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Submitted to: Transactions of the ASAE
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 9/23/1998 Publication Date: N/A Citation: N/A Interpretive Summary: Polyacrylamide (PAM) has been used with tremendous success to control soil erosion in furrow irrigation. One concern with applying high concentration PAM solutions to irrigation water is air temperature fluctuations changing PAM viscosity, causing the PAM flow rate to change. Pumping PAM may also shear PAM molecules, possibly reducing its effectiveness to stabilize the soil surface. This study was conducted to learn more about flow characteristics of two agricultural PAM products. Viscosity measurements for the 30% active ingredient liquid PAM indicate that PAM flow rate changes due to temperature fluctuations should be minimal under field conditions. PAM viscosity for solutions concentrations less than 24 ppm only increased about 5% relative to water for each 10 ppm increase in PAM concentration. Therefore flow differences due to viscosity should be minimal between PAM-treated and untreated irrigation water in furrows. However, pumping a 2400 ppm PAM solution just once through a centrifugal pump reduced the viscosity 15 to 20%. Pumping the solution five times reduced the viscosity about 50%. The viscosity reduction is thought to result from breaking or shearing the PAM molecules. Thus, pumping should be avoided if possible when applying PAM. Technical Abstract: 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 pumping effects on viscosity of two agricultural PAMs: a dry powder and an inverse oil emulsion. Flow tests, using solutions prepared from the dry powder PAM, showed that viscosity decreased as flow rate increased for concentrations greater than 100 ppm. Thus, accurately predicting PAM viscosity at concentrations greater than 100 ppm is difficult because viscosity varies not only with concentration and temperature, but with flow conditions. 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. The two PAM products tested also had similar viscosity relationships with temperature and concentration. PAM viscosity for solutions with concentrations <24 ppm only increased about 5% relative to water for each 10 ppm increase in PAM concentration. Pumping a 2400 ppm PAM solution just once through a centrifugal pump reduced viscosity 15 to 20%; pumping five times reduced viscosity approximately 50%. The viscosity reduction is thought to result from breaking or shearing the PAM molecules, reducing its effectiveness to stabilize the soil surface and reduce soil erosion. |
