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- Fuel-dust flames

1 V cell The partial pressure P O2 is calculated using Dalton s law P O2 x O2 P1 Wherein the mole fraction of O 2 x O2 is related to mass fraction YO2 through molecular masses of O 2 M O2 and the mixture M mix as x O2 M mix M O2 YO2 Kinetic mass transfer coefficient K k C in s m is calculated as K k C 0 1309 e 26850 T2 Diffusion mass transfer coefficient K d C in s m is calculated as follows K d C Sh D O2 M C R gas T 2 SIZE where Sh is a particle Sherwood Number D O2 is the diffusion coefficient of O 2 in air m 2 s M C 12 is the molecular mass of C kg mol R gas 8314 is universal gas constant J mol 1 K 1 and T 2 is particle temperature K The rate of O 2 consumed by char combustion in kg m 3 s 1 is related to R C through stoichiometric coefficient R C O2 0 5 1 w M O2 M C The rate of CO produced by char combustion in kg m 3 s 1 is related to R C through its own stoichiometric coefficient R C CO 1 w M CO M C The rate of CO 2 produced by char combustion in kg m 3 s 1 is related to R C through the stoichiometry as follows R C CO2 w M CO2 M C Carbon monoxide emerging from char further burns to carbon dioxide in the gas phase as a participant of the second step of volatile combustion The formation of NOx NOx is collectively referred to the number of nitrogen oxidation products present in the gases emerging from combustion They are considered as hazardous pollutants NOx emmision consists of mostly nitric oxide NO Less significant are nitrogen oxide NO 2 and nitrous oxide N 2 O Because the species involved are normally present in the low concentarion trace quantities the NOx modeling is assumed not to contribute neither to the gas mixture properties nor to the mass conservation of mixture components The formation of NOx is attributed to thermal NOx formation and fuel NOX formation with subsequent reduction Thermal NOx The rate of the oxidation of atmospheric nitrogen present in the combustion air is modelled here via the steady state simplification of Zeldovich mechanism with partial equilibrium assumptions The thermal NOx formation rate in kg m 3 s is given by R T NO 2 RHO1 K 1 YN2 O M NO M N 2 where M NO 30 is NO molecular mass M N 2 28 is N 2 molecular mass and K 1 1 8 10 8 e 38370 T1 m 3 mol 1 s 1 stands for the reaction rate constant of the forward reaction N 2 O NO H The equilibrium O atom concentration O can be obtained from the expression O 3 97 10 5 T1 0 5 RHO1 YO2 M O 2 0 5 e 31090 T1 mol m 3 wherein M O 2 32 is the molecular mass of oxygen Fuel NOx The extent of conversion of fuel nitrogen to NOx is dependent on the local combustion characteristics and the initial concentration of nitrogen bound compounds Fuel bound nitrogen containing compounds are released into the gas phase when the fuel particles are heated and devolatilized From the thermal decomposition of these compounds the intermediates are formed For simplicity the nitrogen containing intermediates are here grouped to be hydrogen cyanide HCN only The fuel NOx mechanism employed also assumes that fuel nitrogen is distributed between volatiles and char The source terms for NOx and HCN are determined as follows HCN from char It is assumed that all char bound nitrogen converts to HCN Thus R C HCN R C m NC M HCN M N where R C is char burnout rate kg m 3 s 1 m NC is a mass fraction of nitrogen in char specified input parameter M HCN 27 and M N 14 are the molecular masses of HCN and N respectively HCN form volatiles The source of HCN from volatiles is related to the rate of volatile release R V HCN R V m NV M HCN M N where R V is the mass source of volatiles kg m 3 s 1 m NV is a mass fraction of nitrogen in the volatiles specified input parameter NOx formation HCN is oxidised to NO via reaction 4HCN 5O 2 4NO 2H 2 O 4CO The reaction rate in kg m 3 s 1 is given as R NO RHO1 10 11 e 33678 T1 YO2 a YHCN where the oxygen reaction order a is assumed to be unity NOx reduction in a gas phase The homogeneous reaction of NO reduction is modelled as 4HCN 6NO 5N 2 2H 2 O 4CO The reaction rate in kg m 3 s 1 is calculated as R NO 1 RHO1 3 10 12 e 30069 T1 YHCN YNO NOx reduction on char surface The heterogeneous reaction rate in kg m 3 s 1 of NO reduction on the char surface is modelled as R NO 2 4 10 4 e 18042 T2 A s P NO where P NO is NO partial pressure N m 2 The partial pressure P NO is calculated using Dalton s law P NO x NO P1 Wherein the mole fraction of NO x NO is related to mass fraction YNO through molecular masses of NO M NO and the mixture M mix as x NO M mix M NO YNO Thermal radiation Thermal radiation is modelled by the expanding the radiation intensity in terms of first order spherical harmonics Model equations Assuming that only four terms representing the moments of the intensity are used the conservation equation of incident radiation R I in W m 2 accounting for radiating particles and gases together can be

