California State University Sacramento                     CE 135 Hydraulics Laboratory

Department of Civil Engineering                                                Instructor      MEH

For general information go to the Background Presentation

FLOW METERS IN PIPES: CONSTRICTION DEVICES -- PROCEDURES

References:    

    Roberson, J.A. and C. T. Crowe, Engineering Fluid Mechanics, 6th ed., John

                    Wiley and Sons, 1997, Ch. 13 Flow Measurements

   ASME Fluid Meters Research Committee, "The ISO-ASME Orifice Coefficient Equation",

          Mechanical Engineering, July, 1981, pp 44-45. (Magazine available in CSUS Library)

OBJECTIVES:

Introduce flow measurement by constriction meters

Calibrate a constriction flow meter

Compare different kinds of meters

APPARATUS:

             Flow manifold with orifice, nozzle, and venturi meters

             Differential manometer; Weighing tank with scale

             Watch to read at seconds

EXPERIMENTAL PROCEDURE:

Open the surge tank valve.
Turn on the water supply pump and purge air from the pipe system and the manometer tubing.
Make sure the differential manometer is connected to the meter you want to calibrate

Establish a steady flow through the system.
Record the heads on the differential manometer tubes. If Δ h fluctuates, use an average over time.

Gravimetrically determine the flow rate by diverting the flow to a container and measuring the weight of water captured in a measured amount of time.

Repeat those steps for a range of flows spanning the capacity of the supply pump or the differential manometer, whichever is more limiting.

Record the water temperature and essential geometric variables such as the pipe diameter and orifice meter throat diameter.

Compare flow patterns in the orifice, nozzle, and venturi meters

Establish flows through the three flow meters at the same time. .
Observe flows through the clear plastic sections and draw sketches, noting differences in flow patterns and turbulence among the three devices.

Turn off the pump and close the surge tank valve.

            FLOW METERS IN PIPES: CONSTRICTION DEVICES -- RESULTS

Format: Memo Report [Include your team logo somewhere in the report.]

Present the key results and describe any major deviations from the printed procedures and why you did them.

You do not need to turn in the lab procedure sheet with your report, but it is ok to add it as an attachment. You may use a computer sketch of the apparatus in the body of the report, but the attachment must be hand drawn.

RESULTS:

Calculate all flows in cfs (cubic feet per second) and the Reynold’s numbers (Re) associated with the flows. Note which diameter you use in the Reynold’s number.

Plot two rating curves for each device tested and use them to determine the discharge coefficient (K) as follows:

o    Constrained exponent case: Plot Q (y axis) against Δh^1/2 (x axis) on arithmetic graph paper. Units for Q should be cfs and for Δh should be feet. Plot the best-fit line through the data using a linear regression function. (Most spreadsheets now have linear regression functions.) Show the equation of this line and its coefficient of determination (r²). From the parameters of the line, calculate K in Q=KA(2g Δh)^1/2.

o    Unconstrained exponent case: Plot Q against Δh on a log-log paper using the same units as above. Determine the best-fit line, its equation, and its r² value. From the parameters of the line, calculate K. In this case, the exponent on Δh may be different from 0.5. (Using the equations from the Constrained case, plot a curve of Q vs Δh on this graph.)

Using the K values from the constrained case, plot K (y-axis) against Re (x axis)on a semi-log paper to discover whether K is constant over the range of Re in this experiment.

Write the equations for the curves in the form Q=KA(2g Δh) ^x for both constrained and unconstrained cases.

ATTACHMENTS:

Attach your sketch of the experimental set-up and copies of your input data and calculated results.
Write out the key equations used in calculating the results, with one sample calculation for each equation.

Discussion Questions: (Answer each in a few sentences.)

      Discuss which curve – constrained or unconstrained – fits the data better. Indicate how you judged “better”. Discuss what your result means when compared with the theory of constriction meters in the literature.

      Discuss how well or how poorly your K values compare with those in the flow coefficient vs Reynolds number in a table or chart in literature, such as Figure 13.13 of Roberson, et al, 1997.

FLOW METERS IN PIPES: CONSTRICTION DEVICES -- EXPERIMENTAL DATA

                                                           Date of Experiment:
      Lab Team Members:

-------------------------------- CONSTANT DATA ---------------------------------------

Constriction Type: Orifice, Nozzle, or Venturi                      Constriction Diameter _________ inch
Water Temperature _________º F                                          Pipe Diameter _________ inch

--------------------------------- VARIABLE DATA -------------------------------------------

Data from the differential manometer, the weighing scale, and a clock or stop watch.