Re: hot air rising

[brian whatcott <inet@INTELLISYS.NET>]

At 13:04 7/21/99 -0400, you wrote:
> At 12:14 PM 7/21/99 -0400, Robert A Cohen wrote:
...
> Mixing does occur, but IMHO it is not the main point and tends to distract
> attention from the main point.  Suppose you had air parcels in floppy
> plastic bags (to prevent mixing), going up and down on a Ferris wheel.  Any
> given parcel would be cooler when on top and warmer when on the bottom.
>
> > Point (b) by itself doesn't
> > explain why the top floors of a house are the warmest, does it?
>
> No, but it is part of the explanation.  The profile you described (warm on
> top, cool on bottom) corresponds to what is called a temperature inversion
> on those rare occasions where it occurs in the atmosphere.
>
> We should not assume that all the heat sources are upstairs, nor all the
> cool sources downstairs, so it would be better to assume that the hot air
> upstairs typically came from somewhere else.  According to our newfound
> understanding, such air parcels must have been EVEN HOTTER before they went
> upstairs.  This is easy to believe.  Just think how hot the air is coming
> out of the heating-system vents.  That air will cool a tiny bit on its way
> upstairs ...

A reminder of the cooling rates in question will be helpful.
The dry adiabatic lapse rate is given  (in terms familiar to pilots)
as 3 degrees C per thousand feet.
If saturated air rises at a starting temperature of 30 deg C, its
saturated adiabatic lapse rate would be about 1 degC/thousand ft,
it has so much latent heat to release.

This saturated rate (SALR) is sometimes given as 1.5 degC/thousand ft
 - only approximately true for temperate air below 7000 ft.

For a tall building, where a floor represents about 10 feet, 100
stories could provide a 2 degreeC depression for warm moderately humid
air at the ground level.

brian whatcott <inet@intellisys.net>
Altus OK