Experimental evaluation of biopolymer and synthetic polymer drag reduction in industrial scale facilities

In this work experimental tests have been performed to investigate drag reduction by polymers in industrial scale pipes (30, 50 and 100 mm ID). Both synthetic (Polyetylene Oxide, PEO and Partially Hydrolysed Polyacrylamide, HPAM) and bio (Xanthan Gum, XG) polymers have been used with the objective of building a self consistent data base to better understand and predict, polymer drag reduction in industrial scale facilities. To this aim, we run a series of experiments measuring the friction factor at different polymer mass concentrations (100, 500, 750, 1000 and 2000 ppm w/w for the XG; 0.25, 0.5, 1, 5 and 10 ppm w/w for PEO and HPAM) spanning values of Reynolds number in the range 758 to 297 000 (depending on the pipe size). For one polymer (PEO) two different molecular weights have been tested (4 x 10^6 and 8 x 10^6 g/mol). The rheology of each of the working fluids (water plus one of the polymers at many different concentrations) has been characterised experimentally before performing tests to evaluate the friction factor. Results are presented in the form of (1) pressure drop per unit length as a function of the bulk velocity in the pipe, (2) using Prandtl-Kármán coordinates and (3) as percent drag reduction. Our data are in excellent agreement with data collected in different industrial scale test rigs, compare well with data gathered in small scale rigs and scaled up using empirically based design equations and with data collected for pipes having other than round cross section. The data confirm the validity of a design equation inferred from Direct Numerical Simulation which was recently proposed to predict the friction factor. We show that scaling procedures based on this last equation can assist the design of piping systems in which polymer drag reduction can be exploited in a cost effective way. Data have also been compared with correlations developed to predict the upper bound for drag reduction when the mechanical degradation of the polymer is taken into account. Our results confirm that these correlations can be operatively used to identify a priori polymer performances as drag reducing agents in industrial scale facilities. Preliminary results to investigate the potential role of polymeric drag reduction in fibre laden flows are also presented