Tracking U of Heat Exchangers

[u/mrnormality]

Hello,

Is there really a significance for tracking Overall Heat Transfer Coefficient of heat exchangers over time? Monitoring the heat exchanger outlet temperature or simple lculation for the heat duty would already be a good indicator for the fouling that happens within the exchanger. If this is the case, there is no point in calculating U and tracking it, right?

[u/EmergencyAnything715]

Measuring U value is an appropriate way of normalizing exchanger performance for different flow conditions, especially if there is variable flow/temperatures on both sides of the exchanger.

Using outlet temperature is one way to monitor for fouling, but its not a great way to view this. Let's say you have low rates during the winter and dont see much of a change in outlet temp. It May be fouled up going into summer, but you didn't realize it because of the conditions the exchanger is operating in.

[u/tortillabois → u/EmergencyAnything715]

U is better than outlet temp or DT for sure, but U does not normalize for flow. Fouling factor is normalized for flow though, so I prefer to use it

[u/360nolooktOUchdown → u/tortillabois]

You can normalize U as well, knowing that het transfer coefficient for each side is roughly the square of velocity.

[u/tortillabois → u/360nolooktOUchdown]

Yes it can be but not to a squared of velocity.. Pressure drop is square of velocity, heat transfer is not. For turbulent flow it is proportional to Reynolds raised to the power of less than 1

[u/360nolooktOUchdown → u/tortillabois]

Which… Reynolds has velocity in the numerator…

[u/tortillabois → u/360nolooktOUchdown]

Correct, not to the power of 2 though….