Fan Bill Cheung

Bio: Fan Bill Cheung is an academic researcher from Pennsylvania State University. The author has contributed to research in topics: Heat transfer & Boiling. The author has an hindex of 19, co-authored 121 publications receiving 1195 citations.

In-Vessel Retention of Molten Corium: Lessons Learned and Outstanding Issues

Abstract: In-vessel retention (IVR) of core melt is a key severe-accident-management strategy adopted by some operating nuclear power plants and proposed for some advanced light water reactors (LWRs). If the...

A Generalized Pyrolysis Model for Combustible Solids

Abstract: This dissertation presents the derivation, numerical implementation, and verification/validation of a generalized model that can be used to simulate the pyrolysis, gasification, and burning of a wide range of solid fuels encountered in fires. The model can be applied to noncharring and charring solids, composites, intumescent coatings, and smolder in porous media. Care is taken to make the model as general as possible, allowing the user to determine the appropriate level of complexity to include in a simulation. The model considers a user–specified number of gas phase and condensed phase species, each having its own temperature–dependent thermophysical properties. Any number of heterogeneous (gas–solid) or homogeneous (solid–solid or gas-gas) reactions can be specified. Both in–depth radiation transfer through semi–transparent media and radiation transport across pores are considered. Volume change (surface regression or swelling/intumescence) is handled by allowing the size of grid points to change as dictated by mass conservation. All volatiles generated inside the solid escape to the ambient with no resistance to mass transfer unless a pressure solver is invoked; the resultant flow of volatiles is then calculated according to Darcy’s law. A gas phase convective–diffusive solver can be invoked to determine the composition of the volatiles. Oxidative pyrolysis is simulated by modeling diffusion of oxygen from the ambient into the pyrolyzing solid where it may participate in reactions. Consequently, the mass flux and composition of volatiles escaping from the solid can be calculated. To aid in determining the required input parameters, the model is coupled to a genetic algorithm that can be used to estimate the required input parameters from bench–scale fire tests or thermogravimetric analysis. Standalone model predictions are compared to experimental data for the thermo– oxidative decomposition of non–charring and charring solids, as well as the gasification and swelling of an intumescent coating and forward smolder propagation in polyurethane foam. Genetic algorithm optimization is used to extract the required input parameters from the experimental data, and the optimized model calculations agree well with the experimental data. Blind simulations indicate that the predictive capabilities of the model are generally good, particularly considering the complexity of the problems simulated.

Structure of bubble plumes in linearly stratified environments

Abstract: Bubble plumes in a linearly stratified ambient fluid are studied. Four well-defined flow regions were observed: an upward-moving bubble core, an inner plume consisting of a mixture of bubbles and relatively dense fluid, an annular downdraught and beyond that a horizontal intrusion flow. Depending on the gas flow rate with respect to the stratification, three types of intrusions were documented. At large gas flow rates a single intrusion was observed. As the gas flow rate was decreased, the buoyancy flux was insufficient to carry the lower fluid to the surface and a stack of intrusions were formed. At very low gas flow rates the intrusions became unsteady. The transition between these three regimes was observed to occur at critical values of the parameters N3H4/(QBg), QBg/ (4πα2u3sH), and H/HT, where N is the buoyancy frequency, H is the water depth, HT is equal to H + HA, HA being the atmospheric pressure head, QB is the gas flow rate at the bottom, g the acceleration due to gravity, α the entrainment coefficient and us the differential between the bubble and the average water velocity commonly called the slip velocity. The height between intrusions was found to scale with the Ozmidov length (QBg/N3)¼, the plunge point entrainment with the inner plume volume flux ( and the radial distance to the plunge point with (Q0g/N3)¾, where Q0 is the gas flow rate at the free surface.These results were used to construct a double annular plume model which was used to investigate the efficiency of conversion of the input bubble energy to potential energy of the stratification; the efficiency was found to first increase, reach a maximum, then decrease with decreasing gas flow rate. This agreed well with the results from the laboratory experiments.