Flow maldistribution in tubular heat exchangers may cause severe thermal and mechanical operating problems. In this view, the crucial part of a distribution system is the inlet header. Nevertheless, a cylindrical header, the most common one in the process industry, distributes fluid flow into the tube bundle non-uniformly by its nature. One possible way to improve such unsuitable flow conditions is to gradually change the header height. However, variable header height is utilized mainly in equipment with a rectangular cross-section. So far, standard cylindrical headers have not been modified in such a way.
This study presents the results of an investigation into the flow behaviour in three dividing headers with circular cross-sections, two of which featured different changes to their height (linear decrease, optimised shape). The corresponding flow distributions were predicted via a simplified mathematical model as well as steady and transient CFD simulations. The obtained results were validated by experiments using additively manufactured headers, and it was found that the predicted flow distributions agreed with the observed trends. The conducted investigation also showed that the linear change of header height significantly improved flow distribution in the middle of the tube bundle. Nevertheless, the significant decrease in the tube flow rates near the distributor closed end caused degradation of the one-value maldistribution criterion compared to the value observed for the standard header design. The proposed modification of the header shape appears to be promising in terms of its future utilization in complete distribution systems and process heat exchangers, because it equalizes lateral flow rates in the middle of the tube bundle to the max. difference of ca. 2 % compared to ca. 6 % observed in the standard cylindrical shape.