Showing 161 to 170 of 1972 Questions
  • A vertical air space in the wall of a home is 0.1 m thick and 3 m high. The air separates a brick exterior from a plaster board wall, with each surface having an emissivity of 0.9. Consider conditions for which the temperatures of the brick and plaster surfaces exposed to the air are -10 and 18°C, respectively. What is the rate of heat l

  • A flat-plate solar collector is used to heat atmospheric air flowing through a rectangular channel. The bottom surface of the channel is well insulated, while the top surface is subjected to a uniform heat flux q, which is due to the net effect of solar radiation absorption, and heat exchange between the absorber and cover plates. (a) B

  • A flue gas at 1-atm total pressure and a temperature of 1400 K contains CO2 and water vapor at partial pressures of 0.05 and 0.10 atm, respectively. If the gas flows through a long flue of 1-m diameter and 400 K surface temperature, determine the net radiative heat flux from the gas to the surface. Blackbody behavior may be assumed for th

  • A flue passing hot exhaust gases has a square cross section, 300 mm to a side. The walls are constructed of refractory brick 150 mm thick with a thermal conductivity of 0.85 W/m ∙ K. Calculate the heat loss from the flue per unit length when the interior and exterior surfaces are maintained at 350 and 25°C, respectively. Use a grid

  • A fluid at temperature T∞ is flowing at a velocity U∞ over a flat plate which is at the same temperature as the fluid for a distance x0 from the leading edge, but at a higher temperature Ts beyond this point. Show by means of the integral boundary-layer equations that ζ, the ratio of the thermal boundary-layer thickness to the hydrod

  • A freezer compartment consists of a cubical cavity that is 2 m on a side. Assume the bottom to be perfectly insulated. What is the minimum thickness of Styrofoam insulation (k = 0.030 W/m. K) that must be applied to the top and side walls to ensure a heat load of less than 500 W, when the inner and outer surfaces are - 10 and 35°C?

  • A freezer compartment is covered with a 2-mm-thick layer of frost at the time it malfunctions. If the compartment is in ambient air at 20°C and a coefficient of h = 2 W/m2 ∙ K characterizes heat transfer by natural convection from the exposed surface of the layer, estimate the time required to completely melt the frost. The frost m

  • A frozen-food company freezes its spinach by first compressing it into large slabs and then exposing the slab of spinach to a low-temperature cooling medium. The large slab of compressed spinach is initially at a uniform temperature of 21°C; it must be reduced to an average temperature over the entire slab of –34°C. The temperature at

  • A furnace consists of two large parallel plates separated by 0.75 m. A gas mixture comprised of O2, N2, CO2, and water vapor, with mole fractions of 0.20, 0.50, 0.15, and 0.15, respectively, flows between the plates at a total pressure of 2 atm and a temperature of 1300 K. If the plates may be approximated as blackbodies and are maintaine

  • A furnace for processing semiconductor materials is formed by a silicon carbide chamber that is zone heated on the top section and cooled on the lower section. With the elevator in the lowest position, a robot arm inserts the silicon wafer on the mounting pins. In a production operation, the wafer is rapidly moved toward the hot zone to a

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