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Need suggestions about technical difficulties - Drying + Pyrolysis of coal particle

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Old   August 16, 2019, 01:06
Default Need suggestions about technical difficulties - Drying + Pyrolysis of coal particle
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Dear Foamers,
In OpenFOAM by default, the FireFOAM is well supported for solid pyrolysis modelling. With that in mind, I managed to built my solver for a modified version of pyrolysis (for dry coal - without moisture) based on FireFOAM. Now in the case of wet coal pyrolysis, the pyrolysis model should be developed [absence of air - no combustion] involving the influence of moisture drying.
--> Drying and Pyrolysis occur simultaneously in different regions of the same particle (however both phenomenon should be modeled altogether or modeled separately).
(I) Basically, Pyrolysis is modeled based on solidChemistry ==> Chemistry model for solid thermodynamics, solved using Arrhenius type equation.
solve ( fvm::ddt(rho_) == - solidChemistry_->RRg() ); //continuity equ
fvScalarMatrix YiEqn ( fvm::ddt(rho_, Yi) == solidChemistry_->RRs(i) ); //species equ.
(II) In my case, I need to model the continuity equation of drying as:

solve ( fvm::div(rhoU_, Yi) == - XXXX_->RRg() ); //continuity equ
Here, this XXXX cant be used as solidChemistry technically, because the drying is not solved using Arrhenius type equation.

How to proceed with this problem further,
(i) Should I need to couple drying model externally ==> such that it should satisfy the real flow physics (Pyrolysis and Drying occur simultaneously) ?

(ii) Should I need to create sub models based on DRYING ?

I would really appreciate if anyone could give me a hint where to look at or point me about the implementation in OpenFOAM.

Thank you !!

Last edited by Kummi; August 16, 2019 at 02:50.
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Old   August 16, 2019, 01:38
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Following the above post, I would like to describe as how moisture drying need to be modeled in my case.

~ In my case of drying, the heat sink model is based on the assumption that drying occurs at fixed boiling temperature (T=100deg) in infinitely thin zone. The heat sink assumes that there is no resistance to mass transfer and that the water vapor instantaneously leaves the particle. The drying rate is then completely controlled by the heat transfer.

~ conditional test on the temperature equation calculating the evaporation rate. If the temperature is equal to the boiling temperature, the evaporation rate is calculated so that the evaporation rate times the heat of vaporization matches the energy necessary to heat the local element.

T= 100 ==> alpha [moisture content) =0]
Based on it, mass and heat balances are calculated at interface as,
Mass balance (r) = rho * alpha * (dx/dt) [kg/m2.s] // evaporation rate
Heat balance (-K dT/dx) = (r) * latent heat [W/m2]
ENERGY EQU: rho*Cp*(delT/delt) = del/delx[K*delT/delx ] + r*cp*delT/delx + rho*delQ/delT (W/m3)
The evaporation rate is then introduced into the energy equations with corrected temperature as a source term.

Such kind of above equations for MOISTURE DRYING should be introduced within PYROLYSIS section in OpenFOAM
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