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a hot water ar 80°C is mixed with cold water at 20°C in a mixing chamber...

a hot water ar 80°C is mixed with cold water at 20°C in a mixing chamber operating under adiabotic conditions. Flow rate of the cold water is 15.0 kg/s. The outlet stream is warm water at 45°C and 100 kPa. Estimate the flow rate of the hot water.

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Answer #1

Assumptions: This is a steady-state flow process. Kinetic and potential energy changes are negligible. The heat loss from the mixer is negligible. The air streams are ideal gases.


For an ideal gas, enthalpy depends only on the temperature.
Hot air in: m1 = unknown T1 = 353 K; H1 = 350.49 kJ/kg (From Table of Ideal Gas properties of air)
Cold air in: m2 = 15.0 kg/s; T1 = 293 K; H2 = 295.17 kJ/kg (From Table of Ideal Gas properties of air)
Outlet stream: warm air at 318 K and H3 = 320.29 kJ/kg (From Table of Ideal Gas properties of air)

Energy and mass balances are:
m1H1 + m2H2 = m3H3
m1 + m2 = m3


Combining and organizing these equations yield the hot air mass flow rate:

Therefore, flow rate of hot water = 12.48 kg/s

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