RAJ: “dk3171_c009” — 2006/6/8 — 23:05 — page 437 — #1
Most unit operations and processing steps encountered in the handling and processing of rheologically complex systems involve nonuniform temperature and concentration fields, thereby resulting in the net transport of heat (or mass) from a region of high temperature (or concentration) to that of a low temperature (or concentration) within the flow domain. Furthermore, there are instances (such as devolatilization and vaporization of solvents, etc.), which entail simultaneous heat and mass transfer. In either event, the conservation equations are coupled, thereby adding further to the complexity of the analysis. Consequently, considerable research effort has hitherto been devoted toward developing a better understanding of heat and mass transfer phenomena in nonNewtonian systems. In general, heat transfer processes occurring in a variety of geometries and under different conditions of practical interest have been investigated much more extensively than the analogous mass transfer processes. From a cursory inspection of the available reviews (Metzner, 1956, 1965; Skelland, 1966; Porter, 1971; Astarita and Mashelkar, 1977; Irvine and Karni, 1987; Chhabra, 1993a, 1993b, 1999b; Ghosh et al., 1994), it is abundantly clear that the heat and mass transfer processes occurring in external flows (such as between fluid and solid particles and stationary or moving non-Newtonian media) have received much less attention than that accorded to these phenomena in internal or confined flows, such as in pipes and slits (Polyanin and Vyaz’min, 1995). Even some of the available books barely touch upon this subject (Bird et al., 1987; Chhabra and Richardson, 1999; Kreith, 2000; Tanner, 2000; Morrison, 2001; Polyanin et al., 2002). Excellent reviews of the free and forced thermal convection in non-Newtonian systems with special reference to boundary layer flows have appeared in the literature (Shenoy and Mashelkar, 1982; Nakayama, 1988; Shenoy, 1988). No such review for mass transfer in non-Newtonian systems however seems to be available.