Effects of winglets to augment tube wall heat transfer in louvered fin heat exchangers

The louvered fin heat exchanger, a type of compact heat exchanger, has been used heavily in the automotive and air conditioning industries for the last several decades. The majority of past research, aimed towards improving louvered fin exchanger efficiency, has focused on optimizing various parameters of the louvered fin. The experimental study presented in this paper concentrates instead on augmenting the heat transfer along the tube wall of the compact heat exchanger through the use of winglets placed on the louvers. The experiments were completed on a 20 times scaled model of an idealized louvered fin exchanger with a fin pitch to louver pitch ratio of 0.76 and a louver angle of 27°. The Reynolds numbers tested, based on louver pitch, were between 230 and 1016. A number of geometrical winglet parameters, including angle of attack, aspect ratio, direction, and shape, were all evaluated based on heat transfer augmentation, friction factor augmentation, and efficiency index (combination of both augmentations). In an attempt to optimize these winglet parameters, tube wall heat transfer augmentations as high as 39% were achieved with associated friction factor augmentations as high as 23%.