wl = specific work lost due to hydraulic effects (J/kg)
Mechanical components - like transmission gear and bearings - creates mechanical losses that reduces the power transferred from the motor shaft to the pump or fan impeller.
The mechanical efficiency can be expressed as:
ηm = (P - Pl) / P (2)
where
ηm = mechanical efficiency
P = power transferred from the motor to the shaft (W)
Pl = power lost in the transmission (W)
Due to leakage of fluid between the back surface of the impeller hub plate and the casing, or through other pump components - there is a volumetric loss reducing the pump efficiency.
The volumetric efficiency can be expressed as:
ηv = q / (q + ql) (3)
where
ηv = volumetric efficiency
q = volume flow out of the pump or fan (m3/s)
ql = leakage volume flow (m3/s)
The overall efficiency is the ratio of power actually gained by the fluid to power supplied to the shaft. The overall efficiency can be expressed as:
η = ηhηmηv (4)
where
η = overall efficiency
The losses in a pump or fan converts to heat that is transferred to the fluid and the surroundings. As a rule of thumb - the temperature increase in a fan transporting air is approximately 1oC.
An inline water pump works between pressure 1 bar (1 105 N/m2) and 10 bar (10 105 N/m2). The density of water is 1000 kg/m3. The hydraulic efficiency is ηh = 0.91.
The actual water head (water column) can be calculated as:
h = (p2 - p1) /γ
= (p2 - p1) /ρ g
= ((10 105 N/m2) - (1 105 N/m2)) / (1,000 kg/m3) (9.81 m/s2)
= 91.7 m - water column
The pump must be constructed for the specific work:
wc = g h /ηh
= (9.81 m/s2) (91.7 m) / 0.91
= 988.6 (J/kg, m2/s2)
The construction or design head is:
h =wc / g
= (988.6 m2/s2) / (9.81 m/s2)
= 100.8 m - water column
Piping systems and pumps - centrifugal pumps, displacement pumps - cavitation, viscosity, head and pressure, power consumption and more.
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The measure of usefulness.
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Calculate pumps hydraulic and shaft power.
Horsepower required to pump water.
Characterizing of impeller types in pumps in a unique and coherent manner.
Suction Specific Speed can be used to determine stable and reliable operations for pumps with max efficiency without cavitation.
Static pressure vs. pressure head in fluids.
Utilize the system curve and the pump performance curve to select the proper pump for a particular application.
Calculate specific work done by pumps, fans, compressors or turbines.
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