Temperature, concentration, and pumping effects on PAM viscosity

As polyacrylamide (PAM) use in irrigated agriculture increases, new methods are being sought to accurately and automatically apply PAM with irrigation water. PAM is also beginning to be used in sprinkler irrigation. However, little information is available about flow characteristics of PAM solutions . This study was conducted to investigate temperature, concentration and pu mping effects on viscosity of two agricultural PAM formulations: a dry powd er and an inverse oil emulsion. Flow tests, using solutions prepared from t he dry powder PAM, showed that viscosity decreased as flow rate increased f or concentrations greater than 400 ppm. Thus, accurately predicting PAM vis cosity at concentrations greater than 400 ppm is difficult because viscosit y varies not only with concentration and temperature, but with flow conditi ons. Flow rate changes due to temperature fluctuations, however, should be minimal for the oil emulsion PAM over typical temperature ranges occurring under field conditions if tubing diameter is greater than 10 mm and tubing length is less than 1 m, which should be adequate for all surface irrigatio n applications. The two PAM products tested had similar viscosity relations hips with temperature and concentration. PAM viscosity for solutions with c oncentrations < 24 ppm only increased about 5% relative to water for each 1 0 ppm increase in PAM concentration. Pumping a 2400 ppm PAM solution just o nce through a centrifugal pump reduced viscosity 15 to 20%; pumping five ti mes reduced viscosity approximately 50%. The viscosity reduction is thought to result from breading or shearing the PAM molecules, reducing its effect iveness to stabilize the soil surface and reduce soil erosion .