Iron oxide particle deposition is a common form of fouling of heat exchange surfaces and is important in radioactive corrosion product transport. The present work relates to deposition in fully turbulent isothermal conditions from non-boiling aqueous suspensions onto metal tubes using particles of Haematite (Fe303) for which transport through the boundary layer was expected to be predominantly diffusional. A radioactive technique has been used to measure deposition rate onto clean stainless steel and aluminium surfaces, the growth of deposit with time and the rate of removal of particles as clean water is passed over the deposit. In view of the known effect of particle size on mass transfer, attempts were made to use particles of uniform size. The performance of a small diameter hydrocyclone was investigated as a means of obtaining a monodisperse suspension from commercially available powders but these were eventually discarded in favour of particles manufactured using a controlled precipitation process. Water chemistry has been demonstrated to have a profound effect on particle deposition from turbulent flow which is similar to that found by workers experimenting in systems with laminar flow. The mass transfer coefficients measured under favourable conditions of water chemistry agreed extremely well with predicted values. The asymptotic level of deposit was found to decrease as fluid velocity increased approximately to the power 1.3 which cannot easily be explained using currently available mechanistic descriptions. The rate of decrease in deposit thickness as clean 'water is passed over it was finite. However this was around an order of magnitude lower than that required to indicate that continuous removal of particles by turbulent bursting in the laminar sublayer or other fluctuations in the forces of the particles is the major factor responsible for asymptote formation.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:525001 |
| Date | January 1989 |
| Creators | Willaimson, R. D. |
| Publisher | University of Birmingham |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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