Test Instructions. Equipment for Engineering Education

Transcription

1 Equipment for Engineering Education Test Instructions HM Pipe Friction Apparatus G.U.N.T. Gerätebau GmbH P.O. Box 1125 D Barsbüttel Germany Phone (040) Fax (040)

2 Test Instructions Publication no.: A /96

3 Contents 1 Unit description Preparing the experiment Experiments Laminar flow Measured values for laminar flow Turbulent flow Measured values for turbulent flow Graph of measured values

4 1 Unit description The HM unit is used to examine pipe friction losses in laminar and turbulent flow. The pipe section used is a brass pipe with an inside diameter of 3 mm and a length of 400 mm. The pressure losses are measured in laminar flow with a water manometer. The static pressure difference is indicated. In turbulent flow the pressure difference is measured with a mercury-filled U-tube manometer. A level tank is provided to generate the laminar flow. It ensures a constant water inflow pressure on the pipe section at a constant water level. The level tank is not used to generate turbulent flow. The water is fed directly from the water main into the pipe section. The flow rate is set by means of needle valves at each end of the pipe. The water is supplied either from the HM150 fluid technics base module or from the laboratory main. An enclosed water circuit can be established with the HM Unit description 2

5 The unit basically comprises: Demonstration board 2 U-Tube manometer 3 Discharge needle valve 4 Pressure tapping at the end of the pipe Inlet needle valves 8 Hose connection Water supply 9 Ball cock 10 Overflow Pressure tapping at the beginning of the pipe 6 Pipe section 11 Water tank 12 Water manometer 1 Unit description 3

6 2 Preparing the experiment - Set up the experiment on the HM150 so that the discharge directs the water into the sewer. - Connect a hose between the HM150 and the unit. - Open the HM150 discharge. 3 Experiments 3.1 Laminar flow Level Overflowf Pressure lost of laminar flow is to be compared with turbulent flow. - Connect the water manometer to the two pressure measuring nipples. - Open the needle valve at the discharge fully. - Close the valve [1] fully. - Open the valve [2] fully. - Switch the HM150 pump on and adjust the ball-cock so that a constant water level is created at the overflow. Valve [2] Ball cock Valve[1] 2 Preparing the experiment 4

7 - Close the needle valve at the discharge until a constant pressure difference of 2 cm is established on the water manometer. This corresponds to the fall hv. - Determining the volume flow. - Increase the flow in increments (hv increases) and repeat the volume flow measurements. Hose connection hv Discharge needle valve It also needs to be investigated whether the flow is laminar or turbulent. The switch from laminar to turbulent flow form occurs when: Re kr 2300 Re lam means laminar flow Re tur means turbulent flow The Reynolds number is calculated from Re = w d ν where h1 d= inside diameter of the pipe section [m] w= flow rate [m/s] h2 ν= viscosity of the medium [m 2 /s] Mearurement of the fall hv on the water manometer Fall h v = h 1 h 2 h1: static pressure at the entrance to the pipe. 3 Experiments 5

8 . The volume flow V is best measured with a measuring vessel and a stopwatch.. V = V t The flow rate is produced from: w = V. A V. = volume flow A= cross-sectional area of the pipe where A = π d 2 4 and d = 3 mm. The fall hv is set with the drain valve. From the fall the pipe coefficient of friction is calculated λ as: λ = 2 h v d ρ H2 o l w 2 where l = 400 mm pipe section, the value for hv has to be inserted in Pa The theoretical pipe coefficient of friction λ th is to be compared with the measured value. For laminar flow: λ th = 64 Re 3 Experiments 6

9 3.2 Measured values for laminar flow The following measured values were produced for laminar flow. While performing the experiment, ensure that the water level in the tank remains constant. Measured values: hv [cm] t [s] V [l]. V [l/s] w [m/s] Re λ λ th (calculated) ,2 0, , ,141 0, ,2 0, , ,105 0, ,2 0, , ,081 0, ,2 0, , ,056 0, ,2 0, , ,057 0, ,2 0, , ,050 0, ,4 0, , ,040 0,031 3 Experiments 7

10 3.3 Turbulent flow In this experiment the level tank is not used. For turbulent flow a higher flow rate is required. The water is therefore fed directly from the HM150 or from the main into the pipe section. Proceed as follows: - Close the ball-cock fully. - Close valve [2] fully. Ball cock Valve [1] Valve [2] - Close valve [1] fully. - Connect the Mercury U-tube manometer to the two pressure measuring nipples. - Open the needle valve at the discharge fully. - Switch the HM150 pump on. - Open valve [1] fully. Discharge needle valve Hose connections 3 Experiments 8

11 - Close the needle valve at the discharge until a constant pressure difference of 20 mbar is established on the U-tube manometer. This corresponds to a fall hv of 15 mm. (1 mm Mercury Column = 1,33322 mbar) - Determining the volume flow. - Increase the flow in increments (hv increases) and repeat the volume flow measurements. h1 hv h2 Measurement of the Fall hv on the U-tube manometer Fall h v = h 1 h 2 h1: static pressure at the entrance to the pipe section. h2: static pressure at the outlet from the pipe section. The calculations are made in the same way as for the laminar flow. According to Blasius, however, the theoretical pipe coefficient of friction λ th for turbulent flow is calculated as follows: λ th = 0, Re 3 Experiments 9

12 3.4 Measured values for turbulent flow The following measured values were produced for turbulent flow. Measured values: p [mbar] t [s] V [l]. V [l/s] w [m/s] Re λ λ th (calculated) 20 67,42 0,40 0,0059 0, ,0420 0, ,40 0,0069 0, ,0460 0, ,09 0,40 0,0086 1, ,0390 0, ,40 0,0112 1, ,0348 0, ,79 0,40 0,0121 1, ,0395 0, ,91 0,40 0,0143 2, ,0357 0, ,48 0,40 0,0157 2, ,0358 0, ,47 0,40 0,0178 2, ,0324 0, ,26 0,40 0,0188 2, ,0330 0, ,31 0,40 0,0207 2, ,0342 0, Experiments 10

13 3.5 Graph of measured values λ 0,14 Coefficient of pipe friction 0,12 0,10 0,08 0,06 0,04 0, Re Laminar Turbulent Reynolds number λ measured λ th theoretical 3 Experiments 11