Concept explainers
A fan is to be selected to ventilate a bathroom whose dimensions are
(a)
The wattage of the fan-motor unit to be purchased.
Answer to Problem 80P
The wattage of the fan-motor unit to be purchased is
Explanation of Solution
Given information:
The dimension of the bathroom is
Write the expression for the total volume of the bathroom.
Here, the length of the bathroom is
Write the expression for the volume flow rate of the air.
Here, the time taken by fan to replace the entire volume is
Write the expression for the mass flow rate of air.
Here, the density of the air is
Write the expression for the electric power rating of the fan.
Here, the velocity of the air is
Calculation:
Substitute
Substitute
Substitute
Here, the kinetic energy correction factor is
Substitute
Conclusion:
Thus, the wattage of the fan-motor unit to be purchased is
(b)
The diameter of the fan casing.
Answer to Problem 80P
The diameter of the fan casing is
Explanation of Solution
Given information:
The volume flow rate is
Write the expression for the diameter of the casing.
Calculation:
Substitute
Conclusion:
Thus, the diameter of the fan casing is
(c)
The pressure difference across the fan.
Answer to Problem 80P
The pressure difference across the fan is
Explanation of Solution
Given information:
The electric power of the fan is
Write the expression for the pressure difference of the fan by applying the energy equation.
Write the expression for the effective power of the fan.
Calculation:
Substitute
Substitute
Conclusion:
Thus, the pressure difference across the fan is
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Chapter 5 Solutions
Fluid Mechanics: Fundamentals and Applications
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