Effects Of Channel Shape And Water Supply Pressure On Bubble Movement Characteristics In Labyrinth Channel Of Aeration Drip Irrigation

Aeration drip irrigation can effectively slow down the hypoxia in the crop root area and improve the crop water use efficiency and crop yield and quality.The research on aerated drip irrigation at home and abroad mainly focuses on the impact of aerated drip irrigation on crop yield and quality,physiological indexes and soil water,gas and microbial environment,while the research on the performance of aerated drip irrigation on emitters is still less.Emitter is the key part of the whole drip irrigation system.Its performance will eventually affect the operation efficiency and irrigation effect of the whole drip irrigation system.Based on the study of the influence of different types of gas-liquid two-phase flow in the labyrinth and particle velocity measurement technology,the influence of particle velocity in the labyrinth on the operation characteristics of gas-liquid two-phase flow is determined.It provides theoretical guidance for the scientific application of aeration drip irrigation technology.The main conclusions of the test are as follows:(1)Compared with non aeration,micro nano aeration has little difference in pressure flow relationship in labyrinth channel,and the difference in flow coefficient and flow pattern index is slightly small;Under the same inlet pressure,the outlet flow of aeration is slightly smaller than that of non aeration.Considering that the air-water ratio in the channel is of great significance to the water-gas transmission law,the volume method is more accurate and simple,and can be widely used.(2)It is feasible to observe the gas-liquid two-phase flow in the labyrinth channel by using visualization technology.In the labyrinth channel of aeration drip irrigation,bubbly flow is a typical flow pattern,with occasional slug flow,and bubble adhesion is also common,but the law is not obvious.On the whole,smooth and smooth bubble trajectories are observed in the mainstream region and a large number of swirling bubble trajectories are observed in the vortex region.With the increase of inlet pressure,more bubbles enter the vortex area,the number of gyrations increases,and the bubble gyration circumference decreases,so that the average total length of bubble trajectory does not change significantly.(3)Under the condition that the characteristic size of the channel is basically the same,the flow pattern and bubble motion characteristics of gas-liquid two-phase flow are not affected by the channel geometry.The increase of inlet pressure significantly increases the instantaneous velocity of bubbles,and also affects its distribution area.The instantaneous velocity of bubbles in the mainstream area is large,and the direction is consistent with the flow direction;the instantaneous velocity of bubbles in the vortex area is small,and the direction is inconsistent with the direction of water flow.In addition,the maximum value of bubble instantaneous velocity always appears at the tooth tip,and the minimum value always appears at the corner of the back water surface of the tooth groove.(4)There are significant differences in bubble morphology at different positions along the channel.Along the whole labyrinth flow path,the number of bubbles decreases gradually,and larger diameter bubbles appear continuously and the proportion increases gradually,resulting in the gradual increase of the average diameter of bubbles;The average time and average velocity of bubbles passing through the observation window have no obvious change law along the whole process of the channel,and the difference is not significant.(5)The inlet pressure has a great influence on the bubble motion characteristics.At the same position of the flow channel,the higher the inlet pressure,the less the number of bubbles,and the smaller the average diameter and maximum diameter of bubbles.It can be seen that the inlet pressure has a great influence on the distribution of bubble diameter;The average time and average velocity of bubble sample passing through the channel in the shooting window decrease and increase respectively with the increase of inlet pressure;The trace length of single bubble,the maximum value of velocity and the basic velocity of bubble group increase with the increase of inlet pressure.There are significant differences in the number of bubbles in the upper and lower half of the adjacent flow channel,the average velocity and the average distribution time of bubbles in the upper and lower half of the flow channel.Comprehensively considered,under high inlet pressure,more gas is dissolved in water,while the undissolved gas exists in the form of microbubbles,but it has smaller diameter and greater movement speed,so that the system can obtain better water and gas transportation effect.The research provides theoretical support for the scientific operation of micro nano aeration drip irrigation system.