Question

Air at 80 °F is to flow through a 72 ft diameter pipe at an average velocity of 34 ft/s . What diameter pipe should be used to move water at 60 °F and average velocity of 71 ft/s if Reynolds number similarity is enforced? The kinematic viscosity of air at 80 °F is 1.69E-4 ft^2/s and the kinematic viscosity of water at 60 °F is 1.21E-5 ft^2/s. Round your answer (in ft) to TWO decimal places.

Answer 1

Answer:

2.47  ft

Explanation:

Given that:

The initial temperature of air = 80°F

Diameter of the pipe = 72 ft

average velocity  of the air flow through the pipe =  34 ft/s

The objective is to determine the diameter of the  pipe to  be used to move water at:

At a temperature = 60°F   &

An average velocity  of 71 ft/s

Assuming Reynolds number similarity is enforced;

where :

kinematic viscosity (V_air) of air at 80 °F  (V_air)  = 1.69 × 10⁻⁴ ft²/s

kinematic viscosity of water  at 60 °F (V_water) = 1.21 × 10⁻⁵ ft²/s

The diameter of the pipe can be calculated by using the expression:

2.4686  ft

2.47 ft   ( to two decimal places)

Thus; diameter pipe to be use to move water at the given temperature and average velocity is 2.47 ft

Answer 2

Answer:

2.47  ft

Explanation:

Given that:

The initial temperature of air = 80°F

Diameter of the pipe = 72 ft

average velocity $v_{air}$ of the air flow through the pipe =  34 ft/s

The objective is to determine the diameter of the  pipe to  be used to move water at:

At a temperature = 60°F   &

An average velocity $v_{water}$ of 71 ft/s

Assuming Reynolds number similarity is enforced;

where :

kinematic viscosity (V_air) of air at 80 °F  (V_air)  = 1.69 × 10⁻⁴ ft²/s

kinematic viscosity of water  at 60 °F (V_water) = 1.21 × 10⁻⁵ ft²/s

The diameter of the pipe can be calculated by using the expression:

$D_{water} = \dfrac{V_{water}}{V_{air}}*\dfrac{v_{air}}{v_{water}}* D_{air}$

$D_{water} = \dfrac{1.21*10^{-5} \ ft^2/s}{1.69*10^{-4} \ ft^2/s}*\dfrac{34 \ ft/s}{71 \ ft/s}* 72 \ ft$

$D_{water} =$ 2.4686  ft

$D_{water} =$ 2.47 ft   ( to two decimal places)

Thus; diameter pipe to be use to move water at the given temperature and average velocity is 2.47 ft