Head, flow and power are important working parameters for investigating the performance of stainless steel corrosion-resistant centrifugal pumps. For the industry insiders, the calculation formula for the head of stainless steel corrosion-resistant centrifugal pumps is a very common technical data.
1. Flow
The flow rate of the stainless steel corrosion-resistant centrifugal pump is also called water delivery, which refers to the amount of water delivered by the pump in a unit time. It is represented by the symbol Q, and its units are liters/second, cubic meters/second, and cubic meters/hour.
2. Head
The head of the stainless steel corrosion-resistant centrifugal pump refers to the height of the pump that can lift water, usually represented by the symbol H, and its unit is meter. The head of the stainless steel corrosion-resistant centrifugal pump is based on the center line of the impeller and consists of two parts. The vertical height from the center line of the pump impeller to the surface of the water source, that is, the height at which the pump can suck up the water, is called the suction lift, referred to as suction; The height of is called pressure head, or pressure range for short. That is, pump head = suction head + pressurized water head. It should be pointed out that the head marked on the nameplate refers to the head that the pump itself can generate, and it does not include the loss head caused by the frictional resistance of the pipeline water flow. When choosing a water pump, be careful not to ignore it. Otherwise, there will be no water.
3. Power In unit time, the amount of work done by the machine is called power. It is usually represented by the symbol N. Commonly used units are: kg·m/s, kilowatt, horsepower. Usually the power unit of an electric motor is expressed in kilowatts; the power unit of a diesel engine or gasoline engine is expressed in horsepower. The power transmitted by the power machine to the shaft of the water pump is called shaft power, which can be understood as the input power of the water pump. Generally speaking, the power of the water pump refers to the shaft power. Due to the friction resistance of the bearing and the packing; the friction between the impeller and the water when the impeller rotates; the vortex of the water flow in the pump, the backflow of the gap, the inlet and outlet, the impact of the mouth, etc. Part of the power is inevitably consumed, so it is impossible for the water pump to completely convert the power input by the power machine into effective power. There must be a power loss, that is, the sum of the effective power of the water pump and the power loss in the pump is the shaft power of the water pump.
The head and flow calculation formula of stainless steel corrosion-resistant centrifugal pump:
What does the pump head H=32 mean?
Head H=32 means that this machine can raise water up to 32 meters
Flow=cross-sectional area*velocity
The flow rate needs to be measured by yourself: stopwatch
The head estimation method of stainless steel corrosion-resistant centrifugal pump:
The head of the pump has nothing to do with the power. It is related to the diameter of the pump impeller and the number of stages of the impeller. The pump of the same power may have a head of hundreds of meters, but the flow may be only a few squares, or the head may be only a few meters, but the flow may be higher. Hundred parties. The general rule is that under the same power, the flow rate of high head is less, and the flow rate of low head is large. There is no standard calculation formula to determine the head, which is determined by your use conditions and the factory pump model. It can be calculated according to the pump outlet pressure gauge. If the pump outlet is 1MPa (10kg/cm2), the head is about 100 meters, but the influence of suction pressure must be considered. For stainless steel corrosion-resistant centrifugal pumps, it has three heads: actual suction head, actual pressurized water head and actual head. Unless specified, the head is generally considered to refer to the height difference between the two water surfaces.
The most commonly used formula for pump head calculation is H=(p2-p1)/ρg+(c2-c1)/2g+z2-z1.
Among them, H——head, m; p1, p2——pressure of liquid at the inlet and outlet of the pump, Pa; c1, c2——flow velocity of the fluid at the inlet and outlet of the pump, m/s; z1, z2——inlet and outlet height , M; ρ—— density of liquid, kg/m3; g—— acceleration of gravity, m/s2.
Usually, stainless steel corrosion-resistant centrifugal pumps with a specific speed of ns between 130 and 150 are used. The flow of the pump should be 1.1 to 1.2 times the rated flow 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 way per 100 meters of pipe length can be roughly taken as 5mH2O, the pump lift calculation formula (mH2O):
Hmax=△P1+△P2+0.05L (1+K)
△P1 is the water pressure drop of the evaporator of the chiller.
△P2 is the water pressure drop of the one in the loop that accounts for the largest water pressure loss of the air-conditioning end device.
L is the tube length of the most unfavorable loop
K is the ratio of the sum of the equivalent lengths of local resistance in the most unfavorable loop to the total length of the straight pipe. When the most unfavorable loop is longer, the value of K is 0.2～ 0.3, and when the most unfavorable loop is short, the value of K is 0.4～0.6.
