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ThermalMan (Mechanical) (OP)
20 Jan 04 8:41
I need the formula for calcuating the surface area of a helical coil.  I have the pipe diameter, coil height, # of turns, and pitch, but can not seem to remember the formula used.  Any help would be appreciated.

Thanks.
Maui (Materials)
20 Jan 04 10:26
There's a simple alternative method to calculate the surface area of a helical coil. Measure the mass of the coil (in kilograms for example), then divide this by the density. That will give you the volume that the coil occupies. If the cross section is constant and you know its outer diameter D, then you can easily determine the coil length L. Multiply L by pi*D, and you will have the surface area of the coil.


                                               Maui
TD2K (Chemical)
20 Jan 04 12:31
I 'think' I have this formula back in one of my textbooks at home.  I thought Perry's would have it but they don't seem to.  If no one else has answered it by then, I'll dig through it and see if it is there.
Helpful Member!  pesy (Mechanical)
20 Jan 04 13:13
The equation for the length of a helix is:

N*PI*D*sqrt( 1+ (P/(PI*D))^2 )
where:
P=pitch
N=# turns
D=diameter of helix (the helix in the center of the pipe)

Multiply the helix length by PI*d
d=pipe diameter (either ID or OD, whichever you're looking for)

SA=N*PI^2*D*d*sqrt(1+(P/PI*D))^2)

Pesy
25362 (Chemical)
21 Jan 04 5:17
It should be quite simple, the length of one turn, following the theorem of Pythagoras is:

L1=[(2*pi*r)2+p2]0.5

Total coil length,
Lt=N*L1


where N is number of turns, pi =3.1416, r is the coil radius, and p is the pitch.

The external surface:
A=Lt*pi*do

Where do is the coil's pipe external diameter.
katmar (Chemical)
21 Jan 04 8:33
Unless the pitch is very steep, I would not even bother trying to get the exact area (presuming you want to do heat transfer calculations). Simply take the number of turns times the area of a ring of the same diameter.

Any error in this assumption would be no greater than the errors in your physical property data and the heat transfer correlations.

Where ever possible - KISS!

regards
Harvey (Katmar)

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