Steam at 1400 kPa and 350°C [state 1] enters a turbine through a pipe that is 8 cm in diameter, at a mass flow rate of 0.1 kg⋅s−1. The exhaust from the turbine is carried through a 15-cm-diameter pipe and is at 50 kPa and 100°C [state 2]. What is the power output of the turbine?

H1 = 3150.7 kJ/kg V1 = 0.2004 m3/kg
H2 = 2682.6 kJ/kg V2 = 3.4181 m3/kg

Respuesta :

Answer:

Power output, [tex]P_{out} = 178.56 kW[/tex]

Given:

Pressure of steam, P = 1400 kPa

Temperature of steam, [tex]T = 350^{\circ}C[/tex]

Diameter of pipe, d = 8 cm = 0.08 m

Mass flow rate, [tex]\dot{m} = 0.1 kg.s^{- 1}[/tex]

Diameter of exhaust pipe, [tex]d_{h} = 15 cm = 0.15 m[/tex]

Pressure at exhaust, P' = 50 kPa

temperature, T' =  [tex]100^{\circ}C[/tex]

Solution:

Now, calculation of the velocity of fluid at state 1 inlet:

[tex]\dot{m} = \frac{Av_{i}}{V_{1}}[/tex]

[tex]0.1 = \frac{\frac{\pi d^{2}}{4}v_{i}}{0.2004}[/tex]

[tex]0.1 = \frac{\frac{\pi 0.08^{2}}{4}v_{i}}{0.2004}[/tex]

[tex]v_{i} = 3.986 m/s[/tex]

Now, eqn for compressible fluid:

[tex]\rho_{1}v_{i}A_{1} = \rho_{2}v_{e}A_{2}[/tex]

Now,

[tex]\frac{A_{1}v_{i}}{V_{1}} = \frac{A_{2}v_{e}}{V_{2}}[/tex]

[tex]\frac{\frac{\pi d_{i}^{2}}{4}v_{i}}{V_{1}} = \frac{\frac{\pi d_{e}^{2}}{4}v_{e}}{V_{2}}[/tex]

[tex]\frac{\frac{\pi \times 0.08^{2}}{4}\times 3.986}{0.2004} = \frac{\frac{\pi 0.15^{2}}{4}v_{e}}{3.418}[/tex]

[tex]v_{e} = 19.33 m/s[/tex]

Now, the power output can be calculated from the energy balance eqn:

[tex]P_{out} = -\dot{m}W_{s}[/tex]

[tex]P_{out} = -\dot{m}(H_{2} - H_{1}) + \frac{v_{e}^{2} - v_{i}^{2}}{2}[/tex]

[tex]P_{out} = - 0.1(3.4181 - 0.2004) + \frac{19.33^{2} - 3.986^{2}}{2} = 178.56 kW[/tex]

The power output of the Turbine is; 225.69 kW

What is the Power Output?

We are given

Pressure of steam; P = 1400 kPa

Temperature of steam at state 1; T = 350°C

Diameter of pipe; d₁ = 8 cm = 0.08 m

Mass flow rate; m' =  0.1 kg/s

Diameter of exhaust pipe; d₂ = 15 cm = 0.15 m

Pressure at exhaust; P' = 50 kPa

Temperature at state 2; T' =  100°C

Area; A = πd²/4

A = π * 0.08²/4

A = 0.0016π m²

We can find the find initial velocity from the formula;

v₁ = m' * V₁/A

v₁ = (0.1 * 0.2004/(0.0016π))

v₁ = 3.986 m/s

From equation of compressible fluid, we know that;

(A₁ * v₁)/V₁ = (A₂ * v₂)/V₂

A₂ = πd₂²/4

A₂ = π * 0.15²/4

A₂ = 0.005625π m²

(0.0016π * 3.986)/0.2004  = (0.005625π * v₂)/3.4181

Solving for v₂ gives;

v₂ = 19.33 m/s

Finally power output is gotten from  the expression;

P_out = -m'(H₂ - H₁) + (v₂² - v₁²)/2

P_out = -0.1(2682.6 - 3150.7) + (19.33² - 3.986²)/2

P_out = 225.69 kW

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