A4-m-high and 28-cm-diameter cylindrical column of a house is cooled to 15°c during a cold night and heated again during the day by being exposed to ambient air at an average temperature of 32°c with an average heat transfer coefficient of 14 w/m2. k. the column is made of concrete (k 0.79 w/mk, ? -5.9 x10" m2/s, ? 1600 kg/m3, and c,-0.84 kj/kg-k). using analytical one-term approximation method (not the heisler charts), determine: a)-how long it will take for the column surface temperature to rise to 30°c, b)-the amount of heat transfer until the center temperature reaches to 32°c, and c)- the amount of heat transfer until the surface temperature reaches to 30°c.

A3-mm-thick panel of aluminum alloy (k 177 w/m-k, c 875 j/kg-k and ? = 2770 kg/m) is finished on both sides with an epoxy coating that must be cured at or above t,-150°c for at least 5 min. the production line for the curing operation involves two steps: (1) heating in a large oven with air at ts,0-175°c and a convection coefficient of h, 40 w/m2. k, and (2) cooling in a large chamber with air at 25°c and a con- vection coefficient of he 10 w/m2.k. the heating portion of the process is conducted over a time interval te which exceeds the ime required to reach 150°c by 5 min (h = r + 300 s). the coating has an emissivity of ? = 0.8, and the temperatures of the oven and chamber walls are 175 and 25°c, respectively. if the panel is placed in the oven at an initial temperature of 25°c and removed from the chamber at a safe-to-touch tempera ture of 37°c, what is the total elapsed time for the two-step curing operation?