Among all techniques for parameter estimation

the leastsquares analysis in the time domain is the most reliable

but the computational labor is often considered to be prohibitive. In this paper the authors have employed the FFT algorithm for the computation of the convolution integral

thus greatly shortening the computer time for parameter estimation. Liquid backmixing was investigated in a 92 mm I. D. threephase fluid-ized bed with the following conditions: gas velocity Ug 0.9-5.5cm/s

liquid velocity Ul 0.2 - 8.3cm/s. liquid kinematic viscosity r 0.81 - 39.6mm2/s

liquid surface tension a 39.7- 72.0mN/m and particle size 1.0- 1.25mm. Experimental results were correlated as follows: where Pe is the Peclet number. The mean deviation of the correlation is 15%.