Why small radius collects ice faster?

In article ,
(Andrew Sarangan) wrote:

Is there an explanation for why small radii objects collect ice
faster? The NASA icing video simply states this fact without giving an
explanation. I have found the same with most other sources as well.

"Roy Smith" wrote in message
...

Here's a somewhat fuzzy/unscientific answer which may help at an
intuitive level...

A larger radius object disturbs the air a further distance out in front
of it than a smaller object does. So, if a water droplet is sitting
there suspended in the air, with the smaller object, it has less of a
chance to get deflected up or down before the object slams into it.

I don't think it's unscientific. It seems like a rather good scaling
argument. The critical parameter is the ratio of the radius of the droplet
to the radius of curvature of the object. For a very large ratio (e.g. 1,
think baseball-sized droplet vs wing), you wouldn't expect the object to be
much affected by the airflow around the object, and it will simply slam into
the object. For a very small ratio (e.g. 10^-6), the droplet will simply
follow the streamlines around the object. Thus it's clear that there is a
dependence there.

Julian Scarfe

In article Wgb8c.23$Rn4.14@newsfe1-win,
"Julian Scarfe" wrote:

In article ,
(Andrew Sarangan) wrote:

Is there an explanation for why small radii objects collect ice
faster? The NASA icing video simply states this fact without giving an
explanation. I have found the same with most other sources as well.

"Roy Smith" wrote in message
...

Here's a somewhat fuzzy/unscientific answer which may help at an
intuitive level...

A larger radius object disturbs the air a further distance out in front
of it than a smaller object does. So, if a water droplet is sitting
there suspended in the air, with the smaller object, it has less of a
chance to get deflected up or down before the object slams into it.

I don't think it's unscientific. It seems like a rather good scaling
argument. The critical parameter is the ratio of the radius of the droplet
to the radius of curvature of the object. For a very large ratio (e.g. 1,
think baseball-sized droplet vs wing), you wouldn't expect the object to be
much affected by the airflow around the object, and it will simply slam into
the object. For a very small ratio (e.g. 10^-6), the droplet will simply
follow the streamlines around the object. Thus it's clear that there is a
dependence there.

Well, assuming it's not bad usenet form to argue both side of the issue,
here's the problem...

With a smaller object, yes, the droplet has less of a chance to be
deflected, but it also has to be deflected less to miss the leading edge
entirely. The wing on a typical spam can is maybe 8 inches thick, so a
droplet has to move up or down 4 inches to avoid hitting the wing. The
temperature probe is maybe 1/4 inch thick, so the droplet only has to
move 1/8 of an inch.

So, you've got two basic effects working in opposite directions. A
larger object creates a larger disturbance in the airflow, but it also
requires a larger droplet displacement. It's not immediately clear
which wins.