Gas Cooling and Conditioning Guide - SGN Tekniikka Oy

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Spray Testing and ModelingPredetermine performanceUnderstanding drop size in gas cooling applications is criticalMany problems result from premature or incomplete evaporation. If dropsevaporate too quickly, the desired level of absorption may not occur andupstream/downstream equipment may be less efficient or damaged. If dropsdon’t evaporate quickly enough, wetting will occur, entrained liquid mayresult and dust can accumulate in the duct or tower and obstruct gas flow.In many cases, running sophisticated gas cooling calculations providesenough information to determine the number of nozzles required and howthey need to be positioned. However, with complicated gas flows, unusualoperating conditions or atypical duct work or tower shape, gas coolingcalculations alone may not tell the entire story. This is when we headto our spray laboratories and conduct spray characterization studiesto determine dwell time simulating actual operating conditions.Typically these studies include:• Drop size testing to determine the optimal drop sizeand drop size distribution• Determination of gas velocity and density and theresulting impact on drop sizeSpray Analysis and Research Services, a service of Spraying Systems Co.,is our research and testing group that operates the most fully equippedspray laboratory in the world. Phase Doppler Particle Analyzers, LaserImaging, Particle/Image Analyzers and Laser Diffraction Analyzers areamong the instruments we use to measure drop size.Phase Doppler AnalyzerThe Phase Doppler method is basedon the principles of light scatteringinterferometry. These flux samplinginstruments are most effective inmeasuring the drop size and velocityof medium to large sprays.Drop size data: what you need to knowDrop size is the critical consideration in evaporative cooling.It impacts virtually every aspect of gas cooling and can havea significant impact on cooling effectiveness.Drop size refers to the size of the individual spray drops thatcomprise a nozzle's spray pattern. Each spray provides arange of drop sizes. This range is the drop size distribution.Actual drop sizesOne inch = 25,400 µm One millimeter = 1,000 µmKey drop size definitionsD max : This is the maximum drop size by volume presentin the spray. The diameter is also used when completeevaporation of the spray is required.D 32 – Sauter Mean Diameter (SMD): This expresses thefineness of a spray in terms of the surface area produced bythe spray. The SMD is the diameter of a drop having the samevolume to surface area ratio as the total volume of all thedrops to the total surface area of all the drops.500 µm 1,200 µm 5,500 µmµm – micrometersD V0.9 : This is the value where 90% of the total volume ofliquid sprayed is made up of drops with diameters smalleror equal to this value.1.800.95.SPRAY | Intl. 1.630.665.5000 | www.spray.com
Computational Fluid Dynamics(CFD) and gas conditioningCFD is the science of predicting:• Fluid flow• Heat transfer• Mass transfer• Chemical reactionsCFD uses numerical methods and algorithms to solveand analyze problems involving fluid flows. Sophisticatedsoftware performs the millions of calculations required tosimulate the interaction of fluids and gases with relatedphysical phenomena.Some spray operations cannot be replicated in our labs.While we can spray solutions other than water, there aresome gases and liquids that are not safe to use duringtesting. Plus, it is not always feasible to reproduce somemixing conditions and chemical reactions. While we oftenbuild enclosures and/or spray headers to simulate actualspraying conditions, it is not practical to construct somestructures and spray environments. That’s when we relyon our extensive library of proprietary spray characterizationdata and CFD.Spray Droplet ConcentrationLOWThis illustration, created using CFD, showsspray droplet concentration at variouslocations in a gas conditioning tower.HIGHWe use CFD to predict:• Liquid and gas flow in scrubbers,towers and ducts• Internal flow characteristics in spray nozzles• Gas and liquid mixing in dual-fluid nozzlesCFD models illustrate flow patterns, velocity,temperature, gas/liquid distributions, droplettrajectories, pressures within the entiresystem and impact forces and stresscaused by liquid flow.1.800.95.SPRAY | Intl. 1.630.665.5000 | www.spray.com
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