Fundamentals of Thermal-Fluid Sciences
Fundamentals of Thermal-Fluid Sciences
5th Edition
ISBN: 9780078027680
Author: Yunus A. Cengel Dr., Robert H. Turner, John M. Cimbala
Publisher: McGraw-Hill Education
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Chapter 17, Problem 124RQ

(a)

To determine

The rate of heat transfer across the warehouse wall.

(a)

Expert Solution
Check Mark

Explanation of Solution

Given:

Width of the refrigerator wall (w) is 5 m.

Height of the refrigerator wall (L) is 10 m.

Thickness of the aluminum (t1) is 1 cm.

Thickness of the fiberglass (t2) is 8 cm.

Thickness of the gypsum board (t3) is 3 cm.

Thermal conductivity of aluminum (k1) is 200 W/mK.

Thermal conductivity of aluminum (k2) is 0.038 W/mK.

Thermal conductivity of aluminum (k3) is 0.48 W/mK.

Calculation:

Determine the overall heat transfer coefficient.

  U1=11hi+LAlkAl+Lfgkfg+Lgykgy+1ho=1{140 W/m2°C+0.01 m200 W/m2°C+0.08 m0.038 W/m2°C+0.03 m0.48 W/m2°C+140 W/m2°C}=0.451 W/m2°C

Determine the rate of heat transfer through the warehouse.

  Q˙1=U1A(ToTi)=(0.451 W/m2°C)(5 m×10 m)[20°C(10°C)]=676 W

Thus, the rate of heat transfer through the warehouse is 676 W_.

(b)

To determine

The rate of heat transfer for the bolted wall.

(b)

Expert Solution
Check Mark

Explanation of Solution

Determine the rate of heat transfer with the consideration of metal bolts.

  Q˙1=U1A1(ToTi)=(0.451 W/m2°C)[10 m×5 m400×0.25π(0.02 m)2](20°C(10°C))=674.8 W

Determine the overall heat transfer coefficient.

  U2=11hi+Lboltskbolts+1ho=1140 W/m2°C+0.12 m43 W/m2°C+140 W/m2°C=18.94 W/m2°C

Determine the rate of heat transfer with the consideration of metal bolts.

  Q˙2=U2A2(ToTi)=(18.94 W/m2°C)[400×0.25π(0.02 m)2][20°C(10°C)]=71.4 W

Determine the total rate of heat transfer.

  Q˙=Q˙1+Q˙2=674.8 W+71.4 W=746 W

Thus, the rate of heat transfer for the bolted wall is 746 W_.

(c)

To determine

The percent change in the rate of heat transfer across the wall due to metal bolts.

(c)

Expert Solution
Check Mark

Explanation of Solution

Determine the percent change in the rate of heat transfer across the wall due to metal bolts.

  % change =746 W676 W676 W=0.103×100%=10.3%

Thus, the percent change in the rate of heat transfer across the wall due to metal bolts is 10.3%_.

