In this paper the simultaneous mass and heat transfer processes taking place during the absorption of ammonia vapour by lithium nitrate-ammonia solution droplets is numerically simulated. The low-pressure and high-pressure absorbers of a double-stage absorption system are considered. Results obtained are compared with Newman model for mass transfer. Simulation shows that droplets analysed, with diameter equal to 60 and 100 mum, follow Newman model for mass transfer. Droplets achieve the equilibrium state in an approximate dimensionless time equal to 0.5, that corresponds to times lower than 1 s. Effect of subcooling on absorption is evaluated. Results obtained are important for the design of spray absorbers of absorption refrigeration systems. (C) 2004 Elsevier Ltd. All rights reserved.