Turbulent drag reduction with surfactant additives - basic research and application to an air conditioning system

摘要

It is well known that a small amount of chemicals such as water-soluble polymers or surfactants dramatically suppresses turbulence when they are added to liquid ow at large Reynolds number. In the last two decades, the application of surfactants to heat transportation systems such as district heating and cooling systems has attracted much interest among researchers. It has been revealed that 70% of the pumping power used to drive hot water in primary pipelines or district heating systems was saved by adding only a few hundred ppm of surfactant into the circulating water. The technological achievement requires a new design strategy for pipeline networks and heat exchangers to handle the drag reducing liquid flow. In the case of a Newtonian uid such as water or air, the knowledge for designing uid systems has been accumulated and the accuracy of numerical prediction is sufficient. On the other hand, the design system for surfactant solutions is not mature because drag-reducing ow phenomena are much more complicated than for Newtonian ow, for example, the friction factor for a surfactant solution depends not only on Reynolds number but also pipe diameter. In order to provide a design strategy for heat transportation systems using surfactant additives, we are now carrying out both experimental and numerical studies for surfactant solutions. In this lecture, experimental and numerical studies on the turbulence structure in drag reducing flow will be introduced. The result of an application study relating to the air conditioning system will be also shown.