Pipe Flow Hydraulics

Transcription

1 CHE Chemical Engineering Processes I - Laboratory Experiment 1 Pipe Flow Hydraulics BACKGROUND The conveyance of fluids through fixed conduits is the most common unit operation in engineering practice. Applications range from delivery of microliter volumes of medicines over millimeters of distance to delivery of cubic meter volumes of oil over kilometers of distance. The relationship between flow rate, energy consumption (pressure drop), pipe diameter, etc. may be expressed by a semi-empirical correlation, such as Equation (3.0), whose mathematical form may be derived from basic fluid mechanical theory but which relies on experimental data for calibration. Equation 3.0 h f P g f l 4 d u g l 8 d u g OBJECTIVE To observe the relationship between pressure drop and flow rate and to examine the accuracy of semi-empirical expressions used to correlate pipe flow data. PROCEDURE A. Pressure Drop in Straight Pipes 1. Close all manometer valves and open all flow regulator valves. Allow water to flow through the apparatus until all trapped air bubbles are flushed from the system and temperature equilibrium is achieved (approximately 10 minutes). Measure and record the temperature. Values of density and viscosity of water at this temperature may be found in one of the listed references.. Close the appropriate regulatory valves to allow flow through only through the pipe segment whose inside diameter is given as inches. Measure the length of the pipe segment (1) between manometer valves 7 and Reduce water flow to a low rate. Open the two manometer valves. Increase water flow rate until the water level in the upstream manometer tube is at approximately 65 inches. Measure the volumetric flow rate (Q) and pressure drop ( P). PF 1

2 4. Reduce the water flow rate until the pressure drop is 10 to 15% lower than the value measured in part 3. Measure the volumetric flow rate. Repeat for a total of at lest six flow rates between zero and the maximum. 5. Close manometer valves 7 and 8. Adjust the regulatory valves to allow flow through only the pipe segment whose inside diameter is given as inches. Measure the length of the pipe segment between manometer valves 11 and 1. Repeat steps Close manometer valves 11 and 1. Adjust regulatory valves to allow flow through only the pipe segment whose inside diameter is given as inches. Measure the length of the pipe segment between manometer valves 15 and 16. Repeat steps 3-4. B. Fluid Metering 1. Close all manometer valves. Adjust regulatory valves to allow flow through only the pipe segment containing the two flow meters. Reduce water flow to a low rate. Open manometer valves -5. Increase water flow rate until the water level in the upstream manometer tube is at approximately 65 inches.. Measure the volumetric flow rate and the pressure drop across each of the meters. Reduce the flow until the pressure drop across the first meter is approximately 10-15% lower. Measure values of volumetric flow rate and pressure drops. Repeat for a total of at least six flow rates. ANALYSIS A. Pressure Drop in Straight Pipes 1. Calculate pressure values of Reynolds number for each flow rate in each pipe size.. On a single graph, plot experimental values for pressure drop versus volumetric flow rate for each of the three pipe sizes. Do the shapes of the curves agree with that predicted by Equation (3.0)? 3. On a separate (log-log) graph, plot values for the friction factor φ, defined by Equation (3.0), versus Reynolds Number. Compare the shape of the curve to Figure 3.7. Over what range of values of Reynolds Number is the curve reasonably linear? According to Equation (3.37) [φ = 8/Re], what should the value of slope be for that portion of the curve? Compare the value of friction factor corresponding to the highest value of Reynolds Number used to a value PF

3 calculated using the Colburn analogy between heat transfer and fluid friction for turbulent flow in smooth pipes [Equation (10.171), φ = 0.03 Re -0. ]. 4. An empirical correlation for pressure drop as a function of volumetric flow rate may be written as P = kq n. Use the data for the largest diameter pipe to calculate values of k and n. Under what conditions could this correlation be used? B. Fluid Metering 1. Calculate the values of Reynolds number for each flow rate in the Venturi and orifice meters. Present all values in one table.. Plot the volumetric flow rate versus pressure drop data for each meter as Q vs. ( P) 1/. Using the values of slope in each plot and Equation (6.19) [or (6-3)] calculate the values of the coefficient of discharge, CD, for the venturi and orifice meters. The pipe, venturi throat, and orifice diameters are given as Dp = in., Dv = 0.31 in., and Do = 0.45 in., respectively. CD A v( P) Equation 6.19 G Q v A 1 ( ) A 1 Equation 6.3 Q G v C D A A 1 ( A 1 v P A ) 3. Compare the derived CD values to those reported in the literature for various types of orifices and Venturi meters, and discuss any differences. REFERENCE Coulson, J.M., and J.F. Richardson, Chemical Engineering, Vol. 1, 6 th Ed., B-H Press (1999). PF 3

4 Pipe Flow Hydraulics Glossary of Terms PF 4

5 Pipe Flow Hydraulics Glossary of Terms (continued) PF 5

6 Pipe Flow Hydraulics Glossary of Terms (continued) PF 6

7 Figure 1: Pipe Flow Hydraulics Unit PF 7

8 Figure : Pipe Flow Hydraulics Unit Top View PF 8