Question

The mean specific heat (C_ps) for superheated steam at 0.5 bar, between 300°C and 400°C, is:

(Consider h_sup = 3075.5 kJ/kg at 300°C and h_sup = 3278.9 kJ/kg at 400°C)  
1. 1.49 kJ/kg°C
2. 0.03 kJ/kg°C
3. 2.03 kJ/kg°C
4. ​0.49 kJ/kg°C

Answer 1

Correct Answer - Option 3 : 2.03 kJ/kg°C

Concept:

Specific enthalpy of superheated steam is given by:

h_t2 - h_t1 = C_ps(t₂ - t₁)

where ht2 is specific enthalpy at temperature t₂ and h_t1 is specific enthalpy at temperature t₁

Calculation:

Given:

ht2 = 3278.9 kJ/kg, h_t1 = 3075.5 kJ/kg, t2 = 400°C, t₁ = 300°C, Cps = mean specific heat

We know that,

ht2 - ht1 = Cps(t2 - t1)

3278.9 - 3075.5 = C_ps × (400 - 300)

203.4 = Cps × 100

C_ps = \(\frac{203.4}{100}=2.03\) kJ/kg°C