Lab 6 Partial Report TAM335 - Calibration of a Flowmeter

This experiment aims to calibrate flowmeters that use electrical output signals and pressure changes to detect flow. This experiment tests a paddlewheel flowmeter with a hydraulic flowmeter (Venturi or orifice type).

Objectives are: measuring flowrate using weight-time method, relating a flow rate to manometer pressure difference, determining the discharge coefficient for the flowmeter, and determining proportionality of paddlewheel voltage to flow rate.

The supplies required for the objectives listed are:

1. Venturi or orifice plate hydraulic flowmeter
2. Mercury-water differential manometer
3. Differential pressure transducer
4. Paddlewheel flowmeter
5. Water supply
6. Discharge control valve
7. Weighing tank and scale
8. Timer
9. LabVIEW

Before collecting data, ensure the flow system is operating properly. Water starts to flow down the pipe and into the weighing tank when the discharge valve is gradually opened. Before taking any measurements, the flow should be steady. Wait until the manometer levels stabilize before taking readings if they fluctuate too much.

The weight time method is the standard measurement of the flow rate. Water fills the weighing tank. Using a known weight of water, the time that it takes to fill to that weight is measured. The flow rate is calculated using the density of water.

Pressure will drop as fluid flows through the restricted area of the hydraulic flowmeter. This difference in pressure is measured using the mercury manometer. The difference is used to relate the pressure drop to the flow rate.

As water flows through the pipe with the paddlewheel, the rotational speed is converted into an outputted voltage. For this experiment, the voltage and flow rate is recorded.

Multiple flow rates are tested to find different values of pressure difference in the manometer as well as paddlewheel voltage.

The data found is shown in the image. Data should be taken from the labview software and put into a plotting software to create graphs.

A calibration curve was created by plotting flow rate versus manometer deflection. There is a relationship between the two values that is non-linear but that shows that as the pressure difference increases, the flow rate also increases. The curve found can be used to allow the flowmeter to be used as a calibrated device for measuring flow rate.

There seems to be some power law relation occuring but it may not be representative to a theoretical power law exactly.

The discharge coefficient ranges from approx. .28 to .73. A perfect coefficient would be equal to 1 but there are things like friction, turbulence, and non-ideal velocities to consider. A higher more stable coefficient is produced at higher flow rates, indicating higher reliability of the flowmeter.

There is a strong linear relationship between voltage and flow rate, meaning the paddlewheel flowmeter is accurate and functioning properly, even at the lowest or highest rates tested. A cuttoff flowrate that would make the wheel stop rotating may not have been found.

As stated earlier, the discharge coefficient becomes more stable at higher flow rates, so it is not perfectly constant. This shows that flowmeter theory may become more applicable at higher flowrates.

The paddlewheel, from this experiment, is shown to be reliable, and theory supports that it should be reliable at higher flowrates, due to low flowrates not engaging the paddle fully.