Air is compressed in the compressor of a turbojet engine. Air enters the compressor at 270 K and 58 kPa and exits the compressor at 465 K and 350 kPa. Take the average specific heat at constant pressure (cp, avg) of air as 1.015 kJ / kg. K and Rair = 0.287 kJ / kg. K. Find the mass specific entropy change associated with the compression process

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Engineering

Quinn Ramos

8 May, 13:09

Air is compressed in the compressor of a turbojet engine. Air enters the compressor at 270 K and 58 kPa and exits the compressor at 465 K and 350 kPa. Take the average specific heat at constant pressure (cp, avg) of air as 1.015 kJ / kg. K and Rair = 0.287 kJ / kg. K. Find the mass specific entropy change associated with the compression process

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Pooky · Answer 1

Recall the Entropy Balance (Second Law of Thermodynamics) equations for the system below

And for ideal gas, we know that

Change in Entropy of the air kJ/Kg. K, ΔS = S₁ - S ₂ = Cp Ln (T₂/T₁) - R Ln (P₂/P₁)

where R is gas constant = 0.287kJ/kg. K and given

Cp=1.015 kJ / kg. K

T₂ = 465k T₁=270k, P1=58kPa, P2=350kPa

substituting these values into the eqn above, we have

S = (1.015x 0.544) - (0.287x1.798)

S = 0.0363kJ/Kg. K

Hence, the mass specific entropy change associated with the compression process = 0.0363kJ/Kg. K