How to calculate the power of a centrifugal pump I don t know the efficiency

Shaft power = (flow head.

density) (3600 102 efficiency).

The shaft power is the effective power, which is the power left by the motor after removing the slip, and then removing the power after various losses.

Efficiency is divided into: mechanical efficiency.

Volumetric efficiency, hydraulic efficiency. Mechanical efficiency refers to the loss of disc friction, etc., volume refers to the loss of leakage, and hydraulic refers to the loss of friction of the medium. This efficiency is going to have different methods depending on the pump.

There is no one-size-fits-all formula for calculating efficiency, it is all corrected. If you want to know more about this, it is recommended to take a look at Guan Xingfan's modern pump technology manual, which is very detailed, because there are too many contents, I can't list them here.

Pump power (kw) head h (m) flow rate q (cubic meters per second) flow weight (water is calculated as 1000) efficiency (take 70---90) 102

Due to various losses in the operation of the pump, the actual (effective) pressure head and flow rate of the pump are lower than the theoretical value, and the power input to the pump is higher than the theoretical value.

In general, the efficiency of a pump is the ratio of the effective power of the pump to the shaft power. η=ne/n

The power input to the centrifugal pump by the motor is called the shaft power of the pump, which is denoted by n.

The effective power can be written as ne = qh g

Wherein, the effective pressure head of the h pump, that is, the energy obtained from the pump by the unit volume of liquid in the gravity field, m;

q Actual flow rate of the pump, m3 s;

Liquid density, kg m3;

ne The effective power of the pump, i.e., the mechanical energy obtained by the liquid from the pump per unit of time, W.

The efficiency test of the pump is determined by experimentation. The relationship between flow rate q and head h, shaft power n and efficiency is measured through experiments, and the characteristic curve is drawn, and the working principle of centrifugal pump is as follows

After the centrifugal pump is started, the pump shaft will drive the impeller to rotate at high speed, forcing the pre-filled liquid between the blades to rotate, and under the action of inertial centrifugal force, the liquid moves radially from the center of the impeller to the periphery.

The liquid medium gains energy during the movement of the impeller, resulting in an increase in the static pressure energy and an increase in the flow velocity. When the liquid leaves the impeller and enters the pump casing, it decelerates due to the gradual expansion of the flow channel in the casing, and part of the kinetic energy is converted into static pressure energy, and finally flows into the discharge pipeline in a tangential direction.

When the liquid is thrown from the center of the impeller to the periphery, a low-pressure area will be formed in the center of the impeller, and the liquid will be sucked into the center of the impeller under the action of the difference between the liquid level of the tank and the total potential energy of the center of the impeller. Thanks to the continuous operation of the impeller, the liquid is continuously sucked in and discharged. The mechanical energy obtained by the liquid in the centrifugal pump ultimately manifests itself as an increase in hydrostatic energy.

Power and efficiency of centrifugal pumps:

Due to various losses in the operation of the pump, the actual (effective) head and flow rate of the pump are lower than the theoretical value, and the power of the input pump is higher than the theoretical value, and the effective power can be written as ne = qh g

Wherein, the effective pressure head of the h pump, that is, the energy obtained from the pump by the unit volume of liquid in the gravity field, m;

q Actual flow rate of the pump, m3 s;

Liquid density, kg m3;

ne The effective power of the pump, i.e., the mechanical energy obtained by the liquid from the pump per unit of time, W.

The power input to the centrifugal pump by the motor is called the shaft power of the pump, which is denoted by n. The ratio of effective power to shaft power is defined as the total efficiency of the pump, i.e.

NE N Obviously, when the flow rate q is 0, the effective power Ne is 0. The efficiency is also 0, why is the shaft power n not 0? Because the motor is still spinning at this time, the power of the motor input to the centrifugal pump is still there, although relatively small.

