Controlled turbulence enhances performance

Tom Shelley reports on projects that benefit from more turbulence and systems that benefit from less, and how to achieve the desired results.

When working with maximum efficiency and saving energy, turbulence can be a help if it improves heat transfer or keeps solids in suspension, but it does increase flow resistance and pressure drop, whereupon it adds to cost. The trick is to manage it, and introduce it when it helps, and suppress it when it doesn't. Vanes and other elements within the fluid flow stream can be used to both to introduce turbulence and to stop it. Although one might think that all possible configurations have already been invented, Stanko Bezek, from Croatia, has developed and applied for a patent on yet another configuration which he identifies as a "Tube Flow Turbulator type TIP-09/A-B", specifically designed to keep solids in suspension, which he is marketing through his company, ESB Beneing. Configured to fit between pipe flanges and valve inlets in minimal space, it consists of three parts which are screwed together with gaskets between them. The first part is a flange, the second part has three or more channels, and the third part has reversed channels in an output cone. It is available in sizes DN (Diametre Nominal) 20 to 400mm, and can be made from materials compatible with water, waste water, hot water, steam and corrosive media. Pressure ratings are up to PN 40, and temperature range, -20°C to +350°C. Bezek says interest in using it is coming from the MOL Oil company and pharmaceutical and water supply companies. At the British Invention Show, small, plastic inclined vanes placed in a water flow induced sufficient vortex to improve the output of solar vacuum tube panels by as much as10%-20%. In these, cold water flows down an inner tube and warmed water then flows up over the outside, within the vacuum tube collector, with the vanes between the inner tube and the collector tube. The vortex action induced by the vanes improves heat transfer. The idea has been developed and prototyped by Far East University in Taiwan. On the other hand, Atlas Copco's 'AIRnet' compressed air piping system takes advantage of every possible opportunity to reduce turbulence and resulting extra pressure drop. The modular system consists of corrosion-resistant, anodised aluminium pipes with smooth interiors. This is in contrast to steel pipes which normally have rough interiors, especially when they have had a chance to corrode. In addition, the smooth bore fittings have internal fin guides to eliminate any turbulence that has developed. A pressure drop of 1 bar results in 7% energy savings in compressor installed power. Resistance to corrosion also reduces the possibility of leaks. A 3mm diameter hole anywhere within a galvanised steel distribution network caused by corrosion can lead to a compressor requiring an additional 4kW of power to maintain system pressure. The system also makes used of self aligning, fully sealed polymer fittings with integrated 'O' rings that further eliminate the possibility of leaks. Furthermore, the pipe work weighs only on fifth that of its steel equivalent while being robust, easy to install, taking about one third the time compared with a conventional system. The pipes are pushed into the polymer fittings, tightened by hand and secured with a spanner. The system is resistant to mechanical shocks, fire, thermal variations and outdoor weather conditions. The fittings and pipe work can be extended, disconnected, reconnected and re-used many times, without loss of integrity. Design Pointers • 'Turbulator' device inserts between pipe and valve flanges in order to increase turbulence to prevent solids settling within the valve • Vortex inducing vanes dramatically improve heat transfer and efficiency in vacuum tube solar water heaters • Vanes and design within compressed air fittings can on the other hand be used to reduce turbulence and consequent pressure drop