Chapter 1: Problem 4
What is the difference between the analytical and experimental approaches to heat transfer? Discuss the advantages and disadvantages of each approach.
Chapter 1: Problem 4
What is the difference between the analytical and experimental approaches to heat transfer? Discuss the advantages and disadvantages of each approach.
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Get started for freeThe inner and outer surfaces of a 25 -cm-thick wall in summer are at \(27^{\circ} \mathrm{C}\) and \(44^{\circ} \mathrm{C}\), respectively. The outer surface of the wall exchanges heat by radiation with surrounding surfaces at \(40^{\circ} \mathrm{C}\) and by convection with ambient air also at $40^{\circ} \mathrm{C}\( with a convection heat transfer coefficient of \)8 \mathrm{~W} / \mathrm{m}^{2} \cdot \mathrm{K}$. Solar radiation is incident on the surface at a rate of \(150 \mathrm{~W} / \mathrm{m}^{2}\). If both the emissivity and the solar absorptivity of the outer surface are \(0.8\), determine the effective thermal conductivity of the wall.
A cold bottled drink ( $\left.m=2.5 \mathrm{~kg}, c_{p}=4200 \mathrm{~J} / \mathrm{kg} \cdot \mathrm{K}\right)\( at \)5^{\circ} \mathrm{C}$ is left on a table in a room. The average temperature of the drink is observed to rise to \(15^{\circ} \mathrm{C}\) in \(30 \mathrm{~min}\). The average rate of heat transfer to the drink is (a) \(23 \mathrm{~W}\) (b) \(29 \mathrm{~W}\) (c) \(58 \mathrm{~W}\) (d) \(88 \mathrm{~W}\) (e) \(122 \mathrm{~W}\)
A person standing in a room loses heat to the air in the room by convection and to the surrounding surfaces by radiation. Both the air in the room and the surrounding surfaces are at \(20^{\circ} \mathrm{C}\). The exposed surface of the person is \(1.5 \mathrm{~m}^{2}\) and has an average temperature of \(32^{\circ} \mathrm{C}\) and an emissivity of \(0.90\). If the rates of heat transfer from the person by convection and by radiation are equal, the combined heat transfer coefficient is (a) \(0.008 \mathrm{~W} / \mathrm{m}^{2}, \mathrm{~K}\) (b) \(3.0 \mathrm{~W} / \mathrm{m}^{2} \cdot \mathrm{K}\) (c) \(5.5 \mathrm{~W} / \mathrm{m}^{2}, \mathrm{~K}\) (d) \(8.3 \mathrm{~W} / \mathrm{m}^{2} \cdot \mathrm{K}\) (e) \(10.9 \mathrm{~W} / \mathrm{m}^{2} \cdot \mathrm{K}\)
Consider a person whose exposed surface area is \(1.7 \mathrm{~m}^{2}\), emissivity is \(0.5\), and surface temperature is \(32^{\circ} \mathrm{C}\). Determine the rate of heat loss from that person by radiation in a large room having walls at a temperature of (a) \(300 \mathrm{~K}\) and (b) $280 \mathrm{~K}$.
A 2-in-diameter spherical ball whose surface is maintained at a temperature of \(170^{\circ} \mathrm{F}\) is suspended in the middle of a room at $70^{\circ} \mathrm{F}\(. If the convection heat transfer coefficient is \)15 \mathrm{Btu} / \mathrm{h} \cdot \mathrm{ft}{ }^{2}{ }^{\circ} \mathrm{F}$ and the emissivity of the surface is \(0.8\), determine the total rate of heat transfer from the ball.
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