Uneven distribution of phases in plate heat exchangers is a cause of reduction in both thermal and fluid-dynamic performances. With respect to two-phase flows, phase separation in manifolds with several outlets is a complex phenomenon and no general rules are available for predicting the phase distribution at header-channel junctions. The design of compact heat exchangers and their distributors is still based on empirical approaches and both experimentation and numerical analysis are needed for defining the best geometries able to reduce the mass flow rate non uniformities in parallel channels. In this paper a series of CFD simulations are carried out to infer the effects of a protrusion fitting (inside the header) on the single phase distribution in parallel upward vertical channels fed by a common horizontal distributor. The numerical results are compared with both experimental single phase and two phase (liquid/gas) experimental data. The effects of the operating conditions are investigated and general conclusions on the differences and analogies between single phase and two-phase flows in the present problem are discussed.
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