Hi All
We have already used small, commercial pond foggers and learned useful
things about evaporation rates, plume cooling and that spray in cooled
air spreads out like a spilt liquid. The pond foggers used piezo
generation of Faraday waves to generate 2.5 micron drops. They were
helpful but they have done all that they could do. To produce the same
drop rate as a single spray vessel generating 0.8 micron drops the power
requirement would be 250 MW.
The remaining questions are whether back-flushing can prevent nozzle
clogging, how close we can get to a mono-disperse spray, what fraction
of drops get to the cloud top in what meteorological conditions and what
fraction of those will get a successful nucleation. Kohler says that
drop diameter matters for nucleation. Stokes says that falling speed is
affected by diameter. I do not see what we would learn from testing
small quantities of the wrong spray size and would rather spend any
money and time on getting enough spray of the right size.
Stephen
Emeritus Professor of Engineering Design. School of Engineering.
University of Edinburgh. Mayfield Road. Edinburgh EH9 3JL. Scotland
[email protected] Tel +44 (0)131 650 5704 Cell 07795 203 195
WWW.see.ed.ac.uk/~shs YouTube Jamie Taylor Power for Change
On 01/01/2015 10:37, Andrew Lockley wrote:
Salter appears to hold that experiments with existing equipment (eg
pond fogger) is not helpful, as particle size distribution is
inappropriate, and power consumption disproportionate.
I would like to hear opinions on this, as my view is that establishing
plume behaviour, droplet evaporation and cloud mixing is more
important at this stage than the actual albedo modifications.
A
On 1 Jan 2015 00:47, "Rob Wood" <[email protected]
<mailto:[email protected]>> wrote:
Dear All,
I think that some degree of coagulation given such localized point
sources of large numbers of particles is inevitable, as shown in
the paper by Stuart et al. (2013)
<http://www.atmos-chem-phys.net/13/10385/2013/acp-13-10385-2013.html>.
This will also be the case with charged particles. Nevertheless, I
don't think that this is necessarily a fundamental limitation.
After all, shiptrack formation, where even larger numbers of
particles are produced, still occurs. Coagulation must be
considered in the calculations. That said, in our recent paper
(Connolly et al. 2014
<http://faculty.washington.edu/robwood2/wordpress/wp-content/uploads/2014/06/Connolly_etal_PHILTRANS_2014.pdf>),
we found significant albedo enhancement in a parcel model even
with quite broad size distributions. The optimal median particle
size becomes smaller as the size distribution spread broadens
(e.g. from coagulation). For broader distributions typical of
those produced in lab tests, the optimal median droplet diameters
need to be somewhat smaller than 0.1 micron.
I tend to agree with Stephen that near-surface spreading due to
initial negative buoyancy from evaporation of water from the small
seawater droplets may not necessarily be a tremendous problem for
the reasons he states. This has not yet been considered in any
model that I know of, but could easily be done with large eddy
models.
Rob Wood
On 12/30/2014 8:35 AM, Stephen Salter wrote:
Hi All
Piers Forster's concern in his video about spray coagulation
would be reduced if his model had used mono-disperse drops with
an electrostatic charge as specified in our 2008 paper on
sea-going hardware.
His concern about detecting the effectiveness is because the
cloud contrast change needed to save humanity is below the
detection threshold of the human eye. However contrast can be
enhanced by the superposition of satellite aligned images. I
have previously circulated some to this group and hope that the
idea will give quantitative results in a few days.
The picture of spray plumes shown in box 3 of his IAGP
practicalities note must have been using warm air from a
chimney. Depending on the temperature and relative humidity of
the surrounding ambient air there will be several degrees of
temperature drop due to the latent heat of evaporation. The
increase of density will lead to a rapid fall of the cooled air
which will spread out over the sea surface like a spilt liquid
until it has been warmed by the large area of contact with sea.
You can show this fall and dispersion very cheaply with a pond
fogger, £19.99 from Maplin. We want this dispersion because a
low dose over a large area is more effective than a high point dose.
Forster seems to be ignoring completely the idea of coded
modulation of CCN concentration in climate models even though the
satisfactory operation was demonstrated by Ben Parkes doing a PhD
in Forster's own Department at Leeds in 2012. This might allow us
to get an everywhere-to-everywhere transfer function of marine
cloud brightening and win-win result with more rain in dry places
and less in wet. The high frequency response means that we can
give a tactical spraying based local day-to-day observations.
It is a puzzle that the Parkes thesis has, yet again, vanished
from the Leeds University website.
Stephen
Emeritus Professor of Engineering Design. School of Engineering.
University of Edinburgh. Mayfield Road. Edinburgh EH9 3JL.
Scotland [email protected] <mailto:[email protected]> Tel +44
(0)131 650 5704 <tel:%2B44%20%280%29131%20650%205704> Cell 07795
203 195 WWW.see.ed.ac.uk/~shs <http://WWW.see.ed.ac.uk/%7Eshs>
YouTube Jamie Taylor Power for Change
On 28/12/2014 20:03, Andrew Lockley wrote:
Integrated Assessment of Geoengineering
Proposals…:http://youtu.be/FFjzzfCLCqw <http://youtu.be/FFjzzfCLCqw>
Poster's note : I personally have found it very difficult to
access and appraise the science behind the IAGP project. Despite
this, a vast amount of publicity has been obtained for the
project. I think the IAGP team could do more to encourage early,
in-depth access to their material, particularly bearing in mind
the huge media interest.
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