Recirculation cold spots in grain bed

[iralosavic]

I'm just mashing a maiden brew with my HERMS and while calibrating the HX temp probe I'm noticing a disparity in temperatures in various locations of the grain bed.

Obviously the areas closet to the output are the most accurate and I assume the readings would eventually normalise given enough time, but I'd like to know if there's anything I could be doing better?

The recirculation return output sits just on the surface which creates a good flow ontop of the grain bed with minimal disturbance, but this is my perception based on zero experience, so a photo may help:

 

[razz]

It looks to have plenty of flow, perhaps direct the nozzle against the side of the tun to create an even whirlpool/rotation of wort across the surface.
Also check how compressed the grain bed is, if it's starting to thicken it will resist the wort percolating through and cause channeling, that could account for cool spots.

 

[TidalPete]

Perhaps evenly distribute the wort from your HEX return by using something that "scatters" the return flow similar to the pic or just reduce the pump outlet flow enough to gently intermingle with the grain bed without disturbing the bottom section?

 

[iralosavic]

It looks to have plenty of flow, perhaps direct the nozzle against the side of the tun to create an even whirlpool/rotation of wort across the surface.
Also check how compressed the grain bed is, if it's starting to thicken it will resist the wort percolating through and cause channeling, that could account for cool spots.

I initially had it like that and ended up reverting back to it - there were spots where the grainbed settled higher and had no flow over it no matter where I positioned the outlet. I suppose my mash may have been too thick (it did have flaked rice in it)?

Perhaps evenly distribute the wort from your HEX return by using something that "scatters" the return flow similar to the pic or just reduce the pump outlet flow enough to gently intermingle with the grain bed without disturbing the bottom section?

This seems like a good idea, if perhaps thinning the mash and slowing the flow don't work