NONINVASIVE INTERROGATION OF LOCAL FLOW PHENOMENA IN TWISTED TAPE SWIRLED FLOW VIA POSITRON EMISSION PARTICLE TRACKING (PEPT)

Twisted tape inserts are often used to enhance the performance of heat exchangers. Simulations suggest the existence of secondary flows and modified axial velocity profiles in these swirled flows, with only limited experimental evidence for these predictions. In this work, positron emission particle tracking (PEPT) is used to interrogate turbulent twisted tape swirl flow in a pipe. PEPT is a noninvasive, radiotracer based flow measurement technique that does not require optical access, making it suitable for measurements in a number of engineering flow systems. The existence of the altered velocity profile and secondary flows is confirmed, and flow is seen to still be developing 20 diameters downstream of the twisted channel entrance. These results are in line with predictions and point to possible regions of reduced heat transfer and hot spots in twisted tape based heat exchangers. Suggestions are made for future experiments to investigate heated flows, utilizing the ability of PEPT to image flows in opaque systems for validating simulation of flows in engineering equipment.