Backpressure effects on the flow-pressure relation of driplines

ABSTRACT For drip irrigation design and management, it is necessary to know the relation between flow and pressure acting on emitters. In the case of subsurface drip irrigation, the backpressure phenomenon may change the hydraulic characteristics of emitters. Thus, this study aimed at determining such relationship between flow and pressure of different driplines in surface and subsurface conditions; aiming to find possible differences in hydraulic behavior. We tested four emitter types; two pressure compensating (D5000 and Hydro PCND) and two non-pressure compensating (TalDrip and Jardiline). Emitter flow rates were attained in atmospheric conditions and submerged in water, in which submergence levels represented backpressure. Assays were performed using inlet pressures of 80, 100, 120, and 150 kPa for the Hydro PCND dripline and 25, 50, 100, and 150 kPa for the other ones; the backpressures were of 0.49, 1.47, 2.45, 4.41 and 6.37 kPa with four replications. The emitters had their proportionality constants and discharge exponents changed in submerged applications, representing backpressure effect. Non-pressure compensating emitters had their discharge exponent decreased, while in pressure compensating ones, it was increased. Backpressure reduced emitter flow rates at all evaluated pressures.

摘要
滴灌（drip irrigation）设计与管理中，需明确流量与灌水器（emitter）所受压力的对应关系。地下滴灌（subsurface drip irrigation）场景下，反压（backpressure）现象可能改变灌水器的水力特性。为此，本研究旨在明确地表与地下滴灌条件下不同滴灌管（dripline）的流量-压力关系，以探究其水力行为的潜在差异。本研究共测试4类灌水器：2款压力补偿型（pressure compensating）滴灌管，分别为D5000与Hydro PCND；另外2款为非压力补偿型（non-pressure compensating）滴灌管，分别为TalDrip与Jardiline。试验分别在大气环境与浸水工况下测定灌水器流量，其中浸水深度用于表征反压水平。试验采用以下参数开展：Hydro PCND滴灌管的进口压力设为80、100、120、150 kPa，其余滴灌管的进口压力设为25、50、100、150 kPa；反压水平设为0.49、1.47、2.45、4.41与6.37 kPa，每组设置4次重复。浸水工况下，反压作用会改变灌水器的比例常数与流量指数。非压力补偿型灌水器的流量指数会降低，而压力补偿型灌水器的流量指数则会升高。在所有测试的进口压力下，反压均会降低灌水器的流量。