Question

A bath contains 100 kg of water at 60 °C. Hot and cold water taps are turned on to deliver 20 kg per minute each at temperatures of 70 °C and 10 C respectively. How long will it be before the temperature in the bath has dropped to 45 C ? Assume complete mixing of the water and ignore heat losses.

Answer 1

this is a "classic" mixture problem

average inlet temp is 40ºC
... 40 kg/min

(100 kg * 60ºC) + (x kg * 40ºC) = (100 + x) kg * 45ºC

6000 + 40 x = 4500 + 45 x

1500 = 5 x ... x = 300 kg

300 kg / (40 kg/min) = ? min

Answer 2

I don't have