Performance Evaluation of Laminar Fully Developed Flow through Ducts with Non-Circular Shapes Subjected to H1 Boundary Condition. Part 1

Extended performance evaluation criteria (ExPEC) have been used to assess the performance characteristics of single-phase fully developed laminar flow through heat exchangers with axial corrugated, square with rounded corners, and triangular with rounded corners ducts. The heat exchanger with circular tubes has been used as a reference heat transfer unit. The H1 boundary condition has been selected as thermal boundary condition. The performance characteristics of the heat exchangers with non-circular tubes have been evaluated and compared to those of the reference unit for different objectives and constraints imposed. As a common constraint, the cross sectional area of the non-circular duct has been specified. As expected, the analysis of the thermal performance of heat exchangers with non-circular ducts revealed that the selection of the optimal shape of the duct strongly depends on the geometric and thermal-hydraulic constraints imposed on the unit, and the objectives pursued. The use of a general criterion connecting two objectives simultaneously permits to avoid the contradictory results that can be obtained if criteria based on first or second law analysis are implemented alone. The evaluation concerning the superiority of a particular shape of the non-circular duct depends also on the value of the irreversibility distribution ratio, . For the cases FG (fixed geometry criteria) the use of ducts with non-circular shapes is inefficient, whereas in the cases FN (fixed number of tubes) and VG (variable geometry) some benefit can be achieved according to the value of