Question

A steam turbine receives steam steadily at 10 bar with a enthalpy of 3000 kj/kg. The work output is 250 kj/kg. The changes in kinetic and potential energies are negligible the heat transfer from the turbine casing to the surroundings is equal to (a) select one:

a. (a) 150 kj

b. 50 kj

c. (a) 250 kj

d. (a) 0 kj

Answer 1

The heat transfer from the turbine casing to the surroundings is equal to 50 KJ/kg.

Explanation:

• Applying the equation of Steady Flow of Energy.

• Equation when steam enters the turbine.

=  m (h1 + v1^2/2 + gz1 ) + Q(in) + W(in)

• Equation when steam leaves the turbine.

= m (h2+v2^2/2 + gz2) + Q(out) + W(out)

• Taking specific quantities.

(h1)+Qin+W˙in=(h2)+Qout+W˙out

W˙out=250 kJ/kg (specific work output of turbine)

Q˙in=W˙in=0

m˙(h1)=m˙(h2)+Q˙out+W˙out

• Heat transfer from turbine casing to surroundings

Q˙out=[m˙(h1–h2)]–W˙out

=(3000–2700)−250

=50 kJ/kg

Hence the heat transfer from the turbine casing to the surroundings is equal to 50 KJ/kg.

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