Drag reduction and degradation of nonionic surfactant solutions with organic acid in turbulent pipe flow

• We investigate the drag reduction and degradation of nonionic surfactant.
• The addition of a small amount of organic acids improves drag-reducing abilities.
• The drag reduction can be obtained at high Reynolds number owing to organic acids.
• The high level of the drag reduction keeps for a long time owing to organic acids.
• The ability of the present surfactant is comparable with typical cationic one.

We investigated the drag reduction and degradation of nonionic surfactant (Aromox) solutions, which mainly consisted of oleyldimethylamine oxide (ODMAO) and had non-toxic and biodegradable properties, by measuring the pressure drop and flow rate in the circuit pipe flow system using a pump. It is revealed that the addition of a small amount of organic acids such as salicylic and cuminic acids to nonionic surfactant solutions noticeably improves mainly two kinds of drag-reducing abilities. The first is the increase in the critical Reynolds number at which the drag reduction ratio is the maximum, i.e., the drag reduction can be obtained at the larger Reynolds number. The second is the decrease in the level of degradation caused by the continuous circulation of surfactant solutions in the closed pipe system, so that the high level of the drag reduction keeps for a long time. Comparing with the mixture of typical cationic surfactant (Ethoquad O/12) which consists of the oleyl-bis-hydroxyethyl-methyl-ammonium chloride (OBHEMA) and sodium salicylate as a counterion in practical use, the mixture of nonionic solution and salicylic acid proposed in this study shows the comparable or better drag-reducing ability at the same concentration and temperature of surfactant solutions.