Experimental investigation on the fully developed pipe flow of dilute gas-solids suspensions

The prediction of flow regimes of gas-solids flows is one of the most important and challenging problems for optimal operation and control of pneumatic conveying systems. Visual observations have been widely used to identify and classify the flow patterns of gas-solids flows. But due to the subjectivity and arbitrariness of direct visual observations and the fact that in most industrial applications the pipelines are not transparent, new approaches are required.; A diagnostic technique to predict the flow patterns of fully developed flows of dilute gas-solids suspensions inside horizontal and vertical straight pipes has been developed. The gas-solids suspension generates its own characteristic fluctuations as it flows inside the pipe, which is like a "finger print" of each flow regime. The analysis in time, frequency, and amplitude domain of the absolute and differential wall normal stress signals includes statistical properties, probability density function, power spectral density function, correlation coefficients, and rescaled range analysis. Wall normal stress fluctuations, which are stochastic and random in nature, appear to be the most promising technique in flow-regime diagnosis because of its non-intrusive nature.; Successful design and operation of pneumatic conveying systems depends upon predicting the minimum conveying velocity at which the solids may be transported steadily through the pipeline. Both pickup and entrainment mechanisms of solid particles have been also examined in relation to the prediction of the minimum conveying velocity required in horizontal and vertical pneumatic conveying systems that operate in dilute-phase. Keeping the mean gas velocity above minimum conveying velocity ensures no deposition nor fall of solids in the horizontal and vertical pipes.; Several experiments have been carried out to determine pickup, saltation, entrainment and choking velocity of a wide variety of materials using different techniques. The use of dimensional analysis and experimental findings led to simple correlations useful to predict pickup and saltation velocity of coarse particles (above 100 {dollar}mu{dollar}m). Noteworthy is the existence of a pipe diameter effect on the pickup mechanism, important result to be considered in scale-up procedures. For the first time in pneumatic transport pickup and saltation mechanisms of solid particles in horizontal pipelines have been related with the aid of a novel diagram. These ideas open new avenues to fully understand the complex behavior of particles conveyed pneumatically through pipelines.