Centrifugal pump design and analysis

AIM: Centrifugal Pump design and Analysis.

Objectives of the project:

1. To create a 3D model of a centrifugal pump.
2. Run a baseline simulation.
3. To show the performance diagram.
4. To obtain the relationship between pressure ratio and mass flow rate.

Introduction:

A pump is a device that moves fluids (liquids or gases) by mechanical action, typically converted from electrical energy into Hydraulic energy.

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.

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.

• Main Parts of Centrifugal Pump

The Main parts of Centrifugal Pump are:

Impeller:

It is a wheel or rotor which is provided with a series of backward curved blades or vanes. It is mounded on the shaft which is coupled to an external source of energy which imparts the liquid energy to the impeller there by making it to rotate.

Casing:

It is a pipe which is connected at the upper end to the inlet of the pump to the centre of impeller which is commonly known as eye. The double end reaction pump consists of two suction pipe connected to the eye from both sides. The lower end dips into liquid in to lift. The lower end is fitted in to foot valve and strainer.

Delivery Pipe:

It is a pipe which is connected at its lower end to the out let of the pump and it delivers the liquid to the required height. Near the outlet of the pump on the delivery pipe, a valve is provided which controls the flow from the pump into delivery pipe.

Suction Pipe with Foot Valve and Strainer:

Suction pipe is connected with the inlet of the impeller and the other end is dipped into the sump of water. At the water end, it consists of foot value and strainer. The foot valve is a one way valve that opens in the upward direction. The strainer is used to filter the unwanted particle present in the water to prevent the centrifugal pump from blockage.

Applications:

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 vaccum cleaner. The reverse function of the centrifugal pump is a water turbine converting potential energy of water pressure into mechanical rotational energy.

Pressure Ratio:

Pressure ratio is the ratio between the outlet pressure and inlet pressure.

Geometry Of the Model:

Centrifugal Pump Inside View of Pump

Parameters for Baseline Simulation:

Procedure:

• Create a 3D Model in Solidworks.
• After finishing cad model, save the file and go for the flow simulation.
• Now we will create the lids at the two faces and then we will go for wizard option and then select the internal flow option.
• Now we will be selecting rotating option as local averaging region and then click on water as the flow fluid under the wizard option and then click on finish.
• Now we will be defining the boundary conditions at the inlet as 101325 pa and the other boundary condition as outlet velocity at the outlet face.
• Now we will be defining the rotating region by selecting the propeller domain which is the moving frame set at 1000 rad/s.
• Then, the surface goal is set at inlet and outlet face.
• Also, the mesh is created for the model and the automatic mesh level is set upto 3 levels with advanced channel refinement.
• Now, run the simulation and the cut plots are created for the pressure and velocity and get the values for goals.
• Now, we will be doing the parametric study using the input parameter as the outlet velocity and output parameter as the surface goal, mass flow rate, cut plots and flow trajectories.

Results:

Grid Dependency test under Parametric study:

For this test, I have set the input variables as outlet velocity and the values are 10 m/s,15 m/s,20 m/s,25 m/s, and 30 m/s. The level of the mesh is set to 3 with advanced channel refinement. Also, the number of iterations for the solver is set as 500 in the calculation control option under input menu.

Output Results:

• Design Point 1 at velocity 10 m/s

Velocity Plot:

Pressure Plot:

Velocity Trajectory:

Pressure Trajectory:

• Design Point 2 at velocity 15 m/s

Velocity Plot:

Pressure Plot:

Velocity Trajectory:

Pressure Trajectory:

• Design Point 3 at velocity 20 m/s

Velocity Plot:

Pressure Plot:

Velocity Trajectory:

Pressure Trajectory:

• Design Point 4 at velocity 25 m/s

Velocity Plot:

Pressure Plot:

Velocity Trajectory:

Pressure Trajectory:

• Design Point 5 at velocity 30 m/s

Velocity Plot:

Pressure Plot:

Velocity Trajectory:

Pressure Trajectory:

• Graphs and Comparison:

Relationship Between Pressure Ratio and Velocity:

Relationship Between Mass Flow Rate and Velocity:

Relationship Between Pressure Ratio and Mass Flow Rate:

Observation and Conclusion:

• It is observed from the first plot that pressure ratio is high for low velocity and pressure ratio starts to decrease when the velocity increases.
• Also, from the second 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 (by considering the absolute value of mass flow rate) also increases.
• Pressure is created because of the resistance to flow as pump doesnot create pressure it only creates flow.
• With the increase in outlet velocity , the average mass flow rate shows a linear variation in the negative direction(i.e. backflow) and hence it increases.
• Inlet pressure remains the same for all cases but the outlet pressure varies.
• When the flow rate at the outlet is high, then the pressure reduces at outlet which results in the decrease in pressure ratio.