Data on the impact of water pump cavitation on the performance parameters of water pumps
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Currently, there is a double-suction pump with a power of 160 KW, a rated flow rate of 1000 m3/h, a rated head of 40 m. Its rotation speed is 1480 rpm, and its efficiency is 88.14%. The required net positive suction head for this pump is 5.2 m. The motor’s power factor is 0.89, while its efficiency is 94.9%. Used for cooling water circulation, with clean water as the medium. The actual inlet pressure at the water inlet side is currently -4 m, resulting in cavitation, with an actual current of 234 A. The following is the theoretical calculation process under normal conditions. According to the formula: Input power of motor P1 = U × I × cosφ × 1.732 = 380 (V) × 234 (A) × 0.89 × 1.732 = 137,068 (W). Output power of motor P2 = P1 × ηM = 137,068 (W) × 94.9% = 130,077 (W). Hydraulic power Ph = P2 × ηP = 130,077 (W) × 88.14% = 114,650 (W). Theoretical flow rate Q = (Ph / (H × g × ρ)) × 3600 = (114,650 W / (40 m × 9.81 m/s × 1000 kg/m3)) × 3600 = 1,051.8 m3/h. However, due to cavitation, the actual head is only 25 meters. How can I calculate the actual flow rate of this pump? Or are there any authoritative documents indicating that water pump cavitation reduces the performance curve of the water pump?
Cavitation means that this algorithm can no longer be used to determine flow rates; the flow rates calculated are not consistent at all with the head values shown on the curve or with the pressure readings on the pressure gauge in use. Try reducing the valve opening to see if this can bring the pressure reading back to normal, and then use the aforementioned method to calculate the flow rate under normal conditions. I’m also looking for any similar algorithms or documentation that explains how cavitation affects a pump’s flow rate and head.{:2_41:}
Your inlet pressure is -4 meters; you need to check the local atmospheric pressure. If we assume that the local atmospheric pressure is 9.5 meters, then the system’s effective net positive suction head is only 5.5 meters. Taking into account the pressure losses at the pump inlet as well as manufacturing variations in the pump, cavitation is very likely to occur.
You need to increase the inlet pressure or reduce the valve opening
It is impossible to calculate the flow rate of a pump that has experienced cavitation, as its performance curve undergoes unpredictable changes due to cavitation. The flow rate can only be calibrated using methods such as flow meters or level gauges.