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Advances in Mechanical Engineering
Volume 2011 (2011), Article ID 952659, 2 pages
Drag Reduction of Turbulent Flow by Additives
1State Key laboratory of Multiphase Flow in Power Engineering, Xi'an Jiaotong University, Xi'an 710049, China
2Department of Mechanical Engineering, Tokyo University of Science, Chiba 278-8510, Japan
3Beijing Key Laboratory of Urban Oil and Gas Distribution Technology, China University of Petroleum-Beijing, Beijing 102249, China
Received 9 August 2011; Accepted 9 August 2011
Copyright © 2011 Jinjia Wei et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Turbulent drag reduction by additives is a striking phenomenon in which the presence of small quantities of additives in a carrier fluid can reduce turbulent friction greatly compared with the pure fluid at the same flow rate. There are several kinds of drag reducers including surfactants, polymers, bubbles, and fibers, which are promising for saving pumping energy in fluid transportation of pipelines. The key issues related to the drag-reducing flow by additives are the complicated microstructure, rheological properties, turbulence structure, drag reduction and heat transfer characteristics, and heat transfer enhancement. The purpose of this special issue is to collect a series of papers to show the recent advancement of these aspects. We received active submissions from America, Australia, China, Japan, and Russia, and finally 10 papers were accepted to publish in the special issue after peer reviews.
The first two papers of this special issue review the advancement of turbulent drag reduction by additives from two different respects. The first paper gives a full review on the main advancements of drag reduction of fibers, polymers, and surfactants during these 60 years, including background, application, development, theory, and research methods of the three different drag reducers and discusses future directions of development. The second paper summarizes the turbulence drag reduction methods by joint use of compliant coatings with other drag reduction means and shows fine outlooks of turbulence management by joint use of compliant coatings, riblets, polymer additives, and microbubbles.
Drag reduction and heat transfer characteristics of drag-reducing flow are investigated experimentally by four papers in this issue. The third paper investigates the drag reduction performance of bacterial cellulose suspensions and observes a maximum drag reduction ratio of 11%. Suspensions of nata de coco, which is a layered form of bacterial cellulose, show a higher drag reduction at lower concentrations. The fourth paper studies the combined effects of temperature and Reynolds number on heat transfer characteristics of a cationic surfactant solution with different concentrations. The results show that the heat transfer performance of cationic surfactant solution is largely deteriorated and is greatly affected by concentration, temperature, and Reynolds number. It is supposed that temperature and shear stress are two kinds of energy applied on the surfactant microstructure, which can be helpful to the surfactant network formation or dissociation depending on their values. The fifth paper describes the flow drag and heat transfer reduction characteristics of organic (potassium acetate) and inorganic (calcium chloride) brine solutions. The nonionic surfactant oleyl dihydroxyethyl amine oxide (ODEAO) is used as a drag-reducing additive. It is found that the formation of rod-like micelles in a non-ionic surfactant is related to the ionic strength of the brine solution. The sixth paper uses two methods, high-efficiency vortex (HEV) static mixer, and Helix static mixer, to enhance heat transfer performance of drag-reducing flow of Ethoquad O/12 with sodium salicylate. It is found that the Nusselt numbers by using the HEV are three to five times those of normal drag-reducing flow without mixer with only modest energy penalty.
The microstructure and rheology, and turbulence characteristics of drag-reducing fluid flow are investigated by three papers to reveal drag reduction mechanisms. The seventh paper aims at gaining insights of interrelationships among turbulent drag reduction rate, rheological properties and micelle microstructures of drag-reducing surfactant solution by measuring the aggregation number, turbulent drag reduction and shear-rate-dependent shear viscosity of sodium dodecyl sulfate (SDS), and CTAC aided with sodium salicylate. The eighth paper investigates zonal structures in surfactant drag reducing flow. It is found that there appears an area where the root mean square of streamwise velocity fluctuation and the vorticity fluctuation sharply decrease toward the center of the channel, indicating that two layers with different turbulent structure coexist on the boundary of this area. The layer in the near-wall region has a striped structure, and the layer in the center of the channel has a grained structure. The ninth paper mainly analyzes the Reynolds shear stress in drag-reducing flow. The results show that when drag reduction reaches the maximum value, Reynolds shear stress disappears and reaches zero although the RMS of the velocity fluctuations is not zero.
The final paper of this special issue evaluates surfactant drag-reduction effect in a district heating system based on the experimental data from laboratory. The results show that the reduction of the pressure drop in the system reaches 23.28% by the addition of surfactants, indicating a very good energy saving effect and application prospective.