Experimental study of transition flow in packed beds of spheres with different particle sizes based on electrochemical microelectrodes measurement

In the present study, the transition flow in the packed beds of spheres with different particle sizes is experimentally investigated by using electrochemical method. The microelectrodes are inserted into the beds to test the local flow at the pore level with particle Reynolds number (Re) ranging from 20 to 1100. Both the variations of Power Spectrum Density (PSD) and Fluctuating Rate (FR) are carefully analyzed to obtain different flow regions in the packed beds, including laminar, transition and turbulent flow regions. Firstly, it is revealed that, as Reynolds number increases, the high frequency ratios of the current signal increases, and the slope of the PSD curve decreases and tends to reach at -5/3. When the slope of the PSD curve decreases to -5/3, it would become turbulent flow in the packed beds. Secondly, it is found that, the laminar flow in the packed beds would end at Re ≈ 100, while the turbulent flow would start at 230 < Re < 400. Therefore, the transition flow region in the packed beds of present study would be from Re ≈ 100 to 230 < Re < 400.