3 replies to this topic

[Movers]

Hi All.

I simulated mixing two streams. First one contain mainly isobutene, isobutane and buten-1, second one is ethanol (100%). Both streams in the same temperature and pressure, 7°C and 1,3 MPag. results after mixing are 1,3 MPag and -4°C. Could anyone explain me why this temperature is changing during mixing?

 

Best Regards

Edited by Movers, 26 October 2017 - 07:48 AM.

[MrShorty]

More detail might help get a more detailed response. I expect what you are seeing here is the effect of "heat of mixing" or "enthalpy of mixing" (when we want to be precise and not use the nebulous term "heat"). Wikipedia has an article on enthalpy of mixing (https://en.wikipedia...halpy_of_mixing ). Interestingly, this article specifically mentions hydrocarbon-alcohol heat of mixing, references an old JCED paper (see reference 7) that is all about measuring the endothermic heats of mixing for hydrocarbon+alcohol systems.

 

Assuming your mixing operation is roughly adiabatic (constant enthalpy -- no heat exchanged with surroundings), then I would expect that the temperature change you are seeing is related to the endothermic heat of mixing that seems to be common for hydrocarbon-alcohol systems.

[Movers]

Thanks for your advise. In the meantime my colleague gave me an answer. I used wrong thermodynamic model. I used PG model, after change model to NRTL, temperature during mixing is constans.

 

P.S. Article in Wikipedia, to which you gave link, is very interesting.

 

Thanks.

 

Best Regards

[Bobby Strain]

But I think the real system will exhibit a lower temperature after mixing. So, be careful where you get advice. Best to find some actual data for confirmation.

 

Bobby