CEA-Wrap 1.5.5

A Python-Based wrapper for the NASA CEA Thermochemical Code

PyPI NOTE: This package is installed with 'pip install CEA_Wrap' with an underscore. PyPI doesn't show underscores in package names

CEA_Wrap

A Python-Based wrapper for the NASA CEA Thermochemical Code

Upgrading from Version <1.5.0

IF YOU UPGRADE AND YOUR VERSION IS <1.5.0, YOUR CUSTOM THERMO LIB WILL BE OVERWRITTEN

Please make a copy of your thermo_spg.inp, place it in the new data directory, and recompile after upgrading

As of 1.5.0, thermo_spg.inp and all other assets are kept in a data directory, rather than the package assets directory. This means that your custom thermo lib will no longer be overwritten when you upgrade

Installation Instructions

We are now on PyPi! In a command prompt type pip install --upgrade CEA_Wrap to upgrade/install CEA_Wrap

Or you can click on "releases" on the right side of the main page and download the .zip file, then do pip install --upgrade [your zip file name].zip People mess this up, so I don't recommend it anymore

You can import it as any other python module with import CEA_Wrap. Whenever you import the file, it will put the required thermo.lib and trans.lib files into your current directory.

Examples

Examples on basic use can be found in the "examples" directory. Feel free to download them and try them out!

Or you can run a short demo by doing "python -m CEA_Wrap" on the command line!

Documentation

Utilities

open_thermo_lib() Opens the default thermo library input file using the user's default .inp file viewer (should prompt if none)

open_pdfs() Opens the attached NASA pdfs using the user's default pdf viewer

print_assets_directory() Prints to console the current location of the directory where CEA_Wrap assets are located. Also returns this value

Materials

In order to run problems, you must create materials. Materials must be either Fuel or Oxidizer (alias: F or O) objects

Constructor Parameters - Either Fuel() or Oxidizer():

Material(name, temp=298.15, wt_percent=None, mols=None, chemical_composition = None, hf = None):

• name: required parameter, the CEA material name with correct spelling. E.G. aluminum is "AL(cr)" and methane is "CH4".
  • If you specify chemical_composition, name can be whatever single word you want
  • If you try to specify a chemical which is not in the thermo_spg.inp file, a ValueError will be raised. To prevent this check, set Material.check_against_thermo_inp = False
• temp: default 298.15, specified reactant initial temperature, Kelvin
  • If you try to specify a temperature which is not supported for this material in the thermo_spg.inp file, a ValueError will be raised. To prevent this check, set Material.check_against_thermo_inp = False
• wt_percent: A weight-based percentage for the element. Weight percentages do not need to add up to 100, and are calculated on the ratio with other Fuels/Oxidizers
• mols: A mol-based percentage for the element. Can be used as in Oxidizer("O2", mols=1) and Oxidizer("N2", mols=3.76) for air (except CEA has "air" as a reactant...)
• NOTE: wt_percent and mols cannot be specified together, if neither is defined, the Material gets a wt_percent of 1
• chemical_composition: chemical composition such as "LI 1 B 1 H 4" for LiBH4. If defined, will not use CEA default values
  • NOTE: UNTESTED
• hf: Enthalpy of formation, kJ/kg, must be specified if chemical_composition is specified
  • NOTE: UNTESTED

Available Members

• All parameters from the constructor are also members
• .ref - If Material.check_against_thermo_inp is True, this will be a ThermoMaterial representing the material

Available Methods

• .set_wt_percent(wt_percent) - Sets the wt_percent for the Material. Sets mols to None
• .set_mols(mols) - Sets the mols for the Material. Sets wt_percent to None
• .set_temp(temp) - Sets the temp for the Material, in Kelvin. If you try to specify a temperature which is not support for this material, a ValueError will be raised
• .is_mols()/.is_wt_percent() - Checks if the Material is set in weight % or mol ratio

Generic Problem Methods (apply to all problems such as DetonationProblem, RocketProblem, etc.):

Constructor Parameters (making new Problem Objects):

Problem(*, **kwargs):

• NOTE: all parameters must be specified by keyword, e.g. problem = RocketProblem(pressure=500, massf=True)
• pressure: default 1000, Initial problem pressure
• materials: default None, List of Material objects, order doesn't matter, of Oxidizer and Fuel objects e.g. materials=[material1, material2, ...]
  • materials can also be specified when you run a problem like problem.run_cea(material1, material2, ...)
  • materials MUST all have wt_percent specified or all have mols specified, can't have mixtures.
• massf: default False, CEA usually outputs product ratios in mole ratios, if massf is True, mass ratios are specified
• filename: default "my_output", the filename we save our .inp files to and CEA saves our .out and .plt to.
  • DO NOT INCLUDE ".inp" IN YOUR FILENAMES.
• pressure_units: default "psi", the units that your input pressure is in. Possible values are "bar", "atm", "psi", or "mmh"
• inserts: default None, a list of CEA names for species which should be forced into the product considerations. Should be specified as either a space-separated string of names, a list of string names, or a list of Material objects.
  • Note: If you try to specify a chemical which is not in the thermo_spg.inp file, a ValueError will be raised. To prevent this check, set Problem.check_against_thermo_inp = False
  • Tip: If you are doing calculations with Aluminum, I recommend using inserts=["AL2O3(L)", "AL2O3(a)"]
• omits: default None, a list of CEA names for species which should be specifically ignored in the product considerations. Specified similar to inserts.
• NOTE: You must specify one of the following reactant ratio schemes before running a problem. Either during initialization with x=1.0 or later with problem.set_x(1.0) where x is p_f, o_f, etc.

