Development Of Transient Two-phase Thermal-hydraulic Code Base On Two-fluid Model

Flow boiling occurs in petrochemical, thermal power, nuclear power and other industrial applications, the heat transfer and flow characteristics are significantly changed compared to single-phase and far more complex. It directly affects the efficiency,stability and safety the equipment, so it’s needed to research on the complex phenomenon in flow boiling.Two-fluid model treats each phase separately and couples them through the interface mass, momentum and energy interaction terms, with directly applying conservation laws on each phase, it can reflect the local characteristics in two-phase flow field with most abundant informations. Basically, the interface transfer term is proportional to the interface area concentration(IAC) and to a driving force, modeling of interface transfer term and IAC is the key for two-fluid model.In this paper, we choose a typical process of two-phase heat transfer and flow in a heated channel for the study, based on two-fluid model, coupled with the two-dimensional transient heat conduction model and a set of appropriate interface mass, momentum and energy constitutive models, the control equations are closed and a framework of mathematical modeling of heat transfer and flow within the flow channel is established.Staggered grid method is used to mesh the flow channel and the governing equations are discretized using the control volume method. Applying SIMPLE method for pressure correction, a coupled solution of flow and heat transfer of the liquid side and transient heat conduction of the solid side are achieved A transient thermal-hydraulic code based on mathematical and numerical model is successfully developed.Numerical calculations and analysis are run under steady and transient conditions. First, sensitivity effect of wall nucleate boiling heat transfer coefficient(HTC) correlation, partition of wall heat flux, interphase heat transfer coefficient, fraction of wall friction to each phase, and generalized interface drag forces are examined. While using different wall nucleate boiling HTC correlation, the calculated HTC is significantly differs, but other parameters like void fraction, velocity of each phase is about the same. Wall heat partitioned model and interface HTC correlation under liquid subcooled condition is only affect calculated parameters’ value only when the bulk flow is subcooled. The fraction of wall friction to each phase and value of interphase drag force directly affect velocity of each phase. Calculated HTC and pressure drop are compared with experiment data, and a better set of correlations are selected. Finally, transient calculations are run under sharp change of the inlet flow rate, pressure and heating power and inlet flow rate fluctuation conditions, these calculations are to test the capabilities of the code during transient calculations.In the last, one group interfacial area transport equation and related source and sink term are included into two-fluid model, replacing the original static calculation method of interface area concentration based on flow pattern. the IATE module was added into the code to calculate interface area concentration and results was compared to the results calculated without useing IATE module. A preliminary development of the code was achieved.