Steam enters a nozzle at 400°C and 800 kPa with a velocity of 10 m/s, and leaves at 300°C and 200 kPa while losing heat at a rate of 25 kW. For an inlet area of 800 cm2, determine the velocity and the volume flow rate of the steam at the nozzle exit.

Respuesta :

Answer:606 m/s

Explanation:

Given

Steam Inlet temperature [tex]400^{\circ} C[/tex] and pressure 800 KPa

[tex]h_1=3267.7 kJ/kg[/tex]

initial Velocity 10 m/s

Steam Outlet Velocity is [tex]300^{\circ} C[/tex] and pressure is 200 KPa

[tex]h_2=3072.1 kJ/kg[/tex]

[tex]\nu _2=1.31632[/tex]

From steam table

Heat loss 25  KW

inlet area 800 cm^2

applying Steady Flow Energy Equation

[tex]h_1+\frac{1}{2}v_1^2++Q=h_2+\frac{1}{2} v_2^2+W[/tex]

[tex]3267.7+\frac{1}{2000}10^2-25=3072.1+\frac{1}{2000}v_2^2[/tex]

[tex]3267.7-3072.1+0.05-25=\frac{1}{2}v_2^2[/tex]

[tex]v_2=\sqrt{195.65\times 2}=606 m/s[/tex]

and volume flow rate is [tex]m=\dot{m}\mu _2=2.082\times 1.31623=2.74 m^3/s[/tex]

For an inlet area of 800cm², The veloctiy of the steam at nozzle exit is 305.939 m/s while The flow rate of the steam at nozzle exit is 2.740 m^3/s

Steady flow energy equation?

Steady state flow is when the property of fluid does not change with time such properties include pressure, temperature, velocity.

Steady flow energy equation is the equation representing teh steady state flow represented as:

Q - W = m ( h2 - h1 ) + m ( c2^2 - c1^2 ) / 2000  + mg ( z2 - z1 )

where  

Q = heat transfer kW

H = work transfer kW

h = specific enthalpy kj/kg

m = mass flow rate  kg/s

c = velocity m/s

z = elevation m

g = acceleration due to gravity m/s^2

1 = inlet conditions

2 = outlet conditions

from steam table

T1 = 400 C

P1 =  800 kPa

gives h1 =  3267.5613 kj/kg and ρ1 = 2.6023.789 kg/m^3

T2 = 300 C

P2 = 200 kPa

gvies  h2 = 3072.089 kj/kg  and ρ2 = 0.789 kg/m^3

ρ = density

Q + m ( h1 + c1^2 / 2000 ) = W  + m ( h2 +c2^2 / 2000 )

-25 + m ( 3267.5613 + 10^2 / 2000 ) = 0  + m ( 3072.089 +c2^2 / 2000 )

m =  ρ1 * c1 * A1

m = 0.789 * 10 * 0.08

m = 2.0818 kg/s

substituting m into the equation gives

c2 = 305.939 m/s

flow rate of the steam at the exit Q2

Q2 = m / ρ2

Q2 = 2.0818 / 0.7597

Q2 = 2.740 m^3/s

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