Specifying reactant ratios:

Key	CEA Key	Description
p_f	%f	Percent fuel by weight
f_o	f/o	Fuel-to-oxidant weight ratio
o_f	o/f	Oxidant-to-fuel weight ratio
phi	phi	Equivalence ratios in terms of fuel-to-oxidant weight ratios (eq. (9.19) in Gordon and McBride, 1994)
r_eq	r	Chemical equivalence ratios in terms of valences (eq. (9.18) in Gordon and McBride, 1994)

Available Methods

• data = .run([*materials])

Run the CEA problem, returning an "Output" object, which is similar to a dictionary (keys and values specified later in this documentation)

• Inputs are optionally Materials to be used in this run. If materials are not specified as an initial parameter or with .set_materials, you can list them here.

• .set_absolute_o_f()

Have you ever specified all your components in absolute percentages, and then have to manually calculate the o_f ratio based on what is fuel and what is oxidizer?

Well no more! Just call this function and we calculate the correct o_f ratio for you so that your absolute percentages are correctly reflected in the problem. Functions off of the existing material list, so call this after setting materials. This works by summing wt_percent for all oxidizers and then dividing by the same for fuels. Then it sets o/f to this value.

• .set_pressure(pressure) - sets pressure
• .set_materials([material1, material2, ...]) - provided a list of materials, sets the materials list
• .set_massf(massf) - Sets massf to True or False
• .set_inserts(inserts) - Set inserts to a space-separated string or list of materials or Materials
• .set_omits(omits) - Sets omits, similar to inserts
• .set_filename(filename) - Sets problem filename
• .set_pressure_units(units) - Sets input pressure units
• .set_p_f(pf) - Sets % Fuel for problem
• .set_f_o(f_o) - Sets fuel/oxidizer ratio
• .set_o_f(o_f) - Sets oxidizer/fuel ratio
• .set_phi(phi) - Sets equivalence ratio
• .set_r_eq(r_eq) - Sets valence equivalence ratio

Rocket Problem Constructor Additional Parameters:

For RocketProblem(*, **kwargs)

• sup: default 1, supersonic exit area/throat area ratio
  • sup can be specified later with .set_sup
• sub: default None, subsonic exit/throat area ratio
  • sub can be specified later with .set_sub
• NOTE: sup and sub cannot be specified at the same time
• ae_at: alias for sup
  • ae_at can be specified later with .set_ae_at
• pip: Pressure ratio of chamber pressure/exit pressure
  • pip can be specified later with .set_pip
• analysis_type: default "equilibrium", whether to use equilibrium reactions or frozen. For using frozen specify "frozen" or "frozen nfz=1" for frozen at the chamber or "frozen nfz=2" for frozen at the throat

RocketProblem Methods

• .set_sup(sup) - Sets supersonic area ratio
• .set_sub(sub) - Sets subsonic area ratio
• .set_ae_at(sup) - Sets supersonic area ratio
• .set_pip(pip) - Sets pressure ratio

Available Output Dictionary Keys:

All Problem data objects are "Output" objects, which are similar to dictionaries, but can also be accessed with dot notation.

For example if you had "data = problem.run_cea()", and wanted pressure, you could do either data.p or data["p"]

In addition, all product dictionaries are also "Output" objects so to get H2O fraction, you could use data.prod_c.H2O or data["prod_c"]["H2O"] or data["prod_c"].H2O, etc.

Detonation:

• prod_c - dictionary of chamber products, in mole or mass fractions (as specified in problem)
• p - pressure, bar
• t - temperature, Kelvin
• h - enthalpy, kJ/kg
• rho - density, kg/m^3
• son - sonic velocity, m/s
• visc - burned gas viscosity, Pascal-Seconds
• mw - molecular weight of products, kg/kmol
• cp - constant-pressure specific heat capacity, kJ/(kg*K)
• gammas - isentropic ratio of specific heats
• gamma - "real" ratio of specific heats (multiplied by -(dLV/dLP)t)
• vel - detonation velocity, m/s
• mach - detonation mach number
• p_p1 - P/P1, ratio of detonation pressure to initial pressure
• t_t1 - T/T1, ratio of detonation temperature to initial pressure
• m_m1 - M/M1, ratio of detonation molecular weight to initial molecular weight
• rho_rho1 - RHO/RHO1, ratio of detonation density to initial density
• dLV_dLP_t - (dLV/dLP)t, used to convert isentropic gamma to real gamma
• dLV_dLT_p - (dLV/dLT)p
• phi - weight-based equivalence ratio of oxidizer/fuel

