A 100 kg of water in a closed insulated autoclave is heated from 20 to 90 °C by a heating coil made of 12 m of 1-in O.D., 15-BWG-gauge copper tubing (ID=2.174 cm). As steam at 100 °C issued in the coil, it is found that it takes 40 min to heat the water. The steam-side coefficient hf is known to be 12,000 W/m2K. (suppose you can use some average t for water in your calculations.) 

a) If propeller agitator stirs the water, the water-side coefficient ho doubles. How long would the heating now need?

b) If high-pressure steam at 150 0C is used (no agitation), how long would heating take?