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hi

hi iam simulating turbulent flow in concentric double tube heat exchanger. the inner tube is hot water and outer is cold water counter flow. when i have got the heat transfer coefficient for annulus and compare with literature it is wrong ?

for nusslet number in literature i use petkhove also ditus-boilter correlation with hydraulic diameter with wetted PERIMETER for Re. and use heat trasfer PERIMETER(i mean just inner tube diameter) for getting heat transfer from nusslet number.

but when i use wetted PREMETER for claculating heat transfer coefficient from nusslet number i got true answer. but mainly i should use just inner tube PREMIETER for calculating heat transfer coefficient from nusslet.

 ghorrocks February 12, 2014 17:41

FAQ: http://www.cfd-online.com/Wiki/Ansys..._inaccurate.3F

But in this case you also have to be careful the results you are comparing to are correct.

 AKHILESH S L February 13, 2014 02:23

hi,
can you please show a schematic with dimensions of your problem? which material you are using as heat exchanger wall?

1 Attachment(s)
for calculating heat transfer coefficient in the annulus the hydraulic diameter of the annulus is (Dh=D0-Di) and i use this diameter for calculating Re number. then i use petukhov correlation for finding nusslet number. it should be noted that for annulus the nusselt number should be based on the equivalent diameter calculated from (De=(4*Ac)/Ph) which here Ph is the perimeter of heat transfer area.(i mean inner tube perimeter) and then there is different between De and Dh which we use Dh for calculating Re and De for calculating heat transfer coefficient. but when i get the heat transfer coefficient with Dh from petukhov it is the same with fluent .but when i use De for getting heat transfer coefficient(HTC) from nusselt number it is different from fluent HTC. mainly i should use De for calculating HTC from nusselt number.

thanks.

 ghorrocks February 14, 2014 05:20

You seem to be comparing against empirical correlations. You should not expect these to be very accurate.