CENTRIFUGAL PUMP DESIGN AND ANALYSIS

AIM: To Simulate Flow over a CENTRIFUGAL PUMP using SolidWorks

INTRODUCTION:

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 engine or electric motor. They are a sub-class of dynamic axisymmetric work-absorbing turbomachinery. 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 which it exits.

Common uses include water, sewage, agriculture, petroleum, and petrochemical pumping. Centrifugal pumps are often chosen for their high flow rate capabilities, abrasive solution compatibility, mixing potential, as well as their relatively simple engineering. A centrifugal fan is commonly used to implement a vacuum cleaner. The reverse function of the centrifugal pump is a water turbine converting potential energy of water pressure into mechanical rotational energy.

Working of Centrifugal Pump

Like most pumps, a centrifugal pump converts rotational energy, often from a motor, to energy in a moving fluid. A portion of the energy goes into kinetic energy of the fluid. Fluid enters axially through eye of the casing, is caught up in the impeller blades, and is whirled tangentially and radially outward until it leaves through all circumferential parts of the impeller into the diffuser part of the casing. The fluid gains both velocity and pressure while passing through the impeller. The doughnut-shaped diffuser, or scroll, section of the casing decelerates the flow and further increases the pressure.

GOVERNING EQUATIONS:

Pressure Ratio = Output Pressure/Input Pressure

OBJECTIVE:

1. Modelling and simulation of Centrifugal Pump
2. To obtain relationship between Pressure Ratio and Mass Flow Rate.

PROCEDURE:

• Initially, a CAD model of Centrifugal Pump is set up with necessary dimensions. While extruding the geometry, the ‘Merge Result’ option is unchecked to avoid the merging of the existing geometry with the extruding geometry.
• To overcome the limitation of meshing in SolidWorks, ‘Moving Frame Reference’ is employed and a control volume is constructed to provide the rotation for simulation.
• A Flow Simulation is ideated with specified boundary condition and goals to be obtained.

Base Line Simulation:

• Go to Flow Simulation
• Create lids at both the faces of the suction pipe and outlet pipe to make watertight body.
• Create wizard and apply the general settings. Then, go to default unit system.
• Further Internal analysis is applied and select rotation with local region averaging.
• Choose the working fluid as water with laminar and turbulent flow and choose the default wall conditions, thermodynamic condition.
• Add boundary condition, Inlet face at environmental pressure and outlet face at outlet velocity of 10 m/s. Further add mesh and use advanced channel refinement

Add goals,

• Surface goal as Average Total Pressure at outlet lid
• Surface goal as Average Total Pressure at inlet lid
• Surface goal as Mass Flow Rate at outlet lid

• The iterations are fixed with a 500 value to avoid early convergence resulting in unsatisfactory results.
• A Parametric Study is set up with the variable being the Outlet Velocity. The Simulation is run for 5 design points and the results are obtained for verification.

RESULTS (PLOTS):

VELOCITY CUT PLOT (at 10 m/s outlet velocity)

PRESSURE CUT PLOT (at 10 m/s outlet velocity)

VELOCITY FLOW TRAJECTORY (at 10 m/s outlet velocity)

PRESSURE FLOW TRAJECTORY (at 10 m/s outlet velocity)

INLET TOTAL PRESSURE (5 Design Points)

OUTLET TOTAL PRESSURE (5 Design Points)

MASS FLOW RATE (Outlet)

Goal (Value)	Design point 1	Design point 2	Design point 3	Design point 4	Design point 5
Velocity normal to face (Outlet Velocity [m/s])	10	15	20	25	30
SG Av Total Pressure 1 [Pa]	4267678.386	4005504.51	7142746.072	8956227.296	3504225.564
SG Av Total Pressure 2 [Pa]	548222.5187	499225.5611	1003775.859	1114661.211	475737.9097
SG Mass Flow Rate 1 [kg/s]	-0.491014285	-0.738724617	-0.973207386	-1.174373242	-1.480761672

CONCLUSION:

The Simulation carried out gives a clear perception of the working of Centrifugal Pump. It can also be concluded that the impact of mass flow rate is highly significant in determining the outlet total pressure, i.e. our required parameter dependency on the variable.