(77b) Application of the REA (reaction engineering approach) to Model Convective Drying of Various Type and Size of Food Materials and Cyclic or Intermittent Drying of Food Materials

A good drying model is very useful for process engineering and product technology perspective. From process engineering point of view, it can assist in design of better dryer, evaluation of dryer performance, optimization and troubleshooting. From product technology perspective, it is very useful to predict product quality change during drying. Although a lot of drying models were proposed, a good drying model still should be developed. It should be able to capture major physics during drying, simple, accurate, and robust. For ease of industrial application, it should be also favorable towards short computational time. Reaction engineering approach (REA) has been researched for over 12 years (Chen et al, 1997-date). It is revealed that the REA is simple, accurate and robust to model a range of thin layer or small food materials. The REA has also been applied in CFD (computational fluid dynamics) for prediction of spray dryer performance and numerical results matched well with the experimental data.

In this paper, the REA is implemented to model convective drying of various sizes (small and several centimeters thick) of food materials including mango tissues, apple tissues, banana tissues, coffee and rice. For modeling of rather thick materials, the prediction of surface temperature is incorporated in the REA. The REA is also attempted to model cyclic or intermittent drying of mango tissues and rice. For modeling the cyclic drying, the equilibrium activation energy (ΔEv,b) and heat balance are applied according to the corresponding drying conditions in each section.

Results indicate that the REA describes the convective drying of mango tissues, apple tissues, banana tissues, coffee and rice well. The predicted moisture content and temperature matched well with the experimental data. Similarly, the REA models the cyclic drying of mango tissues and rice well. Surface relative humidity, saturated water vapor concentration and surface water vapor concentration during cyclic drying are also illustrated by application of the REA. The profiles are very reasonable supporting the accuracy of the REA to model the cyclic drying.

Therefore, a substantial extension of the REA has been made. The REA is accurate to model not only thin layer or small food materials but also rather thick materials. It is also robust to model the cyclic or intermittent drying. The modeling itself is still revealed to be simple and requires only short computational time. Further applications of the REA for industrial purposes can be conducted.