Lab 6 Partial

The purpose of this instructable is to demonstrate how one goes about the process of calibrating three bulk-flow measuring devices: Venturi meters, orifice-plate meters, and a paddlewheel flowmeter. This is completed by finding their flow coefficients with their respective functions of the flow rate, Q, in terms of the Reynolds number. The rest of this experiment requires a comparison with the coefficients obtained, here, and their ISO published values.

The above images illustrate the devices needed for the calibration in this experiment: Venturi and orifice-plate meter. Both devices use a pressure transducer and a differential manometer to obtain pressure differences. These flow meters measure the pressure at different locations and are represented in both images respectively. The voltage output is found with the paddlewheel flowmeter that is connected to a transmitter. A weighing tank and the weight-time method will also be used as the standard for calibration. LabView will be used for data acquisition (flow coefficients, spreadsheets, etc.).

As a new engineer here, you must do these things first prior to starting the procedure:

You should first check that the discharge valve is closed and that the levels of mercury in the manometer are equal. Adjust accordingly.

Zero the transducer output, as well, and take the readings of the transducer outputs and manometer levels. It is located next to the computer where you can zero the VFn interface box. Then reduce the pressure in the manometer by opening the bleed sleeve labeled "CAL VALVE" Use LabView to record readings off of the transducer and manometer in volts and centimeters; the maximum voltage should not be greater than 10 volts

LabView's linear least-squares analysis will have its slopes and intercepts stored for the procedure.

Lastly, make sure to close the "CAL VALVE."

Below are the steps that you must complete for accurate data acquisition for the experiment. It's step-by-step, so I hope it helps :)

1. You must check that the Gain Adjust control on paddle meter is set to 6.25 turns for P1 and P4.
2. For P3 it should be set to 3 turns.
3. Then, zero the paddlewheel output using the Zero Adjust control.
4. Now, you can open discharge valve slowly until the desired manometer deflection is obtained.
5. As soon as the paddlewheel voltage value is nonzero and significant, record both the differential pressure voltage and the paddlewheel voltage.
6. When max flow rate is reached, record the manometer levels and the paddlewheel readings
7. Then obtain weight-time measurement
8. At this point, you should use the time-averaged pressure transducer voltages provided by LabView, and remember the maximum manometer deflection
9. Repeat the procedure described above 4 more times for a total of 5 data sets

Note: LabView should provide the flow coefficient as a function of flow rate expressed in terms of the Reynolds Number, with the paddlewheel readings on a spreadsheet

All of your work has culminated into these two graphs!

The graph on the left shows the flow rate as a function of deflection using linear scales. But, it's important to show the graph with logarithmic scales, too. That's the graph on the right; it plots with the same variables. The left graph's curve becomes the calibration curve for the flowmeter during analysis. The data is very close to the line of best fit on the right graph, which hints that a power-law relationship may exist, here. In fact, the power-law relationship applies because the flow rate was also lowered from the percentage and max height values from the experiment.

The discharge coefficient should be calculate in LabVIEW using the equation in the image above. The LabVIEW should calculate it on its own, but in any case, V is velocity of flow, D is pipe diameter, and v is the viscosity of the water.

The best fit line shown on this graph is the calibration curve for the paddlewheel flowmeter. The rising cutoff is where flow rate hits 0.004m³/s, with velocity calculated as V = Q/A (4in. pipe diameter) at 0.633m/s. The falling cutoff flow rate was 0.021m³/s with a velocity of 3.25m/s (max velocity).

Now that you've finished the experiment, let's reflect.

The discharge coefficient is relatively constant (around 0.6). That is a bit far from the ideal value of discharge coefficient being 1 - about halfway. But, there could be ways to correct it for next time. An assumption made in the experiment what that the calculations for discharge took a perfectly conserved mass equation. More realistic values could take into consideration fluid loss. Without that, your discharge values might be skewered. Another error to fix would come from the manometers, as they do not stabilize around a point, but oscillate.

The paddlewheel is relatively accurate, but only for a range. It has to have enough of a voltage to read the flow rate, but must be under about 10 volts before it starts reading lots of noise. In the graph, the points deviate a bit from the line of best fit at the higher and lower voltages. That being said, R^2 is at about 0.991, which indicates that the line of best fit is fitting, and the paddlewheel measurements were fairly accurate. But, it's important to remember that there is an ideal range for the paddlewheel.