Looking for Nusselt relationship
Looking for Nusselt relationship
(OP)
I was flipping through my old heat transfer text in search of a Nusselt relationship for forced flow along (ie, parallel to) the outside of a tube or cylinder. Most equations are for flow across (ie, perpendicular to) a tube. It occurs to me that the relationships for forced flow across a flat plate may be applicable to the flow-parallel-to-cylinder case. Is this correct?





RE: Looking for Nusselt relationship
Yes, if you have not the specific correlation, it is "always" correct to take into consideration the closer available correlation
Did you take into account the correlation for annular spaces?
Have you decided what is the characteristic dimension: D or L?
Gianfranco
RE: Looking for Nusselt relationship
I'm not designing a heat exchanger, by the way -- I'm just trying to determine, in a general sense, the effects of temperature on the overall heat transfer coefficient. That is, if water temperature increases by twenty degrees, for example, does the term UA tend to go up or down as a result.
RE: Looking for Nusselt relationship
For the purpose you said the correlation 8-73a, 8-74, or better 8-78, where you introduce the mu/muw parameter on Table 8-6, are enough to performe the sensitivity analysis around one working condition point (nominal).
D UA
^
|
1 -|
|
|
|
|
-------------------->
0,5 1 1,5
tw(nominal)
pw
other parameters
Regards.
Gianfranco.
RE: Looking for Nusselt relationship
Thanks for the feedback! Eqn. 8-74 is actually the one I had used. I just had a lingering doubt as to whether or not I could apply the flat plate relationship to flow along a tube or cylinder. It seemed to make sense, but then, I often find myself having to tell my wife "Well, it made sense at the time...", so I thought I'd try a second opinion just to cover my behind. Thanks again.