非均質可潤濕性表面於紅銅圓管表面對池沸騰熱傳性能影響之研究

Experimental Investigation on Effect of Heterogeneous Wettable Surfaces on Pool Boiling Heat Transfer Performance of Cylindrical Copper Surface

張耀文(Yao-Wen Chang)

指導教授 ： 陳炳煇

國立臺灣大學/工學院/機械工程學研究所/碩士(2017年)

https://doi.org/10.6342/NTU201702081

摘要

本研究使用外徑25 mm、內徑18 mm和長40 mm的中空紅銅圓管，以外側曲面進行點狀的表面改質。 其中，使用不同尺寸和間距的方形疏水圖案以及不同潤濕性梯度結構來製造非均質濕潤性表面，以觀察非均質潤濕性表面對於池沸騰熱傳表現的影響做為目標。 在池沸騰實驗中，使用去離子水為工作流體且在飽和的情況下進行，觀察不同非均質潤濕性表面對於沸騰的氣泡動力學。 之後，以8個量測孔溫度推算表面溫度、熱通量以及池沸騰傳熱係數，評估不同非均質潤濕性表面對於池沸騰熱傳表現的影響。
本研究的實驗分為二部分，首先，使用不同尺寸和間距的方形疏水圖案來製造非均質濕潤性表面。 實驗結果顯示，中心點間距為5 mm且2 mm尺寸的方形圖案是所有設計結構中對於沸騰熱傳表現影響最優異的一項。 由於這種結構適當地整合了氣泡聚結行為的優點，並且還保留了用於再潤濕表面的流動路徑。 另外，本研究利用高速攝影機所記錄的圖片觀察氣泡脫離直徑大小，量測約為2.35 mm，與相關公式所預測的氣泡脫離直徑2.33 mm相當接近；同時，利用建立氣泡模型的方式，預測圖案之間要發生氣泡橫向結合的最大間隔距離，估計約為3.12 mm，此間隔距離影響是否提早發生橫向氣泡結，來間接影響再潤濕表面的流動路徑，造成不同的池沸騰熱傳表現結果。
接著，配合前述最佳的方型圖案大小和間距，搭配不同潤濕性表面組合出不同潤濕性梯度結構。 結果顯示，在疏水性聚合物圖案分別於未改質紅銅表面環境和超親水性環境下，兩者的池沸騰熱傳表現皆有顯著地增強。 與未改質的紅銅圓管表面相比，於15kW/m2熱通量情況下，沸騰熱傳係數增強比率分別約為98.5％和89.8 %。 整體沸騰熱傳表現中，以疏水性聚合物圖案於未改質紅銅表面環境表現最佳，次之為疏水性聚合物圖案於超親水性環境之組合。 由於每個潤濕性梯度結構下，皆有不同的氣泡聚結方式和表現。 因此，隨著熱通量的提升所產生的沸騰傳熱表現差異進而隨之擴大。

關鍵字

池沸騰 ； 表面改質 ； 非均質可潤濕性表面

並列摘要

In this study, pool boiling heat transfer experiments are conducted to investigate the effect of the heterogeneous wettable surfaces with various size and pitch of square patterns and different heterogeneous structures. The heat transfer experiments were carried out on a hollow copper cylinder of 25 mm outer diameter and 40 mm long, using the de-ionized (DI) water as the working fluid. The influences of heterogeneous wettable surfaces on the boiling bubble dynamics, heat fluxes, surface temperatures and the average heat transfer coefficient (HTC) are investigated at the saturated boiling condition.
In this work, among the various square patterns of different size and pitch, 2 mm size of the square pattern with 5 mm pitch (inter-distance = 3 mm) is the best one; due to such surface properly integrate the advantages of the bubble coalescence behavior and also the rewetting phenomenon. In addition, the observed bubble departure diameter is 2.35 mm, which is close to the predicted diameter (2.33 mm) by using the correlation formula. The maximum predicted inter-distance of patterns under the axial inter coalescence of bubble happening is 3.12 mm. It is the significant parameter that determines the earlier axial inter coalescence of bubbles takes place or not. Furthermore, heterogeneous structures show an appreciable enhancement in HTC in the cases of hydrophobic polymer patterns, with the plain copper and superhydrophilic surroundings. Both structures produce the enhancement of 98.5 % and 89.8 %, in the HTC, respectively, at low heat flux region compared to the plain copper surface. However, the boiling heat transfer performance is distinct with an increase in heat flux, because of the different bubble coalescence behaviors.

並列關鍵字

pool boiling ； surface modification ； heterogeneous wettable surface

參考文獻

[1] C. S. S. Kumar, S. Suresh, L. Z. Yang, Q. Q. Yang, and S. Aravind, "Flow boiling heat transfer enhancement using carbon nanotube coatings," Applied Thermal Engineering, vol. 65, pp. 166-175, 2014.

[2] D. Deng, R. Chen, Y. Tang, L. Lu, T. Zeng, and W. Wana, "A comparative study of flow boiling performance in reentrant copper microchannels and reentrant porous microchannels with multi-scale rough surface," International Journal of Multiphase Flow, vol. 72, pp. 275-287, 2015.

[3] J. M. Kim, S. H. Kang, D. I. Yu, H. S. Park, K. Moriyama, and M. H. Kim, "Smart surface in flow boiling: Spontaneous change of wettability," International Journal of Heat and Mass Transfer, vol. 105, pp. 147-156, 2017.

[4] L. W. Fan, J. Q. Li, L. Zhang, Z. T. Yu, and K. F. Cen, "Pool boiling heat transfer on a nanoscale roughness-enhanced superhydrophilic surface for accelerated quenching in water," Applied Thermal Engineering, vol. 109, pp. 630-639, 2016.

[5] J. Kim, S. Jun, R. Laksnarain, and S. M. You, "Effect of surface roughness on pool boiling heat transfer at a heated surface having moderate wettability," International Journal of Heat and Mass Transfer, vol. 101, pp. 992-1002, 2016.