Tomasz Bury

The Finite Difference Method and the Numerical Approach for Modeling the Maldistribution of the Flow of Media in Tube-and-Fin Cross-flow Heat Exchangers

ABSTRACT The work deals with thermal and hydraulic modeling of fin-and-tube cross-flow heat exchangers with a non-uniform flow of media. A maldistribution of media flow is not considered in the standard thermodynamic analysis, and the results of such analysis may be too optimistic. The authors applied two modeling methods to include the information about a non-uniform flow of media through the heat exchangers. The finite difference method and the numerical approach are applied in the first and in the second stage of the analysis, respectively. The general assumption is that the real device can be divided into repetitive elements, thus allowing to consider the media flow non-uniformity. The two methods are used for simulations of selected experiments carried out for a single-row fin-and-tube cross-flow heat exchanger. A traditional computational analysis is also performed and a comparison of the results is made. The results confirmed the applicability of the proposed methods.

CFD modeling of passive autocatalytic recombiners

Abstract This study deals with numerical modeling of passive autocatalytic hydrogen recombiners (PARs). Such devices are installed within containments of many nuclear reactors in order to remove hydrogen and convert it to steam. The main purpose of this work is to develop a numerical model of passive autocatalytic recombiner (PAR) using the commercial computational fluid dynamics (CFD) software ANSYS-FLUENT and tuning the model using experimental results. The REKO 3 experiment was used for this purpose. Experiment was made in the Institute for Safety Research and Reactor Technology in Julich (Germany). It has been performed for different hydrogen concentrations, different flow rates, the presence of steam, and different initial temperatures of the inlet mixture. The model of this experimental recombiner was elaborated within the framework of this work. The influence of mesh, gas thermal conductivity coefficient, mass diffusivity coefficients, and turbulence model was investigated. The best results with a good agreement with REKO 3 data were received for k-ɛ model of turbulence, gas thermal conductivity dependent on the temperature and mass diffusivity coefficients taken from CHEMKIN program. The validated model of the PAR was next implemented into simple two-dimensional simulations of hydrogen behavior within a subcompartment of a containment building.

Evaluation of passive autocatalytic recombiners operation efficiency by means of the lumped parameter approach

Abstract The problem of hydrogen behavior in containment buildings of nuclear reactors belongs to thermal-hydraulic area. Taking into account the size of systems under consideration and, first of all, safety issues, such type of analyses cannot be done by means of full-scale experiments. Therefore, mathematical modeling and numerical simulations are widely used for these purposes. A lumped parameter approach based code HEPCAL has been elaborated in the Institute of Thermal Technology of the Silesian University of Technology for simulations of pressurized water reactor containment transient response. The VVER-440/213 and European pressurised water reactor (EPR) reactors containments are the subjects of analysis within the framework of this paper. Simulations have been realized for the loss-of-coolant accident scenarios with emergency core cooling system failure. These scenarios include core overheating and hydrogen generation. Passive autocatalytic recombiners installed for removal of hydrogen has been taken into account. The operational efficiency of the hydrogen removal system has been evaluated by comparing with an actual hydrogen concentration and flammability limit. This limit has been determined for the three-component mixture of air, steam and hydrogen. Some problems related to the lumped parameter approach application have been also identified.