Living in a port city I notice more water accumulated on table tops in
outdoor restaurants during clear (cloudless sky) months and less
during cloudy months. Relative humidity averages 60 % through the
year, moulded plastic tables show greater volume of water than steel
or wooden tables. Any suggestions/ideas of using some other meterial
for enhanced condensation, the temperature of which falls even more
than the molded plastic tables. This water can be collected and
utilised.

I plan to construct as a pilot project for collecting this natural
resource for a community where potable water is scarce and subsoil
water is saline and unfit for human consumption. If this works larger
water collection units could be made for arid zones where humidity is
high.

"thirstyman" wrote in message
om...
| Living in a port city I notice more water accumulated on table tops in
| outdoor restaurants during clear (cloudless sky) months and less
| during cloudy months. Relative humidity averages 60 % through the
| year, moulded plastic tables show greater volume of water than steel
| or wooden tables. Any suggestions/ideas of using some other meterial
| for enhanced condensation, the temperature of which falls even more
| than the molded plastic tables. This water can be collected and
| utilised.
|
| I plan to construct as a pilot project for collecting this natural
| resource for a community where potable water is scarce and subsoil
| water is saline and unfit for human consumption. If this works larger
| water collection units could be made for arid zones where humidity is
| high.

For a collecting surface you need:

1) A surface which is black at infra-red wavelengths so that the maximum
cooling takes place under clear skies.

2) A material which is as poor as possible a conductor of heat so that
your radiative cooling is not offset by conduction up from below.

3) Obviously, it must be impermeable.

Your plastic table is probably pretty good. The metal table fails on count
(2) - heat is conducted up from the rest of the table, slowing the
temperature drop of the exposed surface. Wood fails on count (3) - some of
the water formed is likely yo be absorbed.


The "ideal" material, oddly enough is ice. Although appearing almost white
in visible wavelengths it is almost jet black in the infra-red. This is why
the polar caps can survive 6 months of constant sunlight - the ice radiates
strongly and so cools yet reflects much of the incoming solar radiation back
into space. Air included in ice formed from snow makes it an even better
insulator that pure ice would be. Anyone who lives in temperate or arctic
areas knows how rapidly the temperature falls at night over fresh snow,
which is an extremely good insulator as so much of it is air.

However, ice is probably not practical for your application. You need
something lightweight, a good insulator, black to infra-red and (if
possible) white or reflective to visible light. For sunny desert areas, you
will also need to consider the effect of prolonged ultra-violet exposure and
extreme temperature changes to your collecting material.
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