Drag reduction with polymers in stainless steel microtubes

Microsystems have been widely used in industry and biological medicine, such as heat exchangers, mixing and separation processes, fuel cells, DNA analysis, artificial blood vessels and so on. However, it is a possible concern that liquid flow resistance in microscale tubes increases significantly compared with that in conventional scale tubes which requires a higher pumping power. Since one of the goals of the microsystem is low energy consumption, the reduction of the required pumping power is highly desirable. It is well known that addition of a small amount of polymer to a Newtonian fluid can lead to a dramatic reduction of liquid flow resistance. Polyacrylamide (PAM), as a common drag reducing agent, has been widely used in conventional scale systems, such as district heating systems and oil transportation, to achieve energy saving and environmental protection goals. However, the application of drag reduction polymer in microtubes has not been well studied. In this work, the performance of PAM (Mw = 3 million) as a drag-reducing agent in stainless steel microtubes was investigated. A systematical investigation of liquid flow drag reduction behaviours through microtubes with diameters varying from 116 - 1016 μm and relative roughness in the range of 0.02–0.5% was performed in the Reynolds number range of 454 - 9680, using different concentrations (0, 1, 5, 10, 20, and 30 ppm) PAM aqueous solution as working fluids. Experimental results indicated that the drag reduction characteristic with PAM solution in microscale was different from that in conventional scale. The drag reduction characteristic curve in the laminar region was delayed and drag reduction appeared in transition region. The drag reduction percentage, DR (%), increased with increasing concentration of PAM and remained stable after a certain amount, decreased with the increasing of diameter, changed with Reynolds number. The maximum drag reduction percentage was found to be 54.56% for 30 ppm PAM when Reynolds number equaled to 5016 and diameter of stainless steel microtuble was 523 μm.