Mass transfer in vertical two-phase flow of liquid coarse particles

Abstract

Wall-to bed mass transfer in single-phase and vertical two phase flow of inert spherical particles 1.20, 1.94 and 2.98mm in diameter in a 25.4mm I.D. tube was studied. Mass transfer coefficients were determined by following the rate of dissolution of a transport tube segment prepared from benzoic acid. The vertical two-phase flow is treated as the pseudofluid, and the modified mixture-wall friction coefficient (fw) is introduced and modified mixture Reynolds number (Rem). The dependence of changes for the mass transfer factor and modified mixture-wall friction coefficient (fw) or modified mixture Reynolds number (Rem) is also described. Wall-to-bed mass transfer in hydraulic transport of particles is much higher than in single-phase flow for lower Reynolds numbers (Re LT 10000), while for high Reynolds numbers (Re > 10000), there is no significant difference. In our hydraulic transport experiments the two characteristic flow regimes were observed: a)"turbulent fluid-particle flow" and b)"parallel fluid-particle flow". Our experimental data show that the mass transfer coefficients in turbulent fluid-particle regime are much higher than in parallel fluid-particle flow.

Ispitivanje koeficijent prenosa mase u jednofaznom vertikalnom toku fluida i dvofaznom toku fluid-inertne sferične čestice prečnika 1,20, 1,94 i 2,98 mm u transportnoj cevi prečnika 25,4 mm. Koeficijent prenosa mase je određivan metodom praćenja dinamike rastvaranju benzoeve kiseline nanesene na segment transportne cevi visine 20 mm. Pri obradi dobijenih podataka za prenos materije u vertikalnom dvofaznom toku, dvofazni tok je tretiran kao pseudofluid i uveden je modifikovani koeficijent trenja smeše fluid-čestice sa zidom cevi (fw) i modifikovani Reynoldsov broj za smešu fluid-čestice (Rem). Takođe je prikazana zavisnost promene bezdimenzionog faktora prenosa materije (jD) i mofdifikovanog koeficijenta trenja (fw) od Reynoldsovog broja za smešu. Eksperimentalni podaci pokazuju da je koeficijent prenosa materije u vertikalnom dvofaznom toku znatno viši u odnosu na jednofazni tok za niže vrednosti Reynoldsovog broja (Re LT 10000), dok za više vrednosti Reynoldsovog broja (Re > 10000), između podataka nema značajnije razlike. Eksperimentalna ispitivanja prenosa mase pri hidrauličkom transportu čestica ukazuju da postoje dva karakteristična režima strujanja: "turbulentni fluid-čestice tok" i "paralelni fluid-čestice tok". Eksperimentalni podaci, takode, pokazuju da je koeficijent prenosa materije znatno viši u turbulentnom od koeficijenta prenosa materije u paralelnom toku.