9420853 ABSTRACT This proposal seeks to use experiment and modeling of transient flow instabilities in fully condensing two-parallel-tube heat transfer systems as a first step in understanding these instabilities in more complex systems. Existing experimental equipment will be used to measure these instabilities, and a model based on the behavior of a single equivalent tube will be used to correlate the behavior of the two-tube system. The work seeks to provide insight into the complex behavior of unstable flow systems, and may have important applications in large-scale equipment such as power plant and chemical process industry condensers where such behavior occurs.