CFD Online Discussion Forums - 1D COAL pyrolysis

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1D COAL pyrolysis - Temperature JUMP

Dear Foamers,
I have created my own solver (cokeOvenFOAM) based on fireFOAM for 1D pyrolysis [considering dry coal]. As a next step, I want to create a SUBMODEL considering moisture evaporation [wet coal] and couple with my pyrolysis solver.

In attachment (DRY COAL) --> Temperature graph (cokeOvenFOAM - my prolysis solver)
In attachment (WET COAL) --> Temperature graph (Expecting result)

The difference between two graphs --> temperature jump at the bottom, which is due to moisture evaporation. I couldn't able to figure out as how to introduce or couple the moisture evaporation (phase change) in 1D pyrolysis solver.

Kindly someone share their ideas to proceed on.
Thank you

Can someone help me out here please?

What happens I guess is when the coal is heated up, is that partly of the heat is needed for the phase change of the water: -> you need to consider this in the energy equation of the pyrolisis of the model maybe as additional source term.

The water vapor is leaving your pyrolis region -> this has to be considered in the mass convervation equation also as source term.

What you additionlly need I guess is how to calculate the rate of evaporation: Here you have to look in the literature for a relation which gives you the evaporation rate inside of liquids inside a porous media as function of the tempartur and maybe pressure.

This is the way I would proceed to solve the problem you described.

Phase transition phenomenon ==> with Only TEqn.H

Dear Michael Alletto,
Thank you for your response. The pyrolysis model in openFOAM is constructed based on solidChemistry model using Arrhenius equation.
So firstly to make it simple, I constructed ONLY phase change as separate solver in OF211 to understand flow physics [Attachment ~ Solver explains the movement of interface from right to left for non-isothermal phase change {Stefan 1D Problem - moving boundary is met} ]

In this case, alpha (moisture content) as a function of T ~ empirical relation ~ as mentioned in TEqn.H in attachment

Quote:

alpha = 0.1*Foam::erf(4.0*(T-Tboil)/(Tv-Tl))+scalar(0.5);

But in my case, alpha is not function of T, instead the position of the interface (boiling plane) is fixed with the condition as follows:

Quote:

Initial moisture content alpha = 0.1 (10%)
@T=100deg (moiture content_alpha=0) (near the heated wall)
@T=100deg >> H2O(l) = H2O (v)
~ And I am confused here - dont know how to implement the conditional statement based on temperature for phase change phenomenon

ATTACHMENT FIGURE: CLEAR info

REF - Clear details here in this MANUSCRIPT ~ https://sci-hub.tw/https://doi.org/10.1016/0016-2361(83)90225-9
*And you are right, additional source term is added in the energy equation for the phase change. In my case, boiling and condensation source terms are not added in main energy equation, instead only convection source term is added in energy equation [details in MANUSCRIPT]
*For an initial case, the movement of water vapor is not considered. So, no mass conservation Equ. The current problem is based on only energy equation [TEqu].

Based on the conditional statement of temperature, evaporation rate (mass balance) and heat balance are calculated as,

Quote:

Mass balance (r) = rho * alpha * (dx/dt) [kg/m2.s]
Heat balance (-K dT/dx) = (r) * latent heat [W/m2]
Heat balance of boiling is expressed in unit of W/m2 ==> where it couldnot be added as source term in energy equation which carries the unit W/m3 ~ And I am confused here as how to implement it as a source term in energy equation?

KINDLY SHARE YOUR IDEAS PLEASE.... THANK YOU !!

Do you know this paper: https://reader.elsevier.com/reader/s...8B2BAEDFDB8CE0

They propose a simple relation for the source term in the energy equation to describe the heat source term due to evaporation/condensation.

This is also helpful https://indico.cern.ch/event/578092/...7/C3OrK-05.pdf

They solve two additional equations transport equations for the liquid and vapour content.

Movement of boiling plane (interface) with CONDITION

Dear Michael Alletto,
Thank you so much for your response. I have gone through these solvers [interThermalPhaseChangeFOAM, interCondensingEvaporatingFOAM] before. However, I checked once again as per your suggestion.

In interThermalPhaseChangeFOAM ==> EEqn.H

Quote:

//Use limited alpha1:
const volScalarField limAlpha1( min(max(alpha1, scalar(0)), scalar(1)) );
--> Here alpha varies between the values 0 and 1
--> alpha1 depends upon thermal phase change model which follows phase change heat, phase change volume and production

But my case looks to be very simple: REF - Clear details here in this MANUSCRIPT ~ https://sci-hub.tw/https://doi.org/10.1016/0016-2361(83)90225-9

I HAVE 2 UNCLEARED POINTS:

(i) BOILING: In my case, w (moisture content) doesn't vary with expression. Moisture content varies with higher (-) and lower (+) temperature sides. How to model Moisture content depending upon high and low-temperature side in openFOAM methodology. (ATTACHMENT 1)

Quote:

Position of boiling plane --> INTERFACE CONDITION
At T=100deg --> (moisture content -> high temp side) w(-) =0 (near the heated wall)
--------------------------------------------------------------------------------------------------------------------------------------------------------------------
(moisture content -> low temp side) w(+) =calculated ==> and substituted in Mass balance (r) = rho * w(+) * (dx/dt)

(ii) The heat balance carries the unit of (ATTACHMENT 1) of W/m2 - So how the heat can be taken into account in source term of ENERGY Equ. because ENERGY Equ. carries the unit W/m3? (I dont know to implement it in OpenFOAM)
ENERGY EQU: rho*Cp*(delT/delt) = del/delx[K*delT/delx ] + r_gas*c_gas*delT/delx + rho*delQ/delT (W/m3)

~ Once BOILING is completed, I will take into account of condensation.
~ At T>100deg -- convection source term is added in energy equation (ATTACHMENT 2)

Could you please give me some direction about it. Thank you once again !!

Hi Kumaresh.
I got your message the problem look similar to my problem statement.
please send the email as I have mentioned in message

Hello Zhiheng Wang,
Thank you for your response.
I will mail you shortly.

^^