Explanation Given information: Thermal conductivity of layer A is 0.8 W / m ⋅ K ,thickness of layer A is 8 cm ,thermal conductivity of layer B is 0.2 W / m ⋅ K , thickness of layer B is 5 cm and the temperature drop across the wall is 18°C Write the expression for resistance offered due to layer A. R A = L A k A ...... (I) Here, the thickness of layer A is L A and the thermal conductivity of layer A is k A . Write the expression for resistance offered due to layer B. R B = L B k B ...... (II) Here, the thickness of layer B is L B and the thermal conductivity of layer B is k B . Write the expression for the total resistance offered by both layers. R t = R A + R B ...... (III) Write the expression for the rate of heat transfer per unit area through the wall. Q = Δ T R t ...... (IV) Here, the temperature drop across the wall is Δ T . Calculation: Substitute 8 cm for L A and 0.8 W / m ⋅ K for k A in Equation (I). R A = 8 cm 0.8 W / m ⋅ K = 8 cm × 1 m 100 cm 0.8 W / m ⋅ K = 0.1 m 2 ⋅ K / W Substitute 5 cm for L B and 0

Heat and Mass Transfer: Fundamentals and Applications

5th Edition

ISBN: 9780073398181

Author: Yunus A. Cengel Dr., Afshin J. Ghajar

Publisher: McGraw-Hill Education

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Question

Chapter 3, Problem 198P

To determine

The rate of heat transfer per unit area through the wall.

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Chapter 3, Problem 197P

Chapter 3, Problem 199P

Chapter 3 Solutions

Heat and Mass Transfer: Fundamentals and Applications

Ch. 3 - Consider heat conduction through a wall of...Ch. 3 - Consider heat conduction through a plane wall....Ch. 3 - What does the thermal resistance of a medium...Ch. 3 - Can we defme the convection resistance for a unit...Ch. 3 - Consider steady heat transfer through the wall of...Ch. 3 - How is the combined heat transfer coefficient...Ch. 3 - Why are the convection and the radiation...Ch. 3 - Consider steady one-dimensional heat transfer...Ch. 3 - Someone comments that a microwave oven can be...Ch. 3 - Consider two cold canned drinks, one wrapped in a...

Ch. 3 - The bottom of a pan is made of a 4-mm-thick...Ch. 3 - Consider a surface of area A at which the...Ch. 3 - How does the thermal resistance network associated...Ch. 3 - Consider steady one-dimensional heat transfer...Ch. 3 - Consider a window glass consisting of two...Ch. 3 - Prob. 16P Ch. 3 - Consider a person standing in a room at 20C with...Ch. 3 - Consider an electrically heated brick house...Ch. 3 - A12-cm18-cm circuit board houses on its surface...Ch. 3 - Water is boiling in a 25-cm-diameter aluminum pan...Ch. 3 - A cylindrical resistor element on a circuit board...Ch. 3 - Prob. 22P Ch. 3 - A1.0m1.5m double-pane window consists of two...Ch. 3 - Prob. 24P Ch. 3 - Prob. 25P Ch. 3 - Prob. 26P Ch. 3 - Prob. 27P Ch. 3 - Prob. 28EP Ch. 3 - To defog the rear window of an automobile, a very...Ch. 3 - A transparent film is to be bonded onto the top...Ch. 3 - To defrost ice accumulated on the outer surface of...Ch. 3 - Prob. 32P Ch. 3 - Prob. 33P Ch. 3 - Prob. 34P Ch. 3 - Prob. 35P Ch. 3 - Prob. 36P Ch. 3 - Heat is to be conducted along a circuit board that...Ch. 3 - Prob. 38EP Ch. 3 - Consider a house that has a 10m20-m base and a...Ch. 3 - Prob. 40EP Ch. 3 - Prob. 41P Ch. 3 - Prob. 42P Ch. 3 - What is thermal contact resistance? 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A and B, with the same surface...Ch. 3 - Prob. 206P Ch. 3 - A room at 20C air temperature is losing heat to...Ch. 3 - Prob. 208P Ch. 3 - A 1-cm-diameter, 30cm-long fin made of aluminum...Ch. 3 - A hot surface at 80C in air at 20C is to be cooled...Ch. 3 - A cylindrical pin fin of diameter 0.6 cm and...Ch. 3 - A 3-cm-long. 2-nuti x 2-mm rectangular...Ch. 3 - Two finned surfaces with long fins are identical,...Ch. 3 - A 20-cm-diameter hot sphere at 120C is buried in...Ch. 3 - A 25-cm-diameter, 2.4-rn-long vertical cylinder...Ch. 3 - Prob. 216P Ch. 3 - The walls of a food storage facility are made of a...Ch. 3 - The equivalent thermal resistance for the thermal...Ch. 3 - Prob. 219P Ch. 3 - Prob. 220P Ch. 3 - Prob. 221P Ch. 3 - The fin efficiency is defined as the ratio of the...Ch. 3 - Prob. 223P Ch. 3 - In the United States, building insulation is...Ch. 3 - Prob. 225P Ch. 3 - A plane brick wall (k=0.7W/m.K) and is 10 cm...Ch. 3 - The temperature in deep space is close to absolute...Ch. 3 - In the design of electronic components, it is...Ch. 3 - Using cylindrical samples of the same material,...Ch. 3 - Find out about the wall construction of the cabins...Ch. 3 - Prob. 231P Ch. 3 - A house with 200-m2 floor space is to be heated...

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