Re: The death of a greenhouse tomato.


"Billy" <wildbilly@xxxxxxxxxx> wrote in message
news:wildbilly-F19EA6.22090221032008@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
In article <fs1reh$ua0$1@xxxxxxxx>,
"David Hare-Scott" <compost@xxxxxxxxxxx> wrote:


"Billy" <wildbilly@xxxxxxxxxx> wrote in message
news:wildbilly-147EA5.18110320032008@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
In article
<c8c4bfe4-9c7f-4f97-b94c-7e0f6a12bfe7@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>,
"www.locoworks.com" <videochas@xxxxxxx> wrote:

On Mar 20, 12:48?pm, Billy <wildbi...@xxxxxxxxxx> wrote:
In article
<479462ae-431a-4ced-a29b-b42459138...@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>,

?"www.locoworks.com" <videoc...@xxxxxxx> wrote:
On Mar 19, 10:43?pm, Billy <wildbi...@xxxxxxxxxx> wrote:

Freezing is 30F. Did it get below 30F in you greenhouse?
--

Billy

Impeach Pelosi, Bush & Cheney to the

Haguehttp://angryarab.blogspot.com/http://rachelcorriefoundation.org/

Freezing is 32F, but it did get down to 30 in the greenhouse. ?I
shall
start new seeds today and welcome the onset of spring.

Take notes. Water drops to 30F before it freezes (crystalizes).

The freezing point of water is 32 F and in practice it generally does
freeze
at that temperature. Liquid water CAN get to lower than that (not 30F
specifically) but it would then be called supercooled.

Upon
crystalizing, it releases the "heat of


crystallization".http://cancerweb.ncl.ac.uk/cgi-bin/omd?heat+of+crystallizat
ion
This heat warms the ice ?to 32F (any warmer and it would melt).

This is somewhat confused.

For liquid water at 32 F to transition to solid water at 32 F requires the
latent heat of crystalisation to be removed from it to an external source,
the
water does not spontaneously give up this heat, it must be taken somewhere
else,
??????????????????????????

oops that would be "taken from somewhere else"

usually by contact with something or radiation to something that is
below 32F. So the latent heat isn't doing any raising of the temperature
but
it will stop the temperature falling for a while.

This is why orchards and vineyards use sprinkler system to protect
their
crops. As long as you are making ice, the temperature will stay at
32F.


Yes the presence of liquid water will tend to keep things "warm" firstly
as it
takes heat to cool it down to 32 F (specific heat) from whatever temp it
is
stored at. This is significant as the specific heat of water is high
compared
to most things and very high compared to air. So spraying water increases
thermal mass, which reduces the rate of cooling.

Secondly the latent heat must be given up during freezing before reducing
the
temperature of water below 32 F. To give some idea of the relative
importance, in round figures it would take ten times as much energy to
freeze
an amount of water at 32 F as to cool the same amount to 32 F from 46F.

But you are likely to get local spots where cooling is taking place faster
than the supply of liquid water and the temp drops below 32F. So while
latent
heat has more effect than specific heat the plants may still get chilled
below
32F. However since plant tissues do not contain pure water their freezing
point will be below 32F and they may not get tissue damage if they don't
freeze. All this is generalising of course and the degree of damage will
depend on the plant and the actual conditions.

??????????????????????????????????????????????

That's a hell of a lot of baffle gab.
--

What (other than the typo above) is wrong with it? Is physics somehow not
relevant to gardening?

David


.

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