MATLAB + REFPROP: How to determine bubble and dew point temperatures for zeotropic mixtures

[atit-sut]

Hello,

I’m using MATLAB to access REFPROP in order to simulate power cycles with zeotropic mixtures as the working fluid. Specifically, after selecting the component fluids and their corresponding mass fractions, I would like to use MATLAB (via the Python wrapper) to determine the bubble point and dew point temperatures of the mixture.

Could someone please suggest the appropriate REFPROP commands or methods to achieve this?

Below is an example of how I currently access the enthalpy of an ammonia-water mixture (mass fraction of ammonia = 0.82, water = 0.18):

---

clear
clc

RP = py.ctREFPROP.ctREFPROP.REFPROPFunctionLibrary('C:\Program Files (x86)\REFPROP');
wf = 'ammonia;water';
z_NH3 = 0.82;
z_wf = {z_NH3, 1 - z_NH3};

% Calculate enthalpy of the mixture
h_wf1 = refp(wf, 'PQ', 3e+06, 0, 'H', RP, z_wf)

---

And here is the content of the helper function refp:

---

function answer = refp(fluid, input, parameter1, parameter2, output, RP, z)
MOLSI = RP.GETENUMdll(int8(0), 'MASS base si').iEnum;
iMass = int8(1); % 0: molar fractions; 1: mass fractions
iFlag = int8(0); % 0: don’t call SATSPLN; 1: call SATSPLN
r = RP.REFPROPdll(fluid, input, output, MOLSI, iMass, iFlag, parameter1, parameter2, z);
G = double(r.Output);
answer = G(1);
end

---

System Information:
REFPROP Version: 10.0
Operating System: Windows 11 Home
Access Method: Python wrapper to connect MATLAB R2022a to REFPROP

Thank you in advance for your guidance on how to determine the bubble point and dew point temperatures of zeotropic mixtures in this setup.

[Matthew-Boyd]

Use SATPdll. Below is example Python code that can be adapted for your MATLAB use:

fluid = "ammonia;water"
z = [0.82, 0.18]
fluid_str = fluid + "|" + ";".join(str(num) for num in z) + " mass"
print(f"fluid_str = {fluid_str}")
RP.SETFLUIDSdll(fluid)

P = 3e3     # kPa

# Get bubble point at defined pressure
kph = 1     # 1 = z is liquid composition
result1 = RP.SATPdll(P, z, kph)
print(f"Bubble point at P = {P} kPa: T = {result1.T} [K]")

# Get dew point at defined pressure
kph = 2     # 2 = z is vapor composition
result2 = RP.SATPdll(P, z, kph)
print(f"Dew point at P = {P} kPa: T = {result2.T} [K]")

which outputs:

fluid_str = ammonia;water|0.82;0.18 mass
Bubble point at P = 3000.0 kPa: T = 351.12665326553423 [K]
Dew point at P = 3000.0 kPa: T = 433.7321720060377 [K]