The mass, momentum and energy exchange between the droplets and particles and the drying medium in a spray dryer is a complex process. One approach to modeling this process is to apply the particle-sourcein- cell model in which the droplets and particles are regarded as sources of mass, momentum and energy to the conveying gas flow. This mode1 is app1ied to a counter-current spray dryer. The results show the strong interaction between the droplet/particle and gas flow fields. The calculations show the inadequacy of predictions in which the exchange between phases is ignored.