Hydrodynamics of the annular circulating fluidised bed drier (ACFBD) with variable gap opening was studied with ragi particles of average diameter 1530 mu m and density 1272 kg/m(3). For openings greater than 40 mm, the mass flux of solids was constant for all air rates studied. A correlation relating mass flux of solids with air velocity and opening is proposed. Models are proposed for calculating pressure drop separately for the dense slugging flow and dilute phase flow regimes. A correction factor, called erratic factor, has been incorporated for the dense slugging flow regime. The average deviation in the calculated values of pressure drop using the proposed model was 10%.