HW 5_EMA 4125

# HW 5_EMA 4125 - EMA 4125 HW 5 EMA 4125 HW 5 2011 Due Friday...

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EMA 4125. HW 5: EMA 4125 HW 5 - 2011 Due: Friday, Nov 4 th , 2011 1) A plate of aluminum alloy with dimensions 6 mm x 300 mm x 300 mm is solutionized at 810 K, and then quenched into water at 365 K. Over the temperature range 810-530 K, the heat transfer coefficient for quenching may be assumed as constant as 510 W m -2 K -1 . In the range 530-365 K, the heat transfer coefficient may be approximated as 2550 W m -2 K -1 . The properties of the aluminum are: k = 78 W m -1 K -1 , C p = 1000 J kg -1 K -1 , ρ = 2880 kg m -3 . a) Calculate the cooling rate during quenching at that instant when the plate is at 590 K. b) Repeat, when the plate is at 420 K. 2) A furnace wall is constructed of 7 in. of fire brick (k = 0.60 Btu h -1 ft -1 ˚F -1 ), 4 in. of red brick ( k = 0.40), 1 in. of glass-wool insulation ( k = 0.40), and 1/8 in. steel plate ( k = 26) on the outside. The heat transfer coefficients on the inside and outside surfaces are 9 and 3 Btu h -1 ft -2 ˚F -1 , respectively. The gas temperature inside the furnace is 2500 ˚F, and the outside temperature is 90 ˚F. a) Calculate the heat transfer rate through the wall (Btu h

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HW 5_EMA 4125 - EMA 4125 HW 5 EMA 4125 HW 5 2011 Due Friday...

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