Archived posting to the Leica Users Group, 2000/12/23
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Greg Locke wrote:
>
> On Sat, 23 Dec 2000, you wrote:
> >
> > Venturi Effect: (n) You've got a bug stuck in your altimeter's pitot tube.
> >
> > OK, seriously: From what I can find, the venturi effect deals with the
> > conversion of some kinetic energy into a pressure differential. So if two
> > fat people are standing close together on a windy day, the low pressure zone
> > created between them will result in them being sucked together.
> >
> > What's that got to do with windchill?
>
> ....ahhhh, that's what happens when you look physics up in a dictionary.
>
> Another affect of air being forced through a constricted place (ala thumb
> over garden hose ... or between to two fat people) such as a venturi, is an
> increase in velocity as is does so.
>
> As the velocity of the air increases, it's tempeture decreases. This is
> why pilots get carburator ice while the ambient tempeture may well be
> above freezing. Yes, I know, the dew point has to be within a certain
> range also to get the condensation which freezes and turns to ice in the
> carburator venturi.... the only place it is cold enough to freeze as this
> is where the fast moving air is cold enough.
>
> It's been awhile since I did the physics for my pilots licence ... or
> flown planes with normally aspirated engines but thats how I remember it.
>
> SO! ... not only will the two fat people we drawn together, their sides
> which are closest will be colder :^) Sound convincing?
>
> .....jeeeez, how do we get into these discussions?
I don't know, you brought this one up ;)
>
> Greg Locke
Greg,
I am sure the icing you mention is more likely caused by the latent heat
of evaporation as fuel moves from the liquid state to the gaseous state.
This carburetor icing has to depend upon the amount of water vapor in
the air ('dew point) along with other factors.
Of course at very low temps there is little water vapor in the air,
doubtful if your Leica will get frost on it in a constant 40 below
environment. Unless you touch your tongue to it of course ;)
Dennis