Question

A well insulated rigid mixing chamber is shown below. The pressure inside the chamber is maintained at 400 kPa and saturation temperature corresponding to 400 kPa is ${156.4}^{0}C$.

Fluid A enters at ${90}^{0}C$, with a flow rate of 0.8 kg/s where fluid B has a flow rate of 0.6 kg/s. If final mixture leaves at ${56}^{0}C$ the temperature of fluid B is

• A. ${10.67}^{0}C$
• B. ${56}^{0}C$
• C. ${90}^{0}C$
• D. ${283.6}^{0}C$

Answer 1

The correct option is A

${10.67}^{0}C$

$\therefore$ All fluid exists in liquid state only.
From mass conservation

${\stackrel{\cdot }{m}}_A+{\stackrel{\cdot }{m}}_B={\stackrel{\cdot }{m}}_{total}$

$0.8+0.6={\stackrel{\cdot }{m}}_{total}=1.4kg/s$

From energy balance

${\stackrel{\cdot }{m}}_A{h}_A+{\stackrel{\cdot }{m}}_B{h}_B={\stackrel{\cdot }{m}}_{total}{h}_{total}$

$\Rightarrow {\stackrel{\cdot }{m}}_A{C}_p{T}_A+{\stackrel{\cdot }{m}}_B{C}_p{T}_B=({\stackrel{\cdot }{m}}_A+{\stackrel{\cdot }{m}}_B)T$

$\Rightarrow 0.8\times 363+0.6T_B=1.4\times 329$

$T_B=283.67K$

$T_B={10.67}^{0}C$