Pump head
The pump head is also called the pump head, which refers to the energy obtained by the unit weight of fluid passing through the pump. The pump head size depends on the structure of the pump (such as the diameter of the impeller, the bending of the blade, etc., and the speed. At present, the pump head cannot be accurately calculated theoretically, and it is generally determined experimentally.
I. Overview
The head of H (m) centrifugal pump is also called the head of the pump, which refers to the energy obtained by the unit weight of fluid passing through the pump.
The pump head size depends on the structure of the pump (such as the diameter of the impeller, the bending of the blade, etc., and the speed. The pump head cannot be accurately calculated theoretically, and it is generally determined experimentally.
Second, experimental determination
The pump head can be determined by experiments, that is, a vacuum gauge is installed at the pump inlet and a pressure gauge is installed at the outlet. If the kinetic energy difference on the cross sections of two tables is not counted (that is, Δu2 / 2g = 0), the energy between the cross sections of the two tables Loss (ie ∑f1-2 = 0), then the pump head can be calculated by the following formula
Note the following two points:
(1) where p2 is the reading of the pressure gauge at the pump outlet (Pa); p1 is the reading of the vacuum gauge at the pump inlet (negative gauge pressure value, Pa).
(2) Pay attention to distinguishing between the two different concepts of head (head) and lift height of centrifugal pumps.
Head refers to the energy obtained after a unit weight of fluid is pumped. In a piping system, the Bernoulli equation is listed between two sections (including the pump) and arranged. In the formula, H is the head, and the lift height refers only to the term Δz.
Example 2-1 The head of a centrifugal pump is measured. The working medium is clean water at 20 ° C and the measured flow rate is 60m ^ 3 / h. The pump inlet vacuum gauge reads 0.02Mpa and the outlet pressure gauge reads 0.47Mpa (gauge pressure). It is known that the vertical distance between the two gauges is 0.45m. The suction pipe of the pump has the same diameter as the pressure pipe. Try to calculate the pump head.
solution:
Check the water density at 20 ℃ 1.0 * 10e3kg / m3,
h = 0.45m (1Mpa is approximately equal to 100 meters of water column)
p outlet = 0.47Mpa (0.47 * 100m water column = 47m water column)
p inlet = -0.02Mpa (0.02 * 100m water column = 2m water column)
ρ is the density of the liquid
H = h + (p-outlet-p-inlet) /ρg=0.45+ (0.47 * 10e6-(-0.02 * 10e6)) / (10e3 * 9.887) = 45.96m (water column)
