SUGAR BEET CLAMP CFD MODELLING: IMPLICIT T IN INTER-PHASE HEAT TRANSFER

OpenFOAM version: 9

A NEW SOLVER VERSION

A lot of small fixes have be made on v3 of clampPimpleFoam. It’s time for a new version. The focus of this version will be to make Ts and Tf in TsEqn and TfEqn implicit instead of explicit. Previously, these were included as some-constants*(Tf – Ts), which means they were taken from the previous time period/ iteration.

To make them implicit, it seems pretty straightforward. The inter-phase heat transfer expression within the temperature equations are basically split in two, with the current Tx constant made implicit, and the non-current Tx constant left explicit. So, for Ts,

- clampDummy * Asf * hsf * (Tf - Ts) / invPor

becomes

- clampDummy * Asf * hsf * (Tf) / invPor 
+ clampDummy * Asf * hsf * fvm::Sp(Ts) / invPor

For Tf

 + clampDummy * Asf * hsf * (Tf - Ts) / (rhof * Cpf * por)

Becomes

 + clampDummy * fvm::Sp (Asf * hsf / (rhof * Cpf * por),Tf)
 - clampDummy * Asf * hsf * (Ts) / (rhof * Cpf * por)

fvm::Sp makes source terms implicit. This explanation was sourced from a post on cfd-online.

BUT THE PROBLEM REMAINS

Whenever there is air velocity, as soon as it settles/ finds an equilibrium, the transfer of heat stops. It doesn’t matter if Asf = 0 (so no connection between the two phases) or = 30.04 (full connection between the two phases), the problem seems linked to the air flow. So, where is the link between TsEqn and UEqn, especially when Asf = 0? Is it through pEqn? Looking at the fields, none of them go to zero, so there are no clues there. What stupid mistake have I made?!?

And just to make this even more confusing, when the diffusion component of the TsEqn is removed from the solver, the problem disappears. Setting thermal conductivity of the solid to zero (Ks = 0) does not solve the issue, only putting // in front of this line.

SUGAR BEET CLAMP CFD MODELLING: IMPLICIT T IN INTER-PHASE HEAT TRANSFER