Rheological properties of high-temperature melts of coal ashes and other silicates S. Vargas * , F.J. Frandsen, K. Dam-Johansen Department of Chemical Engineering, Technical University of Denmark, 2800 Lyngby, Denmark Received 19 January 1999; accepted 15 July 2000 Abstract This paper reviews the 20th century advances within the ®eld of the measurement and the prediction of the rheological properties of high-temperature T . 1000 K silicate melts at atmospheric pressure with a focus on coal ashes and other melts of compositions relevant to coal ashes. Theoretical considerations are represented ®rstly by a synopsis of de®nitions and ¯ow-regimes and secondly by an outline of the ruling network theory and the notations used therein. The in¯uence of different cations on viscosity is discussed thoroughly. Experimental points include a listing of the most common apparatus for viscosity measurements on high-temperature liquids and a summary of existing experimental data. Viscosity vs temperature is reported in tables as well as graphically for melts composed of major amounts of one or more of the species: SiO 2 , Al 2 O 3 , FeO x , CaO, MgO, Na 2 O, K 2 O, Li 2 O, MnO, TiO 2 ,B 2 O 3 . For each experimental source, relevant information is listed (apparatus, sensor material, atmosphere). With a basis in both theory and experimental data, general equations for liquids, are presented, relating viscosity to temperature and/or concentration of dispersed solids, as are more speci®c mathematical models, relating the viscosity of silica melts and glasses to temperature and composition. q 2001 Elsevier Science Ltd. All rights reserved. Keywords: Silicates; Viscosity; Coal ash Contents 1. Introduction .................................................................. 239 2. De®nitions and dimensions ....................................................... 241 3. Classi®cation of ¯ow types ....................................................... 242 3.1. Time-independent ¯ow types .................................................. 242 3.2. Time-dependent ¯ow types ................................................... 242 4. High-temperature viscometers ..................................................... 243 4.1. Capillary viscometer ........................................................ 243 4.2. Falling body viscometer ..................................................... 243 4.3. Rotational viscometer ....................................................... 244 4.4. Rod elongation viscometer ................................................... 244 4.5. Squeeze ®lm rheometer ...................................................... 244 4.6. Choice of viscometer for high-temperature measurements ............................. 244 5. Experimental results ............................................................ 245 5.1. Sources of error ........................................................... 245 5.1.1. Temperature ....................................................... 245 Progress in Energy and Combustion Science 27 (2001) 237±429 PERGAMON www.elsevier.com/locate/pecs 0360-1285/01/$ - see front matter q 2001 Elsevier Science Ltd. All rights reserved. PII: S0360-1285(00)00023-X * Corresponding author. Tel.: 145-252-835; fax: 145-88-2258. E-mail address: sv@kt.dtu.dk (S. Vargas).