Area for crossflow

[reactorshell]

I am very confused. It seems that there can be many different definition for the area for crossflow within the shell of a HX. What should be the more representative intepretion for the flow area under cross flow. Currently, I have always assumed it to be Ac = (Shell_Dia * (Tube_pitch - tube_dia)* Baffle_spacing)/Tube_pitch as stated in Kern's 'Process Heat Transfer'. Would this be good enough?

 

[vpl]

reactor shell

That's what I normally use, but it's not 100% accurate. It depends on the number of baffles and how they're cut and whether the tubes are in a triangular array and a number of other factors. If you really need to be accurate, go back to your heat exchanger manufacturer and ask. Patricia Lougheed

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[reactorshell]

Thank you patrica,

More questions:

I was doing calculations for the heat exchanger and then I have to determine the Reynolds number on the shell side. In that case, can i write Re as (mass flowrate/Ac) * tube_diameter / viscosity?

Secondly, what fraction of the flow on the shellside would we typically expect to be crossflow? What fraction will be bypassed? Leakages through the tube-baffle spacing etc? I did some calculations and i found that the amount of flow in crossflow is ridiculously low (~25% of total flow) Is this reasonable or had I made some wrong calculations and considerations?

 

[vpl]

Reactor shell

Yes, that is the formula for the Reynolds #. Regarding your question on amount of crossflow - I'm afraid I don't have an answer. I can refer you to Thomas, "Heat Transfer - Professional Version", which is my guidance book of choice right now (next to my very old Kreith "Principles of Heat Transfer" which has the best set of property values I've found) Patricia Lougheed

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