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Enthalpy Of Vaporization Below Boiling Point


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#1 cheminst

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Posted 16 June 2019 - 08:58 AM

Can anyone please explain how to calculate the enthalpy change when water is evaporating below the boiling point? e.g. 50 Celsius at 1 atm.

 

Any reference book or webpage link?



#2 PingPong

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Posted 16 June 2019 - 09:10 AM

Use a Steam Table.



#3 cheminst

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Posted 16 June 2019 - 09:39 AM

Use a Steam Table.

Actually in a steam table there are only data for saturated steam and superheated steam. The data I want are the enthalpy change of vaporization of water at 1 atm below boiling point (100 Celsius) e.g 30, 40, 50, 60 Celsius.  This is neither saturated steam nor superheated steam.



#4 PingPong

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Posted 16 June 2019 - 11:06 AM

At low pressure all gases behave like (nearly) ideal gases and therefor impact of pressure on enthalpy is negligible.



#5 PhilippM

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Posted 16 June 2019 - 11:12 AM

 

This is neither saturated steam nor superheated steam.

 

 

What else is the steam supposed to be?



#6 cheminst

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Posted 16 June 2019 - 11:14 AM

At low pressure all gases behave like (nearly) ideal gases and therefor impact of pressure on enthalpy is negligible.

Thanks for the clarification.



#7 cheminst

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Posted 16 June 2019 - 11:15 AM

 

 

This is neither saturated steam nor superheated steam.

 

 

What else is the steam supposed to be?

 

Actually I meant the steam for which only the data are given in steam tables



#8 PingPong

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Posted 16 June 2019 - 11:50 AM

At 50 oC water has a vapor pressure of 0.123 bar, so saturated steam at 50 oC has a partial pressure of 0.123 bar.

 

In air (or whatever gas) at 1 atm the steam partial pressure at 50 oC is only 0.123 bar and the air partial pressure is 0.89 bar.

 

The enthalpy of pure steam at 50 oC and 0.123 bar total pressure will be practically the same as the enthalpy of steam at 50 oC in air at a total pressure of 1 atm.



#9 breizh

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Posted 17 June 2019 - 12:01 AM

https://www4.eere.en..._tool/propSteam

 

Let you try he calculator above , just pay attention to the inputs  (F,PSI g) .

good luck

Breizh



#10 cheminst

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Posted 17 June 2019 - 12:05 AM   Best Answer

Found the data

 

https://www4.eere.en..._tool/propSteam

 

Let you try he calculator above , just pay attention to the inputs  (F,PSI g) .

good luck

Breizh

Thanks for the link. I found NIST data through this link.

https://webbook.nist...Pa*s&STUnit=N/m






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