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Re: Medhurst Table
In a message dated 1/9/99 2:56:59 AM Mountain Standard Time, tesla-at-pupman-dot-com
writes:
> Original Poster: "Barton B. Anderson" <mopar-at-uswest-dot-net>
>
> Has anyone hacked at the Medhurst table to derive k via
> h/d? I'm simply looking for a quick way to calc k in a
> spreadsheet rather than using vlookups, etc... hoping
> someone has already done the hacking.
>
> Thanks,
> Bart
>
>
Bart,
I wanted to know the same thing, so I used Ed Sonderman's awesome excel
spreadsheet(the VLOOKUP table) and did this. I found the K to vary linearly
if H/D was greater than or equal to 2. Since most coilers don't design coils
with a ratio lower than that, this equation works and is very convenient.
K = 0.100976*(H/D) + 0.309630
If you want K for the entire series including (H/D) less that two, it becomes
a forth order equation.
K = 0.0005x^4 - 0.0097x^3 + 0.0648x^2 - 0.0757x + 0.4723
I did both of these by plotting the table onto a chart and inserting a
trendline. Both equation had good correlation coefficients (0.999 or so). I
doubt it is worth the trouble to use the second one, but showed it anyway.
Hope this helps.
Mike