Effects of moisture contents of threshed materials from whole-feeding combine for foxtail millet on their suspension characteristics

The suspension characteristics of the threshed materials of foxtail millet are the basic characteristics for the research of cleaning working parameter optimization and improved design for the cleaning equipment, and the foxtail millet was harvested by the whole-feeding combine harvester. The threshed materials to be cleaned of foxtail millet include the grains, spikelets, stalks and leaves. Based on the requirements of the Chinese national standard test methods for forage seed suspension velocity, using the suspension velocity testing device for agricultural materials, we designed and conducted the staged suspension experiments to measure the suspension velocities of the 4 kinds of threshed materials of foxtail millet respectively, and we also measured the suspension velocities of the threshed materials with different moisture contents, and then we researched the relations between the suspension velocity of each part of threshed materials and its moisture content. Based on the differences among the measured suspension velocities of threshed materials, we estimated the suitable range of cleaning air velocity and conducted the cleaning experiment via cleaning experimental device to verify our estimation. We got the threshed materials with different moisture contents by means of rehydrating and drying. We immersed the threshed materials harvested into the water for 6 h to make their moisture contents saturate, and then we put the saturate threshed materials into the thermostatic drier box to dry for different times at 100 ℃. The drying times were 10, 20, 30 and 40 min respectively, and thus we got other 4 kinds of threshed materials with different moisture contents from the harvested threshed materials', and so we totally measured 5 kinds of threshed materials with different moisture contents. The staged suspension experiments included 3 stages. When there were one third of the materials to be measured suspending in the tapered observed pipe at some height, one suspending stage was reached. We measured the suspension velocity of the suspended materials via DP2000-11 type intelligent pressure air-volume anemometer in every stage, and there were 6 measure points in every stage, and we calculated the average value of the 6 measured values. We used the suspended height ruler to measure the suspension height range of the suspended materials, and we used the average value and the suspension height range to calculate the suspension velocity range of the suspended materials based on the flow consistency principle. Synthesizing the 3 suspension velocity ranges, we got one suspension velocity range of this kind of material with a certain moisture content. There were 6 repeats of suspension velocity measurement for every kind of material with a certain moisture content. Synthesizing the 6 suspension velocity ranges of a kind of material with a certain moisture content, we finally got the suspension velocity ranges of this kind of material. The experimental results showed that the suspension velocities of grains, spikelets, stalks and leaves of threshed materials of foxtail millet harvested by combine harvester were respectively 4.29-8.88, 1.03-5.48, 1.71-5.33 and 1.03-3.09 m/s. There was no overlapping numerical interval between the grains' suspension velocity range and the leaves', while there were some overlapping numerical intervals between the grains' suspension velocity range and the spikelets' or the stalks'. With the decrease of moisture content of foxtail millet, the overlapping numerical intervals were all reducing between the grains' suspension velocity range and the spikelets' or the stalks' or the leaves'. We used the maximum of the suspension velocity range of every kind of material with a certain moisture content to carry out a statistical analysis. The moisture content affected the suspension velocity of every component of the threshed materials significantly, and the significance level P values were all less than or equal to 0.048 8. With the decrease of moisture content, the suspension velocities of grains, spikelets, stalks and leaves were all decreasing, and there were quadratic function relations between the moisture content and the grains' suspension velocity or the spikelets' or the stalks' or the leaves', and the fitting precisions were all greater than or equal to 0.951 2. The results of cleaning experiment proved that the estimation was rational. The suitable range of cleaning air velocity for the threshed materials of foxtail millet was 4.29-5.48 m/s, and the optimal air velocity at air outlet was 4.47 m/s. Under the action of airflow with optimal air velocity, the loss ratio of grain was 4.68%, and the cleanliness of grain was 98.83%. The research results can provide reference for the determination of the timely harvest time and the optimal cleaning working parameters.