Producing and properties of zinc dust flames

ABSTRACT

Premixed and diffusion dust flames of zinc particles dispersed in the gas (particle size d₁₀ = 4.4 µm; metal mass concentration C_f = 0.40 kg/m³) with propane additives of molar concentration C_g = (2–8)% are studied. Two different burning modes of zinc gas suspension are found. The conditions of formation of these modes depend on the burning temperature of such systems. Two-zone structure of the flame—a zinc evaporation and combustion zone and a zinc vapor condensation zone—is observed. Its origin is explained by the unique specificity of a zinc burning process in contrast to other metals—zinc vapor does not react with oxygen in the gaseous phase, therefore, ZnO molecules and zinc oxide clusters are absent in the combustion zone. The morphology and dispersive composition of the condensed zinc oxide also depend on the gas suspension’s burning mode. In a low-temperature burning mode of zinc dust, the combustion products mostly contain tetrapods, needles and nanorods of zinc oxide. At higher temperatures of the flame, zinc oxide nanorods prevail.

KEYWORDS:

• Zinc Dust Flames
• Flame Structure
• Particle Burning Mode
• Combustion Products
• Oxide Particles Morphology
• Gas-Dispersed Synthesis

Nomenclature

d	=	Particle diameter, µm
Cf	=	Metal mass concentration, kg/m3
Cg	=	Propane molar concentration
Tad	=	Adiabatic burning temperature, K
Ti	=	Ignition temperature, K
Tυ	=	Boiling temperature, K
	=	Stoichiometric concentration of zinc, kg/m3
	=	Lean concentration limit (LCL) of the flame propagation, kg/m3
	=	Normal flame velocity, m/s
W	=	Volumetric rate of carrier gas, m3/s

Greek letters

λ	=	Wavelength, µm
τ	=	Burning time, s
α	=	Oxygen excess factor