Chapter 13: Problem 160
The number of view factors that need to be evaluated directly for a 10 -surface enclosure is (a) 1 (b) 10 (c) 22 (d) 34 (e) 45
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What is sensible heat? How is the sensible heat loss from a human body affected by \((a)\) skin temperature, \((b)\) environment temperature, and \((c)\) air motion?
A flow-through combustion chamber consists of long, 15 -cm-diameter tubes immersed in water. Compressed air is routed to the tube, and fuel is sprayed into the compressed air. The combustion gases consist of 70 percent \(\mathrm{N}_{2}, 9\) percent \(\mathrm{H}_{2} \mathrm{O}, 15\) percent \(\mathrm{O}_{2}\), and 6 percent \(\mathrm{CO}_{2}\), and are maintained at $1 \mathrm{~atm}\( and \)1500 \mathrm{~K}$. The tube surfaces are near black, with an emissivity of \(0.9\). If the tubes are to be maintained at a temperature of \(600 \mathrm{~K}\), determine the rate of heat transfer from combustion gases to tube wall by radiation per \(m\) length of tube.
Explain all the different mechanisms of heat transfer from the human body \((a)\) through the skin and \((b)\) through the lungs.
The surfaces of a two-surface enclosure exchange heat with one another by thermal radiation. Surface 1 has a temperature of \(400 \mathrm{~K}\), an area of \(0.2 \mathrm{~m}^{2}\), and a total emissivity of \(0.4\). Surface 2 is black, has a temperature of \(800 \mathrm{~K}\), and has area of \(0.3 \mathrm{~m}^{2}\). If the view factor \(F_{12}\) is \(0.3\), the rate of radiation heat transfer between the two surfaces is (a) \(340 \mathrm{~W}\) (b) \(560 \mathrm{~W}\) (c) \(780 \mathrm{~W}\) (d) \(900 \mathrm{~W}\) (e) \(1160 \mathrm{~W}\)
Consider an equimolar mixture of \(\mathrm{CO}_{2}\) and \(\mathrm{O}_{2}\) gases at \(800 \mathrm{~K}\) and a total pressure of \(0.5 \mathrm{~atm}\). For a path length of \(1.2 \mathrm{~m}\), determine the emissivity of the gas.
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