Abstract:
To study the variation of size distribution of tobacco strips redried by a cylinder dryer, the effects of operational conditions including cylinder wall temperature, hot air temperature, cylinder's rotational speed and material/cylinder volume ratio on the size distribution of redried strips were investigated, and the variation of size distribution of tobacco strips redried by hot air system was analyzed and compared. The results showed that:1) The variation coefficient of moisture content in strips was less than 2% and the moisture content in strips was uniform at large during the whole process of cylinder redrying. 2) Cylinder wall temperature influenced the redrying time, drying rate and redried strips' temperature significantly (
P<0.05); volume ratio affected redrying time and drying rate of strips greatly (
P=0.0047); while the hot air temperature and cylinder's rotational speed did not affect redrying time, drying rate and redried strips' temperature significantly (
P>0.05). 3) After cylinder redrying, the percentage of large size strips decreased, that of middle and small size strips increased; the characteristic area of strips reduced, while uniformity coefficient raised. In general, the percentage of large and middle size strips was higher and shrinkage rate was lower at the conditions of cylinder wall temperature 70℃, hot air temperature 80℃-90℃, cylinder's rotational speed 8 r/min and volume ratio 16.16%. 4) Comparing with hot air redrying, the shrinkage rate of strips was obviously lower and the percentage of large and middle size strips was higher under cylinder redrying at the similar drying rate.