Original URL path: http://www.cham.co.uk/phoenics/d_polis/d_applic/d_comb/dustflam/fur-sing.htm (2016-02-15)

Open archived version from archive - P-1 radiation model

order spherical harmonics Assuming that only four terms representing the moments of the intensity are used this leads to a incident radiation CRAD or R I W m 2 conservation equation div G rad gradR I a 4 s T 4 R I 0 where s 5 68 10 8 is Steffan Boltzman constant W m 2 K 4 The exchange coefficient G rad is expressed by G rad 3 a s C g s 1 where a is the absorption coefficient m 1 s is the scattering coefficient m 1 and C g is the symmetry factor of a scattering phase function The symmetry factor is used to model anisotroping scattering by means of a linear anisotropic scattering phase function C g ranges from 1 to 1 and represents the amount of radiation scattered in forward direction A positive value indicates that more radiant energy is scattered forward than backward with C g 1 corresponding to complete forward scattering A negative value means that more radiant energy is scattered backward than forward with C g 1 standing for complete backward scattering A zero value of C g defines the scattering that is equally likely in all directions i e isotropic scattering The volumetric source term for the mixture enthalpy due to radiation is then given by S H1 rad a R I 4 s T 4 For symmetry planes and perfectly reflecting boundaries the radiation boundary conditions are assumed to be zero flux type For the incident radiation equation the following boundary sources per unit area are used at the walls S R wall 0 5 e w 4 s T w 4 R I 2 e w 1 where e w is the wall emmisivity The sources for incident radiation at the inlets and outlets are computed in

Original URL path: http://www.cham.co.uk/phoenics/d_polis/d_applic/d_rad/p-1/rad-sing.htm (2016-02-15)

Open archived version from archive - Particulate effects in P-1 radiation model

2 K 4 T p and T g are the gas and particle temperatures K The exchange coefficient G rad is expressed by G rad 3 a g s g 3 a p s p C g s g 1 where a g is the gas absorption coefficient m 1 s g is the gas scattering coefficient m 1 a p is the equivalent particle absorption coefficient m 1 s p is the equivalent particle scattering coefficient m 1 and C g is the symmetry factor of a scattering phase function The equivalent particle absorption coefficient is defined as a p e p A p where e p is the emmisivity of particle and A p is the volumetric particle projected area m 1 The latter is calculated from particulate volume fraction r 2 and current particle diameter d p as follows A p 1 5r 2 d p 1 The equivalent particle scattering coefficient is defined as s p 1 s p 1 e p A p where s p stands for particle scattering factor The s p and e p are related by the incident radiation sharing equation s p e p 1 The symmetry factor C g is used to model anisotroping scattering by means of a linear anisotropic scattering phase function C g ranges from 1 to 1 and represents the amount of radiation scattered in forward direction A positive value indicates that more radiant energy is scattered forward than backward with C g 1 corresponding to complete forward scattering A negative value means that more radiant energy is scattered backward than forward with C g 1 standing for complete backward scattering A zero value of C g defines the scattering that is equally likely in all directions i e isotropic scattering Phase energy source terms

Original URL path: http://www.cham.co.uk/phoenics/d_polis/d_applic/d_rad/p-1/p-14part.htm (2016-02-15)

