![]() ![]() Disconnect the test pipe’s supply tube and hold it high to keep it filled with water.Attach a clamp to each of the differential pressure gauge connectors and close them off.The low flow rate will be supplied to the test section by connecting the hydraulics bench outlet pipe to the head tank with the pump turned off. The pressure difference measured by the differential pressure gauge can be converted to an equivalent head loss (h L) by using the conversion ratio: Close the flow control valve, and turn off the pump.For each step, determine the flow rate by timed collection. Adjust the flow control valve in a step-wise fashion to observe the pressure differences at 0.05 bar increments.Determine the flow rate by timed collection.With the flow control valve fully open, measure the head loss shown by the pressure gauge.Close the apparatus flow control valve and take a zero-flow reading from the pressure gauge.Close off the air-bleed valve once no air bubbles observed in the connection tubes.Remove the clamps from the differential pressure gauge connection tubes, and purge any air from the air-bleed valve located on the side of the pressure gauge.Open the bench valve progressively, and run the flow until all air is purged. Close the bench valve, open the apparatus flow control valve fully, and start the pump.The high flow rate will be supplied to the test section by connecting the equipment inlet pipe to the hydraulics bench, with the pump turned off. Figure 4.2: Moody Diagram Figure 4.3: Kinematic Viscosity of Water (v) at Atmospheric Pressure The following dimensions from the test pipe may be used in the appropriate calculations :ĭiameter of test pipe = 0.003 m. The average velocity, v, is calculated from the volumetric flow rate (Q ) as: In this experiment, h L is measured directly by the water manometers and the differential pressure gauge that are connected by pressure tappings to the test pipe. Where v is the average velocity, D is the pipe diameter, and and are dynamic and kinematic viscosities of the fluid, respectively. For turbulent flow in a smooth pipe, a well-known curve fit to the Moody diagram is given by: These formulas are used in engineering applications when computer programs or spreadsheet calculation methods are employed. Instead of using the Moody diagram, f can be determined by utilizing empirical formulas. The Moody diagram relates f to the pipe wall relative roughness ( /D) and the Reynolds number (Figure 4.2). Therefore, f must be determined experimentally. Other factors, such as roughness spacing and shape, may also affect the value of f however, these effects are not well understood and may be negligible in many cases. The head loss due to friction can be calculated from the Darcy-Weisbach equation:įor laminar flow, the Darcy-Weisbach coefficient (or friction factor f ) is only a function of the Reynolds number (Re) and is independent of the surface roughness of the pipe, i.e.:įor turbulent flow, f is a function of both the Reynolds number and the pipe roughness height. The pressure difference (P out-P in) between two points in the pipe is due to the frictional resistance, and the head loss h L is directly proportional to the pressure difference. The energy loss in a pipe can be determined by applying the energy equation to a section of a straight pipe with a uniform cross section: Figure 4.1: F1-18 Pipe Friction Test Apparatus ![]() The air-bleed valve facilitates purging the system and adjusting the water level in the water manometers to a convenient level, by allowing air to enter them. This valve should face the volumetric tank, and a short length of flexible tube should be attached to it, to prevent splashing. The apparatus’ flow control valve is used to regulate flow through the test pipe. For low flow rate experiments, the inlet to the constant head tank is connected to the bench supply, and the outlet at the base of the head tank is connected to the top of the test pipe. For high flow rate experiments, the inlet pipe is connected directly to the bench water supply. This experiment is performed under two flow conditions: high flow rates and low flow rates. Therefore, for this experiment, the water-over-mercury manometers are replaced with a differential pressure gauge to directly measure large pressure differentials. Since mercury is considered a hazardous substance, it cannot be used in undergraduate fluid mechanics labs. ![]() When not in use, the manometers may be isolated, using Hoffman clamps. A set of two water-over-mercury manometers is used to measure large pressure differentials, and two water manometers are used to measure small pressure differentials. The pipe friction apparatus consists of a test pipe (mounted vertically on the rig), a constant head tank, a flow control valve, an air-bleed valve, and two sets of manometers to measure the head losses in the pipe (Figure 4.1). ![]()
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