Wood charcoal is used as a cooking fuel in many developing countries. generally this wood is locally produced, low quality wood charcoal produced at a low temperature. a combustion engineer is working on designing a forced-air, charcoal cookstove with 1500 w of cooking power. to ensure that there is sufficient air to ensure complete combustion while maintaining the stove temperature high, the stove should be designed to have 10% excess air. the stove does not condense the water in the combustion products. the ultimate analysis of the locally produced charcoal is 92% c, 6% o, and 2% h (wt) and the higher heating value is 30 mj/kg. determine: a. the lower heating value of the charcoal, and b. assuming 50% efficiency, the airflow rate in l/min at standard temperature and pressure.

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?