a) Explanation Apply the dry air mass balance on the cooling tower. m ˙ a 1 = m ˙ a 2 = m ˙ a Here, mass flow rate of air at inlet and outlet is m ˙ a 1 and m ˙ a 2 , and mass flow rate of liquid water is m ˙ a . Apply the water mass balance on the cooling tower. m ˙ 3 + m ˙ a 1 ω 1 = m ˙ 4 + m ˙ a 2 ω 2 m ˙ 3 − m ˙ 4 = m ˙ a ( ω 2 − ω 1 ) m ˙ 3 − m ˙ 4 = m ˙ makeup (I) Here, mass flow rate of water at state 3 and 4 is m ˙ 3 and m ˙ 4 , and mass flow rate of required makeup water is m ˙ makeup . Apply the energy balance on the cooling tower. ∑ in m ˙ h = ∑ out m ˙ h m ˙ a 1 h 1 + m ˙ 3 h 3 = m ˙ a 1 h 1 + m ˙ 4 h 4 m ˙ 3 h 3 = m ˙ a ( h 2 − h 1 ) + ( m ˙ 3 − m ˙ makeup ) h 4 m ˙ a = m ˙ 3 ( h 3 − h 4 ) ( h 2 − h 1 ) − ( ω 2 − ω 1 ) h 4 (II) Write the expression to obtain the volume flow rate of air into the cooling tower ( V ˙ 1 ) . V ˙ 1 = m ˙ a v 1 (III) Conclusion: Refer Table A-4E, “Saturated water – Temperature table”, obtain the enthalpy ( h f @ 80 ° F = h 4 ) as 48.07 Btu / lbm at a temperature of 80 ° F . Refer Table A-4E, “Saturated water – Temperature table”, obtain the enthalpy ( h f @ 110 ° F = h 3 ) as 78.02 Btu / lbm at a temperature of 110 °F . Refer Fig A-31E, “Psychrometric chart at 1 atm total pressure”, at inlet temperature ( T 1 = 76 °F ) , and relative humidity ( ϕ 1 = 60 % ) , read the value of inlet enthalpy ( h 1 ) as 30.9 Btu / lbm dry air , inlet specific humidity ( ω 1 ) as 0 b) To determine The mass flow rate of required makeup water.

8th Edition

ISBN: 9780073398174

Author: Yunus A. Cengel Dr., Michael A. Boles

Publisher: McGraw-Hill Education

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Chapter 14.7, Problem 108P

To determine

The volume flow rate of air into the cooling tower.

To determine

The mass flow rate of required makeup water.

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Chapter 14.7, Problem 107P

Chapter 14.7, Problem 109P

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Chapter 14 Solutions

Thermodynamics: An Engineering Approach

Ch. 14.7 - What is the difference between dry air and...Ch. 14.7 - What is the difference between the specific...Ch. 14.7 - Can the water vapor in air be treated as an ideal...Ch. 14.7 - Is the relative humidity of saturated air...Ch. 14.7 - Is it possible to obtain saturated air from...Ch. 14.7 - Moist air is passed through a cooling section...Ch. 14.7 - How will (a) the specific humidity and (b) the...Ch. 14.7 - Prob. 8P Ch. 14.7 - Consider a tank that contains moist air at 3 atm...Ch. 14.7 - Why are the chilled water lines always wrapped...

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