SENSITIVITY OF THIN-WALLED DRIP TAPE EMITTER DISCHARGE TO WATER TEMPERATURE

Abstract

One of the primary goals in the design of microirrigation systems is to have a hydraulic balance to ensure uniformemitter discharge. However, while most design processes focus on pressure distributions and changes associated with frictionand elevation differences, elevated water temperatures will change the physical properties of the water and may change thephysical properties of some emitters. Laboratory studies were conducted to measure the effects of water operating temperatureon the sensitivity and discharge rate of emitters from thin-walled drip tape (collapsible emitting hose) products. Two differentproduct types (Roberts Ro-Drip, RD; and T-Tape, TT,) each with two wall thicknesses, were evaluated. The RD productincluded wall thicknesses of 0.20 mm (8 mil, RD-08) and 0.38 mm (15 mil, RD-15), whereas the TT product included wallthicknesses of 0.25 mm (10 mil, TT-10) and 0.38 mm (15 mil, TT-15). Additional characterization tests included a standardoperating pressure/emitter discharge rate test and a tubing tensile stress (elongation) test. All tests were conducted inaccordance with ASAE Standard S553, Collapsible Emitting Hose (Drip Tape) Specifications and Performance Testing.Increases in water operating temperature from 21.C to 50.C resulted in an 18%, 44%, and 97% increase in emitter dischargefrom the RD-08 product at operating pressures of 55, 69, and 83 kPa, respectively. Emitter discharge rate changes in theRD-15 product were not as great (10 to 12% increase) for similar water temperature changes. Effects of water temperatureon the discharge rate from the TT products were quite different from the RD products. Emitter discharge rate increasedslightly(<5%) with water temperature at 55 kPa, but decreased by up to 7% at 83 kPa. TDR values (also referred to as atemperature flow rate index) relate the emitter discharge at each measured temperature value (qt.) to the emitter dischargeat the initial base temperature (q20.) [TDR = (qt.)/(q20.)]. In this work, the RD-08 product had a quadratic relationshipbetween temperature discharge ratio and water temperature, while the RD-15 product and both TT-10 and TT-15 productshad more linear relationships.<br><br>Designers of microirrigation systems need the hydraulic performance characteristics of the products that they areconsidering in a system design. Such information should come from the manufacturers of the various collapsible emitting hose(drip tape) products. Product information should clearly provide physical characteristic data such as the emitter exponentx, constant of proportionality k, temperature discharge ratio values, and maximum recommended operatingtemperature.