FC-72流量震盪對一可變功率小圓型加熱面之週期性流動沸騰熱傳及氣泡特性研究

Abstract

這項研究目的探索FC-72在矩形流道中流過一小圓型加熱塊同步時間週期性蓄冷劑震盪和熱通量震盪對沸騰熱傳以及氣泡特徵研究。流量震盪為三角波震盪以及熱通量震盪為正旋波震盪。探討流量以及熱通量同向以及反向震盪研究。實驗參數為流量為200,300以及400 kg/m2s震幅為5%,10%以及15%,熱通量範圍為0.1到10W/cm2震幅為10%,30%以及50%週期為10到30秒,次冷度為0到15K,壓力為常壓。 實驗結果顯示在單向流中流量和熱通量同向震盪時會有抑制壁溫震盪的效果然而在雙相流中流量和熱通量反向震盪才能有效抑制壁溫的震盪,由於熱通量以及流量對壁溫的反應時間有延遲因此在加以考慮延遲的因素後確實能驗證說單向流中流量和熱通量同向震盪以及雙相流中流量和熱通量反向震盪能有效的防止壁溫的震盪。

This study intends to explore how simultaneously imposed time periodic coolant flow rate and heat flux oscillations affect the temporal flow boiling heat transfer and associated bubble characteristics of FC-72 over a small circular heated copper plate flush mounted on the bottom of a horizontal rectangular channel. The oscillations of the coolant flow rate and heat flux are respectively in the forms of nearly triangular and sinusoidal waves. Both the in-phase and out-of-phase mass flux and heat flux oscillations are investigated. In the experiment the time-average coolant mass flux is varied from 300 to 400 kg/m2s and the amplitude of the coolant mass flux oscillation is mainly fixed at 5, 10 and 15% of . The mean heat flux ranges from 0.1 to 10W/cm2 with the amplitude of the heat flux oscillation set at 10, 30 and 50% of for the same period of the heat flux and mass flux oscillations varied from 10 to 30 seconds Besides, the time-average liquid subcooling at the inlet of the test section ranges from 0 to 15K and the system is at slightly subatmospheric pressure. The transient oscillatory flow boiling heat transfer characteristics are illustrated by presenting the measured time variations of the heated plate temperature and boiling heat transfer coefficient. The experimental results show that the heated surface temperature also oscillates periodically in time at the same frequency as the mass and heat flux oscillations. Besides, the amplitude of the Tw oscillation is generally smaller in the flow boiling when the out-of-phase G and q oscillations are imposed. But in the single-phase flow the Tw oscillation is normally weaker by imposing in-phase G and q oscillations. These results indicate that the oscillation in Tw caused by the heat flux oscillation can be suppressed by the in-phase G oscillation in the single-phase flow and by the out-of-phase G oscillation in the boiling flow. It is further noted that by imposing the G oscillation at the time instant equal to the difference between the time lags in Tw resulting respectively from the q oscillation only behind the q oscillation, and G oscillation only behind the q oscillation, the Tw oscillation can be significantly suppressed and even completely wiped out.