Inconsistent CO2 property queries
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This post was last edited by chenzx on 2018-5-11 23:14. I want to find the enthalpy of the saturated vapor of CO2 at different temperatures; the values obtained from pressure-enthalpy diagrams differ from those in the tables of saturated liquid and saturated vapor. Why is that? Please give me some advice. Thank you!
For example, at -20 degrees Celsius, the enthalpy value according to the table is only 154.76, while it’s over 400 according to the graph. Why is that?
It’s normal – the reference points for graphs and tables are different; you can see this by looking at them. Take saturated liquid at 0°C as an example: the value in the table is 200, while in the graph it’s around 500, which means there’s a difference of over 300. The origin point for enthalpy values in the graph is 300. In any case, what matters are the differences in enthalpy and entropy, so focus on those values. Also, don’t try to calculate using data from both the table and the graph, as their reference points differ; either use the data from the graph or that from the table. . . .
I think what was said above makes sense; don’t use data from two different sources for calculations
Thank you very much for your reply. I agree with you; the key point is that this diagram and this table are together in one file, with the diagram on top and the table below. It makes sense for the normal reference points to be the same; I see that other material diagrams and tables are consistent, so it’s hard to understand why CO2 is the exception.