Chapter 6: Problem 48
Express continuity equation for steady two-dimensional flow with constant properties, and explain what each term represents.
Chapter 6: Problem 48
Express continuity equation for steady two-dimensional flow with constant properties, and explain what each term represents.
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Get started for freeWhat is external forced convection? How does it differ from internal forced convection? Can a heat transfer system involve both internal and external convection at the same time? Give an example.
In any forced or natural convection situation, the velocity of the flowing fluid is zero where the fluid wets any stationary surface. The magnitude of heat flux where the fluid wets a stationary surface is given by (a) \(k\left(T_{\text {fluid }}-T_{\text {wall }}\right)\) (b) \(\left.k \frac{d T}{d y}\right|_{\text {wall }}\) (c) \(\left.k \frac{d^{2} T}{d y^{2}}\right|_{\text {wall }}\) (d) \(\left.h \frac{d T}{d y}\right|_{\text {wall }}\) (e) None of them
An electrical water \((k=0.61 \mathrm{~W} / \mathrm{m} \cdot \mathrm{K})\) heater uses natural convection to transfer heat from a 1 -cm-diameter by \(0.65\)-m-long, \(110 \mathrm{~V}\) electrical resistance heater to the water. During operation, the surface temperature of this heater is \(120^{\circ} \mathrm{C}\) while the temperature of the water is \(35^{\circ} \mathrm{C}\), and the Nusselt number (based on the diameter) is 5 . Considering only the side surface of the heater (and thus \(A=\pi D L\) ), the current passing through the electrical heating element is (a) \(2.2 \mathrm{~A}\) (b) \(2.7 \mathrm{~A}\) (c) \(3.6 \mathrm{~A}\) (d) \(4.8 \mathrm{~A}\) (e) \(5.6 \mathrm{~A}\)
For the same initial conditions, one can expect the laminar thermal and momentum boundary layers on a flat plate to have the same thickness when the Prandtl number of the flowing fluid is (a) Close to zero (b) Small (c) Approximately one (d) Large (e) Very large
The top surface of a metal plate \(\left(k_{\text {plate }}=237 \mathrm{~W} / \mathrm{m} \cdot \mathrm{K}\right)\) is being cooled by air \(\left(k_{\text {air }}=0.243 \mathrm{~W} / \mathrm{m} \cdot \mathrm{K}\right)\) while the bottom surface is exposed to a hot steam at \(100^{\circ} \mathrm{C}\) with a convection heat transfer coefficient of \(30 \mathrm{~W} / \mathrm{m}^{2} \cdot \mathrm{K}\). If the bottom surface temperature of the plate is \(80^{\circ} \mathrm{C}\), determine the temperature gradient in the air and the temperature gradient in the plate at the top surface of the plate.
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