Source term for EVAPORATION in Energy Equ. - technical difficulty ?

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September 8, 2019, 03:43
Source term for EVAPORATION in Energy Equ. - technical difficulty ?
#1
Senior Member

Kumaresh
Join Date: Oct 2016
Posts: 349
Rep Power: 11
Hello Foamers,
My problem is a kind of 1D pyrolysis (Wet Coal) modelling, which is focussed mainly on heat loss - thus only Energy (heat) equation is included in my work.
Quote:
 ENERGY EQU: rho*Cp*(dT/dt) = del/delx[K*dT/dx ] + rho*dQ/dT + r*cp*dT/dx (W/m3) Unsteady conduction = Diffusion term + SOURCE TERM 1 + SOURCE TERM 2
My query is all about the SOURCE TERM 2. Concerning it, my query is all about.

SOURCE TERM 1 (Pyrolysis) = heat loss due to pyrolysis solved by Arrhenius-like degradation chemistry (SOLVED this source term based on FireFOAM 1D pyrolysis model code- NO ISSUES HERE)
SOURCE TERM 2 (Evaporation) = phase change - moisture to vapor (moisture embedded in the wet coal).
Quote:
 CONDITION for SOURCE TERM 2: T= 100 ==> alpha (moisture content) =0 Based on it, mass and heat balances are calculated at the boiling plane (surface) as, Mass balance (r) = rho * alpha * Velocity [kg/m2.s] Heat balance (-K dT/dx) = (r) * latent heat [W/m2]
Moisture Evaporation is calculated at the surface (Boiling Plane). The calculated mass balance (r) is multiplied with cp and dT/dx as SOURCE TERM 2 gives the unit of W/m3.

REF - Clear details here in this MANUSCRIPT ~ https://sci-hub.tw/https://doi.org/1...361(83)90225-9 (ATKINSON, B., & MERRICK, D. (1983). Mathematical models of the thermal decomposition of coal4. Heat transfer and temperature profiles in a coke-oven charge. Fuel, 62(5), 553–561)
How the source terms can be included in such problems? I have contacted certain people, few replied as they are not familier with pyrolysis, others asked me to look into interFoam solvers. But the approach of interFoam seems to different with separate transport equation for volume fraction, which is not the same in my case. I'm trying to figure out and learn as how the problem can be attacked based on algorithm and importantly how such problems can be approached step by step in OpenFOAM//
Quote:
 How the SOURCE TERM 2 can be technically approached and included in OpenFOAM?
PS ~ Based on real physics, Pyrolysis (source term 1) and Evaporation of moisture (source term 2) occur simultaneously inside the chamber.

Thank you.

September 9, 2019, 09:32
#2
Senior Member

Kumaresh
Join Date: Oct 2016
Posts: 349
Rep Power: 11
Hello Foamers,
As explained above, I've been trying to setup the SOURCE TERM 2 for the pyrolysis solver. I have two ideas to discuss here: (not sure which will go really well for my case)

1) Coupling SOURCE TERM 2 inside the pyrolysis solver under "reactingOneDimCoeffs". Doing this, I guess both pyrolysis and moisture evaporation will occur simultaneously.
Quote:
 pyrolysis { active true; pyrolysisModel reactingOneDim; regionName pyrolysisRegion; reactingOneDimCoeffs { filmCoupled true; gasHSource true; QrHSource false; radFluxName Qr; moveMesh false; // true; minimumDelta 1e-6; useChemistrySolvers true; } }
2) Introducing fvOptions for the source term. My source term is similar to "solidificationMeltingSource" under fvOption, which I need to modify it as per my need.
But in pyrolysis solver, "solidificationMeltingSource" can be a good choice? If I introduce fvOption, I have to edit my main source code pertaining to solidificaionMeltingSource to get it to work right ?
Quote:
 iceZone { type solidificationMeltingSource; active on; solidificationMeltingSourceCoeffs { selectionMode all; Tmelt 273; L 334000; // enthalpy of fusion for water [J/kg] thermoMode thermo; // retrieve thermo properties from themo model beta 50e-6; // thermal expansion coeff [1/K] rhoRef 1000; } }
Does anyone know how this SOURCE TERM 2 will be coded in pyrolysis solver?
Kindly give some suggestions. Thank you

Last edited by Kummi; September 9, 2019 at 09:37. Reason: Inclusion of SOURCE TERM