close to the void fraction that makes intolerable big error in liquid hold-up estimation. In this sense, only limited number of the data were available from Colquhoun-Lee[3] and Specchia[6] because most of their experiments were carried out in high gas and liquid velocity: even their data shown in Fig. 3 seems being a little out of bubble regime. It may be useful to consider the reason of the behavior indicated in Fig. 3. In low ReL regime, the mass transfer rate is mainly dominated by gas turbulence than liquid flow, but the effects of gas flow are not observed explicitly, but implicitly through liquid hold-up. In this regime Sherwood number does not depend on liquid Reynolds number and the plateau levels were proportional to particle diameter. In high ReL regime, the correlating lines asymptotically approached to the single-phase flow relation and the transient value of Re, were depend on the particle diameter as pointed out in previous papcr[8]. Conclusively: hydraulic diameter concept, which was first used by Theones and Kramers[lZ], then its usefulness was demonstrated by Miyauchi[ l3] in successful correlation of a number of data of single phase flow with very wide range as: 10e3 < Re, i I@ and 0.28 x B 5 0.488, seems IO be appropriate, yielding a unique correlation in spite of an inherent simplicity. A smooth correlation in the particle mass transfer phenomena in single-phase flow system and in multi-phase flow system was established by the parameters given in this work. Acknowledgement-Thanks are due to Prof. H. Hofmann, University of Erlangen-Nuernberg, for providing the author with Ph.D. Thesis of Dr. W. Heilmann. Miura Printing Corp. Narashino, Fanabashi Japan 274 S. MOCHIZUKI NOTATION dp characteristic particle diameter, mm & = e,d,,/l.5(1-By), hydraulic diameter based on liquid hold-up dX = ~d,jl.S(l -E), hydraulic diameter based on void fraction Q diffusivity J& column diameter, mm k, liquid-solid mass transfer coefficient ReL = d,,uI/eLvL, Reynolds number Ret = dj: II JEQ, Reynolds number Rez = d&/~vo, Reynolds number SC = vJ&, Schmidt number Sh = k,d,,/&,, Sherwood number she = k,d,,/&, Sherwood number for single phase flow Sh* = k,dX/D,, Sherwood number IA superficial fluid velocity, L for liquid, G for gas Greek symbols E void fraction in packed bed Q gas hold-up Ed liquid hold-up Y kinematic viscosity c interfacial tension JUXERENCES