Impacts of Jets Experiment

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  • Exp 3

    Force due to impact of jet of water

    and comparison with theoretical

    practical calculated values

  • Jet Apparatus

  • Interchangeable target wanes

    = 90 Flat target plate

    = 180 Semi sphere target plate

    = 30 degree target plate

    = 120 degree conical target plate

  • About Apparatus

  • Theory Consider a jet of water which impacts on to a target surface causing the direction of

    the jet to be changed through and angle as shown in Figure. In the absence of friction, the magnitude of the velocity across the surface is equal to the incident velocity Vi

    The impulse force exerted on the target will be equal and opposite to the force which acts on the water to impart the change in direction

    Umar FarooqCalloutwe taking impulse because we consider for short interval of time

  • Derivation

    V i sin

    V i

    V i cos

  • Impact and exit velocity of Jet

    the jet exit velocity can be calculated from the measured flow rate and the nozzle exit area

    V n = Q / A

    Q = discharge through hydraulic bench A= area of jet jet Diameter = 7mm

    However, as the nozzle is below the target, the impact velocity will Be less than the nozzle velocity due to interchanges between potential

    energy and kinetic energy.

    Umar FarooqHighlight

    Umar FarooqHighlight

  • Effect of Height

    Applying the Bernoulli equation between nozzle and target plate.

    P n / +V2

    n /2g +Z n= P i / + Vi2 / 2g + Z i

    Since the jet is open to the atmosphere

    P n / +V2

    n /2g +Z n= P i / + Vi2 / 2g + Z i

    Vi2 = V2n 2gh As Z n - Z i = h

    Where h is height of target above the nozzle exit.

    0 0

  • Procedure

    Set the reference pointer to match the weight support disc after leveling instrument.

  • The pump is started and the water flow is established by steadily opening the bench regulating valve until it is fully

    open.

    The vane will now be deflected by the impact of the jet. Weights (M) are added onto the weight carrier until the

    weight platform is again floating in mid position.

  • The flow rate is measured and the result is recorded on the test sheet,

    together with the corresponding value of weight on the tray. The form of

    the deflected jet is observed and its shape is noted.

  • Shapes of Jets after deflection

  • The weight on the weight carrier is reduced in steps and balance of weight platform is maintained by

    regulating the flow rate in about eight or ten even

    steps, each time recording the value of flow rate and

    weight on the weight carrier.

    The control valve is closed and the pump is switched off.

    The experiment is repeated with different target vanes and nozzles.

  • Theoretical and practical values

    of forces. Theoretical force by impact of jet on target plate is given by

    following formula.

    W= mg

    practical force by impact of jet on target plate is given by following formula.

    F= QVi ( 1-cos)

    Here Vi2 = V2n 2gh

  • Practical Impact Force on

    Normal plate, conical 120 , 30

    and semispherical Target plate

    Normal plate:

    F= QVi ( 1-cos) as = 90 so force will be QVi.

    Conical 120:

    F= QVi ( 1-cos) as = 120 so force will be 1.5QVi.

    Semispherical target plate:

    F= QVi ( 1-cos) as = 180 so force will be 2QVi.

  • Last task is to compare these practical values with theoretical values evaluated by

    w= mg