Abstract:In this work a novel measurement technique for pseudo-2D fluidised beds is developed. The objective is to give an estimation of the overall frictional force between the solids and the front and rear walls of the bed. For doing this, the measured pressure signal in the bed is processed in combination with the solids distribution (i.e. centre of mass position, velocity and acceleration) obtained from digital image analysis of the optically accessible front view of the bed. This is performed by acquiring the pressure signal in the bed simultaneously to the digital images. Both the pressure and the digital images are connected through a simple force balance in the bed, and a particle-wall interaction coefficient is obtained assuming that the overall frictional force is proportional to the centre of mass velocity. The particle-wall interaction coefficient found using this technique is of the order of 40-120 kg/m 2 s in the bed tested, and the standard deviation of the frictional forces reaches more than 70% of the weight of the bed. Therefore, the results indicate that the contribution of the particle-to-wall friction on the fluctuation of the pressure drop in a pseudo-2D bed is not negligible.

Abstract:A statistical method based on approximation of the cumulative energy distribution by Student's t-distribution is proposed for the unbiased frequency domain division. The proposed method fixes the number of samples needed to estimate the power spectrum and its corresponding cumulative energy distribution using the Kolmogorov-Smirnov test. The reliability of the method to divide the frequency domain was shown for different fluidization velocities by changing the bed aspect ratio and using different pressure probes. Water-induced defluidization tests were conducted to illustrate the use of wide band energy as a monitoring tool. The Student's t-distribution results are compared with an analysis performed using the traditional visual inspection method. The energy of the power spectrum contained within the frequency regions obtained by the visual method is not able to detect changes in the bed aspect ratio or the start of the rotating distributor. No meaningful differences could be observed in the frequency regions using different quality pressure sensors because the approach using Student's t-distribution focuses on the sharp energy increase produced by the primary frequencies of the power spectrum. The sensitivity exhibited by the proposed frequency division approach for the range of fluidization conditions tested improves the use of the energy contained in these regions as a diagnostic tool in fluidized bed processes.

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A. (2016). Development of an empirical wallfriction model for 2D simulations of pseudo-2D bubbling fluidized beds. Advanced Powder Technology, 27(2), pp. 521-530.

Experimental study on the characteristic mixing time of solids and its link with the lateral dispersion coefficient in bubbling fluidized beds, Chemical Engineering