Let's take a look at the classic centrifugal pump characteristic curve in the figure below

As can be seen from the figure, it is obvious that when the flow rate is 0, the shaft power n is not 0, and the efficiency is 0

Generally 70% 80%.

The structural characteristics of the centrifugal pump are as follows: in a volute-shaped pump casing, an impeller that can rotate quickly is installed, and there are 2 8 blades on the impeller. There are two interfaces on the pump casing, and the one leading to the center of the impeller is the inlet, which is connected to the suction line; The tangent of the pump casing is the same as the outlet, which is connected to the discharge line.

The main working part of a centrifugal pump is the impeller. The second is the suction chamber, pump body (pump casing), pump cover, shaft sealing device, axial force balance device, bearing, coupling, bracket, extrusion chamber, etc. When the impeller canopy is 1, the liquid can continuously suck people from the suction port, discharge from the discharge port, and make the liquid exert pressure and discharge to a high place.

Precautions for the use of centrifugal pumps.

The maximum starting frequency of the pump should not exceed 12 hours, the differential pressure should not be lower than the design point, and the performance parameters should not fluctuate in the system. The pump outlet pressure gauge value is equal to the differential pressure plus the inlet pressure gauge value.

The reading on the ammeter at full load to ensure that the current does not exceed the value on the nameplate of the motor, the motor with the pump may be selected according to the buyer's requirements, according to the actual medium gravity, and the power of the motor should be considered when conducting trial operation. If the specific gravity of the actual medium is smaller than that of the test run medium, please strictly control the opening of the valve during the test run to avoid overload or even burnout of the motor. If necessary, the pump manufacturer must be contacted.

Due to various losses in the process of operation of the pump, the actual (effective) pressure head and flow rate of the pump are lower than the theoretical value, and the power of the input pump is higher than the theoretical value.

h The effective head of the pump, that is, the energy obtained from the pump by the unit amount of liquid in the gravity field, m;

q Actual flow rate of the pump, m3 s;

Liquid density, kg m3;

ne The effective power of the pump, i.e., the mechanical energy obtained by the liquid from the pump per unit of time, W.

The effective power can be written as ne = qh g

The power input to the centrifugal pump by the motor is called the shaft power of the pump, which is denoted by n. The ratio of effective power to shaft power is defined as the total efficiency of the pump, i.e.

ne/n

The flow, head, power and other parameters of the centrifugal pump are important parameters that need to be paid attention to when selecting the model, and their calculation and confirmation methods are as follows:

Calculation and confirmation of flow rates.

Flow refers to the volume of liquid flowing through the centrifugal pump per unit time, which is generally expressed by the mass of liquid flowing through the centrifugal pump per unit time. The formula for calculating the flow rate is:

q = n * v

where q is the flow rate in m h; n is the rotational speed, and the unit is r min; v is the volume passing through the pump per unit of time in m.

The flow rate is determined by measuring the difference between the inlet and outlet levels and multiplying it by the cross-sectional area per unit of time. It can also be measured by attaching a flow meter directly.

Calculation and confirmation of head.

Head refers to the amount of power required per unit mass of liquid to be pumped to a certain height. The formula for calculating the head is:

h = p2 - p1) /g)

wherein, h is the head, and the unit is m; P2 is the outlet pressure in Pa; P1 is the inlet pressure, the unit is Pa; is the density of the liquid, the unit is kg m; g is the acceleration due to gravity and the unit is m s.

The way to confirm the head is to measure the pressure difference between the inlet and outlet at different flow rates, and then calculate the head according to the above formula.

Calculation and confirmation of power.

Power refers to the power provided by the pump per unit time, and is generally expressed in horsepower or kilowatts. The formula for calculating the power is:

p = q * h * g /

where p is the power, and the unit is kw; q is the flow rate, and the unit is m h; h is the head, the unit is m; is the density of the liquid, the unit is kg m; g is the acceleration due to gravity and the unit is m s. Initiates normal efficiency for the pump.

