In experimental studies using polymeric type drag reducers, mechanical degradation is often a problem. A method is described, based on partially degrading the solution to get a fluid that is stable over time, which greatly simplifies working with DRA. The method has been adopted to demonstrate, and quantify, diameter effects in single-phase flow. Further, the effects of DRA in two- and three-phase flow have been studied in a D=100mm pipe. The overall conclusion is that the drag reduction increases with the inlet fraction of the liquid that carries the DRA.
This paper describes some key findings from experimental work on the effects of polymeric type drag reducing agents (DRA) in multiphase pipe flow, carried out at IFE. The work has supported the development of a mechanistic model that accounts for the effects of DRA in multiphase flow, a work that is hindered by the yet unresolved diameter dependence in the friction law.
The reduction of drag (or pressure drop) in turbulent flows by adding long-chained, high molecular weight polymers was first reported by Toms in 1948. Today, chemical type drag reducer agents are in two classes; the polymer type (PDRA) and the surfactant type drag reducers (SDRA). Only PDRA are dealt with in this paper. The PDRA suffer from permanent mechanical degradation (polymer scission) in pumps and valves, resulting in reduced performance, and are therefore mostly used in once-through applications. The SDRA, on the other hand, are capable of forming very long cylindrical micelles, with self-healing properties. SDRA are therefore more suitable for closed circulating fluid systems such as district heating pipelines and heat exchangers. The oil and gas industry have traditionally used drag reducers to reduce the pressure drop for the transport of single-phase liquids over long distances.