EBK THERMODYNAMICS: AN ENGINEERING APPR
EBK THERMODYNAMICS: AN ENGINEERING APPR
8th Edition
ISBN: 9780100257054
Author: CENGEL
Publisher: YUZU
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Chapter 14.7, Problem 138RP

a)

To determine

The mass flow rate of the cooling water.

a)

Expert Solution
Check Mark

Answer to Problem 138RP

The mass flow rate of the cooling water is 1337 kg/s.

Explanation of Solution

Apply the dry air mass balance on the cooling tower.

m˙a1=m˙a2=m˙a

Here, mass flow rate of air at inlet and outlet is m˙a1andm˙a2, and mass flow rate of liquid water is m˙a.

Apply the water mass balance on the cooling tower.

m˙3+m˙a1ω1=m˙4+m˙a2ω2m˙3m˙4=m˙a(ω2ω1)

m˙3m˙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.

inm˙h=outm˙hm˙a1h1+m˙3h3=m˙a1h1+m˙4h4m˙3h3=m˙a(h2h1)+(m˙3m˙makeup)h4m˙a=m˙3(h3h4)(h2h1)(ω2ω1)h4 (II)

Apply steady flow energy balance equation on the cooling water.

Q˙waste=m˙3h3(m˙3m˙makeup)h4

Q˙waste=m˙3h3(m˙3m˙a(ω2ω1))h4 (III)

Here, rate of heat removal is Q˙waste.

Conclusion:

Refer Table A-4, “Saturated water – Temperature table”, obtain the enthalpy (hf@30°C=h4) as 125.74 kJ/kgH2O at a temperature of 30°C.

Refer Table A-4, “Saturated water – Temperature table”, obtain the enthalpy (hf@42°C=h3) as 175.90 kJ/kgH2O at a temperature of 42°C.

Refer Fig A-31, “Psychrometric chart at 1 atm total pressure”, at dry bulb temperature (Tdb=23°C), and wet bulb temperature (Twb=16°C), read the value of inlet enthalpy (h1) as 44.67kJ/kgdry air, inlet specific humidity (ω1) as 0.008462kgH2O/kgdryair, and inlet specific volume of dry air (v1) as 0.8504m3/kgdryair.

Refer Fig A-31, “Psychrometric chart at 1 atm total pressure”, at temperature (T2=32°C), read the value of exit enthalpy (h2) as 110.69kJ/kgdry air, and exit specific humidity (ω2) as 0.03065kgH2O/kgdryair.

Substitute 125.74 kJ/kgH2O for h4, 175.90 kJ/kgH2O for h3, 44.67 kJ/kgH2O for h1, 110.69 kJ/kgH2O for h2, 0.008462kgH2O/kgdryair for ω1, and 0.03065kgH2O/kgdryair for ω2 in Equation (II).

m˙a=m˙3(175.90 kJ/kgH2O125.74 kJ/kgH2O)(110.69 kJ/kgH2O44.67 kJ/kgH2O)[(0.03065lbmH2O/lbmdryair0.008462lbmH2O/lbmdryair)125.74 kJ/kgH2O]

m˙a=0.7933m˙3 (IV)

Substitute 70 MW for Q˙waste, 0.7933m˙3 for m˙a, 125.74 kJ/kgH2O for h4, 175.90 kJ/kgH2O for h3, 0.008462kgH2O/kgdryair for ω1, and 0.03065kgH2O/kgdryair for ω2 in Equation (III).

70 MW(103kJ/s1 MW)={m˙3(175.90 kJ/kg)(m˙30.7933m˙3(0.03065lbmH2O/lbmdryair0.008462lbmH2O/lbmdryair))125.74 kJ/kg}70000=175.9m˙3125.74m˙3+2.21m˙3m˙3=1337 kg/s

Thus, the mass flow rate of the cooling water is 1337 kg/s.

b)

To determine

The volume flow rate of air into the cooling tower.

b)

Expert Solution
Check Mark

Answer to Problem 138RP

The volume flow rate of air into the cooling tower is 902 m3/s.

