Influence of Particles on Fluid Turbulence in Pipe and Diffuser Gas‐Solids Flow

Abstract

The influence of glass particles with different Reynolds numbers Re P = ½u±u P ½d P r/g on axial and radial gas fluctuations as well as on Reynolds stresses was investigated for pipe and diffuser (continuous pipe expansion) gas-solids flow. Measurements were carried out using phase-Doppler anemometry distinguishing between velocity signals of the solid and fluid phase due to particle or tracer size. In fully developed pipe flow small particles (Re P = 60) damp turbulence but with increasing Re P vortex shedding behind the particles reduces attenuation and finally leads to turbulence enhancement. Behind the diffuser particles are decelerated and cause a steeper velocity gradient and, thus, an increase in turbulence. The measured data are compared to CFD calculations investigating Reynolds stress model and k-e model for the description of turbulence. Using small particles good agreement is achieved considering the momentum transfer between the phases. For larger particles the modeling of vortex shedding by turbulent particle source terms is needed for a satisfactory prediction.

Vibration sensor for particle concentration measurement in pneumatic pipeline flows

“…The Kolmogorov scale is the characteristic scale at which eddies decay due to viscous dissipation, the Taylor microscale is characteristic of the inertial range eddies, and the integral length scale is characteristic of the large, energy-containing eddies. Turbulence quantities for single and two-phase flows are measured by Tsuji et al [37] and Bohnet and Triesch [38] for pipe flow with a similar Reynolds number and diameter to that reported in the current experiments. These studies found that the ratio u 0 /U varies between 0.05 and 0.1 for pipe turbulence, giving on average q ∼ = 0.008U 2 .…”

“…The distinction between the two is determined by the ratio of the particle diameter to the turbulence integral length scale , such that for d/ < 0.1 the turbulence is attenuated by the particles [40]. A review of recent research on effects of particles on turbulent pipe flow is given by Bohnet and Triesch [38]. Assuming that the particle relative velocity is of the same order of magnitude as the average air velocity, the particle Reynolds number varies from about 40 to 630 for the current experiments, and the ratio d/ varies between 0.023 and 0.11.…”

Modeling Two-Phase Gas-Solid Flow in Axisymmetric Diffusers using Cut Cell Technique: An Eulerian-Eulerian Approach

“…The code was validated with different experiments [41,44,58].This validation ensure how the code can be accurate for the experiment data. The geometry of the diffusers have many variables such as inlet radius, outlet radius, length of diffuser and angles.…”

“…For the particles diameters, we use the same parameters in experiment [41], the angle of diffuser 6°…”

“…Lighter particle movement was found to result in higher pressure recovery. Additionally, it was discovered that pressure recovery increased with an increase in the inlet slip velocity ratio [36][37][38][39][40][41][42].Further research [43] examined different area ratios and identified two conflicting effects on pressure recovery. Up to a critical area ratio value (9.97), pressure recovery increased, but it decreased beyond that point.…”