The Application of Shape Memory Alloy as Vortex Generators and Flow Control Devices for Enhanced Convective Heat Transfer

This paper is concerned with convective heat transfer enhancement of heated surfaces through the use of vortex generators and flow control devices. A preliminary proof-of-concept investigation has been carried out into the use of active vortex generators and flow control elements, both manufactured from Shape Memory Alloys (SMAs) which are activated at set temperatures. The vortex generators change their shape to intrude further into the flow at high temperature to enhance heat transfer, while they maintain a low profile at low temperatures to minimise flow pressure losses. One set of vortex generators was made from pre-alloyed powders of SMA material in an advanced rapid prototyping process known as Selective Laser Melting (SLM). Another set of devices was also made from commercially available flat annealed thin SMA sheets for comparison purposes. The flow control elements are devices that preferentially guide the flow to heated parts of a surface, again using temperature-activated SMAs. Promising results were obtained for both the vortex generator and flow control device when their temperatures were varied from 20° to 85°C. The vortex generators responded by increasing their angle of attack from 20° to 35° while the wavy flow control elements straightened out at higher temperatures. As the designs were two-way trained, they regain their initial position and shape at a lower temperature. The surface temperature of the heated plate on which the active devices were positioned reduced between 8 to 51%, indicating heat transfer enhancement due to the generated vortices and changes in air flow rates.