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| Abstract No.: |
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Scheduled at:
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Wednesday, May 05, 2010, Moor Room 11:00 AM
Modeling and Simulation 2
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| Title: |
Effect of using liquid feedstock in a high pressure cold spray nozzle
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| Authors: |
Ali Dolatabadi* / Concordia University, Canada
Ehsan Farvardin / Concordia University, Canada
Oliver Stier/ Siemens AG, Germany
Volkmar Luethen/ Siemens AG, Germany
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| Abstract: |
This study investigates the effect of water injection in the high pressure chamber of a cold spray nozzle. In cold spray nozzles, powder agglomeration as well as the ability to penetrate through the bow shock on the substrate restrict the size of coating powders to be few microns and larger. Water injection can be used as a carrier of nano-particles, and then the consequential droplets due to atomization and evaporation will determine the size of the micron-sized nano-particle agglomerates. Therefore, understanding of simultaneous water breakup mechanism and evaporation and their effects on the main gas flow stream is essential for nano-powder injection and deposition using a cold spray nozzle. A de Laval nozzle geometry with the constant back pressure of 40 bar and temperature of 873K is modeled numerically using Reynolds Stress Model coupled equations. Water spray with droplet size of 10-100 microns is modeled using Rosin-Rammler size distribution. The spray is injected at different locations in the high pressure chamber. The two-phase flow of gas-liquid is modeled using an unsteady discrete phase mass source with two-way coupled with the main gas flow and TAB break up model. Upon injection, the droplets in the water spray break up and evaporate while travelling through the nozzle due to momentum and heat transfer from the gas flow. Evaporation of various droplet sizes with and without the TAB break up model are investigated. In addition, various water flow rates were modeled to determine the optimum gas to liquid flow ratio (GLR) which guarantees the sonic flow at the nozzle throat. Therefore, when water injection results in mostly evaporative droplets before the nozzle throat, it can be used as a carrier of nano-particles in cold spray nozzles. This mechanism can facilitates injection of nano-partilces and deposition of micron-sized nano-particle agglomerates to produce nano-structured coatings.
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