Remove one of the steam turbines on each heat exchanger so there's only one turbine per exchanger. Does the flickering go away?
Energy production/usage figures are a median of the actual energy consumption/production at a given tick. Due to poor fluid simulation with large fluid boxes and small amounts of liquid you can get what is essentially fluid teleportation.
The steam in the two turbines can jump back and forth between the two turbines per tick leaving one completely empty and the other with just enough to operate on that one given tick.
Hence, without the median values, you would actually be seeing a per-tick on/off cycle of half your production capacity.
To resolve the issue (if you perceive it as such) you can put a pump between the turbines so fluid can only flow one direction. But better yet would of course be to ensure you have enough steam to operate all turbines.
EDIT: I am sure this will resolve itself with the fluid mechanics update whenever that's ready.