﻿ Problems and Solutions Chapter 2

# ## Problems and SolutionsChapter 4 Properties of Mixtures

### Textbook Examples:

XPS-file display is available in Internet Explorer. In case of Firefox, select Internet Explorer when asked for the software to open the file.

No Mathcad solutions required for the textbook examples.

P04.01         Change of Relative Humidity and Fog Formation Through Temperature Decrease

The air inside a parking car has a relative humidity j1 = pH2O / PsH2O  = 0.6 at J1 = 20°C. At what temperature do the windows of the car get fogged, when the temperature decreases at night?
Consider the vapor phase to be ideal. The air shall be taken as a mixture of 80% nitrogen and 20% oxygen. The vapor pressure curve of water can be taken from Appendix A.

P04.02       Dew Point of an Ethylene - Propylene - Hydrogen Mixture Using PSRK

A mixture of ethylene and propylene (T = 330 K, P = 23 bar, yC2H4 = 0.2) is cooled down in a heat exchanger. Which temperature has to be set, if the mixture should be DT = 5 K above the dew point? The pressure drop of the heat exchanger is DP = 0.5 bar. Use the PSRK equation of state. How is the result affected if hydrogen is added to the mixture so that the final concentration of hydrogen is yH2 = 0.06 ?

P04.03       Compressibility Factor of a Propane - Methyl Bromide Mixture at Different Compositions  Using the Virial Equation

Calculate the compressibility factors z of the binary mixture propane (1) – methyl bromide (2) at T = 297 K and P = 5 bar for the concentrations y1=0.25, y1=0.5 and y1=0.75 using the virial equation of state truncated after the second term. The second virial coeffcients are
B11 = -394 cm3/mol
B22 = -567 cm3/mol
B12 = -411 cm3/mol

P04.04        Fugacity Coefficients of Propane and Methyl Bromide in a Vapor Mixture

Adopting the results of example P04.03, calculate the fugacities of both components
a) in a mixture of ideal gases
b) in an ideal mixture of real gases
c) in a real mixture

P04.05         Excess Enthalpy of the Mixture Benzene - Cyclohexane Using the SRK EOS

Calculate the excess enthalpy of the system benzene (1) – cyclohexane (2) at
J = 25°C and P = 1 bar for a mole fraction of benzene of x1 = 0.5 using the Soave-Redlich-Kwong equation of state. The constants necessary can be taken from Appendix A. The interaction parameter is k12 = 0.0246.

P04.06         Excess Enthalpy of the Mixture Benzene - Cyclohexane Using Wilson

Acetone (5000 kg/h, JA=40°C) and chloroform (3000 kg/h, JC=50°C) are mixed at P = 1 bar. The mixing procedure is isobaric and adiabatic. The excess enthalpy can be calculated using the binary Wilson parameters given in Table 5.5. What is the temperature of the resulting stream?

P04.07       Temperature Change of Ammonia - Water Upon Mixing

20 kg/h liquid ammonia (-20°C, 20 bar) and 100 kg/h liquid water (20°C, 20 bar) are mixed isobarically at 20 bar. The excess enthalpy is given by the formula: with A = -17,235 and B = 0.97645
Calculate the temperature of the mixture, assuming that
cP,H2O = 4.2 J/g K and cP,NH3 = 4.8 J/g K.