Hi, working through gas turbine problems, when calculating work through the compressor, = Cp(T2 - T1), sometimes Cp is 1.005, sometimes is 1.0035. Is this due to initial temperature?

Yes, Cp is function of temperature. As the temperature increases, the amount of energy required to raise the temperature of unit mass of substance also increases.

Cp = 1.005 kJ/kg.K (at 300 K)

Cp = 1.142 kJ/kg.K (at 1000 K) ......Cp value increases with temperature

While solving gas turbine problems the Cp value is assumed to be constant( Cp value given in the problem statement). But, sometimes they specifically say "use variable specific heats" in the problem.

In that case, average value of specific heat between two state points is calculated and used.

Yes, Cp is function of temperature. As the temperature increases, the amount of energy required to raise the temperature of unit mass of substance also increases.

Cp = 1.005 kJ/kg.K (at 300 K)

Cp = 1.142 kJ/kg.K (at 1000 K) ......Cp value increases with temperature

Thanks Suyog

In addition,

While solving gas turbine problems the Cp value is assumed to be constant( Cp value given in the problem statement). But, sometimes they specifically say "use variable specific heats" in the problem.

In that case, average value of specific heat between two state points is calculated and used.

The person solving this has used a value of 1.0035 for air entering compressor at 15

15 degrees