Fouling particulate

Particulate fouling may be defined es the accumulation of particles from liquid or gaseous suspensions onto heat transfer surfaces. Particulate fouling occurs in a wide range of situations. In liquid streams the best known example is probably that of corrosion products In boiler waters and reactor coolants. In 

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In the case of particulate fouling, one of the more common types, insuring a sufficient flow velocity and minimizing areas of lower velocities and stagnant flows to help keep particles in suspension is the most common means of deahng with the problem. For water, the recommended tubeside minimum velocity is about 0.9 to 1.0 m/s. This may not always be possible for moderate to high-viscosity fluids where the resulting pressure drop can be prohibitive. 

Potential particulate fouling problems if not properly designed... 

Particulate fouling suspended particles setde on heat transfer surface. 

Thonon B, Grandgeorge S, Jallut C. Effect of geometry and flow conditions on particulate fouling in plate heat exchangers. Heat Transfer Eng 1999 20(3) 12-24. 

Figure 10.1. Experimental procedure for the determination of the colloidal index (Cl). The Cl or the silt density index (SDI) test is used to predict and prevent particulate fouling on the membrane surface. It measures the time required to filter a fixed volume of water through a standard 0.45- xm pore-size microfiltration membrane with a pressure of 2.07 bar. The difference between the initial time and the time of a second measurement after normally 15 minutes (after silt was built up) represents the Cl or SDI value.

The processes of interest are NFand RO where the membranes are either nanoporous or essentially nonporous. In these processes the fouling is a surface layer, the effects of which maybe exacerbated by the high retention of solutes by the membrane. Operation is with crossflow and in industry fixed flux is commonly used. This section considers particulate fouling, biofouling and scale formation and then discusses the implications of cake enhanced concentration polarization on fouling outcomes. 

Particulate fouling in RO is most likely to be colloidal due to the formation of a colloidal deposit layer on the membrane surface. Examples of colloidal partides... 

Other important future membranes properties include improved resistivity to extreme pH enabling better cleaning performance and resistance to oxidizers, organic solvents and particulate fouling. More important properties exist, yet the most important may be the resistance to fouling of the different sources. 

Particulate fouling. Particles held in suspension in the flow stream will deposit out on the heat-transfer surface in areas of sufficiently lower velocity. 

Newson, I.H. Miller, G.A. Haynes, J.W. Bott, T.R. Williamson, R.D. Particulate fouling studies of deposition, removal and sticking mechanism in a haematite/water system. Proceedings of the Second U.K. National Conference on Heat Transfer, Glasgow, U.K., Sept 14—16, 1988 Int. Mech. Eng., London, U.K., 1988 137-160. 

It is not proposed to review in some detail the models that have been developed since although they can provide an insight into the underlying mechanisms and the influence of specific variables, they are not generally universally applicable. Reviews of particulate fouling with reference to heat exchangers have been provided by Gudmundsson [1981], Lister [1981], Beal [1983] and Epstein [1988]. 

Bott and Bemrose [1983] reported work on the particulate fouling of an experimental finned tube heat exchanger using calcium carbonate dust with a particle size range of 3 - 30 pm. The spirally wound finned tubes had the following geometry ... 

FIGURE 7.17. The increase in fan power requirement due to particulate fouling... 

Beal, S.K., 1983, Particulate fouling of heat exchangers, in Biyers, R.W. and Cole, S.S. eds. Fouling of Heat Exchanger Surfaces. Proc. Eng. Found. Conf, White Haven. 

Bott, T.R. and Bemrose, C.R., 1983, Particulate fouling on the gas side of finned tube heat exchangers. Trans. ASME, 105, 178 - 183. 

Epstein, N., 1988, Particulate fouling of heat transfer surfaces Mechanisms and models, in Melo, L.F., Bott, T.R. and Bernardo, C.A eds. Fouling Science and Technology. Kluwer Academic Publishers, Dordrecht, 143 - 164. 

Gudmundsson, J.S., 1981, Particulate fouling, in Somerscales, E.F.C. and Knudsen, J.G. eds. Fouling in Heat Transfer Equipment, 357 - 387. Hemisphere Publ. Corp., Washington. 

Watkinson, A.P. and Epstein, 1971, Particulate fouling of sensible heat exchangers. Proc. 4th Int. Heat Trans. Conf Vol. 1. Paper HE 1.6, Elsevier Science Publishers BV, Amsterdam. 

Corrosion products released upstream of a heat exchanger may give rise to particulate fouling on the heat transfer surfaces downstream. 

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