University of Minnesota

ABSTRACT:
An analysis is presented of thermal hydraulic stability of flow in parallel channels. The dissertation presents work which consists of two parts. Part one deals with the development of a numerical (finite difference)
calculational program for analyzing both steady state and transient steam-water flows in a heated channel with a prescribed axial heat flux. The model is based on a one, dimensional drift velocity formulation of the two-phase flow conservation equations, including the effects of radial distribution of void and thermal non-equilibrium between the vapor and liquid phases. The following considerations are incorporated into the model: i) Attention is given to flow regimes so as to more properly define the use of available correlations for the constitutive equations.
iiiii)The analysis is extended to superheat regions. Heat effects due to tube walls are included in the analysis. Steady state as well as stability predictions are compared to available experimental results. In the second part, the equations are linearized by assuming small disturbances about the steady state. The dynamic response of the system to inlet flow perturbations is derived yielding the characteristic equation which predicts the onset of instabilities. For simplicity, the regional uniformly heated system is considered and the particular case of equal characteristic frequencies of two phase region and single phase gas region is studied in detail. The D-partition method and the Mikhailov stability criterion are used for mapping the stability boundary. The effects of various parameters, such as the heat flux inlet subcooling, pressure, inlet velocity, inlet orificing and exit orificing on the stability boundary are studied and the results are compared to available experimental results.… (más)