Transition flow regime

[TaiwoOni]

Why is it advised to remain outside the transitional flow regime when designing heat exchangers?

 

[ione]

It's not always easy to define precise thresholds for transitional flow, although you can certainly find sources in literature that will give you a range for Reynolds number in order to identify transitional regime.
Anyway, despite the efforts done and the correlations available, it's a matter of fact that heat transfer predictions remain unreliable and instability and uncertainty dominate in this region. This is basically why during a design phase it's better to keep away from this "dangerous" zone.

 

[Caloooomi]

If you are in transitional regime, any turndown for the process fluid will reduce the velocity pushing you closer to a laminar regime which will result in a lower heat transfer coefficient. This is due to the increased mixing within the boundary layer and the bulk fluid.

TaiwoOni, your last 4 threads in the previous week have all been on fluid mechanics which can all be easily found in a textbook. If you're going to ask questions, at least post your findings or work done so far so we can help to guide you towards the right place so you can study it yourself.