Date post: | 02-Dec-2014 |

Category: |
## Documents |

Author: | vrushiket-patil |

View: | 730 times |

Download: | 9 times |

Share this document with a friend

Embed Size (px)

Popular Tags:

of 7
/7

Transcript

Impact of Jet on VanesAim Study the relation between the force produced and the change of momentum when a jet strikes a vane. Compare between force exerted by a jet on a flat plate and on a hemispherical surface.

Apparatus Acrylic nozzle stainless steel enclosure with glass viewports interchangeable arcylic circular flat plate and a hemispherical cup

Weights of various mass.measuring tank to measure the discharge and electronic watch

TheoryMomentum conservation principle is applied in order to find out the force applied by jet onto the flat-plate or spherical cup. =

F = Q V F = Q (Vin Vout)Where, F: force applied on plate by jet Q: volumetric flow rate Vin: velocity at the time of striking of jet onto the plate. Vout: velocity of water leaving the plate.

The volumetric flow rate in the equation 'Q' is calculated with the help of measuring tank and stopwatch. = Where, H: height in measuring tank t: time taken to achieve the height Atank: base area of measuring tank ME-313, IIT Gandhinagar, Dept. of Mechanical Engineering Page 1

Vnozzle is calculated by, =

Where, Vnozzle: velocity of jet at the nozzle Anozzle: cross sectional area of nozzle Relation between V and Vnozzle can be given as,in

Vin = Vnozzel 2 g S Where; g: the gravitational acceleration (9.81 m/s ). S: the distance between the jet and the plates. Schematic of jet impact on vanes has been shown in below diagram.2

2

2

Vout generally equals Vin cos , where represents the change in direction of the jet.

For the flat plat = 90, so that Vout = 0. ME-313, IIT Gandhinagar, Dept. of Mechanical Engineering Page 2

For the Hemispherical cup = 180, so that V

out

= -V

in

So the following relations are used for calculating the Predicted values of the force; For the Flat plate: F = Q Vin in

For the Hemi spherical cup: F =2 Q V

The actual force exerted is calculated by the equation, F = 9.81 * w Where, w: mass of weights plus mass of plate and rod.

Procedure Clean the apparatus and make All Tanks free from dust. Close the drain valves provided. Fix desired Vane on the apparatus. Fill Sump tank with Clean Water and ensure that no foreign particles are there. Ensure that all On/Off Switches given on the Panel are at OFF position. Now switch on the Main Power Supply (220 V AC, 50 Hz). Switch on the Pump. Regulate Flow of water through channel with the help of given Flow Control Valve. Put known value of weight on the plate. Now control the valve so that the applied weight on the top is counter balanced by the impact of jet. Measure Flow Rate using Measuring Tank and Stop Watch. Repeat the experiment with different weights. Slowly open the bypass valve. Switch off the pump.

ME-313, IIT Gandhinagar, Dept. of Mechanical Engineering

Page 3

Data Area of measuring tank= 0.25*0.4= 0.1 m2 Diameter of nozzle d=0.01m Area of cross section of nozzle A=d2/4=0.0000785 m2 Density of water= 1000 kg/m3 Weight of aluminum disc + rod = 14.5 gm Weight of flat plate= 89.5 gm Weight of hemispherical vane= 97.5 gm

Additional constant weights: for flat plate = 104 grams for hemispherical vane = 112 grams

ObservationA. For Flat Plate:S.No 1 2 3 4 W (gm) 202.5 296.0 390.0 585.0 Fexp (N) 1.985 2.901 3.822 5.733 S (cm) 15.50 16.50 13.40 12.50 H (cm) 24.20 27.50 29.10 32.20 t (sec) 44.94 45.13 44.63 44.66 Q (m3/s) 0.0005385 0.0006094 0.0006520 0.0007210 Vnozzle (m/s) 6.860 7.762 8.306 9.185 Vim (m/s) 6.635 7.551 8.146 9.050 Ftheo (N) 3.456 4.476 5.210 6.430

B. For Hemispherical vane:S.No 1 2 3 4 W (gm) 210.5 304.0 398.0 593.0 Fexp (N) 2.063 2.979 3.900 5.811 S (cm) 11.60 11.40 11.10 9.400 H (cm) 19.00 21.20 23.60 27.80 t (sec) 44.97 44.53 44.88 44.56 Q (m3/s) 0.0004225 0.0004761 0.0005258 0.0006239 Vnozzle (m/s) 5.382 6.065 6.699 7.947 Vim (m/s) 5.167 5.878 6.534 7.831 Ftheo (N) 4.191 5.424 6.703 9.627

ME-313, IIT Gandhinagar, Dept. of Mechanical Engineering

Page 4

Observation for the sample calculation W= 202.5 gm S= 15.50 cm H= 24.20 cm t= 44.94 s Area of measuring tank= 0.25*0.4= 0.1 m2 Area of cross section of nozzle A=d2/4=0.0000785 m2 Density of water= 1000 kg/m3

Sample CalculationFlow rate = =

=

0.10 0.242 44.94

= 0.0242 m3

Velocity at the nozzle = Vnozzle =

= 6.860 m/s

=

2 2 = = 6.862 2 9.80 .15 = 6.63 m/s

Experimental Force = Fexp = mg = 1.985 N

Theoretical Force = Ftheo = 2 = 3.45 N

ME-313, IIT Gandhinagar, Dept. of Mechanical Engineering

Page 5

Graphs

Flat Plate7

6Force Exerted (N) 5 4 3 2 1 0 0 2 4 6 8 10 Experimental

Theoretical

Velocity (m/s)

Hemispherical Vane12 Force Exerted (N) 10 8 6 4 2 0 0 2 4 6 8 10 Experimental Theoretical

Velocity (m/s)

PrecautionNever start the pump when bypass valve is closed. Slowly close bypass valve in order to avoid sudden impact on the plates. Also open bypass valve slowly before switching off the pump.

ME-313, IIT Gandhinagar, Dept. of Mechanical Engineering

Page 6

Errors Due to use of stop watch manual errors in timings are introduced. Even though the weight was balanced, the height gradually dropped while calculating the H. This may be attributed to drop in pressure head because of drop in water level in supply tank.

Conclusion Experimental force exerted by jet on hemispherical vane is always more than that of flat plate, and almost double to that of flat plate force. As the weight on the plats increased, higher impact velocity or jet velocity is required to counter balance the force.

-Vrushiket Patil(09003044) Mechanical Btech 2009

ME-313, IIT Gandhinagar, Dept. of Mechanical Engineering

Page 7

Recommended