Twin-fluid atomizers are widely used for spray-drying application. The suspension to be dried can be atomized very efficiently if the atomizer is operated at critical conditions. The three-phase flow containing solids, gas and liquid is accelerated inside the atomizer due to a pressure gradient. If the upstream pressure is sufficiently high, a maximum possible mass flow rate is achieved. This operating condition is called “critical”. The velocity of the three-phase flow and the flow pattern in the exit cross section has a major impact on the jet break-up and thus on the spray characteristics. In this experimental work the flow velocity and flow pattern inside the nozzle of the atomizer is measured. A laser-sensor is used to determine the flow velocity via cross-correlation at different operating conditions and positions inside the nozzle. The same sensor is used to measure the flow pattern by analyzing the time dependent laser light absorption of of the flow. The influence of various compositions of the suspension concerning gas volume flow rate and particle concentration on the measured velocities and flow patterns are derived. Higher gas volume flow rates increase the velocities and higher particle concentration have a decreasing influence. For a pure gas-liquid flow the obtained results are in good agreement with a theoretical model. In the exit cross-section plug flow and annular flow is observed depending on the gas volume flow fraction. The particles in the suspension have no significant influence on the flow pattern.

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