ANALYSIS OF COOLING AIR JACKET AND AIR DISTRIBUTOR IN A CO-CURRENT SPRAY DRYER

The purpose of the present study is to simulate a co-current pilot plant spray dryer with cooling air jacket, air distributor and pressure nozzle, using a numerical technique. For the spray dryer, cooled air enters its secondary wall which has a helical passage around the drum and the main process fluid enters in the axial flow direction from an air distributor which is located on the top center position of the dryer. Fluid flow and heat transfer from the inner fluid to the surrounding air jacket is studied with a special treatment to predict convection heat transfer through the helix. By knowing the air temperature and flow velocity entering the jacket and the thermal condition of the process fluid entering the drum in a counter-current direction, combined free and forced turbulent convection heat transfer in the drum are investigated using the RNG k-ε model of a turbulent model. Analyses were carried out using the SIMPLEC scheme and Euler-Lagrange model with and without spray water and milk to determine the pressure field, velocity distribution, temperature field of the process fluid throughout the drum and its wall, as well as the particles temperature and humidity, time of evaporation and diameter. Comparison of transient simulation of the particle size and time of evaporation with empirical relations is made for certain conditions. Validation of the numerical results with the experimental measurements shows good agreement.