管道的阻力特性一般用摩擦阻力係數來描述，而大部分水利工程師採用C值摩擦阻力係數概算可能的水頭損失，但一般教科書、文獻中所查得之C值僅依據管路材料進行概估，實際之阻力值仍不確定。現階段台灣地區自來水事業採用公共工程施工綱要規範第02514章─自來水用延性鑄鐵管件，針對管內壁塗裝可使用“卜特蘭水泥第 II 型、延性鑄鐵管及管件內面用環氧樹脂粉體塗裝”。為了解管路之實際之摩擦阻力係數，本研究採用一般坊間所生產之水泥砂漿襯裡管路，與新研發之環氧樹脂粉體塗裝襯裡管路進行試驗，以了解新型環氧樹脂塗裝襯裡管路實際摩擦阻力係數，以及與水泥砂漿襯裡管路之差異性。
由結果可知水泥砂漿襯裡之C值介於137.5 ~ 147.0之間，而環氧樹脂粉體塗裝襯裡之C值介於147.5 ~ 149.0之間，其摩擦阻力較低。水泥砂漿襯裡之f值介於0.0151 ~0.0170之間，環氧樹脂粉體塗裝襯裡之f值介於0.0132 ~0.0170之間，隨雷諾數而變化，於3 m/s流速下差異百分比最高達到12.3%。查詢Moody圖進行分析可知300 mm管徑之水泥砂漿襯裡管路之e值為0.03 mm，接近光滑混凝土(e = 0.025 mm)之值，而310 mm管徑之環氧樹脂粉體塗裝襯裡管路之e值為0.0031 mm，已接近PVC等光滑管路(e = 0.0025 mm)之表現。
由分析結果可知兩種管路之C值並非為定值，會隨溫度、流速產生變化，但與雷諾數之關聯性又不明顯，以其進行分析將產生較大誤差，於工程上僅適用於現場即時概略估算之用。而Darcy-Weisbach公式之f值則與雷諾數、相對粗糙度、溫度明確相關。且在f值已知的條件下，利用公式亦可快速的計算摩擦損失，亦相當方便。爰此，未來自來水事業機構進行規劃設計、水理分析時，採用Hazen-Williams equation提高安全係數設計確實較為簡便，但建議對應不同設計條件應再以Darcy-Weisbach公式進行評估覆核，以確保設計之準確性，另在智慧管網之應用，建議以Darcy-Weisbach公式計算評估，較為適當與準確。

Normally, the friction characteristics of ductile pipe is described with friction coefficient. Most hydraulic engineers estimate water head loss by C number friction coefficient. However, C number data in textbook and literature usually is estimated by ductile pipe material. Actual friction is not certain. For investigating friction coefficient of ductile pipe, this research performs friction coefficient comparison between civilian produced cement mortar and recently developed epoxy resin powder ductile iron pipe inner linings with experiments.
The experimental results show that the C number of cement mortar inner lining is between 137.5 and 147.0, and epoxy resin powder inner lining, whose C number is between 137.5 and 147.0, has lower friction. The f number of cement mortar inner lining is between 0.0151 and 0.0170, and the f number of epoxy resin powder inner lining is between 0.0132 and 0.0170. The f number which varied with Reynold number has maximum variation of 12.3% when flow velocity is 3m/s. By Moody diagram, the e number of 300mm diameter ductile iron pipe with cement mortar inner lining is 0.03mm and similar to the e number of smooth concrete (e = 0.025mm); the e number of 300mm diameter ductile iron pipe with epoxy resin inner lining is 0.0031mm and similar to the e number of smooth PVC pipe (e = 0.0025mm).
The analysis show that the C numbers of the tubes are not constant and varied with temperature and flow velocity. Since their relationship with Reynolds number is not obvious, C number analysis produces larger error and is only useful for in-situ, quick and rough estimation. The f number derived by Darcy-Weisbach equation is certainly varied with Reynolds number, relative roughness and temperature. Calculating friction loss by deriving f number is quick and easy. Hence, future design plan and hydrological analysis performed by tap water company should ensure safety parameter margin by Hazen-Williams equation. The examination with Darcy-Weisbach equation under different conditions should be performed for better accuracy of design. The intelligent pipe network design should be evaluated by Darcy-Weisbach equation for better accuracy.
Keywords: Tap water, Pipe material, Inner lining, Friction resistance

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