1.        Objectives:

1.    to measure the performance characteristics of a rotodynamic pump at different rotational speed

2.    to test the validity of the Affinity scaling laws;

The main performance characteristics of a pump are:

•         Head vs discharge (H vs Q).

•         Input power vs discharge (P vs Q).

•         Efficiency vs discharge (η vs Q).

2.        Introduction:

Pumps fall into two main categories: positive displacement pumps and rotodynamic pumps. In a positive displacement pump, a fixed volume of fluid is forced from one chamber into another. The centrifugal pump is, by contrast, a rotodynamic machine. Rotodynamic (or simply dynamic) pumps impart momentum to a fluid, which then causes the fluid to move into the delivery chamber or outlet. Turbines and centrifugal pumps all fall into this category. Centrifugal pumps are widely used in industrial and domestic situations. Due to the characteristics of this type of pump, the most suitable applications are those where the process liquid is free of debris, where a relatively small head change is required, and where a single operating capacity or a narrow range of capacities is required. The general design is usually simple with few mechanical parts to fail, however, and it is possible to operate a centrifugal pump outside ideal parameters while maintaining good reliability. The centrifugal pump converts energy supplied from a motor or turbine, first into kinetic energy and then into potential energy. The motor driving the impeller imparts angular velocity to the impeller. The impeller vanes then transfer this kinetic energy to the fluid passing into the center of the impeller by spinning the fluid, which travels outwards along the vanes to the impeller casing at increasing flow rate. This kinetic energy is then converted into potential energy (in the form of an increase in head) by the impeller casing (a volute or a circular casing fitted with diffuser vanes) which provides a resistance to the flow created by the impeller, and hence decelerates the fluid. The fluid decelerates again in the outlet pipe. As the mass flow rate remains constant, this decrease in velocity produces a corresponding increase in pressure as described by Bernoulli’s equation.

3.        Theory and Analysis:

Transport of fluid through closed conduit is a common feature in most industries. It may be necessary to move a liquid against gravity force i.e. into a pressure vessel; or pump it out from a vessel under vacuum as in the case of evaporators. In all these cases, there will be additional loss of energy due to friction as the liquid flows through conduits, fittings and valves. To ensure fluid movement, energy has to be supplied to fluid from an external source. The centrifugal pumps are the most widely used in chemical industries. It has many advantages. It is simple to operate, gives a uniform flow rate, occupies small floor space and has low maintenance cost. It can be used either with a motor or with turbine drive. The capacity of the pump is defined as the volume of the fluid handled per unit time. For incompressible fluids it is given in liter per minute. For compressible fluids, the capacity is given at the inlet temperature and pressure of the fluid. The total head is the energy added by the pump to unit weight of the flowing stream. The head is expressed in units of length. For a steady incompressible flow the total head H is given by,

where point 1 is taken as any point before pump on the suction line and point 2 is any point on the delivery line. Theoretical energy supplied is given by the product (multiplication) of capacity per unit time expressed as kg/ s, the total head, H expressed in meter; and g accelerations due to gravity in m/s2. Efficiency is the ratio of theoretical energy to the actual energy measured by a watt meter. The operating characteristics of a pump are shown by plotting the head developed H, the power supplied W ((T*ω) torque in N.m x rotational speed rad/sec) and the efficiency against the flow rate Q. The optimum conditions for operating a pump are at the conditions of Best Efficiency Point (BEP).

4.        Description of Experimental Setup and Instrumentation:

4.1         The main components of the experimental setup are:

·         Centrifugal Pump.

·         D. C. Motor.

4.2         Instrumentation:

·         RPM Meter.

·         Magneto Flow Meter.

·         Torque Meter.

·         Pressure Gauges.

5.        Test Conditions and Experimental Procedure:

5.1         Precautions:

1.      Keep rpm regulator at zero before starting the pump.

2.      Piping at the inlet must not be closed, when the pump is switched on.

3.      The pump must not run dry, it has to be flooded with water during the whole experiment. Therefore, before switching on the main switch of the control panel, sufficient liquid level in the storage tank must be verified.

4.      Never shut off delivery valve more than a minute.

5.2         Procedure:

1.      Check that all valves of the experimental setup are fully open.

2.      Fill the storage tank with liquid. Switch on the pump and operate it at selected value of RPM.

3.      By operating the valve on the delivery line note down the pressure at fully open and shutoff condition of valve.

4.      Take seven to eight points at least between this pressure and flow capacity ranges for experiment.

5.      For particular set of capacity, note down the pressure gauge’s readings.

6.      Also, note down the readings of the torque meter.

7.      Repeat the experiment for different positions of delivery capacity.

8.      Repeat experiment for different value of RPM.

6.        Results:

Record calculated results on the attached summary results sheets following the recorded measured data tables.

plot the following:

·         H - Q curve at different rotational speeds.

·         η - Q curve at different rotational speeds.

·         I - Q curve at different rotational speeds.

7.        Discussions:

Examine and describe the shapes of the graphs obtained, relating this to the changing performance of the pump as the flow rate changes. Locate the point of maximum efficiency and the flow rate at which it occurs. Verify the applicability of the Affinity scaling laws on the obtained results at different rpm

8.        References:

·         List all references you might have used.

9.        Tables of Experimental Data and  Results Summary:

The experimental data of the Test should fill in the following table.

Table 1 The experimental data of Test.

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