Results from Effervescent Spray Atomization for MCB and a preliminary Proposal for Field Experiments

Abstract:

We report on the preliminary results of spraying saltwater using a variant of effervescent spray atomization (ESA), for the purpose of producing salt nuclei for Marine Cloud Brightening (MCB). ESA is a well known industrial method, where air and water are mixed, to produce a choked two phase flow in a nozzle. The choked flow leaves a pressure residue at the nozzle exit which produces very efficient atomization. The resulting measured salt aerosol appears to be smaller than what is expected from current ESA theories. As measured with standard and well calibrated standard aerosol instruments, the distribution of the salt nuclei has an approximately log normal distribution with mean diameter of 60-80 nm and a GSD close to 2. Measured by electrostatic precipitation of the aerosol on a Si wafer and SEM observation, the median diameter is almost 1.5-2x as large, and this discrepancy has to date not been fully resolved.

While the observed median diameter is perhaps somewhat on the low side for efficient conversion in the clouds, this nuclei distribution should be useful for preliminary field experiments. Assuming this distribution, with very simple means, a single small nozzle 150 um in diameter produces 5.3 x10¹² nuclei/sec. A few hundred nozzles would be sufficient to produce 10¹⁵ nuclei/sec, requiring a power of only 25 kW, although errors on the tail end of the distribution could easily double this figure. To lift the spray, we envision the nozzles easily integrated in standard snowmaking machines, which are estimated by their manufactures to lift the nuclei from 50-100 m in the air, requiring another 20 kW of power. In cooperation with and under the scientific guidance of the U. of Washington, we propose to develop a set of staggered MCB experimental tests in Central California, first on land, and subsequently over the ocean. While this method may not be the ultimate one desired for full deployment (If ever), its simplicity, low cost and ease of deployment would seem to make it a great candidate for initial field experiments.