How to calculate the efficiency of multistage centrifugal pump for coal mine drainage?
Centrifugal pump is a regular equipment for mine water supply and drainage design. The use of high-efficiency multi-stage centrifugal water pumps for coal mine drainage can save power consumption in daily operation and meet the needs of engineering construction. However, how to determine and calculate the efficiency of multistage centrifugal pumps for coal mine drainage is a difficult problem in pump selection.
Efficiency calculation of multistage centrifugal pump for coal mine drainage
The effective power of the multi-stage centrifugal water pump used in coal mine drainage can be calculated by the flow and head, and the density of the conveying medium. To calculate the shaft power, you must know the efficiency. The efficiency refers to the ratio of the effective power of the pump to the shaft power.
η = pe / p
The power of the pump usually refers to the input power, that is, the power transferred from the prime mover to the shaft of the pump, so it is also called the shaft power and is represented by p.
The effective power is: the product of the pump's head and mass flow and gravity acceleration.
pe = ρg
qh (w) or pe = γqh / 1000 (kw) ρ: density of liquid delivered by pump (kg / m3)
γ: the gravity of the liquid transported by the pump γ = ρg (n / m3) g: acceleration of gravity (m / s)
Mass flow qm = ρq (t / h or kg / s)
Because the power of the multi-stage pump N (KW) = head (m) × flow (m3 / s) × 1000 (weight of water Kg / m3) ÷ 102 (power conversion factor) ÷ η (efficiency of multi-stage pump), by This can seek the efficiency of multi-stage pumps. If the current and voltage can be measured (the power of the multi-stage pump can be calculated), the efficiency of the multi-stage pump can be obtained by measuring the flow rate and head. This is the formula for calculating the efficiency of the multi-stage pump.
Shaft power and motor power of multistage centrifugal water pump for coal mine drainage
In actual operation, the multistage centrifugal pump has volume loss (ie leakage loss), hydraulic loss (friction of water flow in the pump, impact loss) and mechanical loss (friction between the rotating impeller and the pump shaft and bearings such as the fixed pump casing). Loss), causing the efficiency of the water pump to decrease; the efficiency of the centrifugal pump is essentially the product of the three efficiencies of mechanical, volume, and hydraulic, which reflects the effective degree of power transmission by the water pump and is an important parameter of the centrifugal pump.
Calculation formula of shaft power of multistage centrifugal water pump for coal mine drainage:
In the formula: N axis one pump shaft power (KW)
Q-pump delivery flow (L / s)
H-pump delivery head (m)
n Pump efficiency (%)
102 is the unit finishing constant
This formula shows that when the flow rate and head are fixed, the shaft power of the pump is inversely proportional to the efficiency of the pump. The efficiency of the water pump is high, and the shaft power is low, otherwise, the shaft power is high.
Matching motor power
In the formula: N machine a motor power (KW)
K-spare coefficient
N-axis water pump shaft power (KW)
Each pump is equipped with a motor rated power or a spare coefficient, also known as a rich coefficient. It takes into account factors such as the mechanical efficiency of the motor, and its value varies with shaft power.
