Pump head calculation formula, how to calculate pump head?
Head (water head) - pump to unit weight
(1kg) The work done by the liquid, that is, the increase in energy of the unit weight of liquid after passing through the pump. It is represented by the letter H and is usually expressed by the height m of the liquid column.
Other units: Pa (kPa), atm (1 engineering atmosphere)
1atm=98.0665 kPa ≈0.1 MPa
The head is calculated as H=E2-E1
The pump head H=z+hw z is the height difference of the pumping height, that is, the water level from the inlet to the water surface at the exit. Hw is the head loss, including the Darcy formula or Xie Cai formula for calculating the head loss hf and the local head loss hw hf along the path.
Hw=&*v^2/2g, & is called the local head loss coefficient. To check the relevant literature, v is the flow velocity in the tube. Generally speaking, hw occurs at the entrance, bend, valve, outlet, etc.
Pump head is an important working energy parameter of the pump. For the industry, the pump head calculation formula is a very common technical data. Below, the world factory pump valve network introduces the pump head calculation formula in detail.
The head is usually the maximum height that the pump can lift, and is indicated by H. The most commonly used pump head calculation formula is H = (p2-p1) / ρg + (c2-c1) / 2g + z2-z1.
Among them, H - head, m; p1, p2 - the pressure of the liquid at the inlet and outlet of the pump, Pa; c1, c2 - the flow rate of the fluid at the inlet and outlet of the pump, m / s; z1, z2 - the height of the inlet and outlet , m; ρ - liquid density, kg / m3; g - gravity acceleration, m / s2.
Generally, a centrifugal clean water pump with a specific number of revolutions ns of 130 to 150 is used. The flow rate of the water pump should be 1.1 to 1.2 times the rated flow rate of the chiller (1.1 for a single unit and 1.2 for two units in parallel).
According to the estimation, the loss along the pipe length per 100 meters can be roughly 5mH2O, and the pump head calculation formula (mH2O):
Hmax=△P1+△P2+0.05L (1+K)
ΔP1 is the water pressure drop of the chiller evaporator.
ΔP2 is the water pressure drop of each of the parallel connected air conditioners in the ring that has the largest water pressure loss.
L is the length of the most unfavorable loop
K is the sum of the local resistance equivalent length and the total length of the straight pipe in the most unfavorable loop. When the most unfavorable loop is long, the K value is 0.2 to 0.3, and when the most unfavorable loop is short, the K value is 0.4 to 0.6.
