Search

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 (ε = 0), two tube‐fin eccentricities are considered with (ε = ±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 (ε = 0) and eccentric fins (ε = ±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 (ε = 0.25). The increase in the double maximized heat density when the fin eccentricity (ε = 0.25) is 7.65% for Be = 103, and it is 12% for Be = 105. [ABSTRACT FROM AUTHOR]

The maximization of volumetric heat transfer density from radially finned tubes in cross‐flow is investigated in this study based on the constructal design method. A row of radially finned tubes is placed in cross‐air flow. The tubes and the radial fins are heated at uniform temperatures and cooled by the air cross‐flow. The cross‐air flow is generated by a finite pressure difference. Two dimensionless pressure differences (Bejan number) are considered (Be = 103 and Be = 105). The objective function, the degrees of freedom, and the constraints in the constructal design method should be identified. The objective function is the maximization of the heat transfer density from the finned tubes. The degrees of freedom are; the fin tip‐to‐fin tip spacing, the number of fins, the tube diameter, the fin thickness, and the angle between the fins. The constraints are the length and height of the space occupied by the finned tubes. The pressure‐driven flow and energy equations (steady, two‐dimensional, and incompressible) are solved by means of the finite volume method. The ranges of the dimensionless fin tip‐to‐fin tip spacing are (0.2 ≤ S ≤ 1 for Be = 103 and 0.05≤ S ≤ 0.3 for Be = 105). The number of fins is changed as (N = 2, 4, 6, 8, 10, and 12). The dimensionless tube diameter is changed as (D = 0.25, 0.5, and 0.75). The dimensionless fin thickness is changed as (T = 0.001, 0.01, and 0.05). The results showed that for both (Be = 103) and (Be = 105), the highest value of the maximum volumetric heat transfer density is for (N = 2) and decreases as the number of fins increases. In addition, the minimum values of the maximum volumetric heat transfer density occur when the vertical fins exist at (N = 4, 8, and 12). [ABSTRACT FROM AUTHOR]

The optimal configuration of two‐scale elliptic tubes in crossflow is found on the basis of the constructal design. The larger tubes are installed inside a domain of fixed length and height. In the same domain, smaller tubes are inserted between the larger tubes in the entrance region at the mid leading edge to leading edge distance of the larger tubes. The spacing between the larger tubes, the semiminor axis of the larger tubes, the major axis of the smaller tubes, and the semiminor axis of the smaller tubes are varied inside the domain freely to find the optimal configuration. There are two optimal configurations: one without the smaller tubes and the other with the presence of the smaller tubes. Both the larger and the smaller tubes are heated at a constant surface temperature. The flow is induced by a fixed pressure difference. The equations for steady, laminar, two‐dimensional, and incompressible flow are solved by finite volume method. In the absence of the smaller tubes, the range of Bejan number (dimensionless pressure drop) is 103