We typically use mixture rules to get a m and b m for the EOS to find these roots. There will be 3 roots: liquid v, vapor v, and an "unreal" middle root. To find the molar volumes: (using Redlich-Kuvorg) Y’s, V’s, P when we calculate a P xy diagram: Instead we might directly use fugacity coefficients for both phases, and. We will also require Cp’s DH vgs’s, (rigorously as f(T), but seldom all available.) Then we may solve the 4 equations iterativey until the proper roots are found.Įxtrapolation of the activity coefficient approach to highter T & P’s may not be possible since: Also the modified Raoult’s Law requires an expression for P i Sat(T)and g i(T). Since we do not know T, x’s, or V we must solve the equation A in conjunction with the previous flash criteria.įor a binary system this gives us 4 equations and 4 unknowns. Here the energy balance must be used in conjunction with the mass balance and equilibrium criteria! (remember H vgs!) (A table may help)Īll of these methods become easy with root finding methods. Guess a value for V, solve for x 1 and x 2 from 1 & 2 : Determine if this satisfies 3. Here we must solve the following criteria: Find how much gas and liquid leave per mole of feed, and find the composition of both streams.Ĭhoose a basis of 1 mole feed/s. (Roots found are sensitive to initial guesses)Ī 40 mol% isobutane 160 mol%n n-pentane mixture flows into a flash chamber ad flashes at 49 °Ĭ and 3.2 bar. Estimate TDP and x’s for 0.36 mole fraction vapor ethanol (1) and hexane (2) at 1.013 bar.Estimate T BP and y’s for acetone (1) – water (2) mixture with x1=0.01, P = 1.013 bar.Find the dew pressure and liquid composition in equilibrium with a 0.314 mole fraction nitromethane vapor, y 1) in carbon tetrachloride at 318K.Pressure and vapor composition for a liquid mixture of ethanol (1) – n hexane (2) at 331 K, X 1=0.412. We must iteratively find the roots which satisfy all of the n + l equations. P i Sat and V i are known, but may require root finding program: For vapor composition:Īll Z i,P, and T are known find X’s, y’s, and V,L
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