Explanation of Solution

Write the expression to obtain the volume flow rate of air into the cooling tower (ν˙1).

ν˙1=m˙av1 (V)

Conclusion:

Substitute 1337 kg/s for m˙3 in Equation (IV).

m˙a=0.7933(1337 kg/s)=1061 kg/s

Substitute 1061 kg/s for m˙a and 0.8504m3/kg for v1 in Equation (V).

ν˙1=1061 kg/s(0.8504m3/kg)=902 m3/s

Thus, the volume flow rate of air into the cooling tower is 902 m3/s.

c)

To determine

The mass flow rate of required makeup water.

c)

Expert Solution
Check Mark

Answer to Problem 138RP

The mass flow rate of required makeup water is 23.5 kg/s.

Explanation of Solution

Write the expression to obtain the mass flow rate of required makeup water (m˙makeup) from Equation (I).

m˙makeup=m˙a(ω2ω1) (VI)

Conclusion:

Substitute 1061 kg/s for m˙a, 0.008462kgH2O/kgdryair for ω1 and 0.03065kgH2O/kgdryair for ω2 in Equation (VI).

m˙makeup=1061 kg/s(0.03065kgH2O/kgdryair0.008462kgH2O/kgdryair)=23.5 kg/s

Thus, the mass flow rate of required makeup water is 23.5 kg/s.

