Centrifugal Pump Design and Analysis

OBJECTIVE

• To Create a 3D Model of Centrifugal Pump and to run a Flow Simulation.
• To Obtain a relation between Pressure ratio and Mass Flow rate.

INTRODUCTION

Centrifugal Pumps are the sub class of the Turbomachinery. Centrifugal pumps are used to transport fluids by the conversion of rotational kinetic energy to the hydrodynamic energy of the fluid flow. The rotational energy typically comes from an electric motor. The fluid enters the pump impeller along or near to the rotating axis and is accelerated by the impeller, flowing radially outward into a diffuser or Volute chamber (casing), from where it exits.

MODELLING

In this Project a 3D model of centrifugal pump is created using solidworks CAD software. In this model I have made some changes in the Impeller. The design parameters are as follows

• Diameter of the Casing = 76 mm
• Thickness of the Casing = 22 mm
• Diameter of the Impeller = 60 mm
• Diameter of the Suction pipe = 22 mm
• Length of the Suction pipe = 40 mm
• Diameter of the Delivery pipe = 12 mm
• Length of the Delivery pipe = 80 mm

ISOMETRIC VIEW OF CASING

ISOMETRIC VIEW OF THE IMPELLER

ISOMETRIC VIEW OF THE CENTRIFUGAL PUMP

PARAMETERS

Analysis type : Internal

Fluid used : Water

Type of Flow : Laminar and Turbulent

Rotation Type : Local Region Averaging

Boundary Condition at Inlet : 1 bar

Boundary Condition at Outlet : 15 m/s

PROCEDURE

1. Create a 3D Model in Solidworks CAD Software.
2. Modify the Components in the Components Control.
3. The Computational Domain is created.
4. The Rotating Region is selected and the speed is set to 1000 rpm.
5. The Inlet Boundary Condition is set as Environmental Pressure of 1 bar.
6. The Outlet Boundary Condition is the Exit Velocity of 15 m/s.
7. The Surface Goal is set in the Inlet and the Outlet faces.
8. Then the Mesh is created for the model and the Automatic mesh level is set into 3 and Advanced Chanel refinement is selected.
9. Run the Simulation and the cut plots are created for the Pressure and Velocity and get the values for the goals.

GRID DEPENDANCY TEST

For this test I have set the input variables as output velocity and the values are 5 m/s , 10 m/s , 15 m/s , 20 m/s , 25 m/s , 30 m/s. The Level of mesh is set as 3. The number of Iteration for the solver is set as 700 in the calculation control option.

RESULTS

Pressure at 5 m/s

Velocity at 5 m/s

Flow Trajectories at 5 m/s

Pressure at 10 m/s

Velocity at 10 m/s

Flow Trajectories at 10 m/s

Pressure at 15 m/s

Velocity at 15 m/s

Flow Trajectories at 15 m/s

Pressure at 20 m/s

Velocity at 20 m/s

Flow Trajectories at 20 m/s

Pressure at 25 m/s

Velocity at 25 m/s

Flow Trajectories at 25 m/s

Pressure at 30 m/s

Velocity at 30 m/s

Flow Trajectories at 30 m/s

COMPARSION OF VELOCITY VS MASS FLOW RATE and VELOCITY VS PRESSURE RATIO and MASS FLOW RATE VS PRESSURE RATIO

For getting the plot between velocity vs mass flow rate and velocity vs pressure ratio the values are stored in text document and a code is written in Python.

Velocity Mass Flow Inlet Pressure Outlet Pressure

05 -0.383884235 101325 677831.8620
10 -0.768631012 101325 673409.4962
15 -1.152979123 101325 641138.4973
20 -1.537618576 101325 614613.5851
25 -1.922297313 101325 560694.9062
30 -2.306761653 101325 358535.3618

import matplotlib.pyplot as plt

velocity = []
mass_flow = []
inlet_pressure = []
outlet_pressure = []

for line in open(\'pump_study.txt\'):
	velocity.append(float(line.split()[0]))
	mass_flow.append(float(line.split()[1]))
	inlet_pressure.append(float(line.split()[2]))
	outlet_pressure.append(float(line.split()[3]))

pressure_ratio = []
for i in range(0,6):
	c = inlet_pressure[i]
	d = outlet_pressure[i]
	x = d/c
	pressure_ratio.append(x)

plt.figure(1)
plt.plot(velocity, mass_flow, color = \"blue\", linewidth = 3)
plt.xlabel(\'velocity\')
plt.ylabel(\'Mass flow\')
plt.title(\'Velocity vs Mass Flow rate\') 
plt.show()

plt.figure(2)
plt.plot(velocity, pressure_ratio, color = \"blue\", linewidth = 3)
plt.xlabel(\'velocity\')
plt.ylabel(\'Pressure ratio\')
plt.title(\'Velocity vs Pressure_ratio\') 
plt.show()

plt.figure(3)
plt.plot(mass_flow, pressure_ratio, color = \"blue\", linewidth = 3)
plt.xlabel(\'Mass flow\')
plt.ylabel(\'Pressure ratio\')
plt.title(\'Mass_flow vs Pressure_ratio\')
plt.xlim(-0.2,-2.5) 
plt.show()

VELOCITY VS MASS FLOW RATE

VELOCITY VS PRESSURE RATIO

MASS FLOW RATE VS PRESSURE RATIO

CONCLUSION

• From the First plot we can see that initially the velocity is less so the mass flow rate is less when the velocity increases the mass flow rate increases.
• From the Second plot we can see that pressure ratio is high for low velocity and pressure ratio starts to decrease when the velocity increases.
• From the Third plot we can see that for lower mass flow rate the pressure ratio is high when the mass flow rate increases pressure ratio decreases.
• A pump does not create pressure it only creates flow.Pressure is a measurement of the resistance to flow.
• First resistance is created by volute casing of pump which catches the liquid and slows it down. When liquid slows down in the casing some of its kinetic energy is converted into pressure energy.
• That\'s why velocity increases pressure decreases and velocity increases mass flow rate increases.