Gas-Substrate Heat Exchange During Cold-Gas Dynamic Spraying

In this study, the Nusselt numbers of impinging compressible fluid jets originating from a cold-gas dynamic spraying nozzle were determined. A low-pressure cold-gas dynamic spraying unit was used to generate a jet of hot compressed nitrogen that impinged upon flat substrates. Computer codes based on a finite differences method were used to solve the governing 3-D temperature distribution equation for the substrate to produce a non-dimensional relationship between the Nusselt number and the radius of the impinging fluid jet. It was found that the Nusselt number decreased as the non-dimensional radius of the jet from the stagnation point increased. It was found further that for small values of the Biot number, a simplified 2-D approximation of the substrate temperature distribution produced substrate surface temperature profiles that were in close agreement with that which was determined from the more complex 3-D temperature distribution model.