Hi betleenkim,
These are really many questions, let me try to give the answers:
1.) The good news about pseudo_3D is that it is possible to make corrections for the systematic error which arise from 2D vs. 3D simulations. The bad side is that it is not easy to do this in a correct way...
Chapter 4.11 of the MICRESS manual describes in detail how this correction is working. As is described there, a good correction is possible as long as the particle or dendrite under consideration is growing freely. In this case, one can just "expand" the 2D domain in a corresponding way into the third dimension, and get a corrected value for the 3D phase fraction (and thus latent heat amount). If there is no free growth (e.g. Scheil-like conditions), then the phase fraction must not be corrected, as the fraction is dominated by thermodynamics and therefore already correct!
The condition for when one case is converting to the other is when the diffusion fields of the growing particle are touching the domain boundary (or the diffusion fields of other particles): Then, thermodynamic limits for the phase fraction start to get important.
Therefore, a good estimate for the critical fraction of the matrix phase (e.g. melt) for terminating correction should be when the diffusion fields start touching. This you can estimate from the simulation itself.
Even if the matrix fraction, where correction should be stopped, is not so easy to estimate, it is still better to estimate than not to correct for 2D effects at all!
2.) In case of a peritectic reaction, only the BCC phase is growing freely, and only at the dendrite tips! If you consider directional solidification using coupling to a 1d temperature field (1d_temp), then the pseudo_3D correction is performed for each z dimension range which is corresponding to one grid cell of the 1d temperature field. Therefore, you should choose the critical fraction of liquid such that the correction applies to the dendrite tips, but not to the lower regions where the diffusion fields of the two dendrites are already touching. FCC should not be corrected at all because there is no free growth!
3.) You get this information directly from the .dTLat output! Therefore, the question is just how to start with the first iteration. You can either start from a simulation without 1d_temp but with lat_heat and add the heat conductivity values by hand, or start from data of a similar alloy/case.
A trick for the first iteration is to already use 1d_temp, but make the 1d temperature field exactly as long as the height of the 2D/3D simulation domain. Then, it doesn't matter if the first dataset is completely wrong, because it is only applied outside the 2D/3D domain
4.) However you like! It depends on the process itself which boundary condition is most realistic. The local solidification conditions depend on both, the distance of the 2D/3D domain from the boundary condition (which is important for the temperature gradient) and the boundary condition itself. I typically use a constant heat transfer coefficient, because I think it is most realistic for typical casting conditions where cooling is not explicitly controlled.
4.
) In that case, temperature diffusion is not solved, and heat extraction is considered as uniform. This is realistic for small particles like in Differential Thermal Analysis (DTA). Heat extraction (per volume) as well as latent heat lead to a uniform rising or dropping of temperature (for this as well as for the homoenthalpic approach see
B. Böttger, J. Eiken, M.Apel, Phase-field simulation of microstructure formation in technical castings – A self-consistent homoenthalpic approach to the micro–macro problem, J. Comput. Phys. 228 (2009), 6784-6795.)
Best wishes
Bernd