Open archived version from archive - Turbulent combustion in a burner

and EP Gas specific enthalpy H1 Mass fractions of gas mixture namely fuel methane YCH4 oxygen YO2 carbon monoxide YCO water vapour YH2O carbon dioxide YCO2 nitrogen YN2 and nitric oxides collectively reffered to as YNOX Although the transport equations are usually solved for all of these variables the nitric oxides are supposed to be presented only in trace quantities non contributing to the state of the gas mixture and mass conservation Turbulence model The standard K epsilon model KEMODL is used to calculate the distribution of turbulence energy and its dissipation rate from which the turbulence viscosity is deduced Combustion model Combustion is treated as a two step irreversible chemical reaction of methane oxidation as follows Step 1 CH 4 1 5 O 2 3 76N 2 CO 2H 2 O 5 64N 2 Step 2 CO 0 5 O 2 3 76N 2 CO 2 1 88N 2 The reaction rates of combustion are obtained as the limiting blend of a Arrhenius kinetics and eddy dissipation rates R com CH 4 min R k CH 4 R e CH 4 and R com CO min R k CO R e CO where R k and R e in kg m 3 s are the kinetic and eddy dissipation rates R e CH 4 4 RHO1 EP KE min YCH4 YO2 3 R e CO 4 RHO1 EP KE min YCO YO2 0 57 R k CH 4 1 15 10 9 RHO1 2 e 24444 T YCH4 0 3 YO2 1 3 R k CO 5 42 10 9 RHO1 2 e 15152 T YO2 0 25 YH2O 0 5 YCO The remaining rates are defined through associated stoichiometric coefficients Step 1 R 1 O 2 3 R com CH 4 R 1 CO 1 75 R com CH 4 R 1 H 2 O 2 25 R com CH 4 Step 2 R 2 O 2 0 57 R com CO R 2 CO 2 1 57 R com CO The net rates of species generation i e the source terms are the balances of formation and combustion as appropriate S CH 4 R com CH 4 S CO R com CO R 1 CO S O 2 R 1 O 2 R 2 O 2 S CO 2 R 2 CO 2 S H 2 O R 1 H 2 O NOX formation model The NOX formation rate in kg m 3 s is given by S NO 2 RHO1 K 1 YN2 O M NO M N 2 where M NO 30 is NO molecular mass M N 2 28 is N 2 molecular mass and K 1 1 8 10 8 e 38370 T stands for the reaction rate constant for the forward reaction N 2 O NO H The equilibrium O atom concentration O can be obtained from the expression O 3 97 10 5 T 0 5 RHO1 YO2 M O 2 0 5 e 31090 T wherein M O 2 32

Original URL path: http://www.cham.co.uk/phoenics/d_polis/d_applic/d_comb/2streact/two-sing.htm (2016-02-15)

Open archived version from archive - Fuel-dust flames

CO YCO2 M CO2 YCO where M CO 28 and M CO2 44 are the molecular masses of carbon monoxide and carbon dioxide respectively The mass split between carbon oxides is assumed to depend on the particle temperature as YCO YCO2 2500e 6249 T2 The char burnout rate R C in kg m 3 s 1 is obtained as an harmonic blend of a kinetic and diffusion controlled mass transfer rates R C A p K k C 1 K d C 1 1 P O2 where A p 6R2 SIZE is volumetric particle surface area 1 m and P O2 is partial pressure of O 2 N m 2 The partial pressure P O2 is calculated using Dalton s law P O2 x O2 P1 Wherein the mole fraction of O 2 x O2 is related to mass fraction YO2 through molecular masses of O 2 M O2 and the mixture M mix as x O2 M mix M O2 YO2 Kinetic mass transfer coefficient K k C in s m is calculated as K k C 0 1309 e 26850 T2 Diffusion mass transfer coefficient K d C in s m is calculated as follows K d C Sh D O2 M C R gas T 2 SIZE where Sh is a particle Sherwood Number D O2 is the diffusion coefficient of O 2 in air m 2 s M C 12 is the molecular mass of C kg mol R gas 8314 is universal gas constant J mol 1 K 1 and T 2 is particle temperature K The rate of O 2 consumed by char combustion in kg m 3 s 1 is related to R C through stoichiometric coefficient R C O2 0 5 1 w M O2 M C The rate of CO produced by char combustion in kg m 3 s 1 is related to R C through its own stoichiometric coefficient R C CO 1 w M CO M C The rate of CO 2 produced by char combustion in kg m 3 s 1 is related to R C through the stoichiometry as follows R C CO2 w M CO2 M C Carbon monoxide emerging from char further burns to carbon dioxide in the gas phase as a participant of the second step of volatile combustion Steam reforming reaction The volatile methane reacts with water vapour creating carbon monoxide and hydrogen according to the reaction CH 4 H 2 O CO 3H 2 The reaction rates are obtained in exemplary manner as the minimum blend of an Arrhenius kinetics and eddy dissipation rates R ref CH 4 min R k ref R e ref and where R k and R e in kg m 3 s are the kinetic and eddy dissipation rates R e ref 4 RHO1 EP KE min YCH4 16 18 YH2O R k ref 3 21 10 2 RHO1e 468 T YH2O 1 3 YCH4 The net rates of species generation in steam reforming are as follows

Original URL path: http://www.cham.co.uk/phoenics/d_polis/d_applic/d_comb/coalgas/coalgas.htm (2016-02-15)

