Sampling and characterisation of particles in flowing gases

This paper is concerned with some aspects of the isokinetic sampling which is a well established means of obtaining representative samples of dust from flowing dust-laden gases. It is based upon aspiration of a sample of the gas from the main stream through a sampling probe (with the sampling nozzle pointing towards the direction of flow) so that the velocity of the gas into the nozzle is identical with the undisturbed local stream velocity. The problem of possible stratification of particles across the duct is overcome by sampling at a number of points in the cross-section. It is demonstrated that isokinetic sampling is a difficult operation, particularly in those applications where extreme sampling conditions are encountered. A recent survey of sampling practices in the chemical industry in the United Kingdom revealed a need for further work, particularly with respect to sampling equipment available. A few contributions by the School of Powder Technology to this field to date are reviewed in this report.