by jasper » 05 April 2017, 19:44
First please correct your pressure (Pa) and temperature (K), unless you want to solve at 30 K and 1 Pa.
Second, indeed you need to put in a composition that you can vary. You may want to put in, for example:
cell E4 = 'X1'
cell F4 = 'X2'
cell E5 = 0.5
cell F5 = '=1-E5'
cell B4 = '=capeSinglePhaseProperty("fugacityCoefficient", "Vapor", 303.15, 100000, E5:F5)'
cell B5 = '=capeSinglePhaseProperty("fugacityCoefficient", "Liquid", 303.15, 100000, E5:F5)'
solver: objective = $B$6, solve for value = 0, by changing $E$5, which might work, if there were an azeotrope in your system at 303.15 K, but there is not. Please check your thermodynamic setup. You can confirm the absense of an azeotrope by plotting vapor and liquid fugacity coefficient at 303.15K and 1 bar vs composition.