correct answer otherwise dislike Example 7.9The filament of a 75 W light bulb may be considered a black body radiating into a black enclosureat 70°C.The filament diameter is 0.10 mm and length is 50 mm. Considering the radiation, determine the filamenttemperature.

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Answered: xample 7.9 The filament of a 75 W light…

Principles of Heat Transfer (Activate Learning with these NEW titles from Engineering!)

8th Edition

ISBN:9781305387102

Author:Kreith, Frank; Manglik, Raj M.

Publisher:Kreith, Frank; Manglik, Raj M.

Chapter11: Heat Transfer By Radiation

Section: Chapter Questions

Problem 11.24P

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A long wire 0.7 mm in diameter with an emissivity of 0.9 is placed in a large quiescent air space at 270 K. If the wire is at 800 K, calculate the net rate of heat loss. Discuss your assumptions.
Example 7.9 The filament of a 75 W light bulb may be considered a black body radiating into a black enclosure at 70°C.The filament diameter is 0.10 mm and length is 50 mm. Considering the radiation, determine the filament temperature.
The tungsten filament of an incandescent light bulb has a temperature of approximately 3000 K. The emissivity of tungsten is approximately 1/3, and you may assume that it is independent of wavelength. To increase the efficiency of an incandescent bulb, would you want to raise or lower the temperature? (Some incandescent bulbs do attain slightly higher efficiency by using a different temperature.)
A body at 1100ºc in a black surrounding at 550ºc has emissivity of 0.4 at 1100ºc and emissivity 0.7 at 550ºc. calculate the rate of heat loss by radiation per unit surface area; i) when the body is assumed to be grey with emissivity 0.4 ii) when the body is not grey. (assume absorptivity is independent of the surface temperature)
A long, horizontal, cylindrical steel reactor, 1 m in diameter, has a surface temperature of 300ºC. The emissivity of the steel is 0.6, and the heat transfer coefficient for natural convection is 5 W m−2 K−1 . Heat is lost by convection to the air at 15ºC, and also by radiation to the surroundings, which can be considered to be a black body at 15ºC. a) Calculate the total heat loss per metre length of the reactor, and the proportions lost by convection and radiation b) The reactor is then insulated with a thin layer of insulation material to reduce the total heat loss to one-tenth of its original value. This causes the surface temperature of the steel to rise to 400ºC. The thermal conductivity of the insulation is 0.01 W m−1 K−1 , and its surface emissivity is 0.2. Show that the resulting surface temperature of the insulation is about 89ºC, and calculate the thickness of insulation required, stating any assumptions made. Specifically need help with part b
4. The filament of a 75 W light bulb may be considered as a black body radiating into a black enclosure at 70° C. the filament diameter is 0.10 mm and length is 5 em. considering the radiation, determine the filament temperature .
A long, horizontal, cylindrical steel reactor, 1 m in diameter, has a surface temperature of 300ºC. The emissivity of the steel is 0.6, and the heat transfer coefficient for natural convection is 5 W m−2 K−1 . Heat is lost by convection to the air at 15ºC, and also by radiation to the surroundings, which can be considered to be a black body at 15ºC. a) Calculate the total heat loss per metre length of the reactor, and the proportions lost by convection and radiation. b) The reactor is then insulated with a thin layer of insulation material to reduce the total heat loss to one-tenth of its original value. This causes the surface temperature of the steel to rise to 400ºC. The thermal conductivity of the insulation is 0.01 W m−1 K−1 , and its surface emissivity is 0.2. Show that the resulting surface temperature of the insulation is about 89ºC, and calculate the thickness of insulation required, stating any assumptions made. can you solve part b please?
An infrared camera is used to measure a temperature at a tissue location. The infrared camera uses the same equation as that in the lecture notes. When the total hemispherical emissivity is selected as &=1.0, the temperature reading on the camera is 45°C. (a) Based on the equation given in the notes, please calculate the radiation heat flux received by the camera qck. The Stefan-Boltzmann's constant ois 5.67*108 W/(m²K¹). (b) However, you notice that the actual emissivity of the tissue surface should be 0.95. The room temperature is 20°C. Use the equation again to calculate the temperature of the tissue location, note that qck should be the same as in (a). What is the absolute error of the measurement if both the room temperature and deviation from a perfect blackbody surface are not considered?
Two concentric spheres of diameter Dj = 0.8 mand D2 T1 = 400 K and T2 = 300 K. = 1.2 m are separated by an air space and have surface temperatures of (a) If the surfaces are black, what is the net rate of radiation exchange between the spheres, in W? 912 i (b) What is the net rate of radiation exchange between the surfaces if they are diffuse and gray with e = 0.5 and e2 = 0.05, in W? 912 i w (c) What is the net rate of radiation exchange if D2 is increased to 20 m, with &2 = 0.05, ɛ 1 = 0.5, and Di = 0.8 m, in W? 912 w = 1.0) and with ej = 0.5, D2 = 20 m, (d) What is the net rate of radiation exchange if the larger sphere behaves as a black body (82 and Di = 0.8 m, in W? 912 = i W
A 3-in-diameter cylindrical wire is coated in 3 inches of polyethylene insulation. The wire can be modeled as a grey body with an emissivity of .85. Due to the electrical resistance, the wire is at a temperature of 300 degrees Celsius. The insulation is also a great body with an emissivity of .95, at a temperature of 40 degrees Celsius. (Assume F12=1). What is the heat flux (W/m^2) of the energy going from the wire to the insulation?
7) Given a window of 20 ft facing east at 40° north latitude, estimate the cooling load due to solar radiation at 4:00 pm for a day in June. Assume the window does not have any interior shading and the shading coefficient is 0.2 (in Btu/hr) (a) 105 (d) 276 (b) 430 (c) 314 (c) 225
Two concentric spheres of diameter D1 of T1 = 390 Kand T, = 300 K. = 0.7 m and D2 = 1.2 mare separated by an air space and have surface temperatures (a) If the surfaces are black, what is the net rate of radiation exchange between the spheres, in W? 912 w (b) What is the net rate of radiation exchange between the surfaces if they are diffuse and gray with & = 0.5 and &2 = 0.05, in W? 912 (c) What is the net rate of radiation exchange if D2 is increased to 20 m, with ez = 0.05, e1 = 0.5, and Di = 0.7 m, in w? 412 = (d) What is the net rate of radiation exchange if the larger sphere behaves as a black body (82 = 1.0) and with ej = 0.5, D2 = 20 m, and Di = 0.7 m, in W? i w 912 = Physical Properties Mathematical Functions

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