Evaluate total heat of steam - thermodynamics, Mechanical Engineering

Evaluate total heat of steam:

10 kg of wet saturated steam at 15 bar pressure is superheated to the temperature of 290°C at constant pressure. Find heat needed and the total heat of steam. The dryness fraction of steam is 0.85.

Sol.: From steam table, we get following data:

Absolute pressure (P)

bar

Saturation

temperature (t) ºC

Specific enthalpy kJ/kg

Water (hf)

Latent heat (hfg)

15

198.3

844.6

1947

Total heat of 10 kg wet saturated steam

=10 × 2499.55 = 24995.5 kJ                                                   .......ANS

Total heat of 1 kg superheated steam can be given by Hsup  = hf  + hfg  + Cp(tsup  - ts) kJ

= 844.6 + 1947 + 2.1 × (290 - 198.3) kJ

= 2984.17 kJ                                                                               .......ANS

Total heat of 10 kg superheated steam =10 × 2984.17 = 29841.7 kJ         .......ANS

= hf + hfg + Cp(tsup - ts) - (hf + xhfg)

= hfg  + Cp(tsup  - ts) - xhfg

=1947 + 2.1 x (290 - 198.3) - 0.85 x 1947 kJ = 484.62 kJ

Heat which is required to convert 10 kg wet saturated steam into 10 kg superheated steam

=10 × 484.62 = 4846.2 kJ                                                        .......ANS

Total heat of 1 kg wet saturated steam can be given by Hwet  = hf  + xhfg  kJ

= 844.6 + 0.85 × 1947 kJ = 2499.55 kJ

Heat which is required to convert 1 kg wet saturated steam into 1 kg superheated steam

= Hsup  - Hwet,

here Hsup = enthalpy of 1 kg superheated steam = hf + hfg + Cp(tsup - ts) kJ

Hwet = enthalpy of 1 kg wet saturated steam = hf  + xhfg  kJ

Heat which is required to convert 1 kg wet saturated steam into 1 kg superheated steam

Posted Date: 10/15/2012 7:24:01 AM | Location : United States







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