Exp___4(final)

Experiment # 4

Energy losses in pipes

Objective To investigate the head losses due to friction in the flow of water through pipe and to determine determine the associated associated friction factor. Both variables are to determine determine in the range of the flow rates and their characteristics identified for both laminar and turbulent flow.

Method By measurement of the pressure difference between two fixed points in a long straight tube of circular cross-section for steady flows. The range of flow rates will cover both laminar  and turbulent floe regimes.

Equipment In order to complete the demonstration we need a number of pieces of equipment. •

• • • •

The F1-10 hydraulics bench which allows us to measure flow by timed volume collection. The F1-18pipe friction apparatus. A stopwatch to allow us to determine the flow rate of water  A thermometer A spirit level for setting up the equipment A measuring cylinder for measuring very low flow rates

Apparatus: The accessory is designed to positioned on the side Channels of the hydraulics bench top channel.

There are two methods of supplying water to the test pipe. For higher flow rates the inlet  pipe is connected directly to the bench supply. For the low flow rates inlet pipe is connected to the outlet at the base of the constant head tank and the inlet to the bench is connected to the bench supply. The test section of the pipe is mounted vertically on the rig and is instrumented using two manometers. Water over mercury manometer is used to measure large pressure differentials and pressurized water manometer is used to measure small pressure differentials. When not in use manometer may be isolated using Hoffman clips. Flow through the test section is regulated using a flow control valve should face the volumetric tank. A short length of flexible piping attached to the valve prevents splashing.

Technical data The following dimensions from the equipment are used in appropriate calculations. If  required these values may be checked as part of the experiment procedure and replaced with your own measurement. Length of test pipe Diameter

L= 0.500 m d= 0.300 m

And the friction, f, is related to the head-loss by equation Δh = flv2/2gd Where d is the pipe diameter and, in this experiment, Δh is measured directly by a manometer which connects to two pressure tapings a distance l apart; v is the mean velocity given in terms of the volume flow rate Q by V= 4Q/Пd2 The theoretical result for laminar flow is F= 64/Re Where Re=Reynolds number  Re= vd /υ And υ is the kinematics viscosity. For turbulent flow in the smooth pipe, a well known curve fit to experiment data is given  by F= 0.316Re-0.25

Procedure – equipment set up

Mount the test rig on the hydraulic bench and, with a spirit level, adjust the feet to ensure that base plate is horizontal and, hence, the manometer is vertical. Check with the demonstrator that the mercury (Hg) manometer is correctly filled; this should not be attempted by student because Hg is hazardous substance. The test rig outlet tube must be held by a clamp to ensure that the outflow point is firmly fixed. This should be above the bench collection tank and should allow enough space for  insertion of the measuring cylinders. Join the test rig inlet pipe to the hydraulic bench flow connecter with the pump turned off. Close the bench gate valve open the test rig flow control valve fully and start the pump.  Now open the gate valve progressively and run the system until all air is purged. Open the Hoffman clamp and purge any air from the two bleed points at the top of Hg manometer. Attach a Hoffman clamp to each of the two manometer connecting tubes and close them off. With the system fully purged of air, close the bench valve, stop the pump, close the out flow valve and remove Hoffman clamp from water manometer connections. Disconnect test section supply tube and hold high to keep it liquid filled. Connect bench supply tube to header tank inflow, run pump and open bench valve to allow flow when outflow occurs from header tank snap connecter, attach test section supply tube to it ensuring no air entrapped. When out flow occurs from header tank over flow, fully open the outflow control valve.

Procedure- taking a set of results 1. Running high flow rate tests

Apply a Hoffman clamp to each of the water manometer connection tubes (essential to  prevent a flow path parallel to the test section) Close the test rig flow control valve and take a zero flow reading from Hg manometer, (may not be zero because of the contamination of Hg and / or tube wall.) With the flow control valve fully open measure the head loss ∆h shown by the manometer. Determine the flow rate by timed collection and measure the temperature of collected fluid. The kinematic viscosity of water at atmospheric pressure can then be determined from the table provided in this manual.

2. Running low flow rate test

Repeat procedure given above but using water manometer throughout With the flow control valve fully open measure the head loss h shown by the manometer determine the flow rate by timed collection and measure the temperature of the collected fluid. The kinematic viscosity of water at atmospheric pressure can then be determined from the table  provided in theory manual.

Observations and Calculations: Test Pipe Length = ……………… m Test Pipe Diameter = …………… m Temperature of water = ………... OC Kinematic Viscosity = …………. m2/s Volume Collected V (m3)

Time To collect t (sec)

Manometer  Reading h1 (m)

Manometer  Reading h2 (m)

Head loss Δh (m)

Flow rate Q

Velocity

Friction Factor  f 

Reynolds’s  No Re

In f

In Re

In h

In v

(m/s)

Application of theory Identify the laminar and turbulent flow regimes. What is the critical Reynolds number? Assuming a relationship of the form f= kRen calculate these values from the graph you have plotted and compare these with the accepted values shown in the theory. What is the cumulative effect of the experimental errors on the value of k and n? What is the dependence of head loss upon flow rate in the laminar and turbulent regions of  the flow? What is the significance of changes in a temperature in a head loss?