Two-phase flow in parallel pipes is associated with the application of direct steam generation (DSG) by solar heating using parabolic troughs focusing solar power. In this process water is fed into parallel pipes from a common manifold. Owing to local cloud cover or difference in the focusing quality, each pipe may receive a different heating power. In this case the flow rate in each pipe will be different. It is the purpose of this work to analyze a system of two parallel pipes with common inlet and outlet manifolds. Subcooled water that enters the system undergoes a process of heating and evaporation. The results show that the solution is not unique and one can obtain 1, 3 or 5 solutions, even for the case of equal heating of the two pipes. Each solution yields the flow rate in each pipe and the distribution of temperature, pressure, quality and holdup along the pipes. It was found that for most cases, the water tend to flow in the pipe which absorb less heat. This is an unfavorable conclusion from the practical operational point of view. (C) 2003 Elsevier Ltd. All rights reserved.