Problems with enthalpy values in HYSYS
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This post was last edited by bigsk on 2018-12-27 at 15:41. Using HYSYS to calculate the enthalpy difference for a wet air treatment process: State 1 has a temperature of 31.3°C, relative humidity of 71%, and an enthalpy value of -266.5 kJ/kg; State 2 has a temperature of 24°C, relative humidity of 50%, and an enthalpy value of -125.3 kJ/kg. The enthalpy difference is thus 141.2 kJ/kg. However, when using several HVAC enthalpy-humidity chart software tools, the enthalpy value for State 1 is 84.2 kJ/kg, and that for State 2 is 47.83 kJ/kg, giving an enthalpy difference of 36.37 kJ/kg. The values obtained using the formula (1.01+1.84t)d+2500d, which is used in HVAC calculations, match those obtained through HVAC software. HVAC uses 0°C as the reference point for calculating enthalpy values, with these values being expressed per kilogram of dry air. It is understandable that different reference points lead to different enthalpy values; logically, the enthalpy difference should not be affected by the reference point. But the difference between these two numbers is quite large. Based on the values relevant to each kilogram of dry air in HVAC systems, the figures calculated in HYSYS will be even higher, resulting in an even larger enthalpy difference. I’m seeking advice from those who are more experienced – where exactly lies the problem?
I simulated it to be 127.7; I’m not sure if that’s correct
Although the result is a bit smaller, it is still several times larger than what HVAC calculates. I don’t know where the problem is. It seems the difference lies in the enthalpy value of water vapor
The sensory simulation results don’t seem very reliable
It can be considered from this perspective: the enthalpy in HYSYS includes chemical enthalpy; if you want to compare the differences in physical enthalpy, you need to eliminate the influence of chemical enthalpy. Since the components in the two states are different, the chemical enthalpies are also different; therefore, it is meaningless to directly compare the enthalpies of the two. It is recommended that you compare the enthalpy differences of the two states from 0°C separately, and then compare these two enthalpy differences in order to eliminate the influence of chemical enthalpy; only then is it meaningful. I did a rough calculation on my end, and the result was 35.5, which is pretty much the same as the HVAC result
Thank you very much. I’m not familiar with the concept of chemical enthalpy; I’d like to ask how it is calculated