Flow profile in a heat exchanger tube

[C4Reactor]

Experiencing fouling at the tube side (Cooling Water) of a heat exchanger. The HX is of straight tubes with a longitudal baffle at the channel cover to allow for two passes design (TEMA type: BEP).
Cooling water enters thru the bottom nozzle of the channel cover, flow thru the tubes and return to exit at the top nozzle of the channel cover. Hot vapour enters from the shell top nozzle.
Fouling at the CW side observed at the top tubes only. CW flowrate registered at the inlet piping is above 1.8 m/s. At this rate the fouling is unexpected.

Understood that the relatively hot section at the top shell will lead to fouling in the top tubes. But a question to the group, for this type of HX:

1. Will the CW flow velocity in each of the tubes the same? Is it possible that the top tubes are having a lower flow velocity, due to the design, which further contributes to the deposition.

2. If we use a U-tubes design, will the occurance be the same?

Appreciate any comment

 

[25362]

What is sure is that the hottest water in the upper tubes meets the warmest vapour. The bottom tubes may be partly submerged in the condensed stream having a much lower HTC. We would assume no water leakage through the channel partition is taking place, to ensure that the linear average water velocity quoted is OK. Under these conditions, the distribution of velocities (turbulent flow regime) wouldn't be large.

I believe that only air being released from warmed up water at the floating end would cause a drop in water flow on the upper tubes, this couldn't happen in U tubes.