Constructal design of crossflow heat exchanger with concentric and eccentric circular fins

A single-row crossflow heat exchanger with concentric and eccentric circular fins is designed and shown in this paper using a constructal design approach. The transverse fins spacing, the spanwise fins spacing, and the fin-tube eccentricity are varied inside a fixed volume. In addition to the concentric case (epsilon = 0), two tube-fin eccentricities are considered with (epsilon = +/- 0.25). The (heat transfer/volume) heat density is to be optimized with respect to the transverse and the spanwise spacing. The height and the width of the heat exchanger occupation space in addition to the fin diameter are fixed as design constraints. The crossflow is motivated by constant pressure drop with two dimensionless pressure drop numbers (Bejan number) (Be = 103 and 105). Both the fins and the tubes are maintained at a constant temperature, and they are cooled by the cross air of ambient temperature. The ratio of the fin to tube diameter is kept at 0.5. Three-dimensional equations for conservation of mass, conservation of momentum, and conservation of energy are solved using finite volume method for incompressible and steady flows. The heat density for concentric fins (epsilon = 0) and eccentric fins (epsilon = +/- 0.25) is maximized two times, one with respect to transverse spacing, and the other with respect to spanwise spacing at Bejan numbers (Be = 103 and 105). The highest double-maximized heat density is attained at the fin eccentricity (epsilon = 0.25). The increase in the double maximized heat density when the fin eccentricity (epsilon = 0.25) is 7.65% for Be = 103, and it is 12% for Be = 105.