Description

The performance and size of refrigerant-to-air heat exchangers (evaporators and condensers) is mainly limited by the relatively low air-side heat transfer coefficients. This warrant that both surface area and convective coefficient on the air -side of the heat exchangers be increased substantially. While traditional solutions include adding high-density fins on the air-side surface, the goal of the design proposed in this study is to complement this by employing a novel trapezoidally corrugated perforated plate-fin core. It alters the convective behavior such that an increase in the heat transfer coefficient is accompanied by a substantial reduction in the friction factor. This allows the heat exchanger to be much more compact with both a smaller volume and frontal area. To highlight this, results of computational simulations for velocity and temperature fields in typical trapezoidally corrugated perforated plate-din ducts are presented. Low Reynolds number (10 < Re < 1000) flow of air (Pr = 0.72) passing through inter-fin passages, where fin walls have perforations that are equally spaced along the length of the duct, is considered and a parametric study of the effects of the duct geometry. This includes variation in fin spacing or fin density and period length of corrugation, with fixed trapezoid inclination angle and perforation spacing. Fin-surface porosity, or perforations is shown to promote the unusual behavior of increasing the heat transfer coefficient while reducing the friction factor relative to its unperforated counterpart, primarily due to surface transpirations, which lend to better flow mixing, and consecutive boundary-layer disruption. The results of Fanning friction factor and Nusselt number over the wide range of Reynolds number covered in this study amply demonstrate the enhanced performance. Quantitatively, the enhancement is evaluated by both the area goodness factor or (??/??), and volume goodness factor, or the relative increase in (??????) for same pumping power (??????3), in comparison with plain plat-fin channels.

Citation: ASHRAE Conference Papers, 2010, vol. 116, pt. 2, Albuquerque, NM

Product Details

Published:

2010

File Size:

1 file , 1.1 MB

Product Code(s):

D-AB-10-C036