Question

30 kg/s of superheated steam at 800 kPa, 200°C is mixed with saturated water at 800 kPa in a desuperheater to produce dry saturated steam at 800 kPa. Determine the flow rate of saturated water required.

Answer 1

Answer:

$\dot{m}$ = 3.8 kg/s

Explanation:

From steam table, we can find :

The enthalpy of the super heated steam at 800 kPa or 8 bar is

    h₁ = 2838.6 kJ/kg

or H₁ = 2838.6 x 30 85158 kJ

Enthalpy of the saturated water at 8 bar is

h₂ = $h_{f}$ = 33.6 kJ/kg

Now let the flow of saturated water is $\dot{m}$

then h₂ = H₂ = 33.6 $\dot{m}$ kJ

Enthalpy of dry saturated steam at 8 bar is

h₃ = $h_{g}$ = 2516.2 kJ/kg

h₃ = H₃ =2516.2 x ( 30+$\dot{m}$ ) kJ

Now we know from energy balance equation,

H₃ = H₁ + H₂

2516.2 x ( 30+$\dot{m}$ ) = 85158 + 33.6$\dot{m}$

75486 + 2516.2$\dot{m}$ = 85158 + 33.6$\dot{m}$

2516.2$\dot{m}$ + 33.6$\dot{m}$ = 85158-75486

2549.8$\dot{m}$ = 9672

$\dot{m}$ = 3.7932

$\dot{m}$ = 3.8 kg/s