DISCHARGE THROUGH PARTIALLY SUBMERGED ORIFICE

We were discussing the basic difference between orifice and mouthpiece, classification of orifices and mouthpieces, advantages and disadvantages of orifices, hydraulic coefficients and also experimental process to determine the hydraulic coefficients, in the subject of fluid mechanics, in our recent posts.

Now we will go ahead to find out the flow through partially submerged orifice, in the subject of fluid mechanics, with the help of this post.

Partially submerged orifice is the one which has its outlet side partially submerged under liquid. Therefore, partially submerged orifice will have two portions i.e. upper portion and lower portion.

Upper portion of partially submerged orifice will behave like an orifice discharging freely and lower portion of partially submerged orifice will behave like a submerged orifice.

We must note it here that only a large orifice will behave like a partially submerged orifice. Partially submerged orifice is also called as partially drowned orifice.

Total discharge through partially submerged orifice will be determined by adding the discharge through upper portion and lower portion of partially submerged orifice.

Total discharge through partially submerged orifice = Discharge through free portion + Discharge through submerged portion

We have already discussed the post related with discharge through fully submerged orifice and we have following equation of discharge as mentioned here.

We have also discussed the post related with discharge through large orifice. Discharge through free portion of the orifice will be equivalent to the discharge through large orifice. We have following equation of discharge through free portion of the orifice as mentioned here.

Now we will determine the total discharge through the partially submerged orifice.

Q = Q₁ + Q₂

Where,

H₁ = Height of water above the top of the orifice on the upstream side

H₂ = Height of water above the bottom of the orifice

H = Difference in level of water

b = Width of the orifice

C_d = Coefficient of discharge

This is the expression for the flow or discharge through the partially submerged orifice.

Now we will go ahead to find out the method to determine the time of emptying a tank through an orifice at its bottom, in the subject of fluid mechanics, in our next post.

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