A NUMERICAL STUDY OF THE EFFECT OF AIR-IMPINGEMENT AND DEHUMIDIFIED AIR ON DRUM DRYING

Drum drying is extensively used for drying of different types of starchy food products, sludge, suspensions and pastes of a wide range of viscosities. During drying, the drum surface temperature is selected on the basis of the heat sensitivity and desired final quality of the dried products. Condensing steam is commonly used as the source of heat for medium to high temperature applications. A simple liquid diffusion-based model is used in the present study to predict the drying performance of a pilot-scale twin-drum dryer. Numerical results are compared with experimental data obtained for a biological sludge. The agreement of model predictions with the pilot scale experimental data is very good. The validated model is then used to examine the effects of drying air relative humidity and impingement on the drying performance of high and low-temperature drum dryers. It is shown that unlike high-temperature drum dryers, drying performance of low-temperature drum dryers can be improved by using drying air of low relative humidity. Air-impingement helps to improve the moisture evaporation rate remarkably for high and low-temperature drum dryers. Effects of impinging air velocity and location are numerically simulated. A simple mathematical model of this type can be conveniently used for design, analysis and scale-up of industrial drum dryers. Retrofits can be designed to enhance performance or productivity of existing drum dryers as well.