CFD simulation for steam distribution in header and tube assemblies

The study of the flow characteristics in manifolds (dividing, combining, parallel or Z-manifold and reverse or U-manifold) is a classic subject of engineering fluid dynamics and hydrodynamics. These manifolds are widely used in chemical processes, electronic cooling equipment, solar collectors, spargers, microchannels, fuel cells, heat exchangers and refrigerant distribution in multi-split type of air conditioner, etc. In the literature extensive work has been done for finding out flow distribution in plate-fin heat exchanger, microchannels and spargers. Present work focuses on the flow and pressure distribution in piping networks, which has gained importance in many areas such as air distribution in diffuser system of aerobic biological treatment, steam distribution in passive decay heat removal systems, etc. The uniformity of flow rates among the parallel tubes of piping manifold is governed by the field of fluid pressure in the system under consideration. In present work, the flow and pressure distribution of pure steam in header and tube assemblies has been investigated with the help of CFD simulations. The effects of design parameters has been investigated over a wide range such as the tube pitch (50 < D-pt < 150 mm), header diameter (50 < D-h < 200 mm), tube diameter (15 < D-t < 32 mm), number of tubes (8 < N-t < 50), inlet or outlet pipe diameter (15 < D-in < 65 mm). The sensitivity of inlet mass flow rate (0.033 < (m)over dot < 0.075 kg/s) has been investigated on the extent of non-uniformity (%ENU) in steam distribution. For validating CFD predictions an experiments have been performed on scaled down geometry of header configuration 'C1' using air and water (35,600 < Re < 68,500) as a working fluid. A good agreement was observed between the predicted and the experimental values of %ENU. It is concluded that the tube diameter, number of tubes and their locational arrangement with respect to inlet and/or outlet pipe are most important design parameters affecting the flow and pressure distribution in the pipeline networks. (C) 2011 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.