Introduction to Thermal Engineering Laboratory Assignment

Flow Rate Measurement and Calibration

The purpose of this laboratory exercise is to introduce you to different fluid flow rate measurement methods, associated experimental uncertainties and the calibration of orifice plate and venturi meters.

Experiment Specifications:

1. Turn on the pump and adjust the control valve on the hydraulic bench, the exit valve of the flow meter demonstration unit and the bleed valve on the manometer manifold to bleed off all air bubbles.

2. Conduct steady-flow experiments, for at least 8 different flow rates (indicated by the variable area flow meter) ranging between 5 and 15 L/min. Start at the highest flow rate. At each flowrate, record the collection time needed to collect 15L in the tank,as well as the eight manometer heights. To do this, close the drain valve at the bottom of the tank of the hydraulics bench. Collect 15 L of water in the tank as indicated by the upper sight scale in the side of the hydraulics bench and record the time required to do so.

3. Derive equations for the uncertainty and relative uncertainty of the indirectly measured volume flowrates using the volume collection method. Express the venturi and orifice meter ideal volume flowrates in terms of the appropriate manometer heights. 

4. For each measured flow rate, calculate and tabulate the volume flow rate given by Eq. (3), as well as the uncertainty and the relative uncertainty of the volume collection flow rate values. In the same table, include the ideal venturi and orifice meter flow rates given by Eq. (1). Note that the uncertainty of the variable area flowmeter measurements is a constant (5% of flow meter full scale).

5. On one graph, plot the volume collection volume flow rate   versus the ideal venturi and orifice meter volume flowrates. Include error bars for the volume collection values. Next, using appropriate trendlines in Excel, plot best fit curves that will allow you to determine the discharge coefficientsfor the venturi and orifice plate meters. Make sure you show the trendline equations and R2 values on the graph.  Think about your choice of the type of trendline (i.e. linear, power law, polynomial, etc.).  Often the theoretical model dictates the best type of trendline.

6. Using the Cd values determined in part 5, calculate and tabulate the corrected venturi and orifice plate meter flow rates. Evaluate the percentagedifference between the variable area, venturi and orifice meter flow rates, and the volume collection volume flow rates.

7. On a second graph, plot the flow rates determined by the three types of flow meters as a function of. Use the same scales for ordinate and abscissa and plot the results from all three methods on the same graph. Include a 45 degree line on the graph. Include error bars for the variable area flow meter vs. volume collection flow rate data.

8. Comment on the results. Which flow meter seems to be most accurate? How could the experimental uncertainties associated with the volume collection method be improved (hint: look at the relative uncertainty equation that you derived in part 3)? What types of applications is each type of flow meter (variable area, venturi, orifice meter) best suited for? What seem to be the pros and cons of each type of flow meter? Make sure you include and properly cite references that you consult.

Armfield Flowmeter Demonstration Unit Operating Procedure

Adapted from Armfield F1-21 Instruction Manual [1]

To operate the unit, please follow the instructions below.

1. Fully open the outlet flow control valve at the top left hand end of the apparatus.

2. Close the bench flow control valve then start the service pump by pressing the switch on the left hand side of the flow bench.

3. Gradually open the bench flow control valve and allow the pipework to fill with water until all air has been expelled from the pipework.

4. If you see air bubbles in the manometer tubes, do the following in order to bleed the air out:

a. Close both the bench flow control valve and the outlet flow control valve and open the air bleed screw.

b. Remove the small cap from the adjacent air inlet/outlet connection (make sure you don't lose it).

c. Connect a length of small bore tubing from the air valve to the volumetric tank.

d. Now, open the bench flow control valve and allow flow through the manometers to purge all air from them and to fill them up; you should see water coming out of the small tube that you just attached.

e. Now, tighten the air bleed screw and partly open both the bench valve and the outlet flow control valve.

f. Next, open the air bleed screw slightly to allow air to enter the top of the manometers, re-tighten the screw when the manometer levels reach mid height.

5. Gradually increase the volume flowrate until the variable area flowmeter indicates full scale or the maximum flowrate that you wish to achieve. You will need to adjust the bench flow control valve and the outlet flow control valve in combination to maintain all of the readings within the range of the manometers.

6. If the manometer pattern is too low on the manometers open the bench flow control valve to increase the static pressure. If the pattern is too high open the outlet flow control valve on the apparatus to reduce the static pressure.

7. The manometer levels can be adjusted further by using the air bleed screw and the hand pump supplied. The air bleed screw controls the air flow through the air valve, so when using the hand pump, the bleed screw must be open. To retain the hand pump pressure in the system, the screw must be closed after pumping.  If the levels in the manometer are too high then the hand pump can be used to pressurize the top manifold. All levels will decrease simultaneously but retain the appropriate differentials. If the levels are too low then the hand pump should be disconnected and the air bleed screw opened briefly to reduce the pressure in the top manifold. Alternatively the outlet flow control valve can be closed to raise the static pressure in the system which will raise all levels simultaneously.

8. Once you are satisfied with your starting manometer levels, use the bench flow control valve and the outlet flow control valve in combination to set the flow rate to the desired value as indicated by the variable area flowmeter.  Experiment by adjusting each valve very slightly to see what effect each has on the manometer heights and the flow rate.

9. Once the flow rate is at the desired value, lower the rubber ball check-valve in the tank and allow water to collect in the tank. Monitor the water level using the sight-glass on the side of the flow bench tank. Once the water level exceeds the zero mark, start a timer and record the time that it takes to collect the volume that was specified in your lab handout. Next record the manometer steady heights.

10. Repeat steps 8 and 9 for the next flowrates. You may wish to drain some of the water that accumulated in the tank by lifting the ball valve then lowering it back down once the sight-glass water level is back at a good starting level.

11. When you are done, slowly close the bench flow and outlet control valves, then switch off the service pump.

12. If you notice any significant leaks, obstructions or other problems, please make sure you notify your course instructor, TA and/or the lab manager.

Attachment:- Assignment.rar