Centrifugal pump design & analysis using Solidworks

OBJECTIVE: To create a centrifugal pump geometry to perform the flow simulation using Solidworks and obtaining the analysis results to view the relationship between the mass flow rate and pressure ratio.

THEORY:

1.1 Centrifugal Pump- Centrifugal pumps are used to induce flow or raise pressure of a liquid. Its working is simple. At the heart of the system lies impeller. It has a series of curved vanes fitted inside the shroud plates. The impeller is always immersed in the water. When the impeller is made to rotate, it makes the fluid surrounding it also rotates. This imparts centrifugal force to the water particles, and water moves radially out. In Fig this process is illustrated. Since the rotational mechanical energy is transferred to the fluid, at the discharge side of the impeller, both the pressure and kinetic energy of the water will rise. At the suction side, water is getting displaced, so a negative pressure will be induced at the eye. Such a low pressure helps to suck fresh water stream into the system again, and this process continues.

From the illustrations of the pump so far, one specialty of the casing is clear. It has an increasing area along the flow direction. Such increasing area will help to accommodate newly added water stream, and will also help to reduce the exit flow velocity.
Reduction in the flow velocity will result in an increase in the static pressure, which is required to overcome the resistance of the pumping system.

What are the main applications for centrifugal pumps?
Centrifugal pumps are commonly used for pumping water, solvents, organics, oils, acids, bases and any ‘thin’ liquids in both industrial, agricultural and domestic applications. In fact, there is a design of centrifugal pump suitable for virtually any application involving low viscosity fluids.

Type of centrifugal pump	Application	Features
Canned motor pump	Hydrocarbons, chemicals where any leakage is not permitted	Sealless; impeller directly attached to the motor rotor; wetted parts contained in can
Magnetic drive pump		Sealless; impeller driven by close coupled magnets
Chopper/grinder pump	Waste water in industrial, chemical and food processing/ sewage	Impeller fitted with grinding teeth to chop solids
Circulator pump	Heating, ventilation and air conditioning	Inline compact design
Multistage pump	High pressure applications	Multiple impellers for increased discharge pressures
Cryogenic pump	Liquid natural gas, coolants	Special construction materials to tolerate low temperatures
Trash pump	Draining mines, pits, construction sites	Designed to pump water containing solid debris
Slurry pump	Mining, mineral processing, industrial slurries	Designed to handle and withstand highly abrasive slurries

• Mass Flow Rate- The mass flow rate of a system is a measure of the mass of fluid passing a point in the (m) system per unit time. The present study aims to analyze the fluid flow in a flowbench and perform the grid dependency and valve lift test and observe the results.
• Pressure Ratio- Pressure ratio is the ratio between the outlet pressure and the inlet pressure.

Pressure ratio = Outlet total pressure/ Inlet totalpressure

PROCEDURE:

3D MODEL:

1. To create the centrifugal pump geometry, starting the sketch from the top plane in Solidworks. Two circles that are concentric with the origin are sketched with diameter 0.04m and dia 0.08m respectively.
2. Constructing two arcs between the two circles for the vanes of the impeller that are concentric. Trimming the extra outer circle and circular patterning the vanes as 5 concerning the origin. Now extruding the sketch from midplane to get the profile.
3. From the top plane, drawing another circle from its origin and extruding from the midplane to get the geometry. *Merge results are unselected. Now from the top plane, a new circle is sketched and extruded.
4. With the centreline, a tangent over the circle from the top plane and a line is drawn parallel and equal to the centreline inside the circle at a distance of 0.005m.
5. A reference plane is drawn on the endpoint of the line drawn and a circle is drawn on that plane and sweeper into the circle. From the top face of the profile, the circle is drawn and extruded for the inlet cavity.
6. Using the direct editing tab, combining the profile into a single geometry. Using the shell, the thickness is provided to the geometry.
7. Now from the top plane, the circle is drawn outside the edges of vanes end extruded in the midplane such that it does not interfere with vanes and other parts.

BASELINE SIMULATION:

1. For the watertight body, the lid is created on both the circular profile of the centrifugal pump. In the wizard menu, the following are provided as inputs for the baseline simulation for the centrifugal pump.
   a) Units: SI units
   b) Fluid: Water
   c) Simulation Type: Internal Flow
2. To perform the flow simulation inside the centrifugal pump, the rotation is included with the local region averaged.
   Boundary Conditions:
   a) Environment Pressure = 101325 pa
   b) Outlet Velocity = 10 m/s
3. Rotating Region = Outside the vanes (Boss Extrude 4) with 1000 rad/s
4. In the component control, boss extrude is excluded from selection, and the number of iteration for the solver is set as 1000 in the calculation control option.
5. Insert Surface Goals of Avg Total Pressure = Outlet Profile (LID2) and a mass flow rate is provided for both the lids.
6. Global Mesh is refined at level 3 and advanced channel refinement. Then the simulation is performed and the cut plots are created for the Pressure and Velocity and get the values for the goals.
7. After the completion of the baseline simulation, the parametric study is calculated.

