Flowmeter Calibration

Hello! Since I have been promoted from my position, I would like to prepare you for the daily task that will now be your responsibility. The task is to calibrate the Flowmeter. I will be providing a step-by-step guide below on how to calibrate it since it is crucial for measuring flow rates of a liquid. The two pieces of equipment you need to be familiarized with is the hydraulic flowmeter and a paddle flowmeter. I have provided examples and data to help you thoroughly understand this procedure. Good luck!

You must first understand the equipment we are working with in this experiment. The hydraulic flowmeter measures the pressure differences between two different area sections of a pipe using a manometer. These two sections will have varying flow speeds due to their cross-sectional area. We can determine the flow rate from the pressure difference produced by the manometer. There are two methods of collecting this data, one is using the Venturi meter which is a smaller section of pipe. The other method is the orifice-plate meter which uses two plates to create a smaller area in which pressure difference can be measured.

The other piece of equipment is the paddle flowmeter. This is a device that is placed in flowing water and rotates with the flow. The flow is determined based on its revolutions.

Before we can begin our calibration we must set up our equipment and controls. To easily compare results we will employ both the hydraulic and paddlewheel flowmeter to measure the same flow rate. We need to have a baseline measurement for the flow rate in the pipes. To do this we fill a large tank in the basement of the laboratory to a specific weight and calculate the time it takes to reach that weight. The respective weight ratios are provided in the lab appendix. Before we can begin collecting data we must make sure the tanks discharge valve is completely shut and all manometers are at equilibrium. You can reach equilibrium by slowly opening and closing the manometer drain valves. Once the initial setup is complete you may follow the list of steps to gather data during the trials. Data produced by the paddlewheel and transducer will be collected on the computer to be easily displayed.

Step 1.) Open the discharge valve and create the max pressure difference which will create a max steady flow

Step 2.) Gather the transducer and paddlewheel voltage reading until the paddlewheel reaches a non-zero voltage

Step 3.) Once maximum flow is reached record all values for the flowmeter, manometer, and paddlewheel as well as weight vs time measurement using a timer as the tank is being filled.

Step 4.) Complete multiple trials of this by changing the manometer height(deltah) in increments of (0.1^2). This will decrease the flow rate and provide new voltage readings by the transducer and paddlewheel. Run trials until paddlewheel voltage becomes 0V.

Using the equation listed above we can create a calibration curve for the flowmeters with a trend curve using experimental data. With the data I have collected from my previous trials, I have plotted a graph with the y-axis consisting of the Flow rate (weight-time measurement) and the x-axis being the manometer height difference.

If you were to plot this data on a logarithmic scale we got the graph provided in the second figure. Examining the curve we can see that there is an evident power law relationship between the flow rate and the manometer height differences which is also evident based on the previous graph and equation provided.

The discharge coefficient (Cd) can be plotted with the Reynolds number as the x-axis. The Reynolds number shows the relationship between viscosity and inertia in a fluid. An example of this data is shown in the third graph.

We can also provide an example of the calibration curves for the paddlewheel based on our previous measurements. The graph for this is the fourth graph provided. In this fourth graph, we can see a linear relationship between voltage and flow rate. The pipe has a uniform area and we can approximate the velocity of the liquid to be proportional to the voltage recorded from the paddlewheel.

Based on all the data we've collected in a previous experiment we can see that the discharge coefficient(Cd) stays fairly consistent around a value of 0.6. This shows its consistency but the discharge coefficient is generally expected to be 1. The discharge coefficient will be 1 under perfect lab experiment conditions. There are many causes or error in our experiment that could lead this value away from 1. This error could be caused by improper data reading, technical issues in data collection, as well as experimental issues such as friction and obstructions in flow.

From the data we've collected in previous experiments, it is safe to assume that the flowmeter has a higher accuracy for smaller flow rates. We can make this assumption from the linear relationship between the calibration curve and flow rate.

Well, that is all the information you need to carry out my daily tasks. I know it may seem daunting, but if all the steps are followed, you should successfully be able to complete your flowmeter calibration and have a better understanding of the main concepts surrounding it. Good luck in your endeavors!