Hello All, I agree with Stephen's comment about the superior accuracy of Alvia's account.
An additional point though, is that the figure Alvia gives for the daily amount of spray required to hold the Earth's temperature constant applies to the case in which the CO2 concentration has doubled. The spray rate would be one or two orders of magnitude less than this for an estimated few decades. Cheers, John Quoting "Stephen Salter" <[EMAIL PROTECTED]>: > > Hi All > > Alvia's account of the Discovery Channel program is much more accurate > than their account of our work. > > At the time I was planning to use a jet pressure of 40 MPa which gives a > nozzle velocity of 280 metres per sec or double this for jet to jet > impact. This is less than 2500 mph. The pumps to do this with salt water > would have used rubber tubes squeezed by an external oil pressure > > The jet impact demonstration used fresh water rather than salt water > because, at the last minute, the pump owner balked at using salt water. > The sub-micron drops generated would have evaporated before getting to > the measuring instrument and so the demonstration was pointless because > there would be no residues. Even if they had used salt the nozzle > diameter and clearing pressure were large enough to remove all problems > about blockage. > > The present spray mechanism uses much lower pressure, only 0.7 MPa and > banks of billions of submicron nozzles etched in silicon wafers. We > have assurances from the filter industry that raw sea water can be > filtered well enough to prevent blockage. We now do have a nozzle dryout > problem and so will keep the wafer drenched in desalinated water when > not in use. > > All the work on the conversion of Cloudia to rotor drive was done by > John Marples. > > Stephen > > Emeritus Professor of Engineering Design > School of Engineering and Electronics > University of Edinburgh > Mayfield Road > Edinburgh EH9 3JL > Scotland > tel +44 131 650 5704 > fax +44 131 650 5702 > Mobile 07795 203 195 > [EMAIL PROTECTED] > http://www.see.ed.ac.uk/~shs > > > > Alvia Gaskill wrote: >> Resuming my review of the Discovery Channel Project Earth series with >> the episode called Brighter World, where the Discovery Channel team >> attempts to help John Latham and Stephen Salter realize their dream of >> building a fleet of 1500 cloud brightness enhancing remote control >> carbon neutral vessels. That shouldn't be any problem. >> >> As before, I will summarize the program and then note any additional >> information found at the Discovery Channel website and from other sources. >> >> Brighter World: Part 1 >> >> Clouds consist of tiny water droplets that reflect sunlight back into >> space. According to John Latham, half of the sunlight striking >> oceanic clouds is returned to space. Thus, physicist Latham and >> engineer Stephen Salter think that the Earth's temperature can be >> returned to normal (and what is that?) by increasing the reflectivity >> of clouds by 10%. >> >> This can be done, they say, by injecting 3.8 million tons of saltwater >> particles per day into the marine atmosphere using a fleet of up to >> 1500 remote controlled ships. >> >> These ships would spray out seawater particles beneath existing clouds >> with a fraction of the particles drifting their way up into the >> clouds. The saltwater particles act to redistribute the moisture, >> making much smaller water droplets than existed before. This >> increases the overall reflective surface area of the cloud water and >> reflects more sunlight back into space. >> >> To assist in developing the cloud ships, the three Discovery Channel >> experts that worked on previous episodes involving covering Greenland >> and aerial reforestation are once again called upon. CEO Kevin >> O'Leary will work on the logistics (spoiler alert: this time there >> are no helicopters, but there are airplanes and boats!), and >> eco-engineer Jennifer Languell will work on the design of the >> prototype cloud ship, while physicist Basil Singer will conduct scaled >> down cloud experiments to try to understand the physics of cloud >> whitening in order to design a way to do it. >> >> There are two primary objectives. Kevin and Jennifer will try to find >> the best type of ship to seed clouds with saltwater particles from sea >> level, while Basil will (1) design an experiment to show that man-made >> particles will rise high enough to brighten existing clouds and (2) >> determine the ideal size and concentration of these man-made particles. >> >> To begin the learning process, Basil wants to study the composition of >> an existing cloud. He travels to the waters off S. Africa where the >> type clouds of interest are said to commonly form. They are called >> marine stratocumulus and form in a layer 200-400 feet above the sea >> surface. They are considered ideal candidates for man-made whitening >> because they float over an endless source of saltwater particles. >> >> (Beats me why they literally had to go to the ends of the Earth to >> find marine stratocumulus. I thought these clouds were just about >> everywhere.) >> >> Basil flies through some of these clouds in an airplane equipped with >> a real-time laser particle counter in order to measure the size and >> number of the water droplets in the clouds so that he can determine >> how many additional droplets will need to be created to achieve the >> brightening effect. >> >> He finds that there are 500,000 water droplets per square inch in the >> clouds. To increase the reflectivity by 10%, however, requires four >> times more particles, not 10% more due to their small size. These >> particles must be no larger than 1/1600 the size of a grain of sand >> (not certain about that ratio-audio was unclear). >> >> Marine stratocumulus clouds, unlike other cumulus clouds that can rise >> to 6000 feet and produce rain as the cloud begins to fall apart, >> remain low, flat and stable, making them good sun reflectors. >> >> Latham says that while computer models indicate increasing >> cloud reflectivity is possible, no one has been able to produce a >> means of generating the spray of saltwater necessary to produce the >> proper size particles. >> >> The spray system must be able to atomize the water droplets to >> 1/25,000 of inch in diameter vs. 1/16 of an inch for a typical raindrop. >> >> In nature, only the ocean can produce such small particles of >> seawater. Latham says that the process of a wave breaking on the >> shore pushes air under the water, forming air bubbles and droplets >> about the size needed for cloud brighteness enhancement. >> >> Basil thinks he can duplicate the wave breaking process by jet >> impingement using a water cannon. This is a high powered pressure >> washer used to blast debris off the hulls of ships. He runs two such >> cannons with the flow of each directed against the other (the >> impingement) to see what size particles are produced. If the process >> works, it could be adapted for used on the cloud ships. >> >> The water cannons spray seawater through the nozzles at 2500 mph, >> generating enough power to cut through a 4-inch piece of wood in seconds. >> >> To see if the nozzle experiment produces small enough particles, >> another laser particle counter is used to measure them. If the >> experiment is successful, the collision of the two jets at a combined >> speed of 5000 mph should produce droplets less than 1 micron in >> diameter, the desired size. >> >> However, the test mostly produced particles of 40-50 microns, too >> heavy to be lifted by winds into the marine cloud layer. >> >> (It was my understanding that these water cannons use freshwater to >> keep the salts from blocking the nozzles. Would the use of freshwater >> make any difference in the size particles produced?) >> >> END PART 1 of My Review >> >> >> > > > -- > The University of Edinburgh is a charitable body, registered in > Scotland, with registration number SC005336. > > > > > --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "geoengineering" group. 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