Answered: An uninsulated steam pipe passes…

Elements Of Electromagnetics

7th Edition

ISBN:9780190698614

Author:Sadiku, Matthew N. O.

Publisher:Sadiku, Matthew N. O.

ChapterMA: Math Assessment

Section: Chapter Questions

Problem 1.1MA

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A long, thin-walled horizontal tube 10.0cm in diameter with an emissivity of 0.80 is maintained at 120.0°C by the passage of pressurized steam inside the tube. To reduce radiation heat transfer losses, a round, tubular radiation shield with an emissivity of 0.10 is installed surrounding the heated tube, with a gap of 1.00cm between the outside of the tube and the radiation shield. At steady-state operating conditions, the temperature of the radiation shield is measured to be 35.0°C. Calculate the total heat transfer rate per meter length assuming that the gap between the pipe and heat shield is now filled with air at a pressure of 1.00 atm.
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
An opaque surface which is insulated at the back side has a total, hemispherical absorptivity a=0.8 for solar radiation and a total, hemispherical emissivity of e=0.2. A solar radiation flux of 800 W/m2 is incident on this surface. The surface is exposed to the ambient air at T 300 K and convective heat transfer coefficient is h=15 W/m2 K. Neglect the sky radiation. • Sketch the heat fluxes received and dissipated by this surface • Estimate the equilibrium temperature of the surface (assume the surface temperature is higher than the ambient air temperature). 1.= 300 K, h-15 W/m*K 800 W/m? a-0.8 , e-0.2

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