Instability in diffusing fluid layers

Abstract

SynopsisA small perturbation analysis is carried out to determine the stability of a fluid containing two layers of dBusing solutes in a common solvent and acted upon by a uniform gravitational field. It is found that instability can arise even though the unperturbed diffusion does not lead to the formation of a density inversion within the fluid.

Bioseparation by Zonal Centrifuges

“…The criterion is similar to that obtained by Sartory (16) except for the powers on the diffusivities. The four diffusivities for three-component systems can be obtained by Fujita and Gosting's procedure (38).…”

“…Diffusion will cause band broadening, which inevitably affects all systems. Another consequence from diffusion is that an initially stable band may rapidly develop instability at its lower boundary if a density inversion is created there by diffusion of a gradient material (16,17). When an equilibrium band is broad, the effective density gradient is more likely to depart from linearity.…”

Diffusion and Double Diffusive Convection in Isothermal Liquid Boundaries

“…The stability analysis of diffusion boundaries was widely discussed in the literature [Veronis, 1965;Baines and Gill, 1969;Sartory, 1969;Turner, 1973;Huppert and Manins, 1973], including the particular case of isothermal multi-component boundaries [McDoughall, 1983;Vitagliano, et al, 1984Ambrosone, et al, 1993] and various experimental cases were examined [Vitagliano, et al, 1972[Vitagliano, et al, , 1984[Vitagliano, et al, ,1988.…”

A diffusion driven instability in systems that separate particles by velocity sedimentation

“…This constraint implies that the particle band must be stable throughout the sedimentation interval. The stability of such bands has received considerable theoretical (7)(8)(9)(10)(11)(12) and experimental (1,5,6,(12)(13)(14)(15)(16) study. The Svensson criterion for stability states that the density gradient of the particle-fluid mixture should be in the same direction as the force producing the sedimentation.…”

“…This mechanism has been analyzed theoretically by Svensson et al (7) but has failed to find experimental support (16). Sartory (11), by regarding the Svensson criterion as a necessary but not sufficient condition for stability, deduced that diffusion of the gradient-producing solute imposed a more severe limit on the macromolecular load than Svensson's diffusion analysis predicted. The experiments of Halsall and Schumaker (16) indicated however that, whereas Svensson's analysis overestimated the load that could be stably sedimented, that of Sartory underestimated it.…”