The power is determined by directly measuring the power of the motor or the torque and speed of the pump shaft, combined with the efficiency of the pump.

The above is the calculation and confirmation method of the flow, head, power and other parameters of the centrifugal pump, which is very important for selection and daily use.

Parameters such as flow, head, and power of centrifugal pumps can be confirmed by experimental measurements or calculations.

Flow calculation: The flow rate of the centrifugal pump can be calculated by the following formula:

q = a * v

where q represents the flow rate in m h; a indicates that the cross-sectional area of the pump inlet or outlet is slippery, and the unit is m; v represents the average flow rate of the pump in m s.

The flow rate of the pump can be calculated according to the inlet and outlet pipe diameter of the pump and the flow calculation formula.

Head calculation: The head of the centrifugal pump can be calculated by the following formula or eggplant:

h = p2 - p1) /g + hs

where h represents the head, the unit is m; P2 indicates the outlet pressure in Pa; P1 indicates the inlet pressure in Pa; Indicates the density of the liquid, and the unit is kg m; g represents the acceleration due to gravity in m s; hs is the sum of the heights of the various resistance losses in m.

In general, the numerical values of liquid density and gravitational acceleration are known, while the inlet and outlet pressures can be measured by pressure sensors.

Power calculation: The power of the centrifugal pump can be calculated by the following formula:

p = qh/3600η

where p represents power in kW; Indicates the density of the liquid, in kg m; q represents the flow rate, and the unit is m h; h represents the head, and the unit is m; Indicates the efficiency of the pump.

The power is calculated based on the flow and head of the pump, and the efficiency of the pump needs to be known, which is usually provided by the manufacturer and can also be confirmed by experimental measurements.

It is important to note that since the physical properties of liquids may change due to factors such as temperature, pressure, flow rate, etc., appropriate corrections need to be made during the calculation. In addition, in actual operation, it is also necessary to consider the influence of factors such as the loss of valves, elbows, pipes, etc., and the start and stop of the pump on the performance parameters of the pump.

Summary. Hello dear, <>

The power of the pump n (kw) = head (m) flow rate (m3 s) 1000 (the gravity of the water kg m3) 102 (power conversion coefficient The efficiency of the pump), from which the efficiency of the pump can be obtained. If the current and voltage can be measured (the power of the pump can be calculated), the efficiency of the pump can be obtained by measuring the flow rate and head.

2. Centrifugal pump.

1. The centrifugal pump uses the rotation of the impeller to make the water centrifugal move to work. Before the pump starts, the pump casing and suction pipe must be filled with water, and then the motor is started to make the pump shaft drive the impeller and water to do high-speed rotation movement, and the water undergoes centrifugal movement, which is thrown to the outer edge of the impeller and flows into the pressurized water pipeline of the pump through the flow channel of the snail pump casing.

How to calculate the efficiency of a centrifugal pump?

Hello dear, <>

1. The efficiency of the centrifugal pump is calculated The power of the pump n (kw) = head (m) flow rate (m3 s) 1000 (the gravity of the water kg m3) 102 (the power conversion coefficient) the efficiency of the pump), from which the efficiency of the pump can be obtained. If the current and voltage can be measured (the power of the pump can be calculated), the efficiency of the pump can be obtained by measuring the flow rate and head. 2. Centrifugal pump 1, centrifugal pump is to use the rotation of the impeller to make the water centrifugal movement to work.

Before the pump starts, the pump casing and suction pipe must be filled with water, and then the motor is started to make the pump shaft drive the impeller and water to do high-speed rotation movement, and the water undergoes centrifugal movement, which is thrown to the outer edge of the impeller and flows into the pressurized water pipeline of the pump through the flow channel of the snail pump casing.

Hello dear, <>

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p= gh, i.e., the pressure disturbance lead strength = the degree of dense plum socks gravity coefficient height (i.e., head) of three kilograms of water pressure attitude excitation is 3bar=300000pah=300000

That is, the corresponding head is.