The present paper goal is to compile a comprehensive database of data on the pressure drop and flow distribution uniformity (FDU) utilizing CFD in a network of parallel tubes arranged in a Z configuration adopted for flat plate solar collectors. A 3D CFD model is implemented to simulate such a system as in the market, including two domains: tube materials and fluid, besides entering and exiting prolonged ports. The model specifications are Z disposition of uniform inlet and outlet headers diameter (D=20 mm), length of 1150 mm, and tube length of 1780 mm. The investigated design parameters include the number of tubes (N=5, 10, and 15) and the diameter to header diameter ratio (d/D=0.25, 0.35, and 0.50). For a wide range of inlet Reynolds numbers from 500 to 5000. The present model demonstrated noticeable agreement with offered experimental findings from the literature. The results affirmed that lowering both; the number of tubes and the diameter of tubes enhances the FDU. The findings indicate that lowering the number of tubes from 15 to 5 at a lower tube to diameter ratio of 0.25 at a higher Reynolds number yields a maximum increase in FDU of roughly 180% with a negative effect on the total pressure drop.