FLOW MEASUREMENT Laboratory Procedure Background InformationThe term flow infers the movem...

FLOW MEASUREMENT Laboratory Procedure Background Information

The term flow infers the movement of matter from one place to another. Flow can be quantified as either instantaneous flow rate or total flow. Instantaneous flow rate is time dependent whereas total flow is not. The rate at which a material is flowing through a pipe will probably be measured as an instantaneous flow such as gallons per minute whereas the water meter al your home measures total flow (gallons).

Under normal automatic process control, a process technician should expect that the control instruments both measure and then stop a flowing material that is filling a tank. There are, in fact, metering instruments with preset shutoff capabilities that can mechanically accomplish this task as well as more sophisticated control schemes that are designed to do the same. In either case, the process technician should know how long it takes for the tank to fill so that he can be available to monitor the shutoff. For example, if the tank is to be charged with 1,000 gallons of a material and that material is flowing into the tank at 80 gallons per minute, then it will take 12 minutes and 30 seconds to charge. The process technician should check to make sure that the charge is completed accurately.

Materials Needed

• low-flow-rate rotameter with a throttling valve

• containment vessel with graduated volume marks on it (the marked units should match the rotameter units if possible).

• water supply and wet sink or drain apparatus

• timkeeping device that indicates minutes and seconds

• fittings and tubing for connecting the apparatus

Safety Requirements

Safety glasses are required in the lab.

Procedure

a. Set up the flow rate apparatus as illustrated below.

b. Place marks at 25%, 50%, 75%, and 100% volume on the vessel wall; 100% should equal a known volume.

c. Connect a water supply to the input of the rotameter and a piece of tubing to its outlet side.

d. With the open end of the tube placed in a basin or drain, fill the supply line, rotameter, and discharge tubing with water and adjust the flow rate to some point about midrange. Let it stabilize at that rate.

e. At the same time, place the discharge tubing from the rotameter into the vessel and start the timing device.

f. Fill the vessel until it reaches the 25%, 50%, 75%, and 100% volume marks. Record the time at each interval. Stop the timing device and remove the tubing from the rotameter.

Percent Level	Elapsed Time
. 25
50
75
100

g. Calculate the average flow rate.

 

Where: Volume units are the same as the rotameter units. EXAMPLE:

 

h. Compare the calculated flow rate to the indicated flow rate on the rotameter.

i. Complete the final report for this lab.

Findings

Compile your observations and readings into a report that includes a sketch of the equipment. the recorded data, an explanation of the results of the experiment, and a conclusion. Include a paragraph explaining the difference between instantaneous flow verses total (accumulated) flow. Reference your class notes if necessary.