Centrifugal pump design and analysis

AIM :- Centrifugal Pump design and analysis

ABSTRACT :- In this project we will model a centrifugal pump in solidworks and then by applying proper boundary conditions flow simulation is analysed. We will study pump behaviour for different conditions and understand the relation between pressure ratio & mass flow rate.

INTRODUCTION:-

1. Centrifugal Pump –

Centrifugal pump is a hydraulic machine which converts mechanical energy into hydraulic energy by the use of centrifugal force acting on the fluid. These are the most popular and commonly used type of pumps for the transfer of fluids from low level to high level. When a certain mass of liquid is made to rotate by an external source, it is thrown away from the centrifugal axis of rotation and a head is impressed which enables it to rise to a higher level. Centrifugal Pumps can be used for viscous and non-viscous liquids and has higher efficiency.

2. Main Components of a CENTRIFUGAL PUMP –

• 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. It is mainly of 3 types –
  • Open Impeller
  • Semi-enclosed Impeller
  • Enclosed Impeller

• Casing – The casing of a centrifugal pumpis an air tight passage surrounding the impeller and designed in such a way that kinematic energy of water discharged at outlet of impeller is converted to pressure energy before leaves the casing. It is a spiral type in which area of flow increase gradually.

Commonly three types of casing are used in centrifugal pump-

• Volute Casing
• Vortex Casing
• Casing with Guide Blades

• 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 & 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.

3. Working- The first step in the operation of a centrifugal pump is priming. Priming is the operation in which suction pipe casing of the pump and the position of fluid with the liquid which is to be pumped so that all the air from the position of pump is driven out and no air is left. The necessity of priming of a centrifugal pump is due to the fact that the pressure generated at the centrifugal pump impeller is directly proportional to density of fluid that is in contact with it.

After the pump is primed the delivery valve is still kept closed and electric motor is started to rotate the impeller. The delivery valve is kept closed in order to reduce valve is opened the liquid is made to flow in an outward radial direction there by vanes of impeller at the outer circumference with high velocity at outer circumference due to centrifugal action vacuum is created.

This cause liquid from sump to rush through suction pipe to eye of impeller thereby replacing long discharge from centre circumference of the impeller is utilized in lifting liquid to required height through delivery pipe.

4. Terms –

• Pressure Ratio :- The ratio of the discharge pressure to the inlet pressure is called the pressure ratio.

Pressure ratio = Inlet Pressure/ Outlet Pressure

• Mass flow rate :- Mass Flow Rate is the mass of a substance that is passed through any cross-sectional area per unit of time.

• BEP :- BEP stands for Best Efficiency Point. It is the point at which the pump operates at peak efficiency. At the BEP, flow enters and leaves the pump with a minimum amount of flow separation, turbulence, and other losses.

5. Applications of a Centrifugal Pump –

• Oil & Energy – pumping crude oil, slurry, mud; used by refineries, power generation plants
• Industrial & Fire Protection Industry – Heating and ventilation, boiler feed applications, air conditioning, pressure boosting, fire protection sprinkler systems.
• Waste Management, Agriculture & Manufacturing – Wastewater processing plants, municipal industry, drainage, gas processing, irrigation, and flood protection
• Pharmaceutical, Chemical & Food Industries – paints, hydrocarbons, petro-chemical, cellulose, sugar refining, food and beverage production
• Various industries (Manufacturing, Industrial, Chemicals, Pharmaceutical, Food Production, Aerospace etc.) – for the purposes of cryogenics and refrigerants.

PROCEDURE :-

• Model generation –

Creation of a hypothetical model of centrifugal pump.

Make the eye of an impeller in sketch section using circle command.

Make the impeller blades by using curve & rotating pattern command. Now, extrude this sketch.

Create casing, covering the impeller & extrude it remembering to uncheck the merge results option.

Create the suction & delivery tube of the pump.

Now, using direct editing option add the casing, suction tube & delivery tube to make it a single unit.

fig:- 3D CAD Model

2.) Flow Simulation –

i.) To carry-out the flow simulation we must make the fig as a controlled volume. Therefore, we use create lid option to close the suction tube and delivery tube.

ii.) Meshing in Solidworks is not that much efficient to rotate/ deform the mesh with rotation of impeller. Therefore, we use moving reference frame approach to simulate the flow.

In this approach we will make reference frame that encloses the impeller as well as surrounding flow completely without touching the casing. The flow outside the impeller region is defined as stationary frame. The interface between these two reference frames is assumed to have steady-state flow conditions, i.e. the interface serves as a surface of revolution, distinguishing the two reference frames.

For the stationary frame, mass, momentum, energy and other equations are solved, while fluid acceleration in moving frame is defined using relative velocity of rotating and stationary frame. The acceleration terms in the moving frame is used to modify the convection and source terms in the momentum equations.

iii.) Create a new project with the parameters given below-

S.No.	Parameter	Condition
1.)	Unit system	MKS or S.I.
2.)	Analysis type	internal
3.)	Physical feature	Rotation [type – Local region(s) (averaging)
4.)	Fluid	Water
5.)	Flow type	Laminar & turbulent
6.)	Cavitation	No

iv.) Define Boundary conditions –

• At inlet (suction tube) – Environment pressure (P = 101325 Pa.,T = 293.2 K)
• At outlet (delivery tube) – Outlet velocity absolute (v = 10m/s.)

v.) Insert rotating region & select it as a reference frame.

vi.) Enter angular velocity as 1000 rad./sec.

vii.) Set iteration = 500 and uncheck all options under calculation control option.

viii.) select grid refinement in between 3-7. Also check the advance channel refinement box.

ix.) insert Goals –

• Surface goal – surface avg. total pressure (at outlet lid).
• Global goal – Avg. mass flow rate.

x.) All set, run the simulation.

3.) Parametric Study – It is necessary to get pump performance curve.

Create new parametric study.

Add boundary condition velocity ( ranging- 10 to 30 with 5 values in between) as input simulation parameters.

Select total avg. pressure at outlet and avg. mass flow rate as output parameters.

In scenario we get 5 different design points.

Run the simulation for all the design points.

RESULTS :-

a.) Solver result:

b.) Pressure & mass flow rate variation :

c.) velocity contour :

fig. - Velocity_contour

d.) Pressure contour

fig. - Pressure_contour

e.) Flow Trajectories :-

f.) Parametric study result :-

S.No.	Design Point	Outlet Velocity (m/s)	Inlet Pressure (Pa.)	Average outlet Pressure [Pa]	Mass Flow Rate [kg/s]	Pressure Ratio
1	Design Point 1	10	101325	3908903	6.39139	38.5778728
2	Design Point 2	15	101325	3912799	7.245719	38.6163253
3	Design Point 3	20	101325	9525290	14.26706	94.007299
4	Design Point 4	25	101325	6053523	10.47103	59.7436266
5	Design Point 5	30	101325	5055362	10.05827	49.8925448

Performance Curve :-

CONCLUSION :-

• On increasing the outlet velocity , initially the flow becomes unstable , after some point it stabalizes & obtains max. total pressure (9525290 Pa.) and max. mass flow rate(14.26706 Kg/s) at its critical point and then decreases again and finally becomes almost constant.
• It is not the perfect performance curve as pump geometry is madeup geometry. But it still shows the parabolic performance curve (like that of an ideal curve).