Question

P4.6 shows a mixing tank initially containing 2000 lb of liquid water. The tank is fitted with two inlet pipes, one delivering hot water at a mass flow rate of 0.8 lb/s and the other delivering cold water at a mass flow rate of 1.2 lb/s. Water exits through a single exit pipe at a mass flow rate of 2.5 lb/s. Determine the amount of water, in lb, in the tank after one hour.

Answer 1

Answer and Explanation:

the answer is attached below

Answer 2

Answer:

Amount of water is 200 lb in the tank after 1 hour.

Explanation:

Initial mass of liquid water in tank = m initial = 2000 lb

Final mass of liquid water in tank = m final

mass flow rate of hot water = m1 = 0.8 lb/s

mass flow rate of cold water= m2 = 1.2 lb/s

mass flow rate of liquid water through a single exit pipe =m3 =2.5 lb/s

time = t = 1hr

So the final mass of water in tank is calculated as following :

Following equation is derived from mass rate balanced equation

m final = m initial + (m1+m2-m3)t

          =2000 + (0.8 + 1.2 - 2.5) x 1

          =2000 + (0.8 + 1.2 -2.5) x (1 x 3600s/hr)

          = 2000 x 4.5

          =200 lb

Hence  Amount of water is 200 lb in the tank after 1 hour.