The fluidity of smelt is an important property that affects smelt flow from recovery boiler spouts. It is strongly related to smelt viscosity. Results of a laboratory study show that molten smelt has a viscosity between 2.5 and 5 cP, and that, as long as smelt is completely molten, its viscosity is not affected appreciably by composition or temperature. However, the viscosity increases drastically as the smelt begins to freeze. If the sudden decrease in smelt fluidity as freezing begins is the main cause of "jellyroll smelt" formation near smelt spouts, then the difference between the smelt temperature and its freezing temperature may determine whether or not a recovery boiler is susceptible to jellyroll smelt formation: the larger the difference, the less likely jellyroll smelt is to form.
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