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Chapter 14 Solutions

EBK THERMODYNAMICS: AN ENGINEERING APPR

Ch. 14.7 - A tank contains 15 kg of dry air and 0.17 kg of...Ch. 14.7 - Prob. 12PCh. 14.7 - Prob. 13PCh. 14.7 - 14–13 A room contains air at 20°C and 98 kPa at a...Ch. 14.7 - A room contains air at 85F and 13.5 psia at a...Ch. 14.7 - An 8-m3 tank contains saturated air at 30C, 105...Ch. 14.7 - Prob. 17PCh. 14.7 - Prob. 18PCh. 14.7 - Prob. 19PCh. 14.7 - Andy and Wendy both wear glasses. On a cold winter...Ch. 14.7 - In summer, the outer surface of a glass filled...Ch. 14.7 - In some climates, cleaning the ice off the...Ch. 14.7 - Prob. 23PCh. 14.7 - Prob. 24PCh. 14.7 - Prob. 25PCh. 14.7 - Prob. 26PCh. 14.7 - A thirsty woman opens the refrigerator and picks...Ch. 14.7 - Prob. 28PCh. 14.7 - The air in a room has a dry-bulb temperature of...Ch. 14.7 - Prob. 31PCh. 14.7 - Prob. 32PCh. 14.7 - How do constant-enthalpy and...Ch. 14.7 - At what states on the psychrometric chart are the...Ch. 14.7 - How is the dew-point temperature at a specified...Ch. 14.7 - Can the enthalpy values determined from a...Ch. 14.7 - Prob. 37PCh. 14.7 - Prob. 39PCh. 14.7 - Prob. 41PCh. 14.7 - Prob. 42PCh. 14.7 - Prob. 43PCh. 14.7 - Prob. 44PCh. 14.7 - What does a modern air-conditioning system do...Ch. 14.7 - How does the human body respond to (a) hot...Ch. 14.7 - Prob. 47PCh. 14.7 - How does the air motion in the vicinity of the...Ch. 14.7 - Consider a tennis match in cold weather where both...Ch. 14.7 - Prob. 50PCh. 14.7 - Prob. 51PCh. 14.7 - Prob. 52PCh. 14.7 - What is metabolism? What is the range of metabolic...Ch. 14.7 - What is sensible heat? How is the sensible heat...Ch. 14.7 - Prob. 55PCh. 14.7 - Prob. 56PCh. 14.7 - Prob. 57PCh. 14.7 - Prob. 58PCh. 14.7 - Repeat Prob. 1459 for an infiltration rate of 1.8...Ch. 14.7 - An average person produces 0.25 kg of moisture...Ch. 14.7 - An average (1.82 kg or 4.0 lbm) chicken has a...Ch. 14.7 - How do relative and specific humidities change...Ch. 14.7 - Prob. 63PCh. 14.7 - Prob. 64PCh. 14.7 - Prob. 65PCh. 14.7 - Humid air at 40 psia, 50F, and 90 percent relative...Ch. 14.7 - Air enters a 30-cm-diameter cooling section at 1...Ch. 14.7 - Prob. 68PCh. 14.7 - Prob. 69PCh. 14.7 - Why is heated air sometimes humidified?Ch. 14.7 - Air at 1 atm, 15C, and 60 percent relative...Ch. 14.7 - Prob. 72PCh. 14.7 - An air-conditioning system operates at a total...Ch. 14.7 - Prob. 74PCh. 14.7 - Why is cooled air sometimes reheated in summer...Ch. 14.7 - Prob. 76PCh. 14.7 - Prob. 77PCh. 14.7 - Air enters a 40-cm-diameter cooling section at 1...Ch. 14.7 - Repeat Prob. 1479 for a total pressure of 88 kPa...Ch. 14.7 - Prob. 81PCh. 14.7 - Prob. 83PCh. 14.7 - Prob. 84PCh. 14.7 - Prob. 85PCh. 14.7 - Atmospheric air at 1 atm, 32C, and 95 percent...Ch. 14.7 - Prob. 88PCh. 14.7 - Prob. 89PCh. 14.7 - Does an evaporation process have to involve heat...Ch. 14.7 - Prob. 93PCh. 14.7 - Prob. 94PCh. 14.7 - Air at 1 atm, 20C, and 70 percent relative...Ch. 14.7 - Two unsaturated airstreams are mixed...Ch. 14.7 - Consider the adiabatic mixing of two airstreams....Ch. 14.7 - Prob. 98PCh. 14.7 - Two airstreams are mixed steadily and...Ch. 14.7 - A stream of warm air with a dry-bulb temperature...Ch. 14.7 - Prob. 104PCh. 14.7 - How does a natural-draft wet cooling tower work?Ch. 14.7 - What is a spray pond? How does its performance...Ch. 14.7 - The cooling water from the condenser of a power...Ch. 14.7 - Prob. 108PCh. 14.7 - A wet cooling tower is to cool 60 kg/s of water...Ch. 14.7 - Prob. 110PCh. 14.7 - Prob. 111PCh. 14.7 - Prob. 112PCh. 14.7 - Prob. 113RPCh. 14.7 - Prob. 114RPCh. 14.7 - Prob. 115RPCh. 14.7 - Prob. 116RPCh. 14.7 - Prob. 117RPCh. 14.7 - Prob. 118RPCh. 14.7 - Prob. 119RPCh. 14.7 - Prob. 120RPCh. 14.7 - 14–121 The relative humidity inside dacha of Prob....Ch. 14.7 - Prob. 122RPCh. 14.7 - Prob. 124RPCh. 14.7 - 14–126E Air at 15 psia, 60°F, and 70 percent...Ch. 14.7 - Prob. 127RPCh. 14.7 - Air enters a cooling section at 97 kPa, 35C, and...Ch. 14.7 - Prob. 129RPCh. 14.7 - Humid air at 101.3 kPa, 36C dry bulb and 65...Ch. 14.7 - 14–131 Air enters an air-conditioning system that...Ch. 14.7 - Prob. 132RPCh. 14.7 - Prob. 133RPCh. 14.7 - Conditioned air at 13C and 90 percent relative...Ch. 14.7 - Prob. 138RPCh. 14.7 - A room is filled with saturated moist air at 25C...Ch. 14.7 - Prob. 141FEPCh. 14.7 - A 40-m3 room contains air at 30C and a total...Ch. 14.7 - Prob. 143FEPCh. 14.7 - The air in a house is at 25C and 65 percent...Ch. 14.7 - On the psychrometric chart, a cooling and...Ch. 14.7 - On the psychrometric chart, a heating and...Ch. 14.7 - An airstream at a specified temperature and...Ch. 14.7 - Prob. 148FEPCh. 14.7 - Air at a total pressure of 90 kPa, 15C, and 75...
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