微纳米曝气增氧滴灌系统水-氧传输特性研究

Transport Characteristics of Water-Oxygen Transfer in Micro-nano Bubble Aerated Drip Irrigation System

摘要:

为阐明微纳米增氧曝气滴灌系统中水氧协同传输规律,以90m长非压力补偿式(HL)和压力补偿式(NT)滴灌带为对象,设置6个工作压力(25~150kPa)以及不加氧(0L/min)和加氧(1.5L/min)两种运行模式,测定滴灌带沿程出流量及均匀性,并在加氧条件下测定溶解氧(DO)的沿程变化,采用方差分析和偏效应量η2评价各因素影响。结果表明:工作压力和距离是影响系统水氧传输的主导因素。HL出流量主要受工作压力(η2≈0.919)和距离(η2≈0.065)影响,NT出流量主要受工作压力(η2≈0.772)及其与距离交互作用(η2≈0.118)影响;与不加氧相比,加氧条件下两类灌水器出流量及其均匀性变化均较小,其中HL为极小效应(η2<0.01),NT为小效应(η2<0.06),表明在本试验加氧条件下,微纳米增氧对系统水力性能扰动有限;溶氧量均随距离增加而衰减,随工作压力先升高后趋于稳定,HL在100kPa时溶氧量均匀性最佳(98.46%),NT在75kPa及以上可保持较高且稳定的出流量与溶氧量均匀性(均大于97%)。

Abstract:

The coupled transport of water and oxygen in a micro/nanobubble-aerated drip irrigation system was investigated, with particular emphasis placed on the effects of operating pressure, distance along the lateral, and emitter type on hydraulic performance and dissolved oxygen (DO) distribution. To address this issue, two 90m drip tapes, namely a non-pressure-compensating tape (HL) and a pressure-compensating tape (NT), were tested under six operating pressures (25~150kPa) and two aeration treatments, i. e., non-aeration (0L/min) and aeration (1.5L/min). Emitter discharge, Christiansen's uniformity coefficient, and DO concentration were measured at multiple locations along the lateral. The independent and interactive effects of pressure, distance, and aeration were quantified by analysis of variance, and their relative contributions were evaluated using partial eta squared η2. It was found that operating pressure and distance were the dominant factors governing water-oxygen transport in both drip tapes. For HL, emitter discharge was controlled primarily by operating pressure (η2=0.919), followed by distance (η2=0.065). For NT, emitter discharge was also governed mainly by operating pressure (η2=0.772), as the interaction between pressure and distance showed a stronger contribution (η2=0.118). Compared with the non-aerated treatment, aeration caused only negligible to small changes in hydraulic performance, with effect sizes below 0.01 for HL and below 0.06 for NT, and with changes in discharge uniformity limited to 2.2% for HL and 1.8% for NT. Under aerated conditions, DO concentration was reduced with the increase of distance along the lateral but was increased with the increase of operating pressure. At 25 kPa, the DO concentration declined from the inlet to the end of the lateral by 17.88% in HL and 22.61% in NT. When the pressure was increased from 25kPa to 150kPa, the DO concentration was increased by 18.36%~36.33% in HL and by 6.73%~33.35% in NT, indicating that high pressure effectively alleviated longitudinal DO attenuation. The highest DO uniformity for HL was obtained at 100kPa, reaching 98.46%, whereas NT maintained both discharge and DO uniformity above 97% at pressures of 75kPa and higher. It was therefore concluded that micro/nanobubble aeration imposed only limited disturbance on the hydraulic characteristics of the drip irrigation system, while operating pressure remained the key factor controlling stable and uniform water-oxygen delivery over long transport distances. The originality of the research can lay in the systematic quantification of the relative contributions of pressure, distance, aeration, and emitter type to both hydraulic behavior and DO transport in a long-distance micro/nanobubble-aerated drip irrigation system, and in the identification of pressure ranges suitable for coordinated water-oxygen delivery in non-pressure-compensating and pressure-compensating drip tapes.