Open archived version from archive - Combustion of moving coal bed

gas enthalpy H1 Specific coal lumps enthalpy H2 Mixture fraction of gas composition f Combustion model The 7GASES model is used to simulate the combustion of pulverised coal fines with the gas phase absorbing the carbon from both the fines and coal lumps The effective ie laminar plus turbulent diffusion coefficients of the gaseous species are all taken as equal and the reaction rates are supposed diffusion limited consequently all gas species concentrations depend on carbon mass fraction in piecewise linear fashion The oxidation of carbon is presumed to proceed in two stages viz to create CO2 and H2O and then to create CO and H2 as more fuel is added Reactions C solid 0 5 O2 CO CO 0 5 O2 CO2 C solid CO2 2CO C solid H2O CO H2 H2 0 5 O2 H2O The gas phase equilibrium composition diagram taking account of the elemental mass fractions of O C and H is used to calculate the gas product composition Moving bed simulation MUSES To simulate the relative motion between two different phases of gas mixture and coal lumps by means of one phase algorithm a two space version of the Multiply SharEd Space MUSES technique is used Specifically the gases and the fines are treated as homogeneous mixture with combustible fines being considered as non gas components which have the same velocity components and temperature as the gas in the space share 1 while the lump solids are treated as the phase of space share 2 The manner in which MUSES are implemented is as follows A computational domain is considered as consisting of two identical spaces occupying the different segments of the polar coordinate system divided by isolation layer The west space of the domain is treated as occupied by fines and gas only part

Original URL path: http://www.cham.co.uk/phoenics/d_polis/d_applic/d_comb/movinbed/movinbed.htm (2016-02-15)

Open archived version from archive - Water-sprayed diffusion flame

instant reaction with fuel CH 4 and oxygen O 2 unable to coexist at the same location CH 4 2O 2 Diluent CO 2 2H 2 O Diluent The stoichiometric ratio s of oxygen to methane is 4 0 i e 4 kg of oxygen are required to complete combustion of 1 kg of methane since the molecular masses of CH 4 and and O 2 are respectively 16 and 32 The combustion products are water vapour H 2 O and and carbon dioxide CO 2 The mixture of N2 liquid water fines WAT and a water vapour associated with evaporating liquid water VAP is regarded as a single substance i e simple total diluent entering no chemical reaction at all The mixture fraction MIXF is represented as MIXF s YCH4 YO2 YO2 in s YCH4 in YO2 in 1 from which the stoichiometric value F stoic can easily be deduced by substituting YCH4 YO2 0 F stoic YO2 in s YCH4 in YO2 in 1 In above YCH4 in and YO2 in are the mass fractions of the methane and oxygen in the fuel and air supply streams accordingly They are defined by the inlet stream compositions Evaporation model Instead of solving two conservation equations for mass fractions of liquid water YWAT and the vapour emerging from it YVAP the composite variable YWPV YVAP YWAT is used The advantage is that the balance of YWPV contains no source term The evaporation rate R ev in kg m 3 s 1 featuring in the conservartion equation for YWAT is modelled as follows In the regions where the gas temperature is significantly higher than the water vapour saturation temperature the rate of evaporation is limited by the rate of dissipation of liquid containing eddies i e R ev C a RHO1 EP KE YWAT In the regions where the mass fraction of water in a liquid state is high and the superheating of the gas mixture is low the rate of evaporation is limited by the dissipation of excess superheated eddies i e R ev C a C b RHO1C p mix T g mix T s H 1 fg EP KE wherein C p mix is the mixture specific heat Jkg 1 K 1 T g mix stands for mixture temperature K and H fg is the latent heat of evaporation Jkg 1 The equation that gives the lowest evaporation rate is the one that determines the local rate of evaporation The constants in the evaporation model have been given the following values C a 4 0 and C b 0 5 Local gas composition The local mass fractions of methane YCH4 oxygen YO2 and nitrogen YN2 are derived from calculated mixture fraction values as if MIXF is less or equal F stoic then YCH4 0 0 and YO2 YO2 in 1 MIXF F stoic if MIXF is greater than F stoic then YO2 0 0 and YCH4 YO2 in MIXF F stoic 1 s 1 for any MIXF YN2

Original URL path: http://www.cham.co.uk/phoenics/d_polis/d_applic/d_comb/spryflam/spryflam.htm (2016-02-15)

Open archived version from archive - howto.htm

relating to dimensionality number of intervals in x y z and time directions num for boxes relating to numerics flo for boxes relating to flow types phy for boxes relating to physical processes tur for boxes relating to turbulence models dat for boxes relating to data input methods or a b cc d e etc for boxes which are alphabetically arranged Click on the small boxes opposite the features which you desire the library cases to possess When you have chosen a sufficient number click on the search button After a short period during which the search is being conducted the inputlib panel will again appear this time with one or more results buttons along its bottom edge Clicking on one of these should result in a scrollable display such as this containing a list of cases which satisfy your search criteria these being in the case shown nx 1 and nz 1 so that only the y direction has more than one space interval transience i e more than one time step and the presence of heat transfer Each case in the list is represented by a Q1 link clicking on which elicits a display of the Q1 file

Original URL path: http://www.cham.co.uk/phoenics/d_polis/d_enc/howto.htm (2016-02-15)

Open archived version from archive

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