Improvement of a mathematical model for low-pressure superheated steam drying of a biomaterial

摘要

Although there currently are a number of works reporting experimental study of low-pressure superheated steam drying (LPSSD), which has proved to be an attractive alternative to drying heat-sensitive biomaterials, there are a very few works reporting the development of a mathematical model to predict the evolutions of product moisture content and temperature during LPSSD. Moreover, the predictions of those few developed models are still not satisfactory because, most of the time, the models do not include the effect of initial steam condensation; the use of mass transfer boundary condition is, in some cases, also not quite realistic. The aim of the present study was thus to develop a more realistic liquid diffusion based model to simulate the transport of heat and mass within a product undergoing LPSSD. The effect of initial steam condensation, in terms of film condensation, was included and a more realistic mass transfer boundary condition, in terms of the vapor pressure gradient and the physical condition at the drying surface, was applied in the newly developed model. The effect of the product shrinkage was also included directly in the model. The predictability of the model was tested against the available experimental data. The model with initial steam condensation was found to be able to predict the center temperature and average moisture content of the product undergoing LPSSD very well. However, at higher temperatures and lower pressures the product core temperature was still under predicted.