介電液 FC-72 在兩平板間的池沸騰研究

Abstract

本論文是以介電液FC-72為工作流體在一大氣壓下進行一大氣壓下，兩平行板間的飽和池沸騰實驗，下方為一片面積1cm×1cm，厚度2mm銅片加熱片，上方為一片不加熱的壓克力板，兩平板之間的間隙S與加熱面與水平的夾角Θ可以改變，即S = 0.5、1.0、1.5及2.0 mm，以及Θ = 0°、45°、90 °，熱通量範圍為0 ~ 210 kW/m2。實驗目的在比較間隙大小、加熱面角度在起始過熱度、核沸騰熱傳與臨界熱通量並與僅一片開放式加熱片時的池沸騰結果比較。實驗結果顯示在這三種角度時，小間隙可以增強小熱通量時的熱傳係數，小熱通量指在Θ = 0°時，熱通量小於20 kW/m2，在Θ = 45°與Θ = 90°時，熱通量小於60 ~ 70 kW/m2。在水平加熱時，四種間隙的臨界熱通量都比開放式的低很多，開放式水平加熱的臨界熱通量約180 kW/m2，四種間隙中最高的臨界熱通量僅55 kW/ m2。當Θ = 45°與Θ = 90°時，間隙0.5 mm及1.0 mm的臨界熱通量並不像水平加熱，間隙0.5 mm及1.0 mm時那麼低，當間隙為1.5 mm及2.0 mm時，一直到臨界熱通之前，熱傳係數都高於開放式，因此可以說小間隙對水平加熱的影響最大，而對加熱面與水平夾角Θ = 45°與Θ = 90°時的影響則需有較小的間隙 ( 本實驗中1.0 mm以下 )。

This experiment is to study the influences of gap sizes on saturated pool boiling under one atmosphere pressure。The so - called two plates is that a heating suface made of a smooth copper plate with 1cm ×1cm in area and 2mm in thicknessis is paralled below an acrylic plate。The space between the two plates S and the angle between the plates and the horizon Θ can be changed，S = 0.5、1.0、1.5 and 2.0 mm，Θ = 0∘、45∘and 90∘，the range of heat flux is 0 ~ 210 kW/m2。Differences of several aspects between the experiment and unconfined ( no acrylic plate ) experiment due to gap sizes and angles are carefully identified，like the onset of boiling、nucleat heat transfer and critical heat transfer。The results show that small gaps can improve heat transfer no matter what the angle is under low heat flux，0 ~ 20 kW/m2 forΘ = 0∘，0 ~ 60 kW/m2 and 70 kW/m2 forΘ = 45∘and 90∘。WhenΘ = 0∘，the critical heat fluxes for four gaps are all severly depressed (the highest，55kW/m2 ) compared to those of the unconfined one ( 180 kW/m2 )，when it comes toΘ = 45∘and 90∘，the depressions are not so severly，especially for S= 1.5 mm and 2.0 mm，the heat transfer coefficients are better than those of the unconfined one till the heat flux reach critical heat flux。So obvious influences of small gaps when the heating plate is horizonally placed are more likely to happen while smaller gaps ( 1.0 mm and less ) are needed for great influence when heating surface is tilted。