CVL502 Lab #4 Energy Losses in Bends (final)

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Lab #6) Energy Losses in Bends Background The energy loss which occurs in a pipe fitting (so-called secondary loss) is commonly expressed in terms of a head loss, ∆H in metres, in the form: ΔH = K V 2 2 g [1] where K = loss coefficient, dimensionless V = mean velocity of flow into the fitting, m/sec g = gravitational acceleration = 9.806 m/s 2 The loss coefficient, K , is usually determined by lab experiments due to the complexity of flow in many fittings. For the pipe fitting experiments, the head loss, ∆H , is calculated from two manometer readings, H 1 and H 2 , taken before and after each fitting. K is then determined from Equation [1] where: K = ΔH V 2 /( 2 g ) When the cross-sectional area of the pipe changes through enlargement or contraction, the system will experience an additional change in static pressure. This change can be calculated as: V 1 2 2 g − V 2 2 2 g [2] To eliminate the effects of this area change on the measured head losses, Equation [2] should be added to Equation [1] for the enlargement and the contraction. Notice that ∆H = H 1 – H 2 will be negative for the enlargement and Equation [2] will be negative for the contraction. ΔH = K V 2 2 g + ( V 1 2 2 g − V 2 2 2 g ) [3] where V = velocity of flow into the fitting (for Armfield, it is the velocity of the fluid in the smaller diameter pipe; for Gunt, it is in the larger diameter pipe). Objective The objective of this experiment is to determine the loss factors for flow through a range of pipe fittings including bends, a contraction, and an enlargement.

Equipment 1 hydraulics bench 1 energy losses in bends and fittings apparatus 1 stopwatch 1 thermometer 1 spirit level clamps for pressure tapping connection tubes Note : For Armfield apparatus: Internal diameter of pipework = 0.0183 m Internal diameter of pipework at enlargement outlet and contraction inlet = 0.0240 m For Gunt apparatus: Internal diameter of pipework = 0.017 m Internal diameter of pipework at contraction outlet and enlargement inlet = 0.0096 m Procedure Measuring Head Losses across all Pipe Fittings on ARMFIELD apparatus: 1) Fully open the gate valve. 2) Adjust the flow from the bench control valve. At a given flow rate, take the height readings from all the manometers after the levels have steady. 3) In order to determine the volume flow rate, a timed volume collection method is applied using the volumetric tank. This is achieved by closing the ball valve and measuring the time taken to accumulate a known volume of fluid in the tank using a stopwatch. The height of the water in the tank can be read from the sight glass. (Note : The measuring time should be greater than one minute to minimize timing errors.) 4) Repeat steps 2 and 3 at least five times over a flow range between 8 L/min and 17 L/min. Record all the experimental results using Table 1. Measuring Head losses on GUNT apparatus There will be 4 different combinations of bends and fittings. The first combination will be the Elbow, Short Bend, and Long Bend. The second combination will be the Mitre alone. The third combination will be the Contraction alone. And the fourth combination will be the Enlargement alone. 1) Adjust the flow using the inlet valve, making sure that the manometer levels remain within the tubes. At a given flow rate, record the height readings from all the manometers

after the levels have stabilized. 2) In order to determine the volume flow rate, a timed volume collection method is applied using the volumetric tank. First close the ball valve on the bottom right and measure the volume achieved in 1 minute. This will give you the flow rate in L/min. 3) Repeat steps 1 and 2 for a total of 3 times to obtain 3 different readings. 4) Setup the second combination and repeat steps 1 and 3. 5) Setup the third combination and repeat steps 1 and 3. 6) Setup the fourth combination and repeat steps 1 and 3. *Please note that if R d > 5 , that is, R (radius of the bend) divided by d (the inner diameter of the pipe) is greater than 5, then the head loss is primarily caused by friction and not because of the change in direction of the flow. Since the HAMBURG apparatus has a 100mm radius for the Long bend and an inner pipe diameter of 17mm, R d > 5 , thus the head loss is primarily due to pipe friction. Discussion Measuring Head Losses across all Pipe Fittings except Gate Valve: 1) Plot graphs of head loss against dynamic head. 2) Plot graph of K against volume flow rate Q. 3) Comment on any relationships of Questions 1 and 2. What is the dependence of head losses across pipe fittings upon velocity? 4) Examining the Reynolds number obtained, are the flows laminar or turbulent? 5) Is it justifiable to treat the loss coefficient as constant for a given fitting? **Must show sample calculations**

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4 Table 1: Experimental Results Fitting Measured Values Calculation Manometer Reading H 1 (m) Manometer Reading H 2 (m) Head Loss ∆H = H 1 – H 2 (m) Volume  (m 3 ) Time t (sec) Flow Rate Q (m 3 /sec) Velocity V (m/sec) V 2 2 g (m) Loss Coefficient K Eqn [1] or [3] Mitre Elbow Short Bend Long Bend Enlargement Contraction

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