Chapter 5: Problem 5
How do numerical solution methods differ from analytical ones? What are the advantages and disadvantages of numerical and analytical methods?
Chapter 5: Problem 5
How do numerical solution methods differ from analytical ones? What are the advantages and disadvantages of numerical and analytical methods?
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Get started for freeWhat is the cause of the discretization error? How does the global discretization error differ from the local discretization error?
Consider a large plane wall of thickness \(L=0.4 \mathrm{~m}\), thermal conductivity \(k=2.3 \mathrm{~W} / \mathrm{m} \cdot \mathrm{K}\), and surface area \(A=20 \mathrm{~m}^{2}\). The left side of the wall is maintained at a constant temperature of \(95^{\circ} \mathrm{C}\), while the right side loses heat by convection to the surrounding air at $T_{\infty}=15^{\circ} \mathrm{C}\( with a heat transfer coefficient of \)h=18 \mathrm{~W} / \mathrm{m}^{2} \cdot \mathrm{K}$. Assuming steady one-dimensional heat transfer and taking the nodal spacing to be \(10 \mathrm{~cm}\), (a) obtain the finite difference formulation for all nodes, (b) determine the nodal temperatures by solving those equations, and (c) evaluate the rate of heat transfer through the wall.
A nonmetal plate is connected to a stainless steel plate by long ASTM A437 B4B stainless steel bolts \(9.5 \mathrm{~mm}\) in diameter. The portion of the bolts exposed to convection heat transfer with a cryogenic fluid is \(5 \mathrm{~cm}\) long. The fluid temperature for convection is at \(-50^{\circ} \mathrm{C}\) with a convection heat transfer coefficient of $100 \mathrm{~W} / \mathrm{m}^{2} \cdot \mathrm{K}\(. The thermal conductivity of the bolts is known to be \)23.9 \mathrm{~W} / \mathrm{m} \cdot \mathrm{K}$. Both the nonmetal and stainless steel plates maintain a uniform temperature of \(0^{\circ} \mathrm{C}\). According to the ASME Code for Process Piping (ASME B31.3-2014, Table A-2M), the minimum temperature suitable for ASTM A437 B4B stainless steel bolts is \(-30^{\circ} \mathrm{C}\). Using the finite difference method with a uniform nodal spacing of \(\Delta x=5 \mathrm{~mm}\) along the bolt, determine the temperature at each node. Compare the numerical results with the analytical solution. Plot the temperature distribution along the bolt. Would any part of the ASTM A437 B4B bolts be lower than the minimum suitable temperature of \(-30^{\circ} \mathrm{C}\) ?
The roof of a house consists of a \(15-\mathrm{cm}\)-thick concrete slab \(\left(k=1.4 \mathrm{~W} / \mathrm{m} \cdot \mathrm{K}\right.\) and \(\left.\alpha=0.69 \times 10^{-6} \mathrm{~m}^{2} / \mathrm{s}\right)\) that is \(18 \mathrm{~m}\) wide and \(32 \mathrm{~m}\) long. One evening at $6 \mathrm{p} . \mathrm{m}$., the slab is observed to be at a uniform temperature of \(18^{\circ} \mathrm{C}\). The average ambient air and the night sky temperatures for the entire night are predicted to be \(6^{\circ} \mathrm{C}\) and \(260 \mathrm{~K}\), respectively. The convection heat transfer coefficients at the inner and outer surfaces of the roof can be taken to be $h_{i}=5 \mathrm{~W} / \mathrm{m}^{2}, \mathrm{~K}\( and \)h_{o}=12 \mathrm{~W} / \mathrm{m}^{2} \cdot \mathrm{K}$, respectively. The house and the interior surfaces of the walls and the floor are maintained at a constant temperature of \(20^{\circ} \mathrm{C}\) during the night, and the emissivity of both surfaces of the concrete roof is \(0.9\). Considering both radiation and convection heat transfers and using the explicit finite difference method with a time step of \(\Delta t=5 \mathrm{~min}\) and a mesh size of $\Delta x=3 \mathrm{~cm}$, determine the temperatures of the inner and outer surfaces of the roof at 6 a.m. Also, determine the average rate of heat transfer through the roof during that night.
Can the global (accumulated) discretization error be less than the local error during a step? Explain.
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