SSC JE Mechanical Engineering 25 Sep 2019 Shift 1 Paper

Question : 188 of 200

Marks: +1, -0

A boiler produces 9 kg steam/kg of coal burnt, which has a calorific value of 27 MJ/kg. The enthalpy of feed water and steam at the exit are 300 kJ/kg and 3000 kJ/kg respectively. Its thermal efficiency is:

90%
83.57%
55%
94.2%

Validate

Solution:

Given:

{m}_{{s}}=9 {kg}, \Δ{h}_{{s}}=(3000-300)=2700 {kJ} \/ {kg},

{m}_{{c}}=1 {kg}, {C}_{{V}}=27 {MJ} \/ {kg}=27000 {kJ} \/ {kg}

\η =({m}_{{s}} \×\Δ{h}_{{s}}) \/({m}_{{c}} \×{CV})

\η =(9 \×2700) \/(1 \×27000)

=0.9=90 \%

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