An electrostatic suspension method for testing spark breakdown, ignition, and quenching of powders

An innovative electrostatic suspension method, referred to as EPS (electrostatic particulate suspension), is used for testing the spark breakdown, ignition, and quenching characteristics of small volume powder suspensions. A highly uniform steady-state suspension is generated between high voltage de parallel plate electrodes that can be ignited with a spark discharge from a high-speed, moving electrode or by pulse discharge from a Ruby or YAG laser. The design methodology and characteristic suspension times are reviewed. Bulk powder resistivities < 10(9) Omega m are recommended for generating a suspension. With cohesive powders such as fine coal it may be necessary to augment the EPS method with acoustic vibration. To demonstrate the utility of the EPS method, representative data for coal, aluminum, and copper powders are presented. Specific results are discussed in the following studies: (I) Spark breakdown of a (inert) copper powder in air, (II) Minimum ignition energy (MIE) of aluminium-oxygen-nitrogen/carbon dioxide mixtures at near-quenching conditions, (III) Wall quenching of coal-air and aluminium-air mixtures, and (IV) Inert particle quenching with copper particle-propane-air mixtures.