Repeat Prob. 6-56 for a water flow rate of 60 L/s.
(a)
The rotational speed of the sprinkler.
Answer to Problem 57P
The rotational speed of the sprinkler is
Explanation of Solution
Given information:
The volume flow rate of the water is
Write the expression for the velocity at the smaller section of the sprinkler.
Here, the cross sectional area at the smaller section of the sprinkler is
Write the expression for the velocity at the larger section of the sprinkler.
Here, the cross sectional area at the larger section of the sprinkler is
Write the expression for the velocity of the jet with respect to smaller jet.
Here, the distance of the smaller jet from the axis of rotation is
Write the expression for the velocity of the jet with respect to larger jet.
Here, the distance of the larger jet from the axis of rotation is
Write the expression for the absolute velocity of the water with respect to larger section of sprinkler.
Write the expression for the absolute velocity of the water with respect to smaller section of sprinkler.
Write the expression for the mass flow rate of the water at larger section of sprinkler.
Here, the density of the water is
Write the expression for the mass flow rate of the water at smaller section of sprinkler.
Here, the cross sectional area at the smaller section is
Write the expression for the mass flow rate of the water.
Here, the volume flow rate of the water is
Write the expression for the total mass flow rate.
Write the expression for the discharge for the smaller section.
Write the expression for the discharge for the larger section.
Write the expression for the angular speed using the angular momentum equation.
Write the expression for the rotation speed of the sprinkler.
Calculation:
Substitute
Substitute
Substitute
Substitute
Substitute
Substitute
Substitute
Substitute
Substitute
Substitute
Substitute
Substitute
Substitute
Substitute
Conclusion:
The rotational speed of the sprinkler is
(b)
The total torque required to prevent the sprinkler.
Answer to Problem 57P
The total torque required to prevent the sprinkler is
Explanation of Solution
Write the expression for the torque on the sprinkler due to the larger jet.
Write the expression for the torque on the sprinkler due to the smaller jet.
Write the expression for the total torque.
Write the expression for the mass flow rate for the smaller section.
Write the expression for the mass flow rate for the larger section.
Calculation:
Substitute
Substitute
Substitute
Substitute
Substitute
Substitute
Substitute
Conclusion:
The total torque required to prevent the sprinkler is
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Chapter 6 Solutions
Fluid Mechanics: Fundamentals and Applications
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