Heater drain systems in fossil and nuclear power plants have proven to be among the most complex systems to design due to the occurrence of two–phase flow phenomena. The overall performance of heater drain systems directly relates to proper sizing and design of the piping and control valves. Proper sizing is highly dependent upon accurate and conservative calculation of two-phase flow pressure losses. This paper outlines the various options of solution methods available to the engineer and details one possible method which is simple, yet adequate, and based on the homogeneous equilibrium model (HEM) for two phase flow for calculation of heater drain system performance. General comparisons are made to the more complex multi-fluid models, flow regime considerations, and non-equilibrium models.

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