Question

In: Mechanical Engineering

Steam at 5MPa and 300°C enters a turbine in a steady flow manner, from the turbine...

Steam at 5MPa and 300°C enters a turbine in a steady flow manner, from the turbine the steam expands to 200kPa with a quality of 90%. Find the following:

  1. The work done by the steam to the turbine in kj/kg
  2. The amount of steam flow rate needed in kg/hr if the turbine produces 200kW of power
  3. The efficiency of the expansion process

Solutions

Expert Solution

Ans

At state 1 (5 MPa and 300 oC)

h1 = 2925.6 kJ/kg

s1 = 6.2109 kJ/kg K

At state 2s ( 200 kPa)

s2s = s1 = 6.2109 kJ/kg K

sf + x2s(sg - sf) = 6.2109

1.53 + x2s(7.127 - 1.53) = 6.2109

x2s = 0.836

Therefore,

h2s = hf + x2s(hg - hf)

= 504.7 + 0.836(2707 - 504.7)

= 2345.82 kJ/kg

At state 2a ( 200 kPa and x2a = 0.9 )

h2a = hf + x2a(hg - hf)

= 504.7 + 0.9(2707 - 504.7)

= 2486.77 kJ/kg

(a)

Work done by the steam turbine per kg = h1 - h2a

= 2925.6 - 2486.77

= 438.83 kJ/kg (ans)

(b)

Steam flow rate needed for producing 200 kW of power, m = 200 / Work done by the steam turbine per kg

= 200 / 438.83

= 0.45576 kg/s

= 0.45576 * (3600) kg/hr

= 1640.73 kg/hr (ans)

(c)

Efficiency of the expansion process,

  

  

= 75.69 % (ans)

samet mamat answered 1 year ago
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