Abstract
Previous work has tied the drag reduction properties of polymer solutions to type and concentration of salts, rather than its ionic strength, although it is a more extensive parameter to investigate the effects of salt contents on fluids behavior. The current study aims at investigating the relationship between ionic strength and drag reduction characteristics of polymer solutions when flowing in straight tubing. 
 
 Nalco ASP-700 and ASP-820, two common anionic AMPS copolymers, are examined with various salts (2% KCl, 4% KCl, and synthetic seawater). Flow tests were conducted using a small-scale flow loop that includes a straight tubing with an outside diameter of 1.27 cm and a length of 4.57 m. 
 
 It has been found that drag reduction performance of polymer solutions is well correlated with ionic strength, rather than salt type and/or concentration. With high ionic strength, lower drag reduction is noticed despite of the reduced salt concentration. Nevertheless, at higher Reynolds number, the effects of ionic strength minimizes. Both polymer solutions exhibit effective drag reduction characteristics and their behavior is greatly affected by polymer type, shear rate, and salt content. Correlations, with acceptable confidence level, between drag reduction ratio and solutions ionic strength are proposed. The correlations are strongly recommended to investigate the effects of salt types and/or concentrations, represented by its ionic strength on drag reduction behavior of polymer solutions in straight tubing.
Highlights
Discovered more than 60 years ago, Toms effect (Toms 1949) or drag reduction is a turbulent flow phenomenon where frictional pressure losses can be reduced drastically by adding a minute amount of high-molecular weight components such as polymers and surfactants
Drag reduction characteristics and rheological behavior of these drag-reducing solutions are very sensitive to the nature and structure of added salts
The aim of the present study is to experimentally investigate the correlation between ionic strength and drag reduction of polymeric solutions flowing in straight tubing
Summary
Discovered more than 60 years ago, Toms effect (Toms 1949) or drag reduction is a turbulent flow phenomenon where frictional pressure losses can be reduced drastically by adding a minute amount of high-molecular weight components such as polymers and surfactants. They are known to lower the friction pressure losses up to 80% over the base solvent (Savins 1964; Lumely 1973). Kamel and Shah (2009), for example, investigated the effect of two different salt solutions (2% KCl and synthetic seawater) on drag reduction characteristic of two anionic polymers (ASP-820 and ASP-700) in straight tubing. The developed correlations in both studies used salt concentration (Cs) to quantify the http://esr.ccsenet.org
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