ENGIN3502 - Subsurface Environmental Engineering Assignment

Assignment Task

Experiment 1: Duct resistance and fan Power

Aim:

1. To show how to find the duct resistance and fan characteristics, and to show how they affect airflow

2. To prove the power law for a fan

Procedure:

1. We are using the data acquisition software VDAS. Start the software and select fan experiments. This software will create a results table for you automatically when you take readings, but you must remember to hit record results to record the results on the computer.

2. Connect the pipework as shown in Figure 1.

Figure 1: Pipe connections for fan experiments.

3. Use the button on the pressure display to zero all pressure readings and record the local ambient pressure (from p4 of the display. Using VDAS the software will record the pressures for you.

4. Make sure the slide valve is fully opened (pushed from the front), to give no flow restriction.

5. Press the start button of the Motor Drive and run the speed to maximum. Adjust the speed to give an inlet pressure of a whole number. Record the speed, shaft powers and pressures.

6. Reduce the speed to reduce the inlet pressure in intervals of 10 Pa until it reaches atmospheric (no flow). At each interval record the speed, shaft powers and pressures.

7. Repeat the experiment for slide valve positions of 80%, 60%, 40% and 20%. (for slide valve positions of 60% and lower, adjust the speed more carefully to give pressure intervals of 2Pa for better results)

Results Analysis

1. From your results, find the volumetric flow rate and the fan air power to complete your results.

2. On one chart (graph) plot the curve for each slide valve position. Plot on a chart that has volumetric flow rate as its x axis and pressure drop along the duct (across the fan) as the y axis.

3. From the results of any one slide valve position, plot a curve of fan shaft power (y axis) against fan speeds (x axis) to prove the power law for a fan.

Experiment 2: Fan Characteristics

1. Create a blank table of results in the computer software package VDAS

2. Connect the pipework as shown in Figure 1

3. Use the button on the pressure display to zero all pressure readings and record the local ambient pressure (from p4 of the display. Using VDAS the software will record the pressures for you.

4. Make sure the slide valve is fully opened (pushed from the front), to give no flow
restriction.

5. Press the start button of the Motor Drive and run the speed to maximum. Adjust the speed to give an inlet pressure of a whole number. Record the speed, shaft powers and pressures.

6. Shut the slide valve to reduce the inlet pressure in intervals of 10 Pa until it reaches atmospheric (no flow). At each interval record the speed, shaft powers and pressures.

7. Repeat the experiment for at least five other speeds, equally spaced, suggestions are approximately 2600 rpm, 2300 rpm, 2000 rpm, 1700 rpm and 1400 rpm. To get a reasonable number of results to plot a suggestion is to adjust the slide valve to give pressure intervals of 2 Pa.

Results Analysis

1. From your results, find the volumetric flow rate and the fan air power to complete your results.

2. On one chart (graph) plot the curve for each fan speed. Plot on a chart that has volumetric flow rate as its x axis and pressure drop along the duct (across the fan) as the y-axis.

3. Mark on your curves the point of maximum efficiency for each flow rate and draw a best fit line through your points, this is also known as the head against flow efficiency.

4. Add the duct resistance curves from experiment 1 and fan characteristic curves from experiment 2 on one chart. The operating points are where the two curves cross.

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