I am currently modeling the combined supercritical Brayton (topping) and transcritical Rankine (bottoming) cycles for waste heat recovery applications in the Engineering Equation Solver (EES).
I already checked the equations that there were no syntax errors, and the problem was neither under nor over-specified. But when I ran the equations, an error message popped up saying "The temperature or pressure is above the critical point. A two-phase condition can not exist."
Do you have any idea on this? I am aware that many people have been using EES to model supercritical states.
You don't need EES to solve a Brayton topping/Rankine bottoming cycle. You could do that in an Excel spreadsheet. This is just a variant of a typical combined cycle power plant (combustion gas turbine/heat recovery steam generator/steam turbine). There are many more efficient options for such calculations. EES shouldn't even be considering a two-phase anything or even have this error message in it. What conditions and particulars are you interested in? I probably already have a model that you can use.
Did you try to change the lower and upper guess values of variables?
Even though I might be late, you could try to give it a shot with TESPy https://tespy.readthedocs.io, which is open source and relies on CoolProp. It will be a step by step work to create your application, if you are new to TESPy, but there are a couple of introductory tutorials, which might be useful for you.
Also, looking at the error message, it kind of implies to my understanding (I do not use EES though), that you are implying something like steam mass fraction in a supercritical state, which cannot be solved.
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