Calibration of Flowmeters

The objective of this experiment is to calibrate flow measuring devices that rely on measurements of pressure change. Different instruments used throughout this lab include the Venturi meters and orifice-plate meters. Using these devices, you will obtain experimental coefficients and compare them with ISO published values from similar devices. Lastly, a paddlewheel flowmeter, a device that provides an electical output signal used for process monitoring and control, will also be calibrated.

1. Hydraulic Flowmeter (Venturi meter)
2. Mercury-water differential manometer
3. Paddlewheel Flowmeter (orifice-plate meter)
4. Signet 3-8511-P0 device
5. Validyne Pressure Transducer

1. To begin the experiment, you will want to check that the discharge valve is close and that levels of mercury connected to the Venturi meter are at equal levels.
2. If they are not, slowly open and close the two manometer drain valves until both mercury levels are equal.

1. Begin by zeroing the Validyne differential pressure transducer output on the VFn interface box located next to the computer.
2. Reduce the pressure artificially in one of the manometer lines by opening the manometer bleed valve and take readings of the transducer output and manometer level using LabVIEW software on the computer.
3. Take data points from zero pressure differential to the maximum pressure differential possible with the bleed valve fully open.
4. Generally 5 data points are used during this range. Make sure that discharge valve is closed during the entirety of this step.

1. To acquire data from paddlewheel, first check that gain adjust control of the paddlewheel flowmeter is set to 6.25 turns for P1 and P4, and is set to 3.00 turns for P3.

1. After preparing the the paddlewheel flowmeter, open the discharge valve slowly until either the valve is fully open, or the allowable manometer deflection is reached.
2. Observe the Validyne pressure reading and paddlewheel voltage reading as the flow is increased and record both readings at the instant when the paddlwheel voltage takes on a significant nonzero value.
3. At the maximum flow rate, record the manometer readings, record the paddlewheel flowmeter readings, take a weight-time measurement, and, using LabVIEW software, record the average time presure-transducer voltage. Also make a note of the maximum manometer deflection.
4. Repeat the procedure at successively slow flow rates so that that total manometer deflections decrease at close to equal intervals (10%)^2 and that that flow rates approximately decrease 10% each trial.
5. For each flow rate, wait until the mercury in the manometer is steady before acquiring data.
6. Acquire 10 data sets, the flow coefficient Cd which is displayed in LabView as a function of the flow rate expressed in terms of the Reynold number Re, and the paddlewheel flowmeter recording with flow rate Q.

Question #1 -

Fig. 1. Manometer deflection vs flow rate (linear scale).

This is a plot for measured flow rates Q as a function of the manometer deflection in the experiment.

Question #2 -

Fig. 2. Manometer deflection vs flow rate (logarithmic scale).

The data does appear to fall along a straight line using logarithmic scales and the power-law relationship of the type Q=k(Δh)^m would be square root relationship where m = 0.5485 ≈ 0.5.

Question #5 -

Fig. 3. ISO discharge coefficient curves for an orifice-plate flowmeter.

Fig. 4. Discharge coefficient vs Reynolds number.

Plotting the discharge coefficient Cd as a function of the Reynolds number Re for the orifice plate flowmeter on linear-log scale, it is evident that the shape of the curve is very similar to Figure 3 for beta β = 50.8mm/102.3mm = 0.5. Both curve have a similar Cd value of 0.60 at a Reynold Number Re = 10^5. After that point, both curves become stagnant and straighten out.

Question #6 -

Fig. 5. Paddlewheel voltage vs flowrate.

Looking at our calibration curve for the paddlewheel flowmeter, the falling cutoff value rate is V = 0V given by the y-intercept 0.0001 ≈ 0m^3/s indicating that the paddlewheel would appear to be motionless. The rising cutoff value for a maximum voltage V = 10V from the paddlewheel transmitter would be Q = 0.0369m^3/s. The maximum fluid velocity achieved in the experiment was 0.02062m^3/s from a voltage V = 3.238.

Question #9 -

The discharge coefficient Cd is essentially constant over the range of Reynold numbers tested. The value of Cd range from 0.44 < Cd < 0.64 with 8 out of the 10 values being between 0.60 and 0.64. These values are not close to ideal because our expirement does not take into consideration the energy in the system. Instead when using the Bernolli equation, we should apply the Reynold's Transport Theorem in order to factor energy into our data.

Question #11 -

The paddlewheel flowmeter is reliable however can be inaccurate at very low or high flow rates. At low flow rates, the paddlewheel is more susceptible to friction resulting in inaccurate data. At high flow rates, there is turbulence impacting the streamlines in the paddlewheel resulting in opposing force affecting our data results.