A flat roof is modeled as a flat plate insulated on the bottom and placed in the sunlight. If the radiant heat that the roof receives from the sun is
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Chapter 1 Solutions
Principles of Heat Transfer (Activate Learning with these NEW titles from Engineering!)
- Determine the rate of radiant heat emission in watts per square meter from a blackbody at (a) 15C, (b) 600C, and (c) 5700C.arrow_forward1.25 A spherical vessel, 0.3 m in diameter, is located in a large room whose walls are at 27°C (see sketch). If the vessel is used to store liquid oxygen at –183°C and both the surface of the storage vessel and the walls of the room are black, calculate the rate of heat transfer by radiation to the liquid oxygen in watts and in Btu/h.arrow_forward1.28 The sun has a radius of and approximates a blackbody with a surface temperature of about 5800 K. Calculate the total rate of radiation from the sun and the emitted radiation flux per square meter of surface area.arrow_forward
- 1.29 A spherical interplanetary probe with a 30-cm diameter contains electronic equipment that dissipates 100 W. If the probe surface has an emissivity of 0.8, what is its surface temperature in outer space? State your assumptions in the calculations.arrow_forwardTwo infinite black plates at 800°C and 300°C exchange heat by radiation. Calculate the heat transfer per unit area. ANSWER MUST BE IN KW/m2arrow_forwardConsider a very thin plate that is mounted and attached on a horizontal board. The plate is subject to an infrared lamp providing a uniform thermal radiation of 2000 W/m?. The plate absorbs 80% of the infrared irradiation and has an emissivity of 0.498. The plate is also exposed to an airflow of temperature of 20 °C and large surroundings with a temperature of 30 °C. The surface area of the plate is 1 m2 and it's surface temperature is measured to be at 104 °C. Required: Draw a clear and consistent schematic of the problem and label the operating conditions on the schematic. Perform systematic analysis, state your assumptions and justify the equation used and determine the convection heat transfer coefficient of airflow. (circle your final answer)arrow_forward
- Heat radiates from a small sphere suspended in a large room. The surfaceof the sphere of 1.5 sq. Ft. is at a temperature of 580 °F, and the insidesurfaces of the room are at a temperature of 80 °F. Assuming the emissivity ofthe sphere surface to be 0.30, calculate the radian-heat transfer in BTU/hr.arrow_forwardAn electric hot plate is placed in a room which is maintained at a temperature of 297 K. The plate is maintained at a temperature of 403 K and has an emissivity of 0.8. If the plate surface resembles a circular disc of diameter 250 mm, electrical power consumed by the hot plate will be?arrow_forwardEarth absorbs solar energy and radiates infrared energy. The intensity of the solar radiation incident on earth is J = 1350 Wm-2, also known as the solar constant. Assume earth’s surface (ground) temperature to be uniform at Ts, and that the ground and atmosphere are black (emissivity = 1) for infrared radiation. The radius of the earth is 6.378 x 106 m. The diagram shows the ground at the surface temperature Ts and the atmosphere, represented as a thin black layer, at temperature Ta . Suppose the atmosphere absorbs 100% of the infrared radiation emitted by the ground. Assume that the ground absorbs 47.5% of the incident solar energy, and that the atmosphere absorbs 17.5% of the incident solar energy (for a total of 65% absorbed by the planet). Calculate the "steady state” numerical values of the earth’s ground temperature Ts and the atmospheric temperature Ta taking into account the “greenhouse effect” of atmospheric infrared absorption and emission described above.arrow_forward
- A one-dimensional plane wall is exposed to convective and radiative conditions at x = 0. The ambient and surrounding temperatures are T. exposed surface is a = 0.78. Determine the convective and radiative heat fluxes to the wall at x = 0, both in W/m2, if the wall surface = 20°C and Tsur = 40°C, respectively. The convection heat transfer coefficient is h = 20 W/m²-K, and the absorptivity of the temperature is T, = 30°C. Assume the exposed wall surface is gray, and the surroundings are large. gbonv i W/m? Tad i W/m2arrow_forwardA hot water heater 150 mm wide, 2 m long and 1 m hight is at a surface temperature of 50°C in the surroundings of 20°C. The heat transfer coefficient for convection is given by h = 1.31(AT)1/3 where h is in W/m²K and AT is in K. Take the emissivity of the heater as 0.95 and assume that it is completely surrounded by black surroundings. Take o as 5.67 x 10-8 W/m²K4. The total rate of heat flux from the heater is W/m². [Rounded upto two decimal places]arrow_forward2. Consider steady heat transfer between two large parallel plates at constant temperatures of T1 = 295 K and T2 = 155 K that are L = 2 cm apart. Assuming the surfaces to be black, determine the rate of heat transfer between the plates per unit surface area assuming the gap between the plates is (a) filled with atmospheric air,(k = 0.01979 W/m- o C) (b) evacuated,(c) filled with superinsulation having an apparent thermal conductivity of 0.00015 W/m · °C.arrow_forward
- Principles of Heat Transfer (Activate Learning wi...Mechanical EngineeringISBN:9781305387102Author:Kreith, Frank; Manglik, Raj M.Publisher:Cengage Learning