In multi-component miscible systems where homogeneous single phase solution behavior is critical, it is necessary to model and predict regions of instability through the process. Changes in the temperature, pressure, and composition of multi-component systems may cause separation into two distinct liquid phases. This is detrimental in some unit operations such as mixing, reaction, and heat transfer, but is advantageously used in some unit operations such as separations. Knowing the boundaries for thermodynamic phase equilibrium behavior becomes important as processes are optimized. We report an application of the improved technique for modeling, using Perturbed Chain-Statistical Associating Fluid Theory, which better incorporates the asymmetrical multi-component thermodynamic phase solution behavior. As process conditions change through these unit operations, the system temperatures and pressures can be controlled as needed for each composition to avoid the two phase separation of the Liquid-Liquid Equilibrium. In one demonstration, this application was used to optimize the performance of a heat exchanger by predicting and controlling the point of Liquid-Liquid Equilibrium for the process through the exchanger tubes.