Chapter 2: Problem 128
How is integration related to derivation?
Short Answer
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Chapter 2: Problem 128
How is integration related to derivation?
These are the key concepts you need to understand to accurately answer the question.
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Get started for freeIs the thermal conductivity of a medium, in general, constant or does it vary with temperature?
The outer surface of an engine is situated in a place where oil leakage can occur. Some oils have autoignition temperatures of approximately above \(250^{\circ} \mathrm{C}\). When oil comes in contact with a hot engine surface that has a higher temperature than its autoignition temperature, the oil can ignite spontaneously. Treating the engine housing as a plane wall, the inner surface \((x=0)\) is subjected to \(6 \mathrm{~kW} / \mathrm{m}^{2}\) of heat. The engine housing \((k=13.5 \mathrm{~W} / \mathrm{m} \cdot \mathrm{K})\) has a thickness of \(1 \mathrm{~cm}\), and the outer surface \((x=L)\) is exposed to an environment where the ambient air is \(35^{\circ} \mathrm{C}\) with a convection heat transfer coefficient of \(20 \mathrm{~W} / \mathrm{m}^{2} \cdot \mathrm{K}\). To prevent fire hazard in the event the leaked oil comes in contact with the hot engine surface, the temperature of the engine surface should be kept below \(200^{\circ} \mathrm{C}\). Determine the variation of temperature in the engine housing and the temperatures of the inner and outer surfaces. Is the outer surface temperature of the engine below the safe temperature?
Consider a large plane wall of thickness \(L=0.3 \mathrm{~m}\), thermal conductivity \(k=2.5 \mathrm{~W} / \mathrm{m} \cdot \mathrm{K}\), and surface area \(A=\) \(12 \mathrm{~m}^{2}\). The left side of the wall at \(x=0\) is subjected to a net heat flux of \(\dot{q}_{0}=700 \mathrm{~W} / \mathrm{m}^{2}\) while the temperature at that surface is measured to be \(T_{1}=80^{\circ} \mathrm{C}\). Assuming constant thermal conductivity and no heat generation in the wall, \((a)\) express the differential equation and the boundary conditions for steady one-dimensional heat conduction through the wall, \((b)\) obtain a relation for the variation of temperature in the wall by solving the differential equation, and \((c)\) evaluate the temperature of the right surface of the wall at \(x=L\).
Consider the uniform heating of a plate in an environment at a constant temperature. Is it possible for part of the heat generated in the left half of the plate to leave the plate through the right surface? Explain.
Consider a spherical reactor of \(5-\mathrm{cm}\) diameter operating at steady condition has a temperature variation that can be expressed in the form of \(T(r)=a-b r^{2}\), where \(a=850^{\circ} \mathrm{C}\) and \(b=5 \times 10^{5} \mathrm{~K} / \mathrm{m}^{2}\). The reactor is made of material with \(c=\) \(200 \mathrm{~J} / \mathrm{kg} \cdot{ }^{\circ} \mathrm{C}, k=40 \mathrm{~W} / \mathrm{m} \cdot \mathrm{K}, \rho=9000 \mathrm{~kg} / \mathrm{m}^{3}\). If the heat generation of reactor is suddenly set to \(9 \mathrm{MW} / \mathrm{m}^{3}\), determine the time rate of temperature change in the reactor. Is the heat generation of reactor suddenly increased or decreased to \(9 \mathrm{MW} / \mathrm{m}^{3}\) from its steady operating condition?
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