介電液FC-72在兩平板間的增強池沸騰研究

Abstract

本論文主要是進行介電液FC-72在一大氣壓下，兩平行板間的增強池核沸騰實驗。利用兩種不同的加熱面，光滑面與鰭片面，並且改變間隙S與加熱角度，即S=0.25mm、0.5mm、1mm、2mm及3mm，而加熱角度有垂直與水平的改變，以觀察不同加熱表面在不同間隙與加熱角度下的起始過熱度、核沸騰熱傳與臨界熱通量的差異。實驗結果顯示，小間隙(0.5mm)可以增強小熱通量時的熱傳係數，但當間隙小至接近氣泡脫離加熱表面尺寸(0.25mm)時，熱傳係數反而降低。在水平加熱時，兩種加熱面在間隙小於2mm時，其臨界熱通量皆比開放式的低，直到間隙為3mm時臨界熱通量才接近開放式。在垂直加熱時，對兩種加熱面而言，間隙在2mm或3mm時其臨界熱通量皆超越開放式，其中間隙2mm才是最佳熱傳性能間隙。另外，鰭片加熱面在任何相同角度、相同間隙的條件下實驗，其臨界熱通量與熱傳係數皆比光滑面高約2倍。

This experiment is to study the influences of gap size on enhanced pool boiling of dielectric fluid FC-72 under one atmosphere. Two different test surfaces，smooth surface and fin surface，were used with gap sizes，S=0.25mm、0.5mm、1mm、2mm、3mm，and with horizontal as well as vertical angles of heating surface. The differences of onset of pool boiling，nucleat boiling heat transfer and critical heat flux under different conditions were observed. The results showed that the small gap of 0.5mm could improve heat transfer coefficient but when the gap size was reduced to bubble departure radius of about 0.25mm，the heat transfer coefficient were found smaller instead. For horizontal heating，with gap size smaller than 2mm，the critical heat fluxes were found lower than those of open space case. When the gap size is 3mm，the critical heat flux was found close to open space case. For vertical heating with two different gaps of 2mm and 3mm，the critical heat fluxes were found higher than the open space case，which gap of 2mm is the highest. Besides，the critical heat flux and the heat transfer coefficient of the fin heating surface were found almost two times of those of the smooth heating surface under the same conditions.