A 2 m long cylindrical rod (radius r = 75 mm) is coated by an insulation layer (thickness: 2 mm). The rod is uniformly, heated by an electrical current. The air flows around the coated rod at 300 K and 4 m/s. Ignore radiation and the heat transfer at two ends of the rod. (a) What is the convection heat transfer coefficient h between the air and the coating outer surface? (b) Calculate the Biot number of the rod. (c) The electrical current is suddenly cut off (no heat generation any more). How long does it take for the rod temperature to drop from 1000 K to 600 K? Properties of the air: pa = 0.7 kg/m³, Cp,a= 1030 J/kg K, a = 38.8×106 m²/s, ka = 0.041 W/mK, da 56.7×106 m²/s, and Pra = 0.684.. = Properties of the rod: pr = 7832 kg/m³, Cpr = 559 J/kg K, and ky = 48.8 W/m.K. Properties of the coating: ke = 0.4 W/m.K.
A 2 m long cylindrical rod (radius r = 75 mm) is coated by an insulation layer (thickness: 2 mm). The rod is uniformly, heated by an electrical current. The air flows around the coated rod at 300 K and 4 m/s. Ignore radiation and the heat transfer at two ends of the rod. (a) What is the convection heat transfer coefficient h between the air and the coating outer surface? (b) Calculate the Biot number of the rod. (c) The electrical current is suddenly cut off (no heat generation any more). How long does it take for the rod temperature to drop from 1000 K to 600 K? Properties of the air: pa = 0.7 kg/m³, Cp,a= 1030 J/kg K, a = 38.8×106 m²/s, ka = 0.041 W/mK, da 56.7×106 m²/s, and Pra = 0.684.. = Properties of the rod: pr = 7832 kg/m³, Cpr = 559 J/kg K, and ky = 48.8 W/m.K. Properties of the coating: ke = 0.4 W/m.K.
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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