Acopper sheet of thickness 2 mm has an initial temperature of 170°c. it is suddenly quenched in liquid water, resulting in boiling at its two surfaces. for boiling, newton’s law of cooling is expressed as , where is the solid surface temperature and is the saturation temperature of the fluid (in this case 100°c). the convection heat transfer coefficient may be expressed as . determine the time needed for the sheet to reach a temperature of 104°c.

At steady state, air at 200 kpa, 325 k, and mass flow rate of 0.5 kg/s enters an insulated duct having differing inlet and exit cross-sectional areas. the inlet cross-sectional area is 6 cm2. at the duct exit, the pressure of the air is 100 kpa and the velocity is 250 m/s. neglecting potential energy effects and modeling air as an 1.008 kj/kg k, determine ideal gas with constant cp = (a) the velocity of the air at the inlet, in m/s. (b) the temperature of the air at the exit, in k. (c) the exit cross-sectional area, in cm2