Ex2. Two large parallel plates are exchanging radiation. One plate has a temperature of 1000 K and an emissivity of 0.8. The other plate is at 350 K and has an emissivity of 0.4. (a) What is the radiant heat flux between the plates? (b) It is desired to reduce the heat transfer between the plates by inserting a thin radiation shield between them. The shield has an emissivity of 0.1 on one side and 0.05 on the other. What is the new rate of heat transfer after the shield is in place, and what is the temperature of the shield? (c) An additional shie kd like the one of Part (b) is placed in the system to further reduce the heat transfer. What is the resulting heat flux, and what are the temperatures of the two shiclds?

Ex2. Two large parallel plates are exchanging radiation. One plate has a temperature of 1000 K and an emissivity of 0.8. The other plate is at 350 K and has an emissivity of 0.4. (a) What is the radiant heat flux between the plates? (b) It is desired to reduce the heat transfer between the plates by inserting a thin radiation shield between them. The shield has an emissivity of 0.1 on one side and 0.05 on the other. What is the new rate of heat transfer after the shield is in place, and what is the temperature of the shield? (c) An additional shie kd like the one of Part (b) is placed in the system to further reduce the heat transfer. What is the resulting heat flux, and what are the temperatures of the two shiclds?

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 11.23P

See similar textbooks

Similar questions

Two large parallel plates with surface conditions approximating those of a blackbody are maintained at 816C and 260C, respectively. Determine the rate of heat transfer by radiation between the plates in W/m2 and the radiative heat transfer coefficient in W/m2K.
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.
1.28 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.
11.41 Determine the steady-state temperatures of two radiation shields placed in the evacuated space between two infinite planes at temperatures of 555 K and 278 K. The emissivity of all surfaces is 0.8.
Determine the rate of radiant heat emission in watts per square meter from a blackbody at (a) 15C, (b) 600C, and (c) 5700C.
11.31 A large slab of steel 0.1 m thick contains a 0.1 -m-di- ameter circular hole whose axis is normal to the surface. Considering the sides of the hole to be black, specify the rate of radiative heat loss from the hole. The plate is at 811 K, and the surroundings are at 300 K.
1.25 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.
Three thin sheets of polished aluminum are placed parallel to each other so that the distance between them is very small compared to the size of the sheets. If one of the outer sheets is at 280C and the other outer sheet is at 60C, calculate the temperature of the intermediate sheet and the net rate of heat flow by radiation. Convection can be ignored.
1.26 Repeat Problem 1.25 but assume that the surface of the storage vessel has an absorbance (equal to the emittance) of 0.1. Then determine the rate of evaporation of the liquid oxygen in kilograms per second and pounds per hour, assuming that convection can be neglected. The heat of vaporization of oxygen at –183°C is .
1.11 Calculate the heat loss through a glass window 7-mm thick if the inner surface temperature is 20°C and the outer surface temperature is 17°C. Comment on the possible effect of radiation on your answer.