Flow Induced Vibrations (FIV) are a significant threat to the life of major power plant components such as heat exchangers. The most dangerous of these excitation sources is fluidelastic instability (FEI). Early FEI models focused on predicting the stability threshold of heat exchanger tubes subjected to fluidelastic forces based on empirical data, but the inability of empirical predictions to account for the variability in tube array geometry, pitch, and single or two phase flow limited the usefulness of these models. This thesis investigates the properties of unsteady flow in a normal triangle tube array with a pitch-to-diameter ratio of 1.5. Stability simulations are conducted over a mass damping parameter range 9--200, using a reduced order model of the moving tube. This investigation provides a direct observation of the channel area. When implemented into the time domain model the new parameters provide better agreement with the experimental stability threshold data available.