Determine the change in specific enthalpy for air that is heated from 25°C to 1000°C considering (a) the specific heats to be constant, with a value taken at 25°C, (b) the specific heats to be constant, with a value taken at 1000°C (cp = 1.185 kJ/kg-K), (c) the specific heats to be constant, with a value taken at 500°C, and (d) considering the specific heats to be variable.
Given: T1 = 25°C; T2 = 1000°C; Air
What will be an ideal response?
For constant specific heats:
(a) At 25oC, cp = 1.005 kJ/kg-K ?h = cp (T2 – T1) = 979.9 kJ/kg
(b) At 1000oC, cp = 1.185 kJ/kg-K ?h = cp (T2 – T1) = 1155.4 kJ/kg
(c) At 500oC, cp = 1.081 kJ/kg-K ?h = cp (T2 – T1) = 1054.0 kJ/kg
(d) For variable specific heats, h1 = 298.18 kJ/kg, h2 = 1363.95 kJ/kg ?h = h2 – h1 = 1065.8 kJ/kg
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