Modeling of Heat Flow and Solidification during Spray Deposition Process

The solidification behavior of droplets as well as spray-deposit of Al-4.5 wt% Cu alloy is simulated by modeling based on heat flow analysis. The model incorporates droplet dynamics and their thermal states during atomization process. The resultant spray enthalpy is used to analyze heat flow during solidification of the spray deposit. The effect of process variables like atomization pressure, melt superheat and nozzle to substrate distance on the solid fraction and enthalpy of the spray is analyzed. The results of modeling are compared with the experimentally determined thermal profile of the spray deposit. The results indicate that the cooling rate for a wide size range of droplets varies from 103-105 Ks-1 in contrast to a slow cooling rate of 1 to 10 Ks1 of the spray deposit. Empirical correlation between cooling rate of the spray deposit and the grain size has been established. It is inferred that cooling rate is not the sole determining factor in controlling grain size of the deposit during spray deposition process. h Convective heat transfer coefficient at droplet gasinterface W m-2 K-1 htop Heat transfer coefficient at deposition surface W m-2 K-1 hbot Heat transfer coefficient at substrate-deposit interface W m-2 K-1 Hd Enthalpy of droplet per unit mass J kg-1 Hd Hf (CL-CS)(TL-Td) J kg -1 Hf Latent heat of fusion per unit mass J kg-1 H Enthalpy in the deposit per unit mass J kg-1 HSPRAY Spray enthalpy per unit mass J kg -1 k Average thermal conductivity of the alloy W m-1 K-1 kg Thermal conductivity of gas W m -1 K-1