Cantera / Stancan Primer

Transcription

1 Cantera / Stancan Primer Matthew Campbell; A.J. Simon; Chris Edwards Introduction to Cantera and Stancan Cantera is an open-source, object-oriented software package which performs chemical and thermodynamic equilibrium and kinetics calculations. Interfaces to the Cantera package exist for MATLAB, Python, C++ and FORTRAN. Cantera is able to retrieve thermodynamic properties (enthalpy, entropy, pressure, etc.) for some pure simple, compressible substances. It is also able to retrieve properties, compute equilibrium compositions and perform kinetic simulations for mixtures of ideal gases. Cantera replicates much of the functionality of TPSA, STANJAN and CHEMKIN, but it does all of this within the MATLAB environment. Stancan (formally known as Stanford-Cantera or SCTv2) is a layer on top of the MATLAB-Cantera interface which is in development here at Stanford. Stancan fixes some of the shortcomings of the base Cantera package. However, the functionality of Stancan is limited to property and equilibrium calculations (not kinetics). Stancan was written specifically to enable keeping track of multiple thermodynamic states. In the original Cantera package, a gas mixture is represented by a large programming object in the computer's memory. In order to compare thermodynamic properties between states, a programmer had two choices: (1) create multiple gas objects (a time and resource-intensive process) (see Figure 1) or (2) continually update a single "gas object," but extract all relevant thermodynamic properties from each state and store them in separate variables (see Figure 2). Stancan tries to address this by introducing a set of wrapper-functions which can store data more readily (see Figure 3). Stancan also fills in some gaps in the original Cantera code. Most notably, Cantera is unable to set some combinations of thermodynamic properties. With Stancan, for example, the user can simultaneously set temperature and entropy. This was impossible under Cantera. The ability to import thermodynamic input files is absent from this distribution of Cantera. This distribution includes the GRI 3.0 thermodynamic data set, which should be sufficient for most students to work problems on the H, C, O, N system. It also includes a data set suitable for coal gasification simulations, as well as an input file which enables access to Cantera's liquid/vapor water calculations.

2 Figure 1: Schematic of Cantera done the wrong way. Multiple objects are created at multiple states simultaneously, and properties (temperature, pressure, enthalpy, etc) are drawn from each object-state. Figure 2: Schematic of Cantera done the right way. One object is created and is assigned to one state at a time. While the object-state is active, all properties necessary are drawn out and saved in variables.

3 Figure 3: Schematic of Stancan. One object is employed, and multiple states are kept active simultaneously. The properties at each state can be drawn out at any time.

4 Installing Cantera and Stancan 1. Instructions for Windows computers: a. Make sure MATLAB is installed, but not running b. Download the CanteraStancanWindows.msi file c. Double-click it to install it. Make a note of the directory on your hard drive where it was installed (for example, C:\Users\MCampbell\Documents\Cantera ) d. Open MATLAB e. File Menu Set Path Add with Subfolders f. Navigate to and select the installation Cantera folder noted above g. Click OK Click Save Click Close h. Type the following commands in the MATLAB command window to test the installation: i. cantera_primer1 ii. cantera_primer2 iii. SCTv2_primer 2. Instructions for Macintosh computers with a partitioned hard drive: a. Install Windows on a partition of your hard drive, and then boot to Windows. b. Download the CanteraStancanWindows.msi file c. Install using the Windows instructions above 3. Instructions for Power PC Macintosh computers (thanks to John Lawler) a. Make sure MATLAB is installed, but not running b. Download the CanteraPowerPCMac.zip file c. Unzip the file using WinZip or an equivalent program d. Move the 'Cantera' folder to your Applications directory e. Open MATLAB f. File Menu Set Path Add with Subfolders g. Navigate to and select '/Applications/Cantera/matlab/toolbox' h. Click OK Click Save Click Close i. Type the following commands in the MATLAB command window to test the installation: i. cantera_primer1 ii. cantera_primer2 iii. SCTv2_primer 4. Instructions for Intel Macintosh computers (thanks to John Lawler and Ghyrn Loveness) a. Make sure MATLAB is installed, but not running b. Download the CanteraIntelMac.zip file c. Unzip the file using WinZip or an equivalent program d. Move the 'Cantera' and numarray folders to your home directory (aka your username). It will have the icon of a house. e. Open MATLAB f. File Menu Set Path Add with Subfolders g. Navigate to and select '/<yourusername or homedirectory>/cantera/matlab/toolbox' h. Click OK Click Save Click Close i. Type the following commands in the MATLAB command window to test the installation: i. cantera_primer1 ii. cantera_primer2 iii. SCTv2_primer

