斜線交錯之非均質可潤濕性表面於紅銅圓管表面對池沸騰熱傳影響之研究

Abstract

本研究使用網版印刷技術對紅銅圓柱進行表面改質，其中，使用外徑為25mm、內徑為18mm及長為40mm之中空紅銅圓柱為基材。並且在圓柱外表面進行不同傾斜角度之交錯疏水線狀圖形之改質，使其成為異質交錯潤濕性表面，以此觀察非均質潤濕性表面對池沸騰熱傳表現之影響。在本研究中，以去離子水為工作流體進行池沸騰實驗，並觀察且探討不同傾斜角度之交錯疏水線圖形對沸騰氣泡動力學之影響。最後以表面溫度、熱通量及池沸騰熱傳係數評估不同表面之池沸騰熱傳表現。 本研究中有4種不同交錯疏水線圖形之傾斜角，分別為0∘、30∘、60∘及90∘，其中，θ=30∘之異質潤濕交錯表面擁有最好的池沸騰熱傳表現。由於此表面使得氣泡擁有內部結合及外部結合，且此兩種結合之發生頻率相同，此現象使得銅表面能夠保留再潤濕表面所需之水流動路徑，因此不會產生巨大之氣膜覆蓋表面。另外，本研究也藉由高速攝影機所紀錄之影像觀察可得，θ=30∘之異質潤濕交錯表面上，因為在浮力方向擁有較為恰當之距離，提供氣泡能夠較容易地在浮力方向發生結合現象，造成氣泡之脫離半徑下降且脫離頻率上升。 在本研究中，於低熱通量之條件下，θ=0∘、30∘、60∘及90∘之非均質潤濕性表面擁有分別為89.27%、 104.59%、 103.99% 及 71.65%之池沸騰熱傳係數增益質。由於每種表面有不同之氣泡結合現象，因此隨著熱通量上升，不同的交錯疏水線狀圖形傾斜角度之表面間池沸騰熱傳表現之差異逐漸擴大。

In this study, screen printing technique was used to fabricate the heterogeneous wettable structure on a copper surface. The pool boiling heat transfer experiments were conducted with a hollow copper cylinder of 25mm outer diameter and 40mm long, using DI water as the working fluid. The effect of the heterogeneous wettable surfaces with various inclination angles of inclined line pattern was investigated by carry out pool boiling heat transfer experiments. The bubble dynamics, heat fluxes, surface temperatures and average heat transfer coefficient (HTC) were surveyed in this experimental work. The influences of different inclination angles of interlaced lines pattern on bubble dynamics were observed in this study. There are two types of bubble coalescence happen on the heated surface. Different frequency of these two merge ways result different heat transfer performance. There are four different inclination angles of interlaced line patterns, 0°,30°,60° and 90°, respectively. Among these surfaces, surface with θ=30° patterns produced the best heat transfer performance. Due to the proper distance in buoyancy direction causes excellent bubble coalesce behavior and better rewetting phenomenon. The highest enhancement in HTC of θ=0°,30°,60° and 90° is 89.27%, 104.59%, 103.99% and 71.65%, respectively.