A brief review on frictional pressure drop reduction studies for laminar and turbulent flow in helically coiled tubes

• Review on pressure drop reduction studies in helically coiled tubes.
• Air bubbles, surfactant and polymer additives are effective in diminishing drag.
• Drag reduction is diminished in relation to straight tubes.
• Drag reduction is predominantly evident in turbulent flow.
• Drag reduction diminishes with higher coil curvatures and excessive Re numbers.

This review, summarises the pertinent literature on drag reduction (DR) in laminar and turbulent flow in coiled tubes. Due to their compact design, ease of manufacture and superior fluid mixing properties, helically coiled tubes are widely used in numerous industries. However, flow through coiled tubes yields enhanced frictional pressure drops and thus, drag reduction is desirable as it can: decrease the system energy consumption, increase the flow rate and reduce the pipe and pump size. The main findings and correlations for the friction factor are summarised for drag reduction with the: injection of air bubbles and addition of surfactant and polymer additives. The purpose of this study is to provide researchers in academia and industry with a concise and practical summary of the relevant correlations and supporting theory for the calculation of the frictional pressure drop with drag reducing additives in coiled tubes. A significant scope for future research has also been identified in the fields of: air bubble and polymer drag reduction techniques.