| Drag reducing additives can reduce turbulent pressure loss by nearly 90% and can decrease pumping energy requirements and increase flow rates in fluid flow systems. Unfortunately, drag reduced flow is accompanied by lower convective heat transfer coefficients, which is undesirable in otherwise attractive applications such as district heating and cooling systems, heated tube bundles for undersea petroleum production, and other recirculating heat transport systems.;In this work, two projects were completed in which heat transfer was successfully enhanced in water-based surfactant drag reducing solutions. In the first study, three different rotating agitators were installed inside the inner tube of a concentric tube heat exchanger to enhance heat transfer in a surfactant drag reducing solution. An earlier mathematical model for heat transfer in scraped surface heat exchangers was adapted for this application so that the effectiveness of agitators with different geometries could be compared quantitatively. In addition, an enhancement efficiency factor was defined to compare power efficiency with previous methods. It was found that agitation can increase the effective inner heat transfer coefficient to exceed that of pure water; heat transfer reduction compared to water was reduced from 60% to --20%. In addition, the enhancement was found to be more energy-efficient than static mixing devices across a wide range of flow rates.;In the second study, the behavior of a mixed cationic / zwitterionic drag reducing surfactant system was explored. Precipitation of the solution into surfactant-rich and water-rich phases was observed under certain conditions, and this behavior was found to be extremely sensitive to composition, temperature, and shear. A heat transfer enhancement scheme exploiting the phase behavior was successfully demonstrated in which heat transfer reduction was eliminated while drag reduction performance was maintained. |
