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Journal of Materials Science

, Volume 43, Issue 17, pp 5930–5941 | Cite as

Droplet cooling in atomization sprays

  • Arvind Prasad
  • Hani Henein
Article

Abstract

Transport between droplets/particles and a gas phase plays an important role in numerous material processing operations. These include rapid solidification operations such as gas atomization and spray forming, as well as chemical systems such as flash furnaces. Chemical reaction rates and solidification are dependent on the rate of gas-particle or gas-droplet transport mechanisms. These gas-based processes are difficult to analyze due to their complexity which include particle and droplet distribution and the flow in a gas field having variations in temperature and velocity both in the jet cross-section and in the axial distance away from the jet source. Thus to study and properly identify the important variables in transport, these gas and droplet variations must be eliminated or controlled. This is done in this work using models based on a single fluid atomization system. Using a heat transport model (referred to as thermal model) validated using single fluid atomization of molten droplets and a microsegregation model, the effect of process variables on heat losses from droplets was examined. In this work, the effect of type of gas, droplet size, gas temperature, gas-droplet relative velocity on the heat transport from AA6061 droplets was examined. It is shown that for a given gas type, the most critical process variable is the gas temperature particularly as affected by two-way thermal coupling and the droplet size. The results are generalized and applied to explain the difference in droplet cooling rate from different atomization processes.

Keywords

Cool Rate Droplet Size Thermal Model Droplet Temperature Freezing Range 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

List of symbols

A

Surface area of the droplet

Cp

Heat capacity of the droplet

Cpm

Integral heat capacity

fs

Fraction solid

Fo*

Modified Fourier number for droplet-gas thermal transport

htotal

Total heat transfer coefficient

hconv

Convective heat transfer coefficient

H

Droplet enthalpy

ks

Gas thermal conductivity

ΔLatent

Solidification enthalpy

m and (m + 1)

Indices for the numerical calculation

Nu

Droplet Nusselt number

Pr

Prandltl number

Re

Droplet Reynolds number

t

Time

t*

Reference time

tf

Solidification time

Tliq

Liquidus temperature of AA6061

Tm

Droplet temperature during solidification

Tnuc

Nucleation temperature for simulation

Tsol

Solidus temperature of AA6061

Tu

User-defined primary undercooled temperature

T

Gas temperature in the free stream

V

Volume of the droplet

ρ

Droplet density

μbulk

Gas viscosities at the temperature of the free flow gas

μsurf

Gas viscosities at the temperature of the droplet

θ

Dimensionless temperature

τ

Dimensionless time

Notes

Acknowledgements

The author wishes to acknowledge funding for this work from the Natural Science and Engineering Research Council of Canada (NSERC) and from the Canada Council for the Arts for award of a Killam Research Fellowship. The contribution of Karine Navell in making the cell spacing measurements presented in Fig. 12 are also acknowledged.

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Copyright information

© Springer Science+Business Media, LLC 2008

Authors and Affiliations

  1. 1.Department of Chemical and Materials EngineeringUniversity of AlbertaEdmontonCanada

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