Moreover, Fig. 4a also indicates that the removal efficiency first
increases and then tends to stable with the particle size. This can
be explained as follows. The fine particles from coal combustion
are mainly insoluble aluminosilicates, which are not perfectly wettable
substances [17]. According to the classical heterogeneous
condensation theory of Fletcher [18,19], the critical supersaturation
Scr of partially wettable, insoluble spherical particles can be
expressed as follows: