Numerical and experimental investigation of subcooled film boiling on a horizontal plate
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abstract
Analytical study of 3-D Taylor instability in cylindrical polar coordinates were performed. The predictions for wavenumber, based on this analysis, were found to be in good agreement with experimental data for subcooled film boiling. Numerical simulations of non-linear Taylor instability were performed to determine: the effect of heater thermo-physical properties on saturated film boiling, and the effect of subcooling on film boiling using static and dynamic models. The computations were restricted to 2-D incompressible and laminar flow which were described in axisymmetric coordinates. The finite volume method was used to simultaneously solve the equations governing conservation of mass, momentum and energy in the vapor and liquid phase. The governing equations were discretized by employing coordinate transformation, numerical grid generation and contravariant velocity vectors. Second order projection method for decoupling velocity from pressure was used to solve the governing equations. Results show that the heater material properties have a significant effect on the heater local temperature distribution resulting in the formation of cold spot. The intensity of the cold spots are of the order of 10C. The time period for vapor bubble pinch-off obtained from the calculations agree with experimental results and are found to be dependent on the heater material properties. The static model employed to study effects of subcooling in film boiling show that the degree of subcooling is a more important factor than the height of the vapor bulge. The dynamic model was used to obtain the flow patterns and isotherm distribution in the liquid and vapor phase. The wall heat transfer was predicted to increase with increase in subcooling while the contribution to vapor generation was found to decrease. Experimental validation of numerical predictions were performed by high speed photography, 2-D Particle Tracking Velocimetry (PTV) in the liquid phase and thermal measurements for subcooled film boiling under pool boiling conditions on a horizontal a copper plate. Experimental results for interfacial hydrodynamics were in agreement with the numerical results to within 1015%. The steady state experimental results for heat transfer measurements were underpredicted by the a numerical model by about 25%. 2-D PTV measurements were in good agreement with numerical predictions.
