Study On Heat And Mass Transfer Of Porous Medium In Vacuum Belt Dryer

A great deal of practice and researches confirm vacuum belt drier is quite fit for drying biological, pharmaceutical, food material which are viscous, heat sensitive, easy oxidation, which makes people more and more attention. In the research areas of the vacuum belt drying, however, most only stay at the experimental level and production experience to master the stage, but if can give effective guidance for production and equipment manufacturing R & D depend on in-depth theoretic is also very rare. This paper has selected carrot pulp as porous media materials, to study the heat and mass transfer properties in vacuum belt dryer, through theoretical analysis and experimental verification to obtain the relevant mathematical model. The vacuum belt dryer is a large scale equipment in this experiment, so it is more closed to the manufacture reality than the vacuum oven invented by the people in laboratory by themselves. In the later period, a set of temperature detectors are added, which supply reliable guarantee to the experimental study and optimization. Material thickness, heating temperature and vacuum pressure are chosen as variable quantity. Combined with drying kinetic theoretical knowledge, by analyzing result of many groups of experiments, it proves that the thin-layer drying model of carrots pulp can be represented by Page equation. At the same time, by recording exactly the changes of material surface temperature in the drying process, mathematical model of heat conduction from hot plates, to convey and finally to material is formed. Then the mathematical expression of evaporation capacity at constant drying rate period in vacuum belt dryer is set up, which provide commercial run and equipment manufacture with theoretical basis. By analyzing of the drying curve, the varying temperature curves of superficial material and the product acquired from experiments, they improve successfully the benefit on vacuum drying. Owing to the pressure in the drying room below atmosphere in the vacuum drying process, rarely molecular number in gas state, small density and little oxygen content, the vacuum drying is appropriate for the material which is prone to be metamorphic for oxide and the inflammable and explosive goods, at the meantime, it can play the role of sterilization and disinfection. The higher of vacuum pressure, the lower of the material surface temperature, but this situation goes against heat transmission. So it is wrong that the higher of the vacuum pressure, the helpful to increase drying velocity, because lots of the impacts factors, we should consider the state on the given material.