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Unformatted text preview: STEVENS INSTITUTE OF TECHNOLOGY CHARLES V. SCHAEFER, JR. SCHOOL OF ENGINEERING MECHANICAL ENGINEERING DEPARTMENT FLUID MECHANICS LABORATORY FLOW METERS AND PIPE FLOW PURPOSE To determine the characteristics of a common type of fluid flow meter, the sharp-edge orifice, and to analyze the flow development in a straight pipe using the Air-flow facility. INTRODUCTION The movement of fluid is a concept which relates to many disciplines in engineering. The losses incurred in pipes or ducts, the losses in associated fittings and measurement of the fluid flows involved form a basic part of most engineering courses and demand a practical demonstration in the laboratory. The following two aspects of fluid flow systems that are of importance in flow metering and design of piping systems are considered in this laboratory experiment. I) Orifice-plate flow meter: Orifice-plate flow meter is a device which causes a pressure drop in a flowing fluid by providing a changing flow area. Since the pressure drop depends on flow rate, the orifice-plate flow meter may be calibrated for use in pipe systems. Many other types of fluid flow meters are used in practice, based on different operating principles1. II) Flow development: Another aspect of piping system design involves the estimation and control of the flow development in a straight pipes. The entrance length in any piping system is the region wherein the boundary layer develops to merge along the pipe axis2. APPARATUS The experimental apparatus consists essentially of a long smooth walled pipe supported on a steel frame with a centrifugal blower at the suction side as shown in the accompanying sketch. The pipe is segmented so that it can be rearranged to insert flowmeInlet Flow Nozzle ters and pipe fittings. A Orifice Plate & Flow Straightener (removable) conical diffuser is used to Test Pipe connect the piping sysDiffuser Blower Test Pipe tem to the centrifugal Control blower that is mounted on Reservoir Panel a floor standing metal Manometer Board frame. A control panel with a frequency-based motor speed control is used for flow control, while pressure taps along the complete length of the pipe permit the determination of pressure gradients. A traversing Pitot tube enables the measurement of the velocity profile at three different stations along the pipe. A fourteen tube bank manometer allows for head loss and velocities in the pipe to be measured. A precalibrated 80 mm inlet nozzle with a fixed coefficient of discharge (Cd) of 0.98 and contraction ratio of 4/7 is 1.See Fluid Mechanics, F. M. White, 6th edition, McGraw Hill, N.Y, pp. 402-424 2.See Fluid Mechanics, F. M. White, 6th edition, McGraw Hill, N.Y, pp. 346-349 Fluid Mechanics Laboratory: Flow Meters & Pipe Flow Page 1/2 used for all flow measurements. The nominal inlet diameter of the pipe is 80 mm, while the orifice is 50 mm in diameter. PRE-LAB ASSIGNMENT Please read the appropriate sections in the text to familiarize yourself with the concepts dealing with pipe flow and losses in pipe fittings, and the principles of operation of orifice meter and other flow meters. PROCEDURE 1) Use the preset configuration to measure the pressure drop across the orifice meter at two different flow rates. 2) Remove the orifice meter and using the traversing Pitot tube, measure the velocity profile in the straight pipe at three different (preassigned) locations for two different flow rates. RESULTS 1) Plot the velocity profiles in the piping system (at the three locations where the measurements were made) and determine the entrance length as a function of the flow Reynolds number. 2) Determine the coefficient of discharge, Cd, for the orifice meter and calculate its loss coefficient, Km. DISCUSSION 1) Can the elbows and bends be used for flow metering? Use the results and the data for the orifice meter (as well as others, such as the venturimeter or the flow nozzle) to discuss their feasibility. 2) Using the experimental data and the discharge coefficient, Cd, for the orifice meter, specify the range of values for these coefficients which result from experimental error and uncertainty. How does the discharge coefficient, Cd, and the loss coefficient, Km, for the orifice meter compare with results from the literature? 3) How well did the functional relation for entrance length compare with the theory? In answering this question, be sure to allow for the effects of measurement errors. 4) How do the loss coefficients for the orifice plate, elbows, bends, and inlet nozzle, differ? Why? What significance does this difference have in selecting a meter for a specific application? Page 2/2 Fluid Mechanics Laboratory: Flow Meters & Pipe Flow ...
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