Differential-Flow Induced Chemical Instabilities “DIFICI patterns”

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Presentation transcript:

Differential-Flow Induced Chemical Instabilities “DIFICI patterns”

DIFICI differential-flow induced chemical instability requires selective diffusivity but can be any species Menzinger and Rovinsky Phys. Rev. Lett., 1992,1993

BZ reaction: DIFICI immobilise ferroin on ion- exchange resin flow remaining reactants down tube above a “critical” flow velocity, distinct “stripes” of oxidation (blue) appear and travel through tube

Experiment = 2.1 cm c f = cm s  1 f = 2.8 s frame  1 [BrO 3  ] = 0.8 M [BrMA] = 0.4 M [H 2 SO 4 ] = 0.6 M Rita Toth, Attila Papp (Debrecen), Annette Taylor (Leeds)

Experimental results imaging system: vary “driving pressure” slope ~ 1 Not possible to determine “critical flow velocity”

BZ reaction Involves competition between: HBrO 2 + Br - 2BrMA and HBrO 2 + BrO M red 2HBrO 2 + 2M ox Also BrMA + 2M ox f Br - + 2M red

Theoretical analysis: Dimensionless equations u = [HBrO 2 ], v = [M ox ] : take  = 0  and f depend on initial reactant concentrations

main results DIFICI patterns in range of operating conditions separate from oscillations f absolute instability convective instab. no instability no instab.  cr = 0  cr   cr increasing

Space-time plot showing position of waves note: initiation site moves down tube back to dimensional terms : predict c f,cr = 1.3  10  2 cm s  1 For c f,cr = 2.4  10  2 cm s  1 = 0.42 cm