PARAMETRIC STUDY:

1. To perform the parametric study on the compressor pump, the followings are provided:
   Input parameters = Velocity normal to face (outlet velocity)
   The input values are ranged from 10m/s to 30m/s with number of values 6 (i.e.) 10m/s, 14m/s, 18m/s, 22m/s, 26m/s & 30m/s.
   Output Parameters = All goals and all results are inserted.
2. Running the simulation, we get the following results.

Results

• BASELINE SIMULATION:

Goal Name	Unit	Value	Averaged Value	Minimum Value	Maximum Value	Use In Convergence	Delta	Criteria
SG Av Total Pressure Outlet	[Pa]	2937645	3002310	2816078	3151638.32	Yes	187959.75	789972.7
SG Av Total Pressure Inlet	[Pa]	298255	311344.7	298255	324434.93	Yes	23872.64	7462.11
SG Mass Flow Rate Outlet	[kg/s]	-0.4892	-0.4892	-0.4892	-0.4892	Yes	1.79E-05	0.0049
SG Mass Flow Rate Inlet	[kg/s]	-4.1887	-4.4052	-4.6564	-4.1648	Yes	0.3607	0.5512

A) Cut plot for Pressure

B) Cut plot for Velocity

C) Flow Trajectories for Pressure

D)Flow Trajectories for Velocity

E)Plot for SG Av Total Pressure Inlet

F) Plot for SG Av Total Pressure Outlet

G) Plot for SG Mass Flow Rate Inlet

H) Plot for SG Mass Flow Rate Outlet

• PARAMETRIC STUDY: Table of various design points with various goals-

Goal	Design Point 1	Design Point 2	Design Point 3	Design Point 4	Design Point 5	Design Point 6
Velocity normal to face (Outlet Velocity 1) [m/s]	10	14	18	22	26	30
Environment pressure (Environment Pressure 1) [Pa]	101325	101325	101325	101325	101325	101325
SG Av Total Pressure Outlet [Pa]	2032861	5982077	1321818	1027223	1086635.19	995890.55
SG Av Total Pressure Inlet [Pa]	194570.5	665362.6	115928.8	114364.1	110036.04	125608.32
SG Mass Flow Rate Outlet [kg/s]	-0.4936	-0.692	-0.8904	-1.0888	-1.2867	-1.4803
SG Mass Flow Rate Inlet [kg/s]	-2.3353	-8.902	-0.3852	-0.2469	-0.0429	-0.3111
Pressure Ratio	10.44794	8.9907	11.40198	8.98204	9.875266	7.92855

Plots with various design points

• Goals SG Av Total Pressure Inlet (Value)

• Goals SG Av Total Pressure Outlet (Value)

• Goals SG Mass Flow Rate Inlet (Value)

• Goals SG Mass Flow Rate Outlet (Value)

• Pressure Ratio vs Mass Flow Rate (Outlet)

CASE 1: OUTLET VELOCITY = 10 m/s

A) Cut plot for Pressure

B) Cut plot for Velocity

C) Flow Trajectories for Pressure

D)Flow Trajectories for Velocity

CASE 2: OUTLET VELOCITY = 14 m/s

A) Cut plot for Pressure

B) Cut plot for Velocity

C) Flow Trajectories for Pressure

D)Flow Trajectories for Velocity

CASE 3: OUTLET VELOCITY = 18 m/s

A) Cut plot for Pressure

B) Cut plot for Velocity

C) Flow Trajectories for Pressure

D)Flow Trajectories for Velocity

CASE 4: OUTLET VELOCITY = 22 m/s

A) Cut plot for Pressure

B) Cut plot for Velocity

C) Flow Trajectories for Pressure

D)Flow Trajectories for Velocity

CASE 5: OUTLET VELOCITY = 26 m/s

A) Cut plot for Pressure

B) Cut plot for Velocity

C) Flow Trajectories for Pressure

D)Flow Trajectories for Velocity

CASE 6: OUTLET VELOCITY = 30 m/s

A) Cut plot for Pressure

B) Cut plot for Velocity

C) Flow Trajectories for Pressure

D)Flow Trajectories for Velocity

CONCLUSION: The following are observed during the analysis of the centrifugal pump:

1. From the plots 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. We also can see that the pressure ratio is high for low velocity and pressure ratio starts to decrease when the velocity increases. The negative sign indicates the flow of the fluid at the outlet port.
2. Inlet pressure remains the same for all the cases but the outlet pressure varies. When we comapre mass flow rate with the pressure ratio we can clearly see from the graph that it is inversly proportion, that is we can see that with the increase in mass flow rate the curve first rise and then it falls continously. We conclude that as an increase in mass flow rate, the pressure ratio value decreases upto certain limits after that pressure will become constant.
3. Here the variation is not linear as because the geometry of the centrifugal pump is not sketched with the standard centrifugal pump i.e. with dimensions and values. If the standard values are used, the resulted plot will be linear and accurate i.e. the pressure ratio will decrease in an increase in velocity at the outlet.