Example:.A steel ball [c-0.46 kJ/kg C, k-35 W/m. C] 5.0 cm in diameter andinitially at a uniform temperature of 450°C is suddenly placed in acontrolled environment in which the temperature is maintained at 100°C.The convection heat-transfer coefficient is 10 W/m². C. Calculate thetime required for the ball to attain a temperature of 150°C.Solution:We anticipate that the lumped-capacity method will apply because of the low value ofh and high value of k.We can check by using Equation (3.9):hLcB₁ =k3Lc =T 0.025=-== 0.00833A₂4mr² 33hle10-0.00833B₁ === 0.0023 < 0.1k35The lumped system capacitance method is valid and can used. Therefore, may can useequation 3.4:t=pvc In0₁hAs 092HEAT TRANSFERt = pvc Inpvc Ti-ToohAsT-TooT = 150 °C, p = 7800 kg/m³.Too-100 °C, h=10 w/m².C.T₁-450 °C, c-460 J/kg. "C.pvc InTi-Toot =hAs T-Toot=Pr³cIn Ti-Tooh4r² T-Tt= 1In Ti-Topre3h T-TV-==7800+0.025-460In3.10450-100150-100= 5818.3 s= 1.62 h6

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. A steel ball [c-0.46 kJ/kg C, k-35 W/m. C] 5.0 cm in diameter and initially at a uniform temperature of 450-C is suddenly placed in a controlled environment in which the temperature is maintained at 100°C. The convection heat-transfer coefficient is 10 W/m². C. Calculate the time required for the ball to attain a temperature of 150°C.

. A steel ball [c-0.46 kJ/kg C, k-35 W/m. C] 5.0 cm in diameter and initially at a uniform temperature of 450-C is suddenly placed in a controlled environment in which the temperature is maintained at 100°C. The convection heat-transfer coefficient is 10 W/m². C. Calculate the time required for the ball to attain a temperature of 150°C.

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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