Steam tracing pitch calculation

[DJPA1234]

Dear Experts,

We have to provide the two concentric spiral wound steam tracing coil on the one of the tank dia 25meter. Tracer diameter is 1.5inch. We have calculated the required length of tracer by heating calculation,

Main query is regarding Tracing pitch, (i.e. Pipe to Pipe center line) do we have any imperial formula which enable the requirement of this for spiral layout.
Or is there any relation between Overall heat transfer coefficient and Pitch.

We need the find the spacing/pitch so tracing can be further developed.

Thanks in advance.

 

[chicopee]

You can reference Kent Mechanical Engineering Handbook "Power". My 12th edition(9th printing,1/1967) pg3-20 Turbulent Flow of Liquids Inside Helical Coil" may answer your question. The formula for the coefficient of convective heat transfer(h*) for straight pipe is too complicated, however, if you can get it from Kent or other references; then according to Kent the "h" value for helicoil can be h= (1+(3.50(d/d*))h* whereby d/d* is the ratio of pipe diameter to the helix diameter. There will be some caution presented in Kent such as reduction of h due to corrosion and dirt; the effect of pipe length may be negligible when length exceed 20 diameters; for shorter length h may be appreciably higher. There is no mention as to the effect of the pitch on the h value.