HP (Specified Enthalpy and Pressure):

• prod_c - dictionary of chamber products, in mole or mass fractions (as specified in problem)
• p - pressure, bar
• t - temperature, Kelvin
• h - enthalpy, kJ/kg
• rho - density, kg/m^3
• son - sonic velocity, m/s
• visc - burned gas viscosity, Pascal-Seconds
• mw - molecular weight of products, kg/kmol
• cp - constant-pressure specific heat capacity, kJ/(kg*K)
• gammas - isentropic ratio of specific heats
• gamma - "real" ratio of specific heats (multiplied by -(dLV/dLP)t)
• dLV_dLP_t - (dLV/dLP)t, used to convert isentropic gamma to real gamma
• dLV_dLT_p - (dLV/dLT)p
• phi - weight-based equivalence ratio of oxidizer/fuel

Rocket:

• NOTE : Properties are by default at exit. Chamber parameters are prefixed "c_" and throat properties "t_"
• NOTE : Properties not defined for frozen flow are marked with an asterisk (*)
• prod_c - dictionary of chamber products, in mole or mass fractions (as specified in problem)
• *prod_t - dictionary of throat products, in mole or mass fractions (as specified in problem)
• *prod_e - dictionary of exit products, in mole or mass fractions (as specified in problem)
• p - pressure, bar
  • t_p - throat
  • c_p - chamber
• t - temperature, Kelvin
  • t_t - throat
  • c_t - chamber
• h - enthalpy, kJ/kg
  • t_h - throat
  • c_h - chamber
• rho - density, kg/m^3
  • t_rho - throat
  • c_rho - chamber
• son - sonic velocity, m/s
  • t_son - throat
  • c_son - chamber
• visc - burned gas viscosity, Pascal-Seconds
  • t_visc - throat
  • c_visc - chamber
• mw - molecular weight of all products, kg/kmol
  • t_mw - throat
  • c_mw - chamber
• m - molecular weight calculated as the weight of all products divided by the number of gaseous moles (same as mw if no condensed phases as mw=m), kg/kmol
  • t_m - throat
  • c_m - chamber
• condensed - True if there are condensed phase products (measured by m originally = 0), False otherwise
  • t_condensed - throat
  • c_condensed - chamber
• cp - constant-pressure specific heat capacity, kJ/(kg*K)
  • t_cp - throat
  • c_cp - chamber
• gammas - isentropic ratio of specific heats
  • t_gammas - throat
  • c_gammas - chamber
• gamma - "real" ratio of specific heats (multiplied by -(dLV/dLP)t) (same as gammas for frozen flow)
  • t_gamma - throat
  • c_gamma - chamber
• isp - ideal isp (ambient pressure = exit pressure), s
  • t_isp - throat
• ivac - vacuum isp, s
  • t_ivac - throat
• cf - ideally expanded thrust coefficient
  • t_cf - throat
• *dLV_dLP_t - (dLV/dLP)t, multiply gammas by negative this to convert isentropic gamma to real gamma
  • *t_dLV_dLP_t - throat
  • *c_dLV_dLP_t - chamber
• *dLV_dLT_p - (dLV/dLT)p, see the Mathematical Analysis in CEA_Wrap/assets for explanation
  • *t_dLV_dLT_p - throat
  • *c_dLV_dLT_p - chamber
• cstar - characteristic velocity in chamber, m/s
• *mach - mach number at exhaust
• o_f - oxidizer/fuel weight ratio
• phi - weight-based equivalence ratio of oxidizer/fuel

Using ThermoInterface

Provided with this library is an interface to the thermo_spg.inp file provided with the library.

You can access materials as if ThermoInterface is a dictionary using materials' CEA Names. E.G. ThermoInterface["CH4"]. This object support checking for inclusion and iterations, such as "CH4" in ThermoInterface and for name in ThermoInterface. It supports dictionary methods such as .keys(), .values() and .items().

The value returned by ThermoInterface accesses is a ThermoMaterial object, which is an Output object (dictionary that can be accessed with .dot notation) with the following keys:

• name - Name of the material
• reference - Reference, if given. Otherwise ""
• elements - Dictionary of element: numerical value specified
• condensed - True if condensed phase, False otherwise
• mw - Molecular weight in g/mol
• hf - float heat of formation at 298.15 in kJ/mol (or assigned enthalpy if 0 temp range)
• temp_ranges - List of two-tuples of [range start, range end] (K)
• reactant_only - True if material only shows up in reactants, False otherwise

Available Methods

• ThermoInterface.get_close_matches(name, [n]) - Gets close matches to a given material name. For example "Al(cr)" returns 'AL(cr)', 'ALN(cr)', 'Ag(cr)', 'W(cr)'. n influences the number of results returned, and is the maximum number of results returned.
• ThermoMaterial.defined_at(temp) - Returns True if the material is specified at the given temperature, False otherwise. Materials specified at one temperature are actually allowed at that temperature +- 10K.