Probe effects on the local gas holdup conditions in a fluidized bed

Abstract

Fluidized beds are found in the energy production industry, and knowing their hydrodynamic conditions, such as local gas holdup or volumetric gas fraction, is important for effective operation. Local measurement probes are commonly used to measure local gas holdup. Although the probes are typically as small as possible to mitigate their influence on the local conditions, the invasive nature of this measurement technique has the potential to alter the fluidized bed behavior. This study used a noninvasive measurement technique, X-ray computed tomography (CT) imaging, to determine the local time-average gas holdup everywhere within a 10.2 cm diameter fluidized bed filled with 500-600 m glass beads in which simulated probes were inserted. Three different simulated probe tips (pointed, rounded, and flat) and two different orientations (horizontal and vertical) were investigated at four different bed heights and two different fluidization velocities. The results show increases in local time-average gas holdup when the probes were present, but the scale of the effects was dependent upon the height at which the probes were placed; the lower the probe within the fluidized bed, the larger the local effects. The shape of the probe tip did not show any differences in the local gas holdup. On the

Generation and evaluation of an artificial optical signal based on X-ray measurements for bubble characterization in fluidized beds with vertical internals

“…Due to their intrusive character, it cannot be excluded that the flow pattern gets disturbed by the sensor. To deal with this issue, the influence of intrusive probes on the flow structure in fluidized bed systems is investigated in Bai et al (2010) , Maurer et al (2015a) , Tebianian et al (2015Tebianian et al ( ,2016 , Whitemarsh et al (2016) . The possibility to design an optical sensor in a way that the flow structure is almost not influenced by the intrusive character of the sensor is shown in Maurer (2015) , Maurer et al (2015a) , and Whitemarsh et al (2016) .…”

Characterization of multiphase flows integrating X-ray imaging and virtual reality

“…This opaque nature limits any optical measurements to the surface of the flow (van Ommen and . Furthermore, many common flow sensors, such as pitot tubes and hot wire anemometers, intrude into the flow creating the potential for the sensor to change the flow characteristics (Boyer et al, 2002;Whitemarsh et al, 2016). The way around these limitations is to use noninvasive measurement methods.…”