本研究利用液晶熱像法來量測微小管溫度以求得水流經微小管的對流熱傳係數，這個方法可以有效的避免用熱偶計等接觸式溫度量測方法所產生的熱分流問題，本研究中微小管的管徑大小分佈從123到962微米，實驗結果顯示完全發展流的摩擦係數及熱傳係數與傳統理論十分吻合。不同管徑下轉換流皆發生在雷諾數從2,300到3,000，與傳統大管徑下轉換流發生的雷諾數一樣。隨著管徑越小層流的熱完全發展長度有較傳統預測式更長的趨勢，在熱發展區管徑962微米所測得的紐賽數與Shah and Bhatti [1987]預測結果十分吻合。在本研究中液晶熱像法的準確度可以高達0.4 oC，這個方法可以更進一步應用到管徑更微小，熱分流更嚴重微小管的溫度量測。 This study proposes a non-contacted Liquid Crystal Thermography (LCT) method for micro tube surface temperature measurement. It avoids the thermal shunt error caused while using the direct contact thermocouples. Forced convective heat transfer performance of water flowing through six micro tubes with inner diameters ranging from 123 to 962 μm were tested. The test results show that the conventional heat transfer and flow resistance correlations for laminar and turbulent flow can well be applied for predicting the fully developed heat transfer performance and friction factor in micro tubes. The transition occurs at Reynolds number from 2,300 to 3,000. This is also the same range as that for conventional larger tubes. The laminar thermal entrance length for micro tubes is longer than that estimated by the conventional correlation. The developing Nusselt numbers for 962 μm tube agrees well with those correlations predicted by the Shah and Bhatti [1987]. The uncertainty applied to measure the micro tube surface temperature is lower than 0.4 oC. It can be further applied for measuring smaller tube surface temperature that the thermal shunt may be more significant by using direct contact temperature measurements methods.
