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# Air Enthalpy Calculation

3 replies to this topic

### #1 slmn

slmn

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Posted 09 April 2012 - 02:02 PM

in gas turbine performance book , i found this equation for air enthalpy calculation
H=a(T-T0)+b(T^2-T0^2)/2-c(1/T-1/T0)
the constants a,b,c and the mass fraction of air constituents are provided
T0=273k
T=288k
i did apply in the equation as in the attached sheet

by sum the last column i got this value for enthalpy, the book says the enthalpy is 14.876 kj/kg

any idea

#### Attached Files

Edited by slmn, 09 April 2012 - 02:18 PM.

### #2 kkala

kkala

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Posted 13 April 2012 - 06:40 AM

Heat capacity of air is roughly 0.24 kcal/kg, so you need 0.24*4.19*15 ~ 15 kJ to heat 1 kg air from 0 to 15 oC, which is in rather good agreement to 14.876 kJ/kg of the book.
Attached "Rev0.xls" contains the spreadsheet of enthalpy calculation, with some remarks on it. No arithmetic errors could be traced, it seems that the application of enthalpy formula for gases contains some error. Probably the units? Resulting heat capacities for gases are not realistic, as indicated in the added columns.
Check formula for enthalpy again, error cannot be specifically located by me. Hopefully tracing will be easy.

Editing note: Added "1 kg" on Apr 15th, 2012

#### Attached Files

Edited by kkala, 15 April 2012 - 05:48 AM.

### #3 ankur2061

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Posted 13 April 2012 - 11:03 PM

slmn,

What you are looking for is psychrometric calculations for wet or humid air including the entahlpy of wet / humid air.

In such a case refer the excel spreadsheet, "Psyschro.xls" attached in the link below:

http://www.cheresour...6833#entry26833

Regards,
Ankur.

### #4 slmn

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Posted 13 April 2012 - 11:17 PM

thank you fot the great help