Consider two full 100 gallon mixing tanks. The tanks initially contain purewater and 100 lbs. salt, respectively. Mixture from tank 1 is pumped intotank 2 at a rate of 2 gallons/min and mixture from tank 2 is pumped intotank 1 at a rate of 2 gallons/min so that each tank is always completely lled. How long until the amount of salt in tank 1 reaches 40 lbs.?

Apipe with an outside diameter of 15 cm is exposed to an ambient air and surrounding temperature of -20°c. the pipe has an outer surface temperature of 65°c and an emissivity of 0.85. if the rate of heat loss from the pipe surface is 0.95 kw per meter of length, the external convective heat transfer coefficient (h) is: (a) 12.5 w/m"k (b) 18.6 w/mk (c) 23.7 w/mk (d) 27.9 w/mk (e) 33.5 w/mk