乙烷冷媒

並列摘要

Nanofluid is expected to be one of the most potential techniques for heat transfer enhancement. Hence, recently studies have been carried out on the heat transfer behavior of nanofluids in two-phase heat transfer regimes such as pool boiling. However, the amount and performance of proposed works are scant and insignificant. Therefore, the aim of this article attempts to explore whether a further enhancement could be achieved by altering the nanoparticle/base-fluid combination used in previous studies. This research, a two-step procedure was used to disperse titania (TiO2) nanoparticles into 1,1,1,2-tetrafluoroethane (R-134a) to prepare nanofluid. The preliminary qualitative analysis of the pool boiling heat transfer enhancement of nanofluid was conducted through nanofluid and pool boiling correlations in order to indicate the relationship between thermal conductivity and boiling heat transfer coefficient.
Results of this study showed the boiling heat transfer coefficient of R-134a was shown to be increased by up to 150 % for nanofluid consisting of R-134a containing approximately 0.005 %vol. TiO2 nanoparticles of mean diameter 20 ~ 25 nm. On the other hand, the critical heat flux maintained the same by little deposition of nanoparticles. The short-range re-dispersibility and repeatability of data were found to be acceptable.
To conclude, the R134a-based nanofluids may be better than water-based in pool boiling heat transfer enhancement application. Further, our modified empirical correlations need to be proved by detail experiments and theories precisely.

並列關鍵字

Heat transfer enhancement ； Pool boiling ； Nanofluid ； Titania ； R-134a

參考文獻

Bang, I. C., Chang, S. H., "Boiling Heat Transfer Performance and Phenomena

Journal of Heat and Mass Transfer, 48(12), pp. 2420-2428, 2005.

Baraton, M. I., "Surface Functionalization of Semiconducting Nanoparticles," In Encyclopedia of Nanoscience and Nanotechnology, American Scientific. In Press., 2004.

Bergles, A. E., Two-Phase Flow and Heat Transfer, 1756-1980, Two-Phase Flow and Heat Transfer in the Power and Process Industries, Ch 24, Hemisphere Publisher Corporation, Washington, USA, 1981.

Bergles, A. E., "Enhancement of Pool Boiling," International Journal of Refrigeration, 20(8), pp. 545-551, 1997.