Experimental Procedure

Added on - 25 Sep 2019

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Experimental procedureYou are provided with two long and one short 84.6 mm nominal bore PVC pipes, an inletelement and a pipe section with extensions which are flanged at both ends, see fig. 6, anumber of nuts and bolts, fexible hoses, a panel of 16 manometers, and an anemometer.An electrically driven air blower is fiited at the end of the pipe section with extensionsnear to the fan outlet. The flow velocity of air through the pipe assembly varied bychanging the potentiometer setting (0 to maximum of 90) on the electrical air blower. Theair flow velocity has been set to increase linearly with the potentiometer settings.Tappings at selected positions in the pipe wall allow for connections to watermanometers using the hoses provided, to measure head loss. The anemometer can bepositioned centrally at the front of the inlet element, to determine the velocity of the airwhen required. Use only the I and J inlets on the manifold for experiments using thePitot tubes.Figure 6. The pipe section without any valves or fittings. The measurement points arenumbered.Assembling the pipe sections in the GUNT equipmentThe pipe sections will have been assembled as shown in fig. 6. An orifice plate, nozzle,Venturi tube, two Pitot tubes, an iris diaphragm valve, and three pipe bends are providedand which can be installed at different positions in the pipe sections for the experimentsdiscussed in the individual sections below.Determination of the air flow characteristics of the orifice plate and nozzle1.Unscrew the two long pipe sections at the position shown by the red arrow on fig. 1,and slightly push away the intake pipe which is connected through the short pipesection to the inlet element, giving enough space for the measuring flange whichcontains the orifice plate or nozzle. Position the intake pipe bench and the fan benchnext to each other, and make sure that the pins on the fan bench are guided into theholes on the intake pipe bench. Use the tow clamps to connect the frames to eachother. Lock the rollers on the intake pipe bench and the fan bench to prevent themrolling away.2.Install the orifice plate or nozzle into the measuring flange, see fig. 7, by looseningthe four screws on the measuring flange, and carefully pulling the right half of themeasuring flange to the side. Put the 50mm internal diameter orifice plate or nozzleinto the measuring flange until it sits cleanly in the groove (take note of the directionof flow: airflow should be into the wide end of the nozzle). Put the two halves of the
measuring flanges together and bolt them back together.Figure 7. The measurement flange.3.Screw the measuring flange between the intake pipe and the pipe section on the fanbench, as shown in the Figure 8. Remove the pinhole from the fan outlet.Figure 8. The pipe section with the measurement flange in place.4.Use the hoses to connect measuring points 15 and 16 to the inlets on the manometerpanel, ensuring that there are no kinks in the hoses.5.Switch on the fan, with the potentiometer set to zero. Note the level of water in themanometers before starting the experiment.6.Orifice plate and nozzle: for five different potentiometer settings record thedifferential manometer Δh (mm of water), and measure the corresponding air flowvelocities using the anemometer.Treatment of resultsThe velocity of flow of air through is proportional to the square root of the differentialhead across the manometer. Tabulate your measured and derived values under theheadings shown in Table 1.Potentiometer settingshPPAir velocity
/mm/N.m-2/N0.5.m/m.s-1Table 1. Measured and calculated parameters for air flow through a orifice or nozzleCalculateP andP between measurement points 15 and 16for each of the fivepotentiometer settings. Ploton one graph theair flow velocities versusP for bothorifice plate and nozzle, and compare your results with the expressionfor flow throughorifice plate and nozzle:V1= constant xP.Determination of the velocity profile of air flow using the Pitot tube.1.Repeat parts 2 – 6 of the instructions for “Determination of air flow characteristics ofthe orifice plate and nozzle” on pages 89 & 90.2.Screw the Pitot tube in pipe section between the intake pipe and the pipe section onthe fan bench, as shown in figs. 9(a) & (b). Use hoses to connect measuring points 19and 20 to manometer inlets I and J (these manometers have smaller internal diameterto improve the sensitivity of the Pitot tube) to the two inlets on the manometer paneldedicated to the Pitot tube experiments, ensuring no kinks in the hoses.3.Switch on the fan, with the potentiometer set to zero. Note the level of water in themanometers before starting the experiment.4.Pitot tube: for 3 different potentiometer settings (3 - 9), record and tabulate thedifferential manometer readings Δh (mm of water),and the vertical distances (y) ofthe Pitot tube from the center of the pipe (-40, -20, 0, 20 and 40mm).(a)
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