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bimalbs
27-10-2008, 07:29 AM
I'm a mechanical engineer & used a refrigeration data book for solving the vapour compression system problems...

But now, I got another book where all the values of hf & hg were different. I think the values of hfg are similar in these 2 books. In the second book, it's given that the datum taken is -40 degree celsius. So, will there be any trouble when I slove problems using this book?

If anybody wants, I can quote some values of any refrigerant at a particular temperature from these 2 books....

Please help...

Regards,
Bimal :-)

US Iceman
27-10-2008, 12:22 PM
The difference in the values is probably due to the reference lines for liquid enthalpy. If you use one or the other, you should be OK. But never mix the data between two sources. The hfg values should not change very much because this is a delta value, not an absolute value like hf or hg.

bimalbs
27-10-2008, 04:45 PM
Yeah.. That's what I said. The hfg values are similar in the 2 books, but when we take the individual values of hf & hg, they are different.

So, I'm asking whether if we take these values for an exam, will there be any problem while listing the datas. Is there any standard datum that is universally followed?

US Iceman
27-10-2008, 05:23 PM
Well, if this is for a test you may want to specify the reference datum. Otherwise, someone may score you wrong because your absolute numbers do not match the answer expected.

ASHRAE has their reference at -40C where the liquid enthalpy is 0.

Another possibility is using the normal boiling point at atmospheric pressure.

bimalbs
28-10-2008, 04:27 PM
Oh..OK
Thanks for the fast & clear answer, my friend :)