酯類冷凍潤滑油在池沸騰中熱傳效能影響之研究

Abstract

本研究以實驗方法探討冷媒與潤滑油池沸騰中熱傳效能之研究，加熱器為平板銅塊，以R-134a跟R-1234ze為工作流體，再混合不同種類的潤滑油進行實驗，系統溫度操作於0度與10度，並改變不同的實驗參數，探討其潤滑油對熱傳效果的影響。其控制的實驗參數分別為實驗參數有溫度(10℃、0℃)、黏度(170、150、120、與68)、不同的潤滑油混合比例(1%、3%、5%與10%)、油品(POEA、POEB、POEC與POED)，再配合高速攝影機觀察本實驗系統的沸騰氣泡，分析三種因子對熱傳係數的影響，因子有頻率、氣泡速度、氣泡大小。實驗結果顯示，熱傳係數在高熱通量的時候，3%油比例的冷媒會優於1%或者優於純冷媒的熱傳係數，此趨勢可能歸因於氣泡生成頻率較快與成核址密度較高的緣故；當冷媒混合較高黏度的潤滑油，其熱傳係數會較高，因為黏度較高，熱邊界層較厚，成核址密度較多；當操作溫度離冷媒與潤滑油的臨界溶解溫度越遠時，可能會增加氣泡量，進而增加熱傳效果。而本實驗數據也有與Jensen and Jackman 跟Kedzierski的經驗式去做比較，以Jensen and Jackman比較下，平均絕對誤差都在40%以內，而與Kedzierski比較下，誤差在70%到90%，兩者都無法預測出氣泡對熱傳係數的影響，故沒預測出3%油比例會高於1%油比例的情況

The present study examines the nucleate boiling heat transfer characteristics of refrigerant/oil mixture on copper flat surface. The refrigerant is R-134a and R-1234ze, and seven different lubricant oils are used on the associated refrigerants. The tests were carried out at 0℃and 10℃, respectively and the oil concentrations range from 0 to 10%, and the supplied heat fluxes spans from 70 to 10 kW/m2. High-speed camera is used to record the bubble formation film of the pure and mixtures subject to nucleate boiling. The recorded images are used to analyze some important factors to impact the heat transfer performance. The important factors include the frequency, the bubble velocity and the size of bubbles. The experimental results indicate that the heat transfer coefficients of oil concentration of 3% may exceed those of 1%. he phenomenon is attributed to faster bubble frequency and more site density. Normally, the refrigerant mixes with higher lubricant viscosity shows higher heat transfer coefficients as compared to those of low viscosity. The temperature difference between the operating temperature and critical solution temperature of refrigerant/oil mixture also play essential roles in the performance of the refrigerant/lubricant mixtures. When the operation temperature is raised to be away from the critical solution, an increasing bubble density is seen and a higher heat transfer performance is encountered. The experimental results for the copper flat surface are compared with the correlations by some previous correlations like Jensen and Jackman and Kedzierski. The magnitude of mean error is within 40% against the Jensen and Jackman’s correlation, and the magnitude of mean error are within 70% and 90% against Kedzierski’s correlation. Both correlations are unable to predict the influence of bubble density