Chapter 6: Problem 61
Under what conditions can a curved surface be treated as a flat plate in fluid flow and convection analysis?
Chapter 6: Problem 61
Under what conditions can a curved surface be treated as a flat plate in fluid flow and convection analysis?
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A metallic airfoil of elliptical cross section has a mass of $50 \mathrm{~kg}\(, surface area of \)12 \mathrm{~m}^{2}$, and a specific heat of \(0.50 \mathrm{~kJ} / \mathrm{kg} \cdot \mathrm{K}\). The airfoil is subjected to airflow at \(1 \mathrm{~atm}\), \(25^{\circ} \mathrm{C}\), and $5 \mathrm{~m} / \mathrm{s}$ along its 3 -m-long side. The average temperature of the airfoil is observed to drop from \(160^{\circ} \mathrm{C}\) to \(150^{\circ} \mathrm{C}\) within 2 min of cooling. Assuming the surface temperature of the airfoil to be equal to its average temperature and using the momentum-heat transfer analogy, determine the average friction coefficient of the airfoil surface. Evaluate the air properties at \(25^{\circ} \mathrm{C}\) and 1 atm. Answer: \(0.000363\)
A metal plate $\left(k=180 \mathrm{~W} / \mathrm{m} \cdot \mathrm{K}, \rho=2800 \mathrm{~kg} / \mathrm{m}^{3}\right.\(, and \)c_{p}=880 \mathrm{~J} / \mathrm{kg} \cdot \mathrm{K}\( ) with a thickness of \)1 \mathrm{~cm}$ is being cooled by air at \(5^{\circ} \mathrm{C}\) with a convection heat transfer coefficient of \(30 \mathrm{~W} / \mathrm{m}^{2} \cdot \mathrm{K}\). If the initial temperature of the plate is \(300^{\circ} \mathrm{C}\), determine the plate temperature gradient at the surface after 2 minutes of cooling. Hint: Use the lumped system analysis to calculate the plate surface temperature. Make sure to verify the application of this method to this problem.
The _____ number is a significant dimensionless parameter for forced convection, and the ___________ number is a significant dimensionless parameter for natural convection. (a) Reynolds, Grashof (b) Reynolds, Mach (c) Reynolds, Eckert (d) Reynolds, Schmidt (e) Grashof, Sherwood
What is forced convection? How does it differ from natural convection? Is convection that is caused by winds forced or natural convection?
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