Predicting the efficiency of a DRA is still dependent on the use of models developed through field tests. Two forms of the model are widely used for liquid pipelines, one correlates Drag Reduction (DR) as a function of DRA concentration only, and the other correlates DR as a function of DRA concentration and Reynolds number. Both are pipeline and fluid specific, that is, have limitations to pipelines similar to the tested in pipe size and fluid property, and the former also has limitations in flow rates. This paper presents a comprehensive model in which three more variables are introduced - type of DRA, pipe diameter and fluid viscosity - in addition to DRA concentration and Reynolds number so the model applies to a variety of pipelines and a wider range of fluid properties.
Field tests show that DRA degrades, or the effective concentration of a DRA decreases as it flows through pipelines. So, a DRA degradation coefficient was also introduced in the model as a supplement to the variable of DRA concentration.
The type of DRA used for crude oils is usually different from that for refined products and, most of all, the difference in fluid viscosity, therefore in Reynolds number, is so great that it is hard to develop a model suitable for both crude oils and refined products, so a separate model is developed for the products.
Drag reducing agents or DRA have been used in the pipeline industry for decades to improve fluid flow in pipelines. They are any material that reduces frictional pressure loss during fluid flow in a conduit or pipeline. Pressure loss reduction is achieved by reducing the level of turbulent motion in the flow. Using DRA allows increased flow using the same amount of energy or decreased pressure drop for the same flow rate of fluid in pipelines.[1]
