Pressure Produced when Fluid is Introduced under Pressure into a Soil-Bed Layer (IV)

Draft Reduction of Sub-soiler by Introducing Water Dissolved Air to Break down Soil

Abstract

This paper reports a study of draft reduction a sub-soiler which introduces water dissolved air (Photo 1) under pressure in order to break down soil, based on the previously reported experiment in the draft reduction of the sub-soiler which introduces pure water. Since water dissolved air causes air bubbles which plug flow in the soil-bed layer and a high resistance pressure is produced among soil particles; the resulting draft reduction of the sub-soiler increases by the large breakdown power. A device which produces water dissolved air continuously (Fig. 2) was made and the draft of the sub-soiler was tested introducing continuously this water dissolved air from the top under pressure into the soil-bed layer In this paper, the solvent in which the air is dissolved is water but in the future we are planning to replace the water with liquid fertilizers in slurry form, and it will be introduced into pasture fields where the soil-bed layer around plant roots is compacted and hard. This provides plants with fertilizer and aerates plants and makes the soil soft. The results of this experiment are as follows;
1. The rate of air which can be dissolved into water in a high pressure tank, is shown in Fig. 3. The ratio of oxygen and nitrogen discharged when water dissolved air is released in the atmosphere is about 1:2 and therefore the concentration of oxygen becomes higher than that of general air at a rated 1:3.8.
2. When the temperature of water is less than 15°C, the dissolving of air into water requires much time and when the temperature of water becomes high, the whole rate of dissolved air decreases as shown Fig. 3. Consequently the optimal temperature of water is around 15-20°C.
3. The resistance pressure produced when water or water dissolved air flowed in one direction (in one dimensional flow) into the soil in a soil cell shown in Photo 2, was shown in Fig. 4. The resistance produced pressure of the flow of water dissolved air became higher than that of water flow in proportion to the increase in flow rate and was 1.5 times as large as that of water flow at about 10gf/s. cm² in flow rate.
4. When water dissolved air was forced under pressure into the soil-bed layer at the fixed condition of the sub-soiler in an acryle resin soil-bin prior to the traction test in the field, a cavity was formed around the nozzle port as shown in Photo 3.
5. In this case, the produced pressure at the nozzle port was changed vs. time as shown in Fig. 5 and the resulting waves recorded on a oscillograph at flow of water dissolved air showed a more severe jigzag change than the water flow.
6. Comparing the draft reduction of sub-soiler when water dissolved air was introduced with that of the water flow, a sufficient rate of draft reduction was observed in case of the former even under a condition where no draft reduction was observed in case of the water flow as shown in Fig. 7.
7. The rate of draft reduction is shown collectively in Fig. 9 vs. the flow rate, including the traction velocity and primary draft. The flow rate of 15cm³/cm per unit traction distance was required at a minimum for draft reduction when water was introduced, on the other hand, when water dissolved air was introduced, a sufficient draft reduction was obtained in 6cm³/cm in flow rate at minimum per unit traction distance.
8. The profits and expenditures of energy of this method are shown in Fig. 10. When the traction speed of the sub-soiler was slower than 6.0cm/s, the energy required for producing water dissolved air was more than the energy reduced by the draft reduction and therefore no merit of energy reduction was evident. But when the traction speed became about 25cm/s and the flow rate of 310cm³/s was introduced, a large amount of draft reduction was observed and energy was reduced by 30%.
The writer wishes to express his gratitude to the Hokkaido University Computing Center for allowing h