Posted by **Janus** on Tuesday, February 16, 2010 at 10:30am.

A centrifugal pump compresses 3000 liters/min of water from 98 KPa to 300KPa. the inlet and outlet temp are 25°C. The inlet and discharge pipe are on the same level but the diameter of the inlet piping is 15cm whereas that of the discharge piping is 10cm. Determine the pump work in kW

- Thermodynamics -
**drwls**, Tuesday, February 16, 2010 at 1:34pm
Calculate the inlet and outlet velociies V1 and V2 using the contiuity equation

V * A = 3000 liters/min = 3*10^6 cm^3/min

A1 = pi*(15)^2 = 706.9 cm^2

A2 = pi*(10)^2 = 314.2 cm^2

V1 = 3*10^6/706.9

= 4244 cm/s = 42.44 m/s

V2 = 95.48 m/s

The steady state energy equation says that

Mdot*(U + P*v + KE + PE)out = Mdot*(U + P*v+ KE+ PE)in + (Power)in

Mdot is the mass flow rate

U is the internal energy, which does not change because inlet and outlet temperatures are equal. KE(per mass) = V^2/2. PE is potential energy which does not change since the inlet and outlet are at the same elevation. P v

is pressure times specific volume, which is the same as pressure divided by density.

The energy equation simplifies to:

Power in = Mdot*[P/density + V^2/2]out -Mdot*[P/density + V^2/2]in

For water, density = constant = 1000 kg/m^3

Mdot = 3 m^3/min * 1000 kg/m^3 = 3000 kg/min = 50 kg/s

First let us calculate the power needed to increase the pressure.

Mdot*(Pout-Pin)/density

= 50 kg/s*(202*10^5 N/m^2)/1000 kg/m^3

= 60.6*10^6 J/s = 1.01 Megawatts

You need to add to that the additional power needed to increase the kinetic energy

Mdot*[V2^2/2 - V1^2/2]

Take it from there and check my numbers.

## Answer this Question

## Related Questions

- Fluid Mechanics - An ideal mixing (total volume inlet = total volume outlet) of ...
- physics - A large water tank has an inlet pipe and an outlet pipe. The inlet ...
- Physics - A large water tank has an inlet pipe and an outlet pipe. The inlet ...
- algebra - A certain toilet tank can be emptied in 6 sec through its drain when ...
- math - A 500-litre water storage tank is situated at the top of a building at a ...
- physics 203 - Water (p=1000kg/m^3) enters a pipe on the ground with an inside ...
- Fluid Mechanics - Water enters a turbo-machine at a velocity 12 ft/s. The flow ...
- physics - Search: the ratio of the inlet pistol force and outlet pistol force is...
- science - the ratio of the inlet pistol force and outlet pistol force is 2:7....
- engineering - The flow system as shown in the Figure, the centrifugal pump(3500 ...

More Related Questions