The present work was undertaken to evaluate the effects of slight line inclinations ({dollar}\theta\ \le\ 18\sp\circ{dollar} from the vertical) on the hydrodynamics of non-slugging dense phase upwards cocurrent gas-solids flows. Previous research and operating experience has focused on the dilute phase flow regime where ({dollar}\rm\partial(\partial P/\partial z)\rbrack/\partial U\sb{lcub}g{rcub}\ \u3e\ 0{dollar}. This thesis is restricted to the regime where ({dollar}\partial(\partial P/\partial z)\rbrack/\partial U\sb{lcub}g{rcub}\ \u3c\ 0{dollar} and for which refluxing of particles, without slug flow, dominates in the flow patterns.;Experiments were conducted with 197 {dollar}\mu{dollar}m sand particles and 441 {dollar}\mu{dollar}m glass beads in a 3.2 cm diameter Plexiglas tube. Use of the two particle sizes (Geldart Group B powders) enabled the characterization of different systems: the first with sand, showed a slow transition from the non-slugging dense (reflux flows) to the dense slugging regime; the other using glass beads, collapsed abruptly into a slugging flow with a slight decrease of gas velocity near the choking point.;The pressure gradient and solids holdup ({dollar}\alpha{dollar}) in the fully developed riser test section increased linearly with both the solids flux (50-300 kg/m{dollar}\sp2{dollar}s) and solids mass loading ratio (5-40), but decreased with the gas velocity for both sand (4.5-12 m/s) and glass beads (6-16 m/s). The solids-wall frictional pressure gradient contributed between {dollar}-{dollar}25% and 25% of the total gradient, and was negative whenever there was solids refluxing at the wall. A 2-parameter semi-empirical model was developed which was successfully employed for the correlation of negative solids-wall friction factors.;A lifting efficiency of 2-phase transport in oblique risers ({dollar}\eta{dollar}) was defined, which decreased with {dollar}\theta{dollar}, from 75% (of the theoretical single particle lifting efficiency in dilute phase transport), to 35-45% for {dollar}\theta\ \ge\ 11\sp\circ{dollar}. The decrease of {dollar}\eta{dollar} was attributed to extensive refluxing near choking. A previous study has shown that {dollar}\eta \u3c 10\%{dollar} for dilute phase transport.;The dominant frequency from the power spectrum of the pressure gradient time series was 5 Hz for sand and 3 Hz for glass beads. The pressure gradient time series could be stochastically modelled with a linear stationary ARIMA model of the form AR(2) or AR(3)