5 Cantera with Ideal Gas Mixtures This tutorial should help you get started working with ideal gas mixtures (ie, mixtures of ideal gases) in Cantera. Use a semicolon ( ; ) at the end of each line to suppress output to the MATLAB command window. Also, a percent symbol ( % ) means that anything following is a comment; in MATLAB comments usually appear in green text. Clear everything and start fresh. clear all close all cleanup format compact clc Note that if MATLAB goes haywire while running a script, you can stop it by clicking in the command window (where the output from functions is displayed) and press CTRL+C. Get a list of all Cantera commands. methods thermophase You can also get a more complete list of commands. methods solution -full Create an ideal gas object. gas = IdealGasMix('gri30.xml') Note that gri30.xml is the file which contains the thermodynamic data about a mixture of gases with a pre-specified set of possible components. Other files can also be used; they should simply be put in the same file as the script you are running. Display the state of the gas mixture by typing the variable name. gas Now create a gas with 10% CH4, 20% CO2, 50% N2, and 20% O2. Note that Cantera automatically normalizes vectors, such that you can put in numbers of moles as well. In the case below, our gas vector has 10 moles of CH4, 20 moles of CO2, 50 moles of N2, and 20 moles of O2. We could just as easily specified 0.1 CH4, 0.2 CO2, 0.5 N2, and 0.2 O2. Or we could have said CH4, 2.05 CO2, N2, and 2.05 O2. gasvector = zeros(nspecies(gas),1) gasvector(speciesindex(gas,'ch4')) = 10 gasvector(speciesindex(gas,'co2')) = 20 gasvector(speciesindex(gas,'n2')) = 50 gasvector(speciesindex(gas,'o2')) = 20 Set the gas object to have this gas vector, a temperature of 25 C, and a pressure of 10 bar. Note that to enter temperature and pressure you MUST use units of Kelvins and Pascals (K and Pa). T1 = %K P1 = 10*1e6 %Pa set(gas, 'T', T1, 'P', P1, 'X', gasvector)

6 Now find the enthalpy at this state. h1 = enthalpy_mass(gas) Reset the gas object to a new state with T = 500 C, and P = 5 bar. Note that we do not have to set the gas vector again, because it was set previously. T2 = %K P2 = 10*1e6 %Pa set(gas, 'T', T2, 'P', P2) Find the enthalpy at this new state, per unit mass. You can also find properties per unit mole. Note, however, that you must set properties on a per-mass basis (in both Cantera and Stancan). h2 = enthalpy_mass(gas) Now burn the gas mixture. This essentially means that we allow equilibrium products to form from the mixture. You can choose what is held constant during equilibration. In the case below, use enthalpy (H) and pressure (P) constant, as might be found in a flow combustor whose goal was to create the highest temperature gas products possible. It is also possible to do other types of equilibration; for example, TP equilibration keeps temperature and pressure constant, as you may find in a reactor designed to determine heats of formation. equilibrate(gas,'hp') Now find the new temperature, enthalpy, and mole fractions for the combustion products. h3 = enthalpy_mass(gas) T3 = temperature(gas) productvector = molefractions(gas) Also, find the entropy (referenced to molecular species at K) for the products. s3 = entropy_mass(gas) Next, reset the product gas to have the original pressure and enthalpy (those values of state 1). Note again that since gas still has the mole fractions of the products from equilibration, we do not have to specify mole fractions here. set(gas, 'P', P1, 'H', h1) Find out how many elements are present in the product gas. Then tell how many species are present. Finally, tell how many C atoms there are in C2H4 (the answer is of course 2, but this can be important for a generic case). nelements(gas) nspecies(gas) natoms(gas,speciesindex(gas,'c2h4'),elementindex(gas,'c'))

