An engineering stability technique for unsteady, two-phase flows with heat and mass transfer

This paper considers the stability of an unsteady, two-phase flow with heat and mass transfer. The model problem is motivated by loss of coolant accidents in nuclear power plants. For the example problem, two flow geometries are considered: inverted annular flow boiling and an annular mist flow. The model is comprised of coupled Mathieu equations so that stability can be determined using a Floquet analysis. The flow is found to be mathematically unstable to all perturbative wavenumbers, but for practical purposes there are regions of stability. Using the solution's growth behavior and doubling-time, the notion of practical stability, which is termed herein as "engineering stability," is quantified and a method is provided for application to other engineering stability problems.