Study on the moisture uniformity of paddy drying in a deep fixed-bed

A new concept of drying moisture uniformity which shows properties of mathematical statistics is defined for paddy drying in a deep fixed-bed based on analyzing the existing indexes. A series of paddy drying experiments including single-factor experiments, quadratic orthogonal rotary combination experiments and duplicate tests were conducted in a deep fixed-bed. Influence laws of each experiment factor on the new index were analyzed and uniformity characteristics of paddy drying in the same layer but at different position were also investigated. The results showed that paddy samples at the first measuring point from which to the centre of cross section the distance is 1/6R, and at the third measuring point from which the distance is 1/3R, firstly and finally reached the moisture content of safe storage (14%, w.b) respectively with the maximum frequency, which not only can be regarded as a general law but also prove that the effect of the material outlet structure on paddy drying can be neglected. The experimental method of the five-factor quadratics rotary orthogonal combination is adopted to establish the relationship between performance function and each factor, and the effects of each factor on the drying moisture uniformity are investigated. An optimum range under 95% probability of drying moisture uniformity more than 0.30 has been summarized for drying air temperature, drying air velocity, paddy thickness, original moisture content and tempering time at 68.6 ^°C~69.8 ^°C, 1.06 m·s^-1~1.11m·s^-1, 31.9cm~33.4cm, 21.83%~22.34%, 2.86h ~3.10h respectively by frequency analytical method, which provides useful formation for improving the drying moisture uniformity of paddy in the practice and the research of paddy drying process simulation.