7 Cantera with Pure Simple Compressible Substances This tutorial should help you get started working with pure simple compressible substances in Cantera. Clear everything and start fresh. Using the semicolons ( ; ) allows you to type multiple commands on one line. clear all; close all; cleanup; format compact; clc; Create a water pure substance object. water = importphase('liquidvapor.xml','water'); Find the critical temperature and critical pressure of this water, then find the enthalpy, internal energy, specific volume, and entropy there. Tc = crittemperature(water) Pc = critpressure(water) set(water, 'T',Tc, 'P',Pc) hc = enthalpy_mass(water) uc = intenergy_mass(water) vc = 1/density(water) sc = entropy_mass(water) Find the saturated pressure of water at 25 C. T = %K Psat = satpressure(water,t) Now set the state of the water at a saturated state with pressure equal to 1 atmosphere and a quality of 100% vapor. Find the vapor fraction there, just to check (it should be 1). Then set the state to a temperature of 400 Kelvins, with a quality of 25% vapr. Find the vapor fraction there just to check (it should be 0.25). P1 = 1* %change from atm to Pa q1 = 1 setstate_psat(water, [P1,q1]) vaporfraction(water) T2 = 400 q2 = 0.25 setstate_tsat(water, [T2,q2]) vaporfraction(water)

8 Stancan with Ideal Gas Mixtures This tutorial should help you get started working with ideal gas mixtures in Stancan. Recall that Stancan is able to store information about multiple states of gases and simple compressible substance at the same time. In Cantera, one must set the state of the gas, get all the information needed, and then reset the gas to a new state to find other information. But in Stancan, one can keep track of multiple states for one gas object simultaneously, and get properties from each state as needed. Clear everything and start fresh. clear all; close all; cleanup; format compact; clc; Create an ideal gas object. gas = newidealgasmix('gri30.xml') Set state 1 with engineering air (79% N2, 21% O2) at 500 K and 3 atm. T1 = 500 %K P1 = 3* %Pa state1 = IdealGasMixState(gas,'moleTP','N2:0.79, O2:0.21',T1,P1); Find the specific volume in this state. v1 = getvolume_mass(state1) Create state 2 from state 1, by specifying a pressure of 1 bar and the specific volume of state 1. Remember that whenever setting properties in Cantera and Stancan, you must specify them on a per-mass basis. P2 = 1e6 %Pa v2 = v1 state2 = setstate_pv(state1, P2, v2) Find the difference in enthalpy between state 1 and state 2. h1 = getenthalpy_mass(state1) h2 = getenthalpy_mass(state2) enthalpydifference = h2 - h1 Find the exergy of state 2, if the dead state (state 0) is considered standard temperature and pressure (ie, 25 C, 1 atm). First set the dead state using temperature and pressure, then find the entropy at states 2 and 0, and finally compute the exergy. Set the dead state based on state 2 (we could also have set the dead state based on state 1). P0 = 1* %convert atm to Pa T0 = %K state0 = setstate_tp(state2, T0, P0) h0 = getenthalpy_mass(state0) s2 = getentropy_mass(state2) s0 = getentropy_mass(state0) xrg2 = (h2 - h0) - T0*(s2 - s0)

9 Display information from all three states. state1 state2 state0 Create a new gas object using the gasification species set (gasification.xml) with a composition of 1 mole CO, one mole H2O. Set its temperature and pressure to be 45 C and 600 mmhg. Consider this to be state A. gas2 = newidealgasmix('gasification.xml') TA = %K PA = 600/760* % convert mmhg to atm, then to Pa statea = IdealGasMixState(gas2,'moleTP','H2O:1,CO:1', TA, PA) Burn the mixture at constant temperature and pressure. Set the products to be at state B. stateb = Equilibrate(stateA, 'TP')

10 Stancan with Pure Simple Compressible Substances This tutorial should help you get started working with pure simple compressible substances in Stancan. Clear everything and start fresh. clear all; close all; cleanup; format compact; clc; Set state 1, with a temperature of 450 K and a quality of T1 = 450 %K q1 = 0.25 state1 = PureSubstanceState(water,'Tx',T1,q1) Find the enthalpy, the entropy, the internal energy, the density, and the pressure at this state. h1 = getenthalpy_mass(state1) s1 = getentropy_mass(state1) u1 = getintenergy_mass(state1) v1 = getvolume_mass(state1) P1 = getpressure(state1) Set state 2 from state 1, with the same enthalpy at state 1 but a pressure which is 10% higher. h2 = h1 P2 = P1*1.1 state2 = setstate_hp(state1, h2, P2) Find the change in internal energy between states 1 and 2. u2 = getintenergy_mass(state2) deltaintenergy21 = u2 - u1 Set state 3 from state 2, with the same pressure as state 2 but the same entropy as state 1. Find the difference in internal energy from state 3 to state 1. P3 = P2 s3 = s1 state3 = setstate_ps(state2, P3, s3) u3 = getintenergy_mass(state2) deltaintenergy31 = u3 - u1

