  Iron dust counter-flow flames have been studied with the low-Mach-number
combustion approximation. The model considers full coupling between the two
phases, including particle/droplet drag. The dispersed phase flow strain
relations are derived under the assumption of low Reynolds number conditions.
The importance of solving a particle flow strain model is demonstrated by
comparing three different models: a free unstrained flame, a counter-flow flame
where particle flow strain is assumed equal to gas flow strain and one case in
which the particle flow strain is solved. All three cases showed preferential
diffusion effects, due to the lack of diffusion of iron in the fuel mixture,
e.g. DFe,m = 0. The preferential diffusion effect causes a peak in the fuel
equivalence ratio in the preheat zone. At the burned side, the combined effect
of strain and preferential diffusion showed a decrease in fuel equivalence
ratio. Inertia effects, which are only included in the resolved particle flow
strain case, counteract this effect and result in an increase of the fuel
equivalence ratio at the burned side. A laminar flame speed analysis is
performed and a recommendation is given on how to experimentally determine the
flame speed in a counter-flow set-up.
