Rheologica Acta Rheol Acta 28:316-320 (1989) Steady shear behaviour of coal-oil suspensions M.K. Baloch Department of Chemistry, Gomal University, Dera Ismail Khain, Pakistan Key words: _Suspension; s_hear v_iscosity; v_iscometer; N_ ewtonian behaviour; _yield s_tress The study of rheological behaviour of concentrated coal-oil mixtures (COM) is of special significance because of the difficulty in handling these materials and the many peculiar properties that are exhibited at higher concentrations of coal. Until now very little work has been reported in the literature on the rheology of either dilute or concentrated coal-oil suspensions. Moreover the conclusions drawn by dif- ferent investigators [1-8] about the cause of non- Newtonian behaviour (specially in low shear rates) vary from author to author. Therefore the aim of this communication is to in- vestigate the effect of size and size distribution of the particles and the viscosity of fluid on the rheological properties of the suspension. Moreover, this work will provide the facility to test the validity of the Krieger equation for irregularly shaped particles. Coal from Kalabagh, Pakistan, was ground in a ball mill and dry-sieved to prepare four stock samples. Stock I was passed through a 400-mesh sieve size (par- ticle diameter, D< 62.5 gm). Stock II was collected be- Table 1. Characteristics of suspension used and the parame- ters of the system obtained from the Newtonian part of the data System No. Coal Stock Viscosity of ~m [/7] No. oil SI-I 1 0.11 S1-2 2 0.11 S1-3 3 0.11 SI-4 4 0.11 $2-1 1 0.06 S 2-2 2 0.06 S 2-3 3 0.06 S 2-4 4 0.06 tween sieve sizes 500 and 150 (107_>D_>50 gm), stock III was collected between sieve sizes 200 and 150 (167>_D_>125 gm), and stock IV was collected be- tween sizes 900 and 400 (62.5 >D> 27.8 gin). The par- ticle size distribution of these four stocks is given in Fig. 1. The figure shows that stock numbers I and II have wide particle size distribution, whereas III and ,Ooi 10 30 50 70 't b O --I 20 160 0.593.08 2:t l 0.58 3.59 0.55 4.68 , F?- I 0.52 4.18 10 30 ~50 ' 70 0.59 3.15 Diameter (/~rn) 0.58 3.94 0.54 5.35 Fig. I. Particle size distributions for each of four coal 0.53 5.01 powder stocks used in making suspensions; a) stock-l; b) stock 2; c) stock 3 and d) stock 4