Flow distribution is encountered widely in nuclear reactor systems including distribution of liquid coolant, feedwater or steam sparger, and high energy fluid into condenser of steam turbine. Distributors with parallel ports or openings are common designs which may be very sensitive to variations of structure and dimensions of a manifold and its ports. Non-uniformity of flow distributions causes largely potential malfunction and poor efficiency, even failures. In this paper, a theoretical model was developed for a tapered distributor. Analytical solutions were obtained for evaluation of influence of operating conditions and structures and dimensions of distributor and ports on flow distributions. Structural parameters were identified and hydraulic characteristics were analysed. The orifices, slope and tube protrusion are useful for improvement of the flow distributions. The uniformity of the flow distributions can be improved about-10-60% by fitting orifice rings or tube protrution with a range of the minor loss coefficients: 0.5-3. Finally design criteria were suggested for industrial applications. This provides a simple and easy-to-use tool for design of the flow distribution in nuclear reactors and power boilers. Crown Copyright (C) 2012 Published by Elsevier B.V. on behalf of The Institution of Chemical Engineers. All rights reserved.