3 replies to this topic

[npp]

The head coefficient coefficient or pressure coefficient Ψ is a dimensionless parameter defined by
Head per impeller (m) = Ψ * u² / g
The head coefficient is dependend of impeller design, having a value of 0.5 to 0.65. The average value is 0.55 ( at the best efficiency point).

The flow coefficient Φ is a dimensionless parameter described relationship of the suction gas flow rate to impeller diameter and tip speed.
Φ = Q / (3.1416* D²/4* u)
The value of flow coefficient ranges from 0.01 to 0.14
The curve of Ψ venus Φ is equivlent to Capacity-Head curve, is characterised only for impeller design & shape and should be valid for different inler gas conditions and speed.
Where:
u : tip speed (m/s) = N (rpm) * 3.1416 * D (m) / 60
N : rotation speed (rpm)
g: gravity constant = 9,81 m/s2
D: impeller diameter (m)
Q: suction gas flow (m3/s)

[npp]

These parameters are only a mean to characterise a machine. I don’t think they have relation to reliability and effective of the machine. The vendor should give some guarantee about energy consumption and performance. They tell how effective the machine is. Check the references to evaluate the reliability.The most downtime is due to problem of the shaft, impeller, motor, seal and bearing. Estimate the cost for downtime and compare the total annual cost of the machine (annual cost of investment, utility cost, cost of maintenance, cost of downtime, etc.)