Questions about simulating heat transfer based on example packedBedTemp

Dear all,

I am simulating the heat transfer aiming to calculate the effective thermal conductivity of a sphere packing.

I started by modifying the example "cfdemSolverPisoScalar/packedBedTemp" and have the following questions.

1. Why are both in.liggghts_init and in.liggghts_run required in DEM folder?
ParDEMrun.sh calls "in.liggghts_init" but I got error if I delete in.liggghts_run.
Which file calls "in.liggghts_run"? and why is "run 0" defined in "in.liggghts_run"?

2. Why are files 'alphat' and 'nut' created in the CFE/0/ folder. I know the CFDEM coupling needs parameter Prt, but Prt has already been defined in transportProperties (see figure "why-alphat"). Additionally, according to the official web https://www.cfdem.com/media/CFDEM/docu/cfdemSolverPisoScalar.html, alphat = nut/Prt, since alphat is created as a file and Prt is defined in the alphat file, nut can be computed using the equation. Why should a separated nut file be created (see figure "why nut")?

3. Why is voidfraction 1?
In CFD/0/voidfraction file, 1 is assigned to voidfraction . But should it be smaller than 1 since particles inside?

4. Why should Ksl be defined for boundary condition?
in CFD/0/Ksl, Ksl=zeorGradient is assigned to the boundary condition.
For my understanding, Ksl is used to calculate the drag force at the interface between particle and fluid. Why should it define for boundary condition?
What does Ksl=zeorGradient (i.e. no change of Ksl on the boundaries) mean?

5. Boundary condition
I assigned a temperature of 300 degrees to the inlet, but the result only shows only the centre of the inlet has 300 degrees (see figure temp-inlet-boundary). Is anything else I need to define?

6. How to compute the z-directional heat flux?
What are the commands I need to use to export the z-directional heat flux on a cross-section?
Additionally, since both liggghts and openFoam calculate the heat transfer, should I export the z-directional heat flux from both software and add the heat flux together to achieve the heat flux on a cross-section?

7. Steady-state simulation (stationary solver)
At this stage, I do not need the particle move. Hence, it will be good if CFDEM can simulate steady-state fluid and heat flow. I checked the equations on the official web, https://www.cfdem.com/media/DEM/docu/fix_heat_gran_conduction.html and https://www.cfdem.com/media/CFDEM/docu/cfdemSolverPisoScalar.html, both the equations are transient. However, OpenFOAM has several solvers for steady-state such as chtMultiRegionSimpleFoam. Also, to simulate steady-state, it just needs to delete the time-related term in the transient equations. Is there an existing method to run steady-state simulation in CFDEM? or is a way to do it?

8. Heat conduction in the air?
Does CFDEM consider the particle-air-particle conduction? If so, could anyone explain how the particle-air-particle conduction is calculated in equations?

I am also thinking whether particle-air-particle conduction can be simulated only using liggghts if neglecting heat convection.
From the web https://www.cfdem.com/media/DEM/docu/fix_heat_gran_conduction.html, I think liggghts can only simulate particle-particle heat conduction but has not included the particle-air-particle conduction. Am I right?
However, as shown in the figure "heat-conduction-air", the simulation of particle-air-particle conduction just need another empirical equation. which file would I work on if I want to add the equation?

Thanks for your patient to read through the long questions.
I appreciate it if you give your comments about any above questions.

Best regards,
Brian