Centrifugal pump design and analysis using Solidworks

AIM : To design and analyse a Centrifugal Pump.

OBJECTIVES :

1. To create a 3D model of a centrifugal Pump.
2. To obtain the relationship between Pressure ratio and mass flow rate using Performance diagram.

THEORY : Centrifugal Pumps are the most popular and commonly used type of pump for the transfer of fluids. In simple words, it is a pump that uses a rotating impeller to move water or other fluids by using centrifugal force. These are the undisputed pump choice especially for delivering liquid from one location to another in numerous industries including agriculture, municipal (water and wastewater plants), industrial, power generation plants, petroleum, mining, chemical, pharmaceutical, and many others. Centrifugal Pumps are useful since they can generally handle large quantities of fluids, provide very high flow rates (which may vary with the changes in the Total Dynamic Head (TDH) of the particular piping system) and have the ability to adjust their flow rates over a wide range. Centrifugal pumps are generally designed and suitable for liquids with a relatively low viscosity that pours like water or light oil. More viscous liquids such as 10 or 20 wt. oils at 68-70 deg F will require additional horsepower for centrifugal pumps to work. For viscous liquids of more than 30 wt. oils, positive displacement pumps are preferred over centrifugal pumps to help lower energy costs.

Working of a Centrifugal Pump - Let us understand in detail, how a Centrifugal pump works. Centrifugal pumps are used to induce flow or raise a liquid from a low level to a high level. These pumps work on a very simple mechanism. A centrifugal pump converts rotational energy, often from a motor, to energy in a moving fluid. The two main parts that are responsible for the conversion of energy are the impeller and the casing. The impeller is the rotating part of the pump and the casing is the airtight passage which surrounds the impeller. In a centrifugal pump, fluid enters into the casing, falls on the impeller blades at the eye of the impeller, and is whirled tangentially and radially outward until it leaves the impeller into the diffuser part of the casing. While passing through the impeller, the fluid is gaining both velocity and pressure.

The following chief factors affect the performance of a centrifugal pump and need to be considered while choosing a centrifugal pump:

• Working Fluid Viscosity – can be defined as resistance to shear when energy is applied. In general, a centrifugal pump is suitable for low viscosity fluids since the pumping action generates high liquid shear.

• Specific density and gravity of working fluid – The density of a fluid is its mass per unit of volume. A fluid’s mass per unit volume and gravity of a fluid is the ratio of a fluid’s density to the density of water. It directly affects the input power required to pump a particular liquid. If you are working with a fluid other than water, it is important to consider the specific density and gravity since the weight will have a direct effect on the amount of work performed by the pump.

• Operating temperature and pressure – Pumping conditions like temperature and pressures are an important consideration for any operation. For example - High-temperature pumping may require special gaskets, seals and mounting designs. Similarly, an adequately designed pressure retaining casing may be required for high-pressure conditions.

• Net Positive Suction Head (NPSH) and Cavitation – NPSH is a term that refers to the pressure of a fluid on the suction side of a pump to help determine if the pressure is high enough to avoid cavitation. Cavitation refers to the formation of bubbles or cavities in liquid, developed in areas of relatively low pressure around an impeller and can cause serious damage to the impeller and lead to decreased flow/pressure rates among other things. One must ensure that the system’s net positive suction head available (NPSHA) is greater than the pump’s net positive suction head required (NPSHR), with an appropriate safety margin.

• Vapour pressure of the working fluid – The vapor pressure of a fluid is the pressure, at a given temperature, at which a fluid will change to a vapor. It must be determined in order to avoid cavitation as well as bearing damage caused by dry running when the fluid has evaporated.

Owing to the use in the diverse range of applications, pumps come with different capacities and in various sizes. You should also consider the pressure and volume requirements of the specific operations for which you need the pump. The horsepower required is another important consideration when it comes to volume and discharge pressure.

Applications of Centrifugal Pumps - The fact that centrifugal pumps are the most popular choice for fluid movement makes them a strong contender for many applications and as mentioned previously, they are used across numerous industries. Supplying water, boosting pressure, pumping water for domestic requirements, assisting fire protection systems, hot water circulation, sewage drainage and regulating boiler water are among the most common applications. Outlined below are some of the major sectors that make use of these pumps:

• 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, petrochemical, 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 :

• Geometry Modelling of Pump -
• At first 3D model of the pump is made using ideas from the video. It comprises sketching of impeller,casing,inlet and outlet channels and a rotating extrusion for flow simulation.

• Flow Simulation Setup -
• After sketching, flow simulation was setup and lids were applied at the two open face of inlet and outlet passages. From wizard inputs were given as,
• Analysis Type: Internal,
• Type of fluid: Water,
• Type of flow: Laminar and Turbulant,
• Wall conditions: Adiabatic with 0 micrometer roughness,
• Initial conditions: Pressure(`101325 Pa`), Temperature(`293.2 K`), Velocity x-direction(`10 (m/s)`)
• Then it was run to observe results. Now to obtain the relationship between Pressure ratio and mass flow rate using Performance diagram, a parametric study was needed, so it was setup with initial conditions of varying velocity from `10(m/s)` to `70(m/s)` in `7` steps and outputs as required and was made to run.

RESULTS :

• Case 1 (For outlet velocity as `10m/s`)-
• Velocity Surface Flow Trajectory -

• Pressure Surface Flow Trajectory -

• Case 2 (For outlet velocity as `20m/s`)-
• Velocity Surface Flow Trajectory -

• Pressure Surface Flow Trajectory -

• Case 3 (For outlet velocity as `30m/s`)-
• Velocity Surface Flow Trajectory -

• Pressure Surface Flow Trajectory -

• Case 4 (For outlet velocity as `40m/s`)-
• Velocity Surface Flow Trajectory -

• Pressure Surface Flow Trajectory -

• Case 5 (For outlet velocity as `50m/s`)-
• Velocity Surface Flow Trajectory -

• Pressure Surface Flow Trajectory -

• Case 6 (For outlet velocity as `60m/s`)-
• Velocity Surface Flow Trajectory -

• Pressure Surface Flow Trajectory -

• Case 7 (For outlet velocity as `70m/s`)-
• Velocity Surface Flow Trajectory -

• Pressure Surface Flow Trajectory -

• Pressure Ratio = Pressure 1/Pressure 2,
• The negative sign in mass flow rate indicates that mass is leaving the control volume, and for performance curve it's been removed.
• Performance diagram between Pressure ratio and mass flow rate -

CONCLUSION :

1. It is clearly shown in the pressure and velocities flow trajectories that at inlet pressure is high and velocity is low and vice-versa at outlet.
2. From the performance diagram between Pressure ratio and mass flow rate, it can be concluded that as the pressure ratio increases, mass flow rate of water coming out from outet also increases and vice-versa and it helps in achieving the desired purpose of the pump as it pumps to a high pressure from low pressure and more amount of mass rate coming out from outlet.

REFERENCES :

https://www.powerzone.com/resources/glossary/centrifugal-pump