Date:         Fri, 28 Jun 2002 15:40:11 -0700
Reply-To:     pensioner <al_knoll@PACBELL.NET>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         pensioner <al_knoll@PACBELL.NET>
Subject:      Re: Humid Air - Some Comments
In-Reply-To:  <200206282146.g5SLkNxc447194@www1-int.prodigy.net>
Content-type: text/plain; charset=iso-8859-1

What he said.  plus a few observations.

Dry air is a very good thermal insulator.

Damp air is not as good as a thermal insulator.

In still dry air, (no motion) the convective currents will be dominated by
the air just next to the hot thing by moving upwards as it's local density
decreases.  This warm air will be replaced by ambient air at "room"
temperature.  The air accepts heat by either becoming less dense (higher
molecular motion) or hotter (higher molecular motion).  Same effect but
pressure dependent.  Thats' why you hold a candle by the end that's not
burning for best long lasting results.

PV=NRT is the relationship.  Left of course for the reader to muse about.

The real critter is the ability of the "wet" air to absorb heat.  This
capability varies as the non-atomized water vaporizes.  (what he said agin).
One could consider this capability as specific heat.  Or how much heat it
takes to raise one unit of air one degree.

When the air is the same temperature as the hot thing no heat transfer
occurs.  When the air is hotter than the hot thing the hot thing gets
hotter.  When the air is cooler than the hot thing the air gets hotter.  How
hot it gets is partially a result of it's specific heat.  The temperature of
BenT is -273K according to his previous relationships and he has a very high
specific heat.  Terry K has a minuscule specific heat.  He heats up with
very little provocation.  BenT on the other hand hardly heats up at all.

The heat taken away is measured in thermal units and is dependent on the
difference in temperatures between the two mediums and the heat transfer
characteristics of the interface between the two.  As a low specific heat
medium can accept less heat per degree rise, it's clear that it is easy to
get a rise out of Terry K and according to his previous girlfriend almost
impossible to get a rise out of BenT.  So if you need someone to cool it,
BenT is your man.

As the temperatures between Schwenk and Terry reach an equilibrium, the heat
transfer stops.  But you noticed that.

As the temperatures between the mediums approach equitemperature the amount
of heat transferred decays to zero.

This is called decadence in some cases and boring in others, if you're into
heated discussions.

So what we need, kids, is the curve that plots heat transfer as a function
of specific heat for various wet air conditions.  They'rrl be a quiz on
monday.

Only Frank can afford the highpriced stuff, I stick to Controy, the Se Vende
substitute available at your local south of the mango-man purveyor of "fine
sprits".

p


Date:    Fri, 28 Jun 2002 17:45:46 EDT
From:    Frank Grunthaner <FrankGRUN@AOL.COM>
Subject: Re: Humid Air - Some Comments

What a great day for culture on the list! Avogadro's number and Vanagon in
the same dissertation! There is hope for our society yet. Even the mere
mention of the mole was gave a tingle in the cranium surprisingly similar to
an ounce of Cointreau on ice.

Nonetheless, Stan, Ed and Arlan are all quite correct ... humid air is less
dense than dry. Also, the extraction or heat transfer ability of the flowing
gas is related primarily to temperature and secondarily to velocity , then
to
turbulence and finally to macroscopic porosity or surface area per unit
areal
dimension.

However, this is not the case when the water has not been fully atomized.
Small water droplets (can range from nanoclusters to sub-mm aerosols) offer
the ability to volatilize (get to use the heat of vaporization). This can
significantly enhance net thermal transport and reduce chamber detonation.
Taken to the extreme, a thin layer of water (2 to 4 monolayers) on the
radiator surface at the turbulent air boundary will give superb heat
transfer
. Of course, one needs to keep the water film thickness below the level
where
the bulk thermal conductivity of the water would dominate. Such thickness
control is generally beyond the ability of most practitioners of the
automotive arts!

BTW a thin film of Cointreau would work wonderfully as well; what a fine
aroma, but what a waste.

Have a chemically interesting day!

Frank Grunthaner