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nlexa [21]
3 years ago
13

A hot-water stream at 80 ℃ enters a mixing chamber with a mass flow rate of 0.5 kg/s where it is mixed with a stream of cold wat

er at 20 ℃. If it is desired that the mixture leave the chamber at 42 ℃, determine the mass flow rate of the cold-water stream. Assume all the streams are at a pressure of 250 kPa
Physics
1 answer:
rewona [7]3 years ago
4 0

Answer:

\dot{m_{2}}=0.865 kg/s

Explanation:

\dot{m_1}= 0.5kg/s

from steam tables , at 250 kPa, and at

T₁ = 80⁰C ⇒ h₁ = 335.02 kJ/kg

T₂ = 20⁰C⇒ h₂ = 83.915 kJ/kg

T₃ = 42⁰C ⇒ h₃ = 175.90 kJ/kg

we know

\dot{m_{in}}=\dot{m_{out}}

\dot{m_{1}}+\dot{m_{2}}=\dot{m_{3}}

according to energy balance equation

\dot{m_{in}}h_{in}=\dot{m_{out}}h_{out}

\dot{m_{1}}h_{1}+\dot{m_{2}}h_{2}=\dot{m_{3}}h_{3}

\dot{m_{1}}h_{1}+\dot{m_{2}}h_{2}=(\dot{m_{1}}+\dot{m_{2}})h_{3}\\(0.5\times 335.02)+(\dot{m_{2}}\times 83.915)=(0.5+\dot{m_{2}})175.90\\\dot{m_{2}}=0.865 kg/s

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