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Chapter 17 Solutions

Fundamentals of Thermal-Fluid Sciences

Ch. 17 - Consider a surface of area A at which the...Ch. 17 - How does the thermal resistance network associated...Ch. 17 - Consider steady one-dimensional heat transfer...Ch. 17 - Consider a window glass consisting of two...Ch. 17 - Prob. 15PCh. 17 - Prob. 16PCh. 17 - Prob. 17PCh. 17 - Prob. 18PCh. 17 - Prob. 19PCh. 17 - Consider a power transistor that dissipates 0.2 W...Ch. 17 - A 1.0 m × 1.5 m double-pane window consists of two...Ch. 17 - Consider a 1.2-m-high and 2-m-wide glass window...Ch. 17 - Prob. 23PCh. 17 - Prob. 24PCh. 17 - Prob. 26PCh. 17 - Prob. 27PCh. 17 - Prob. 28PCh. 17 - Prob. 29PCh. 17 - Prob. 30PCh. 17 - A 2-m × 1.5-m section of wall of an industrial...Ch. 17 - The wall of a refrigerator is constructed of...Ch. 17 - Prob. 34PCh. 17 - Prob. 35PCh. 17 - Prob. 36PCh. 17 - What is thermal contact resistance? How is it...Ch. 17 - Will the thermal contact resistance be greater for...Ch. 17 - Explain how the thermal contact resistance can be...Ch. 17 - A wall consists of two layers of insulation...Ch. 17 - A plate consists of two thin metal layers pressed...Ch. 17 - Consider two surfaces pressed against each other....Ch. 17 - Prob. 43PCh. 17 - Prob. 44PCh. 17 - Prob. 45PCh. 17 - Prob. 46PCh. 17 - Prob. 47PCh. 17 - Prob. 48PCh. 17 - Prob. 49PCh. 17 - Prob. 50PCh. 17 - Prob. 51PCh. 17 - Prob. 52PCh. 17 - Prob. 53PCh. 17 - When plotting the thermal resistance network...Ch. 17 - Prob. 55PCh. 17 - Prob. 56PCh. 17 - Prob. 57PCh. 17 - A typical section of a building wall is shown in...Ch. 17 - Prob. 59PCh. 17 - Prob. 61PCh. 17 - Prob. 62PCh. 17 - Prob. 63PCh. 17 - In an experiment to measure convection heat...Ch. 17 - What is an infinitely long cylinder? When is it...Ch. 17 - Can the thermal resistance concept be used for a...Ch. 17 - Consider a short cylinder whose top and bottom...Ch. 17 - Prob. 68PCh. 17 - 50-m-long section of a steam pipe whose outer...Ch. 17 - Superheated steam at an average temperature 200°C...Ch. 17 - Steam exiting the turbine of a steam power plant...Ch. 17 - Repeat Prob. 17–72E, assuming that a 0.01-in-thick...Ch. 17 - A 2.2-mm-diameter and 10-m-long electric wire is...Ch. 17 - Prob. 76PCh. 17 - Chilled water enters a thin-shelled 5-cm-diameter,...Ch. 17 - Steam at 450°F is flowing through a steel pipe (k...Ch. 17 - Prob. 79PCh. 17 - Prob. 80PCh. 17 - An 8-m-internal-diameter spherical tank made of...Ch. 17 - What is the critical radius of insulation? How is...Ch. 17 - Consider an insulated pipe exposed to the...Ch. 17 - A pipe is insulated to reduce the heat loss from...Ch. 17 - Prob. 86PCh. 17 - Prob. 87PCh. 17 - A 0.083-in-diameter electrical wire at 90°F is...Ch. 17 - Prob. 89PCh. 17 - Prob. 90PCh. 17 - Prob. 92PCh. 17 - What is the reason for the widespread use of fins...Ch. 17 - What is the difference between the fin...Ch. 17 - The fins attached to a surface are determined to...Ch. 17 - Explain how the fins enhance heat transfer from a...Ch. 17 - How does the overall effectiveness of a finned...Ch. 17 - Hot water is to be cooled as it flows through the...Ch. 17 - Consider two finned surfaces that are identical...Ch. 17 - The heat transfer surface area of a fin is equal...Ch. 17 - Prob. 101PCh. 17 - Prob. 102PCh. 17 - Two plate fins of constant rectangular cross...Ch. 17 - Two finned surfaces are identical, except that the...Ch. 17 - A 4-mm-diameter and 10-cm-long aluminum fin (k =...Ch. 17 - Consider a very long rectangular fin attached to a...Ch. 17 - Consider a stainless steel spoon (k = 8.7...Ch. 17 - A DC motor delivers mechanical power to a rotating...Ch. 17 - A plane wall with surface temperature of 350°C is...Ch. 17 - Prob. 111PCh. 17 - Steam in a heating system flows through tubes...Ch. 17 - Prob. 113PCh. 17 - A hot surface at 100°C is to be cooled by...Ch. 17 - Prob. 116PCh. 17 - A 40-W power transistor is to be cooled by...Ch. 17 - Prob. 118PCh. 17 - Prob. 119RQCh. 17 - Cold conditioned air at 12°C is flowing inside a...Ch. 17 - Prob. 121RQCh. 17 - Prob. 122RQCh. 17 - Prob. 123RQCh. 17 - Prob. 124RQCh. 17 - Prob. 125RQCh. 17 - Prob. 126RQCh. 17 - Prob. 127RQCh. 17 - Prob. 128RQCh. 17 - Prob. 129RQCh. 17 - Prob. 130RQCh. 17 - Prob. 131RQ
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