Finless; Fractal; Heat exchanger; Heat transfer
Air-to-refrigerant heat exchangers are a main component in air-conditioning and heat pump systems and are therefore a topic of major research focus. Such heat exchangers, mainly made of fin-and-tube and microchannels, use fins to augment the heat transfer area of the air-side. Recently it has been shown that finless designs using â‰¤ 1 mm hydraulic diameter bare tubes can deliver better air-side heat transfer performance than conventional heat exchangers. In current study, a novel air-to-refrigerant heat exchanger consisting of branching bare tubes with two different tube diameters is designed using fractal theory. The tubes in the first level split into two or more tubes at certain angles. The secondary tubes then merge back to the first level tube again. Principles of fractal design are applied to improve both air-side heat transfer area and heat transfer coefficient. The heat transfer and pressure drop characteristics are numerically analyzed using a 3-D model and compared with the bare tube heat exchangers. The novel finless heat exchanger based on fractals is found to have intrinsic advantage of increasing heat transfer performance and is a promising area for future investigations.