Examveda

The fluid jet discharging from a 2" diameter orifice has a diameter of 1.75" at its vena-contracta. The co-efficient of contraction is

A. 1.3

B. 0.766

C. 0.87

D. None of these

Answer: Option B


This Question Belongs to Chemical Engineering >> Fluid Mechanics

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  1. Dhayaal
    Dhayaal :
    1 year ago

    The coefficient of contraction (
    𝐶
    𝑐
    C
    c

    ) is defined as the ratio of the area of the jet at the vena-contracta to the area of the orifice.

    Given:

    Diameter of the orifice (
    𝐷
    1
    D
    1

    ) = 2 inches
    Diameter of the jet at the vena-contracta (
    𝐷
    2
    D
    2

    ) = 1.75 inches
    First, we need to calculate the areas of the orifice and the jet at the vena-contracta.

    The area of a circle is given by:
    𝐴
    =
    𝜋
    (
    𝐷
    2
    )
    2
    A=π(
    2
    D

    )
    2


    So, the area of the orifice (
    𝐴
    1
    A
    1

    ) is:
    𝐴
    1
    =
    𝜋
    (
    𝐷
    1
    2
    )
    2
    =
    𝜋
    (
    2
    2
    )
    2
    =
    𝜋
    (
    1
    )
    2
    =
    𝜋
    A
    1

    =π(
    2
    D
    1



    )
    2
    =π(
    2
    2

    )
    2
    =π(1)
    2


    The area of the jet at the vena-contracta (
    𝐴
    2
    A
    2

    ) is:
    𝐴
    2
    =
    𝜋
    (
    𝐷
    2
    2
    )
    2
    =
    𝜋
    (
    1.75
    2
    )
    2
    =
    𝜋
    (
    0.875
    )
    2
    =
    𝜋
    (
    0.765625
    )
    A
    2

    =π(
    2
    D
    2



    )
    2
    =π(
    2
    1.75

    )
    2
    =π(0.875)
    2
    =π(0.765625)

    Next, the coefficient of contraction (
    𝐶
    𝑐
    C
    c

    ) is the ratio of
    𝐴
    2
    A
    2

    to
    𝐴
    1
    A
    1

    :
    𝐶
    𝑐
    =
    𝐴
    2
    𝐴
    1
    =
    𝜋
    (
    0.765625
    )
    𝜋
    =
    0.765625
    C
    c

    =
    A
    1


    A
    2



    =
    π
    π(0.765625)

    =0.765625

    Therefore, the coefficient of contraction is:
    𝐶
    𝑐
    =
    0.765625
    C
    c

    =0.765625

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