暫態熱線法由於量測速度快、不受熱對流影響、設備架設容易等優勢，因此在流體之熱傳導係數的量測上應用相當廣泛。近年來由於奈米流體與生醫產業發展的需求，針對局部生物組織以及微量樣品的研究逐漸增加，而相關樣品之價位大多偏高且生產不易，如今隨著微製程技術的進步，發展以微量樣品進行量測的元件與技術也將逐漸起步。本文將利用微機電系統(MEMS)的製程技術配合數值模擬，設計並製作微型的熱線法量測元件。 在暫態熱線法的量測中，需由加熱的時間配合熱源的溫度以求得樣品之熱傳導係數，而系統的邊界將對其結果產生影響，該現象在微量樣品的量測中更為明顯。因此本文首先利用數值模擬針對熱源幾何外型進行探討，發現熱源截面的長寬比將影響資料選取的時間規劃，而配合適當的外邊界設定，可以精確的規劃出量測合適的資料選取範圍。此外，線熱源的長度與端部效應之間有著密切的關係，藉由增加線熱源的長度可以有效的減少端部效應的影響。在計算樣品之熱傳導係數的研究上，當熱源介於兩樣品的交界面，所測得的熱傳導係數為兩樣品熱傳導係數之算術平均數，而量測過程中端部效應的影響程度將由熱擴散係數較低的一方主導。在針對以不同電流對樣品的量測實驗中，發現所得之熱傳導係數隨著電流增加而上升，若當樣品熱傳導係數與溫度關係越密切，則使用越大的電流將導致越大誤差。本研究針對空氣、水與不同濃度的甘油進行量測，藉由比較發現其結果與文獻之間差異約5 %，可以準確地進行量測，未來該元件將應用於微量奈米流體的量測與相關研究上。元件之後的量測中發現，本研究所設計的元件其量測結果與文獻比較約低了4 ~ 6 %。 The transient hot-wire method (THW) is widely used for measuring the thermal conductivity of fluids, due to its fast measurement, less convectioneffect, and relatively simple set up. In recent years, nanofluids and biological fluids have drawn attention in thermal transport applications. The high-cost or diffcult-to-produce samples draw the need of defeloping miniaturized devices to measure fluid samples in small quantity. In this study, we develop a micro-THW device to measure the thermal conductivity of fluid with micro-litter volume using MEMS (micro-electromechanical system) fabrication techniques. Numerical simulations are performed to assist the geometric design and evaluation of the measuremnt errors. First, we study the effect of the heating line geometry, and find the length-to-width ratio of the heating-line cross-section affects the measurung time interval selection. With the appropriate design of the outer boundary of the testing domain, we can obtain the right data selection of the measurements. Furthermore, the end effect has a close relation to the length of the heating-line, which can be alleviated by increasing the length of the heating-line. In the case when two media are present in the measurement, we find that the measured thermal conductivity is the arithmetic mean of the meadia and the influence of end effects is dominated by the one with lower thermal diffusivity. Different current measurements are tested, and it is found that the error increases as the current increas, which should be taken into account for high-accuracy measurements. Finally, we measure the thermal conductivity of water and glycerin with different concentration. The measured results are around 5% deiated from the literature value.
