A steady-state countercurrent staged distillation column is separating ethanol from water. The feed is a 30.0 wt% ethanol, 70.0 wt% water mixture that is a saturated liquid at 1 atm pressure. Flow rate of feed is 10,000 kg/h. The column operates at a pressure of 1 atm. The reflux is returned as a saturated liquid. A reflux ratio of L/D = 3.0 is being used. Bottoms composition is XB = 0.05 (weight fraction ethanol), and distillate composition is xp = 0.80 (weight fraction ethanol). The system has a total condenser and a partial reboiler. The column is well insulated. Use the Lewis method to find the number of equilibrium contacts required if the feed is input on the second stage from the top.

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?