Elemantary Lab Procedures Explanation

The purpose of this laboratory is to get familiar with the procedure of measuring characteristics of a steady flow of water using the water flow system in class. The system consisted of a weighing tank connected to Bourdon pressure gages where we timed a certain volume of water flow, and pressure differences in the system itself. The system set up is pictured.

From the diagram you can find Bourdon gages at points A and B, in data acquisition, these letters correspond to 1 and 2 respectively. The Bourdon gages offer a gage pressure measured in kPa for our two different points.

In the system you will find this system also contains a Differential Manometer that holds Mercury. This is a second method of pressure measuring that the system allows. Heights for the Differential Manometer. For simplification of measurements, L and R were taken as the heights of the water in the Differential Manometer with a consistent datum in each experiment. This datum simplifies the measurement since we only are concerned about the difference in height in the manometer and not the total heights of each side. This simplification means that L (in trial table hL) will be a positive value and R (in trial table hR) will be a negative value (1). 

Lastly, there is a weighing tank where we set a certain volume of water to be measured for each trial. The weight of water is timed following the balancing beam equilibrium being reached. After each trial, the beam is balanced once again and increased by a scale of 100 lbs.

The steps for data acquisition are below, explaining the process of working the water system. Although the steps are simple, there are certain precautions that need to be taken to avoid the weighing tank overflowing, as well as increasing the weight desired.

From your trials, the data produced should reveal certain trends and accuracy. Two graphs from my personal data are shown above [comparisons of pressure measurements, and the relationship between pressure difference and volume respectively]. 

Looking at the results of the experiment in Graph.2, we can see a more concise linear relationship between pressure difference and volumetric flow rate from the manometer method of measurement, as opposed to the Bourdon gages. This leads me to conclude that the Manometer is more accurate in measuring pressure difference for this system. Looking at the graph overall, the Bourdon gages do not have a consistent output for pressure difference through any flow rate. I believe that the discrepancy in results from these two methods might come from human error reading the Bourdon gages as in certain trails the gage arm would tremble between values, making us estimate the pressure readings. This could explain why there was a lack of linearity for the Bourdon gages.

In order to verify the accuracy of these trials, we will calculate the relationship between the slowest (Qs=45.75s) and fastest (Ql=46.41s) time recordings of the first trial. 

e=QS-QL0.5(Qs+Ql)

This reveals an accuracy of about 0.0143, or 1.43%, which is just around where we would deem acceptable for a trial.

Now that the laboratory and expected results were explained. The process can now be explained below.

Outside of the water system, the only supplies needed are for data aqusition. They are as follows :

1) Timer

2) Data table template [photo included]

3) Pen/Pencil

With the drain open in the weighing tank, open the system to a steady water flow.

Once a steady flow is established in the system, set timer to zero.

Before begining the timer, overbalance the scale of the weighing tank by moving the position of the cursor on the balancing beam. The arm of the balance beam should hit the bottom of the stop.

After overbalancing and the beam reaching the bottom stop, close the drain of the weighing tank. Begin the timer when the beam reaches the balance mark.

Now that the timer has begun, immeditatly add a desired weight to the balance pan*, The pan will hit the bottom stopper once again.

*Note that the weight added is not the actual weight that will fill the water tank. The weight is only 1/100 the actual weight that will be filled by the weighing tank.

While the tank is filling, four measurements should be taken

1) Bourdon gage #1 reading

2) Bourdon gage #2 reading

3) Left height of Differential Manometer

4) Right height of Differential Manometer

At this point the tank is filling with water, and recorded data has been taken. Once the beam arm hits the top stopper, the timer should be stopped. This indicates that the weight of the water tank has reached the desired amount.

Once everything has been recorded. Begin to drain the weighing tank and reblance the beam arm to the next desired weight for trial. Each trial should begin with an emtpy tank.