Tom wrote:

"Ian Stirling" wrote in message
...
Tom wrote:

"IMM" wrote in message
...

"Rick Dipper" wrote in message
...

More is always better.

Except around a pipe!!

Even around a pipe, but to a much, much lower degree.

On a pipe, I assume the surface area of the insulation increases by a factor
of approx 6.3 times the thickness of the insulation, I'm afraid my maths is
not good enough to work out at which point it starts to be non effective.
Perhaps there are some mathematicians out there that can help on this one.?

It never starts to be non-effective, it's always better than air.
It rapidly starts to have a vanishingly small effect.
Consider the heat flow.

The heat flow from the surface of the pipe is the same as the heat flow from
the surface of the insulation. (once it's all reached steady temps)
This means that the temperature difference across the last little bit
of insulation depends on its area.
So, at ten times the pipe diameter, the insulation is only doing
1/10th as good a job as that just next to the pipe.
If you need a very well insulated pipe (or worse, tank that's small
compared to the insulation) then it usually pays to buy some really
expensive insulation to put next to the pipe,

For example, considering the insulation at various numbers of times
the pipe diameter from the surface of the pipe. (1 is next to the pipe)

Distance from pipe Relative insulation
1 1
2 1/2
3 1/3
4 1/4
5 1/5

Total=2.28 (this is inaccurate, finer and finer graduations would give a
more accurate idea, but this is ballpark)


So the last fifth has contributed about a tenth.
But it's a third of the total volume.