The objective of the present study is to simulate a co-current pilot plant spray dryer with cooling air jacket, using a numerical technique. From a blower fan air enters the secondary wall which has a helical passage around the drum and the main process fluid enters in an axial flow direction from an air distributor which is located in a top center position. To model the fluid flow and heat transfer from the inner fluid to the surrounding air jacket, a special treatment was developed to predict convection heat transfer through to the helix. Knowing the air temperature and air velocity entering the jacket and the process of fluid entering the drum in a counter-current direction, combined free and forced turbulent convection heat transfer in the drum was investigated, using RNG k-ε model. Analyses were carried out using SIMPLEC scheme with and without spray water and milk to determine the pressure field, velocity distribution, the temperature field of the process fluid throughout the drum and its wall, as well as time of evaporation and particle diameter. Comparison of the simulation of particle size and time of evaporation with empirical relations and validation of the results with experimental measurements showed both to be within an acceptable range of agreement.