TAM335 Lab 6 Partial Report

Laboratory setup is shown in the image above. The purpose of this manual is to calibrate bulk-flow measuring devices including the Venturi flowmeter, orifice-plate flowmeter, and the paddlewheel flowmeter. The Venturi and orifice-plate flowmeters are referred to as the "hydraulic" devices.

The key to the symbols of the laboratory setup above is given here.

The internal mechanisms of the Venturi and orifice-plate flowmeters are shown here in this diagram. Notice how these devices run on a pressure transducer, meaning they rely on electronics to function.

There might be air trapped within the pipes, this can alter the readings of the manometer displacement. This might be the problem if the manometer is reading out a pressure difference when there is no flow within the pipe. To fix this problem, try opening the valve to drain out some of the water within the manometer setup, this also allows entrapped air to escape.

Data for all flowmeters are read and collected through LabVIEW software. Make sure the flowmeters are set to zero when no flow is being discharged through the pipe. To calibrate the pressure transducers connected to the hydraulic flowmeters, use the valve to induce pressure differences across the transducers, this data will be processed by LabVIEW and should produce a linear relationship between output voltage and pressure difference.

To collect data from the flowmeters, establish the maximum flowrate in the pipe, and record voltage readings for descending flowrates. This data should be automatically processed by LabVIEW. When taking voltage readings from the flowmeters, make sure the readings are stable, the stability of manometer displacement can also be used a reference for when data can be collected. For every flowrate tested, obtain a direct measurement with the "weight-time" method. This measures the amount of time it takes for an accumulated amount of fluid from the flow to balance out a certain amount of weight.

The output of the transducer is only useful if the relationship between the voltage reading and the observed flowrate exhibits a stable, monotonic relationship. The observed output for the manometer displacement against the flowrate is shown here. According to theory, the relationship between the manometer displacement and the volumetric flow rate Q, is non-linear, namely, the flow rate Q is proportional to the square root of the manometer displacement. While these diagrams imply that the power relation holds true, the exact power is 0.6056. This disparity is likely caused from the loss of energy due to friction and viscous forces, from the which the theory given by Bernoulli's equation assumes negligible. (LRQ1)(LRQ2)

The relationship between Reynolds number and the discharge coefficient is somewhat proportional, as shown. This is also a useful output, as the relationship is definitely stable. However, these values are much lower that the theoretical ideal value of unity as derived. A more accurate measure of the discharge coefficient can be given through the consideration of viscous and friction forces, as they affect the pressure distribution within the pipe, altering the mass flow rate. The discharge coefficient is the ratio of the actual discharge to the ideal discharge. (LRQ5)(LRQ9)

The paddlewheel flowmeter is a "lo-flo" device, which means if operates within a specific range of fluid velocities, specifically, 0.3-20 ft/s. Very useful data can be collected from the paddlewheel flowmeter when testing within this range of velocities. As shown in the graph, the output voltage of the paddlewheel flowmeter exhibits a strong and stable linear relationship with the observed flow rate. During the collection of this data, we did not approach cutoff velocities, the lowest velocity being 0.639 m/s, or 2.09645669 ft/s, and the highest velocity being 3.209 m/s, or 10.5282152 ft/s, well within its range of operation. While the given example demonstrates accurate readings throughout, keep in mind that the paddlewheel flowmeter operates more effectively toward the high end of its velocity range. Low flow rates contain more inconsistencies which could be detrimental to the accuracy of the paddlewheel flowmeter. (LRQ6)(LRQ11)