CENTRIFUGAL PUMP DESIGN AND ANALYSIS (using SOLIDWORKS)

AIM:

To obtain the relationship between Pressure Ratio and Mass flow rate of the volute of a centrifugal pump using SOLIDWORKS

OBJECTIVE:

1. To understand the working principle the volute of suction pump
2. To derive the relationship as mentioned in the aim of the experiment
3. To understand the working of flow simulation in 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.

Volute:

A volute is a curved funnel that increases in area as it approaches the discharge port. The volute of a centrifugal pump is the casing that receives the fluid being pumped by the impeller, maintaining the velocity of the fluid through to the diffuser. As liquid exits the impeller it has high kinetic energy and the volute directs this flow through to the discharge. As the fluid travels along the volute it is joined by more and more fluid exiting the impeller but, as the cross sectional area of the volute increases, the velocity is maintained if the pump is running close to the design point. If the pump has a low flow rate then the velocity will decrease across the volute leading to a pressure rise causing a cross thrust across the impeller that we see as vibration. If the pump flow is higher than design the velocity will increase across the volute and the pressure will decrease according to the first law of thermodynamics. This will cause a side thrust in the opposite direction to that caused by low flow but the result is the same - vibration with resultant short bearing and seal life.

The volute does not convert kinetic energy into pressure - that is done at the diffuser by reducing liquid velocity while increasing pressure.

FORMULAS USED:

Bernoulli's Equation:

Bernoulli's Equation is not directly used here but to get the results from the graph, the formula is necessary.

Between two points, Bernoulli's equation can be stated as follows:

`(P1−P2)=ρ/144[(Z2−Z1)+((v2)^2−(v1)^2)/(2g)+H_L]`

where `P` = pressure,

`rho` = density of fluid,

`Z` = elevation of the fluid measured from a reference plane,

`v` = velocity of fluid at that point,

`H_L` = head loss between the upstream and downstream locations,

`g` = acceleration due to gravity

Pressure Ratio = Outlet Total Pressure `/` Inlet Total Pressure

PROCEDURE OF COMPLETION:

1. First, a simple volute was designed with the rotor diameter = `50mm` and width `20m` having `8` rotor blades.
2. Then, the outer casing was made of width `35mm` and the inlet pipe of length `150mm` was made.
3. Then, the outlet pipe of two different circular endings was made with diameters `25mm` and `54.86mm` using lofting tool.
4. Then, another solid was made inside the casing big enough to engulf the rotor for making it the rotating region.
5. Then, flow simulation is created with cancelling out the 'made-to be' roating region from the component control. Then, the rotating region is rotated with 1000 rad/s.
6. Then, boundary condition as environmental pressure of `1` bar and outlet velocity as `10` m/s was provided.
7. Then, a paramtreic study was done with velocities `20` m/s, `30` m/s, `40` m/s, `50` m/s, `60` m/s.

The region is not visible as it has been made to transparent one.

OBSERVATIONS:

The region of velocity-flow is as follows:

The region of pressure-flow is as follows:

The flow trajectory is as follows:

https://youtu.be/vqKnHxJ4BRI

The performance table is as follows:

The pressure ratio was calulated using MATLAB. The script file is as follows:

%% CALCULATION OF PRESSURE RATIO AND MASS FLOW RATE
% 
clear all;
clc;

%% CALCULATION AND PLOTTING
% initialization of variables
% outlet pressure
outlet_p = [1704567.85	832468.83	6457707.70	1.41e+07	2.61e+07	4.09e+07];

% mass flow rate
mass_fr = [19.8170	39.6290	59.4261	79.2047	98.9362	118.6101];

% inlet pressure
inlet_p = 101325;

% calculation
ratio = outlet_p./inlet_p;

% ploting
hold on;
plot(mass_fr, ratio, 'ro-', 'markersize',5,'markerfacecolor','r');
xlabel('Mass flow rate(kg/s)','fontsize',15);
ylabel('Pressure Ratio','fontsize',15);
title('Pressure Ratio vs Mass flow rate','fontsize',15);
grid on;

The graph is as follows:

CONCLUSIONS:

1. The pressure ratio increases as the mass flow rate increases which is trivial. It tends to increase in a parabolic trend which satisfies in regards with the Bernoulli's Equation.
2. The mass flow rate is negative in the table as the mass flows out from the outlet.
3. From the cut-plot of pressure flow, it can be concluded that the static pressure of the fluid actually increases from inlet to outlet.
4. From the velocity cut-plot, it can be concluded that velocity decreases from inlet to outlet.