Z- and U-type parallel pipe network configurations are widely used in engineering applications such as solar collectors, fuel cells, microchannels, spargers, and irrigation systems. Although the Z configuration is more commonly employed, the U configuration may provide advantages under specific operating conditions. This study presents a comparative analysis of the two configurations in terms of flowdistribution uniformity and pressure drop. A three-dimensional computational fluid dynamics (CFD) model was developed to simulate realistic solar collector conditions, including both fluid and solid domains together with detailed inlet and outlet junctions. The system consists of manifolds and headers with a diameter of 20 mm and a length of 1150 mm, connected to ten parallel tubes of 7 mm diameter and 1780 mm length. The analysis was conducted over a wide range of inlet Reynolds numbers (ReD = 100–5000) to represent diverse practical operating conditions. The CFD model was validated against experimental data from the literature and showed good agreement. Flowdistribution uniformity was evaluated using two quantitative indicators. The results show that flow maldistribution increases with Reynolds number in both configurations; however, the U configuration exhibits significantly improved flow uniformity at higher Reynolds numbers. In addition, both configurations exhibited comparable pressure drop characteristics over the investigated operating range. The findings suggest that the U configuration is better suited to high-flow-rate applications that require improved hydraulic and thermal uniformity, while the Z configuration remains effective at lower Reynolds numbers.
Alsharif et al. (Sun,) studied this question.