| 中文摘要 |
依據一般船舶熱交換器設計基本要求，以海水平均溫度25℃為基準，大多將船舶中央冷卻系統進口海水最高溫度設計在32℃而出口淡水溫度固定為36℃，而使海水冷卻泵全速運轉來抽取所需海水流量以進行熱交換。然因只在某些季節與特定海域，海水溫度才可能會上升至很高溫度，通常進口海水溫度是低於32℃，甚至低於25℃且可視為可變，故海水冷卻泵之實際抽取所需海水流量應該是可以較少的，即海水冷卻泵無需全速運轉而可減少其功耗。本文擬比較變頻與閥控海水冷卻泵於抽取船舶冷卻系統所需海水流量之節能效益，吾人利用泵浦特性曲線以計算克服管路摩擦損失之海水冷卻泵的最低流量，並以熱平衡法分析實際所需海水流量，再估算海水冷卻泵之功耗。本文以小型冷卻系統來驗證所提理論模擬方法，再應用該方法於大型實船之實際航程，進而評估變頻與閥控調速海水冷卻泵於抽取所需海水流量之節能效益，期能作為未來船舶設計之參考。
With basic principles in the design of heat exchangers in a ship's central cooling system, seawater cooling pumps are normally designed to maintain the temperature of inlet seawater at 32℃ and outlet freshwater at 36℃ based on the average temperature of seawater at 25℃ when the pumps are under full speed to reach the flow nowadays. However, seawater temperatures have ever gone up this high only in limited areas in the seas around the world within certain seasons, and their temperatures are usually below 32℃ and are changeable. Thus, the actual in-take seawater flow can be reduced, resulting in a large reduction of the required amount of electrical energy. This paper compares energy consumption reduction in seawater pumps using a variable frequency drive (VFD) and throttle valve to continuously supply seawater flow to a ship's cooling system. A pump characteristic curve is used in this study to calculate the minimum flow rate of seawater cooling pumps for overcoming the friction losses in the pipe. The actual seawater flow needed is obtained from thermal equilibrium calculation, and then the flows are used to calculate the energy consumption for seawater cooling pumps. In addition, the theoretical results obtained from this paper are validated by an experiment of a small-scale cooling system and this theoretical method is applied to assess the energy-saving benefit of the actual voyage for a practical ship. Hopefully, the study of this paper can be used for ship design for future reference. |
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