Vapor/Liquid Equilibrium VLE

Chemical Reaction EngineeringVenSim Exercises - 1IntroductionHow to use VenSimExercise 1: Reaction RatesDescriptionEquations and input dataSetup in VensimCheck/RunResultsRemarksAssignment

ChE 24A E.1 VenSim Exersizes 1111/23/2013IntroductionVenSim is software for Systems Dynamic ModelingSystems Dynamic Modeling became well known in the seventies by the Club of Rome report Limits to Growth. *)Systems Dynamics are used in a wide spectrum of social and physical sciencesBasically it solves sets of Ordinary Differential Equations (ODE)VenSim comes with a large toolset, enhancing the efficient application, including model calibration and verification.However, the objective of our course is not to study System Dynamic Modeling and we will focus on part needed for Chemical Reactions Engineering.

*) links in the notes

ChE 24A E.1 VenSim Exersizes 1211/23/2013See also http://vensim.com/, http://www.clubofrome.org/, http://www.systemdynamics.org/

2Exercise 1 Single ReactionTo learn VenSim and to apply it to Chemical Kinetics we will stepwise make our first model.Consider the following elementary reaction with stoichiometric equation:

Since it is an elementary reaction, the rate equation is:

For a constant volume batch reactor (to be discussed in section 3) the concentration change can be described with 2 ODEs:ChE 24A E.1 VenSim Exersizes 13ARk111/23/2013Exercise 1 Equations / dataThis set can be solved for [A] and [R] if we have initial conditions and a value for the rate constant. We will use:

The subscript 0 refers to the initial condition.Before we put this in VenSim, please take a second to think about the expected results.ChE 24A E.1 VenSim Exersizes 14VariableValueUnitVariableValueUnit[A]01mol/m3k10.11/s[R]00mol/m3Final Time100s11/23/2013Exercise 1 VenSim Start ScreenChE 24A E.1 VenSim Exersizes 15

Analyses Tools(Input/Output)Main ToolbarMenuTitle

Press New Model11/23/2013

Exercise 1 Model SettingsChE 24A E.1 VenSim Exersizes 16SecondPut info for documentation11/23/2013

Exercise 1 Model ScreenChE 24A E.1 VenSim Exersizes 17Box Variable(Stock, Integration)Status BarSketch Drawing AreaSketch ToolsRate, change in timeArrow,connectorVariable(for calculation)Move, Size, Edit

Lets 1st saveAlways save11/23/2013

Exercise 1 Box, Rate, VariableChE 24A E.1 VenSim Exersizes 18Use Box Variable, Rate and Variable to make a drawing like this.r1 is reaction rate based on a stoichiometric coefficient of 1: r1= k1 [A]For calculate of r1 we need k1 and [A]: use arrows to make this info available in r111/23/2013

Exercise 1 EquationsChE 24A E.1 VenSim Exersizes 19Use Equations to edit the Equations

11/23/2013

Edit C AChE 24A E.1 VenSim Exersizes 11011/23/2013

Check model and unitsChE 24A E.1 VenSim Exersizes 111

11/23/2013Result file Simulate - ResultsChE 24A E.1 VenSim Exersizes 112

Check OutputCheck control panelCreate custom graph Enter a new name tostore the calculationoutput dataRun11/23/2013Graphs from Analyses ToolsChE 24A E.1 VenSim Exersizes 113

As expected the change of [A] in time decreases, since reaction rate is proportional to [A].The decrease of [A] results in an equal increase of [R].11/23/2013Tables from analyses toolsCan be exported to Excel, compare with analytical solution [A]t=A0e-k1t ChE 24A E.1 VenSim Exersizes 114

Why is the VenSim concentration a bit lower than the concentration according the analytical solution?

Straight line due to log(C) ordinate11/23/2013Compare input of 2 variants in Analyses ToolsChE 24A E.1 VenSim Exersizes 115

11/23/2013Compare Graphs of runs in Control Panel ChE 24A E.1 VenSim Exersizes 116

11/23/2013Exercise 1 RemarksThe exercise shows how a single chemical reaction can be converted in VenSim input and after simulation how to process the results.Comparison with an analytical solution showed that in this case the Vensim calculated concentrations are slightly lower than the analytical solution. This is due to ...It is recommended to perform some more simulations as exercise.

ChE 24A E.1 VenSim Exersizes 11711/23/2013General RemarksPlaying around with VenSim is OKThere is however a point you might get lostTherefore at a certain point you have to documentThe purpose of the calculation.The input of the model (data)The model structureWhat did the model calculate (output)Is the output what you expected and answers it the purpose of the calculation?

ChE 24A E.1 VenSim Exersizes 11811/23/2013