11 Example Code The following is a transcript of the code used in the above tutorial. Copy and paste it into a matlab *.m file, save it, and run it. Note that each new section clears the screen from the old one (the clc command), so in order to see all the output, comment out each clc by putting a percent sign ( % ) in front of them. % Cantera and Stancan Demonstration Code % Matthew Campbell %% Cantera with Ideal Gas Objects clear all close all cleanup format compact clc methods thermophase methods solution -full gas = IdealGasMix('gri30.xml') gas gasvector = zeros(nspecies(gas),1) gasvector(speciesindex(gas,'ch4')) = 10 gasvector(speciesindex(gas,'co2')) = 20 gasvector(speciesindex(gas,'n2')) = 50 gasvector(speciesindex(gas,'o2')) = 20 T1 = %K P1 = 10*1e6 %Pa set(gas, 'T', T1, 'P', P1, 'X', gasvector) h1 = enthalpy_mass(gas) T2 = %K P2 = 10*1e6 %Pa set(gas, 'T', T2, 'P', P2) h2 = enthalpy_mass(gas) equilibrate(gas,'hp') h3 = enthalpy_mass(gas) T3 = temperature(gas) productvector = molefractions(gas) s3 = entropy_mass(gas) set(gas, 'P', P1, 'H', h1) nelements(gas) nspecies(gas) natoms(gas,speciesindex(gas,'c2h4'),elementindex(gas,'c')) %% Cantera with Pure Simple Compressible Substances clear all; close all; cleanup; format compact; clc; water = importphase('liquidvapor.xml','water');

12 Tc = crittemperature(water) Pc = critpressure(water) set(water, 'T',Tc, 'P',Pc) hc = enthalpy_mass(water) uc = intenergy_mass(water) vc = 1/density(water) sc = entropy_mass(water) T = %K Psat = satpressure(water,t) P1 = 1* %change from atm to Pa q1 = 1 setstate_psat(water, [P1,q1]) vaporfraction(water) T2 = 400 q2 = 0.25 setstate_tsat(water, [T2,q2]) vaporfraction(water) %% Stancan with Ideal Gas Mixtures clear all; close all; cleanup; format compact; clc; gas = newidealgasmix('gri30.xml') T1 = 500 %K P1 = 3* %Pa state1 = IdealGasMixState(gas,'moleTP','N2:0.79, O2:0.21',T1,P1); v1 = getvolume_mass(state1) P2 = 1e6 %Pa v2 = v1 state2 = setstate_pv(state1, P2, v2) h1 = getenthalpy_mass(state1) h2 = getenthalpy_mass(state2) enthalpydifference = h2 - h1 P0 = 1* %convert atm to Pa T0 = %K state0 = setstate_tp(state2, T0, P0) h0 = getenthalpy_mass(state0) s2 = getentropy_mass(state2) s0 = getentropy_mass(state0) xrg2 = (h2 - h0) - T0*(s2 - s0) state1 state2 state0 gas2 = newidealgasmix('gasification.xml') TA = %K PA = 600/760* % convert mmhg to atm, then to Pa statea = IdealGasMixState(gas2,'moleTP','H2O:1,CO:1', TA, PA) stateb = Equilibrate(stateA, 'TP')

13 %% Stancan with Pure Simple Compressible Substances clear all; close all; cleanup; format compact; clc; water = newpuresubstance('water','liquidvapor.xml'); T1 = 450 %K q1 = 0.25 state1 = PureSubstanceState(water,'Tx',T1,q1) h1 = getenthalpy_mass(state1) s1 = getentropy_mass(state1) u1 = getintenergy_mass(state1) v1 = getvolume_mass(state1) P1 = getpressure(state1) h2 = h1 P2 = P1*1.1 state2 = setstate_hp(state1, h2, P2) u2 = getintenergy_mass(state2) deltaintenergy21 = u2 - u1 P3 = P2 s3 = s1 state3 = setstate_ps(state2, P3, s3) u3 = getintenergy_mass(state2) deltaintenergy31 = u3 - u1