12.冷凍系統中，下列何者不影響壓縮機之啟動？ (A)出、入口閥未開 (B)冷卻水泵未啟動 (C)冷卻水溫度過低 (D)高、低壓開關故障

10.Longitudinal vibration of propulsion shafting systems is often excited by the variable thrust developed by the propeller due to the non-uniform wake pattern in which it operates. The predominant periodic component of the thrust developed by a propeller occurs at blade-rate frequency, i.e., the number of propeller blades times the rotational frequency of the shaft. For a four-blade propeller running at 60 rev/min, what is the predominant periodic frequency that excites the longitudinal vibration of the propulsion shafting systems? (A)1 Hz (B)2 Hz (C)3 Hz (D)4 Hz

12.冷凍系統中，下列何者不影響壓縮機之啟動？
(A)出、入口閥未開
(B)冷卻水泵未啟動
(C)冷卻水溫度過低
(D)高、低壓開關故障

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