A mixing tank has two inlets and two exits. Cold water enters at 5degree C with
ID: 2323621 • Letter: A
Question
A mixing tank has two inlets and two exits. Cold water enters at 5degree C with a volumetric flow rate of 5.0 m^3/hour. Hot water enters at 98degree C with a volumetric flow rate of 2.0 m^3/hour. Warm water leaves the tank from two outlets, one with a mass flow rate of 1.00 kg/s, and the other with a mass flow rate of 0.50. Determine the change in the mass of water in the tank in 20 min? Specify whether it is an increase or decrease. (You may assume that the tank contains 1000 kg of water and is 1/4 full at the start of the process.)Explanation / Answer
Cold water inlet 1 = 5 m3/hr , 5oC
Cold water inlet 2 = 2 m3/hr , 98oC
Change in mass of water = Mass of water leaving - Mass of water entering
Mass of water leaving = mass flow rate x time
Mass of water entering = mass flow rate x time = density x volume flow rate x time
Mass of water leaving = 1.5 kg/s x 20 min x 60 s= 1800 kg
Mass of water entering = 999.96 kg/m3 x 5 m3/hr x 20/60 hr + 959.79 kg/m3 x 2 m3/hr x 20/60 hr = 1666.6 + 639.86
= 2306.46 kg
As mass of water entering is greater than the mass of water leaving the water level in the tank will increase.
Change in mass = 2306.46 - 1800 = 506.46 kg
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