Centrifugal pump simulation project

Intoduction

Main goal of this project is to simulate centrifugal pump with 3 different values of massflow rate and figure out how it affects pump's performance, in other words, if and how it will change the pressure head and the efficiency.

Thoery

Centrifugal pump is a device, which's purpose is to convert kinetic energy into thermal energy.

The Centrifugal pump consists of several components: An impeller (rotor) which is rotating, Casing (Volute) which is used to effectively move fluid inside the centrifugal compressor and increase the pressure head.

Initially fluid enters into the centrifugal pump through "Eye" along the rotating axis of the impeller, which transfers it's rotational energy into the hydrodynamic energy of the fluid flow. meaning, when the fluid leaves the impeller it will have high velocity, in other words high kinetic energy in order to convert the kinetic energy into thermal (potential) energy, Volute is used, spiral shape casing in order to gradually increase flow cross section decreasing fluids velocity in order to increase the pressure head.

SET UP

In our case we have water as an operating fluid. We are simulating 3 different cases, where we have 3 different values of the mass flow rate: 130kg/s, 156kg/s and 180kg/s. However the rotational speed (RPM) is constant and equals to 2000RPM (12000deg/s)

• MESH

• Run parameters

• Simulation time parameters

• Boundary conditions

• Turbulence modeling

POST PROCESSING

• Case 1) Massflow rate: 130kg/s
  
  

Total pressure at the Inlet and the Outlet Boundaries

When the mass flow rate is 130kg/s Total pressure at the outlet is approximately 5bars, according to this infromation we can calculate pressure head.

`P_h = (DeltaP)/(rhog) = (400000(Pa))/(1000((kg)/m^3)*9.81) = 40.8(m)`

Now we can calculate Hydraulic power with the following equation:

`P_H = (QDeltaP)/600` - Where Q is flow rate (L/min)

`DeltaP` is Total pressure difference

`P_H` in our case for 130kg/s mass flow rate is approximately 52KW

• Torque

With the Torque we can calculate shaft power with the following equation

`P_(shaft)=T*omega` - Where `omega` indicates rotational speed in rad/s

In our case when mass flow rate is 130kg/s shaft power `P_(shaft) = 314*(2000(RPM)*2pi)/60 = 65.7KW`

Efficiency of the centrifugal pump could be calculated by the following equation

`eta = P_H/P_(shaft)*100= 52/65.7 = 79%`

• Velocity and Pressure contours

• Case 2) Mass flow rate: 156kg/s

Total pressure at the Inlet and the Outlet Boundaries

In this case Total pressure at the outlet has been decreased from 5bars to 4.8bars.

`P_h = (DeltaP)/(rhog) = (380000(Pa))/(1000((kg)/m^3)*9.81) = 38.7(m)`

`P_H = (QDeltaP)/600` - Where Q is flow rate (L/min)

`DeltaP` is Total pressure difference (bar)

`P_H` in our case for 156kg/s mass flow rate is approximately 59KW

• Torque

In our case when mass flow rate is 156kg/s shaft power `P_(shaft) = 345*(2000(RPM)*2pi)/60 = 72.3KW`

Efficiency of the centrifugal pump could be calculated by the following equation

`eta = P_H/P_(shaft)*100= 59/72.3 = 81.6%`

• Velocity and Pressure contours

• Case 3) Mass flow rate: 180kg/s

Total pressure at the Inlet and the Outlet Boundaries

In this case Total pressure at the outlet is 4.3bars.

`P_h = (DeltaP)/(rhog) = (330000(Pa))/(1000((kg)/m^3)*9.81) = 34.1(m)`

`P_H = (QDeltaP)/600` - Where Q is flow rate (L/min)

`DeltaP` is Total pressure difference (bar)

`P_H` in our case for 180kg/s mass flow rate is approximately 60.3KW

• Torque

In our case when mass flow rate is 180kg/s shaft power `P_(shaft) = 360*(2000(RPM)*2pi)/60 = 75.4KW`

Efficiency of the centrifugal pump could be calculated by the following equation

`eta = P_H/P_(shaft)*100= 60.3/75.4 = 79.9%`

• Velocity and Pressure contours

PERFORMANCE PLOT

According to the plot above it's clear that as we increase the mass flow rate and remain the same rotational speed, pressure head decreases and at some point it will reach so called "choke". instead of it we may encounter phenomenon called "surge", which happens when pressure head increases so much that we do not have mass flow any more.

CONCLUSION

We successfully simulated centrifugal pump problem and found out how pressure head and efficiency behaviour when mass flow rate is increased.

(results could be much more accurate, but unfortunately computational time is too expensive for me).