Experimental Study of Augmented Heat Transfer on the Endwall of a Square-Sectioned Sharp-Turn Channel Using Novel-Type Vortex Generators

This study presents a newly designed endwall equipped with novel-type vortex generators (NVGs) in a 180 degree sharp-turn channel for heat exchange devices. Two types of NVGs with different heights are applied in this study, i.e., V-type and arc-type forms. The NVGs are arranged parallel and equally spaced on the internal endwall but perpendicular to the flow direction. Liquid crystal thermography, pressure difference measurements, and a statistical method are utilized to analyse the heat transfer, friction factor, thermal enhancement factor and uniformity in temperature on the endwall equipped with an array of parallel NVGs of a sharp-turn channel. Three Reynolds numbers are considered, namely, 10,000, 15,000, and 20,000. The current design is compared with conventionally turbulated endwalls of sharp-turn channels presented in the open literature. The results indicate that the heat transfer rate is greatly augmented by inserting an array of NVGs compared to a smooth endwall channel. The endwall with NVGs can strengthen the lowest Nusselt number zone on the smooth endwall, which has uneven heat transfer, to achieve enhanced and uniform heat transfer. The geometric parameters of the height and V-type form of the NVGs can stimulate incremental heat transfer. The high V-type forms of the NVGs provide the maximum increment of the normalized Nusselt number and thermal enhancement factor in a sharp-turn channel, which are 32% and 18% higher than the corresponding values of the smooth endwall, respectively. This work demonstrates the potential of an array of parallel NVGs to provide endwall heat transfer enhancement in a sharp-turn channel with an acceptable pressure drop penalty