Deposition of magnetite particles from flowing suspensions under flow-boiling and single-phase forced-convective heat transfer

The deposition rate of colloidal magnetite particles was measured under bot h single-phase forced-convective and flow-boiling conditions. All measureme nts were made at alkaline pH where both the heat transfer surface and the s urface of the magnetite particles appear to be negatively charged. For sing le-phase forced convection, the deposition rate constant is lower than the mass transfer coefficient for colloidal particles, and the difference is at tributed to the force of repulsion between the negatively charged surfaces of the particle and substrate. The deposition rate measured under flow-boil ing conditions is lower than that reported for the deposition of colloidal particles at neutral pH. The difference is, again, attributed to the force of repulsion between the particle and substrate. Particle removal rates wer e significantly lower than deposition rates; analysis using the theory of t urbulent bursts suggests a removal efficiency of only 10(-9)% for each turb ulent burst. The low removal efficiency is consistent with the particle dia meter being significantly smaller than the thickness of the laminar sublaye r in these tests.