[ROY4]

Hello everyone,
I am using the adaptive time step to find a proper time step for my 2 phase-Eulerian Bubble column(Air-Water with air source points at the bottom of the column as spargers) with 48000 grids. I used the settings that dear Glenn Horrocks suggested me in this thread:

Error code 255

But since my question was lost in another thread, I decided to open another one. in that thread Glenn suggested me to use his settings that were chosen due to his precious experience.
Total Time = 1000[s]
First update = 0[s]
Time step update freq = 1
Initial Time step = 1e-6[s]
Maximum timestep = 0.05 [s]
Minimum time step = 1e-10[s]
target max = 5
target min = 3
decrease factor = 0.8
increase factor = 1.06
when I changed the settings to these suggested values, my timestep decreased (instead of increasing) and finally stopped with an overflow massage at timestep 5.903e-9 (for Double precision run) and stayed unchanged at 1e-10 when double precision was off. which both of them show a serous problem for my solution.

I also read in tutorial that:
(If the actual number of coefficient loops used is less than the Target Minimum Coefficient Loops, the timestep size is increased. If the actual number of coefficient loops used is greater than the Target Maximum Coefficient Loops, the timestep size is decreased)
I have no idea that what can I do to get an increasing time step..

1)Can anyone please help me since its 2 month that I'm really stocked in this problem.

2) As my 2nd question, which one I should do first? Grid study? time study? or convergence criteria study? some people say there is no difference but I feel there must be a preference,

3) If I use larger grid size, will it help me to increase the time step? if yes, do you recommend it for me?
Thanks