The total air budget in oxygenated water flowing in a drip tape irrigation pipe

In this work we concentrate on the measurement of the total air volume profile along an irrigation drip tape and the pilot testing of a visualization assembly suitable for use in the irrigation industry under field conditions. The visualization system is based on continuous image capturing and can be used to determine the number and size of bubbles, as well as estimate the void fraction percentage of air in aerated water stream.The research results produced a number of positive outcomes for continuous monitoring of bubble behaviour during irrigation. We obtained data on the air fraction in aerated water using our experimental setup for three treatments – open end drip tape, closed end drip tape and closed end drip tape with surfactant added to the air/water stream. From these data we determined the void fraction of air in the irrigation water stream along the length of drip tape, showing a decline with distance from the Mazzei Venturi model 384 air source, an effect offset to some extent by addition of 2 ppm of surfactant to the irrigation water. The void fraction estimates derived from the images from the camera system are consistent with the system specifications from the Mazzei air injectors performance based on Bernoulli’s principle.

► Bubbles profiles collected over 10 min using multisizer to find bubble distribution over time.
► Bubble visualization unit developed to photographically capture bubble images.
► Air/water mixed using venturi and bubble profiles determined for three treatments at six stations.
► Void fraction of air at the six stations in drip tape was estimated from the bubble images.
► Void fraction of air higher along drip tape stations due to addition of a small amount of surfactant.