Nicola Forgione

Statistical characteristics of a water film falling down a flat plate at different inclinations and temperatures

Abstract In this work, the statistical characteristics of the surface of a water film, freely falling down a vertical or inclined flat plate, have been investigated. The study was carried out in the frame of a research on passive cooling of heated surfaces by the evaporation of thin water films. The experiments, performed to confirm and extend previous results by the same authors, involved relatively cold water (ambient temperature or slightly warmer 20–30 °C) and warm water (50 and 70 °C). The range of Reynolds numbers includes the classical threshold for the transition between the laminar-wavy and the turbulent regimes. Two different plate inclinations with respect to the vertical position have been addressed (0° and 45°). Capacitance probes were adopted to collect discrete film thickness time series, which have been processed to extract relevant statistical data. A specific probe configuration including an electrical heating system has been developed in order to overcome the problem of vapour condensation onto the active surfaces of the electrodes in the presence of warm water. Data on mean, minimum and maximum film thickness as well as standard deviation and wave velocity are presented, discussing the trends observed as a function of film flow rate, plate inclination and film temperature, also considering the information coming from previous experimental campaigns.

A flexible bioreactor system for constructing in vitro tissue and organ models.

To develop in vitro models of cells, tissues and organs we have designed and realized a series of cell culture chambers. Each chamber is purpose designed to simulate a particular feature of the in vivo environment. The bioreactor system is user friendly, and the chambers are easy to produce, sterilize and assemble. In addition they can be connected together to simulate inter‐organ or tissue cross‐talk. Here we discuss the design philosophy of the bioreactor system and then describe its construction. Preliminary results of validation tests obtained with hepatocytes and endothelial cells are also reported. The results show that endothelial cells are extremely sensitive to small levels of shear stress and that the presence of heterotypic signals from endothelial cells enhances the endogenous metabolic function of hepatocytes. Biotechnol. Bioeng. 2011;108:2129–2140.

Computational Study of Evaporative Film Cooling in a Vertical Rectangular Channel

The present work is focused on the computational analysis of evaporative film cooling, in connection with an experimental campaign carried out at the University of Pisa by the EFFE facility ( E xperiments on F alling F ilm E vaporation). The aim of the study is to contribute to the understanding of the heat and mass transfer mechanisms involved in the problem and to check the possibility of making use of a multipurpose commercial computational fluid dynamics (CFD) code for simulating mass transfer phenomena of interest in the nuclear field. After a description of the assumptions adopted in the mathematical formulation of the problem, the governing equations and the boundary conditions implemented in the code are briefly reported. In particular, the method used to evaluate the mass transfer through the interface is described. Then, the calculated results are analyzed and a comparison with experimental data is made. The improvement in the cooling capabilities of the heated plate due to evaporation with respect to the case of pure convection is also evaluated.

Experiments and Modelling Techniques for Heat and Mass Transfer in Light Water Reactors

The paper summarizes the lesson learned from theoretical and experimental activities performed at the University of Pisa, Pisa, Italy, in past decades in order to develop a general methodology of analysis of heat and mass transfer phenomena of interest for nuclear reactor applications. An overview of previously published results is proposed, highlighting the rationale at the basis of the performed work and its relevant conclusions. Experimental data from different sources provided information for model development and assessment. They include condensation experiments performed at SIET (Piacenza, Italy) on the PANTHERS prototypical PCCS module, falling film evaporation tests for simulating AP600-like outer shell spraying conditions, performed at the University of Pisa, experimental data concerning condensation on finned tubes, collected by CISE (Piacenza, Italy) in the frame of the INCON EU Project, and experimental tests performed in the CONAN experimental facility installed at the University of Pisa. The experience gained in these activities is critically reviewed and discussed to highlight the relevant obtained conclusions and the perspectives for future work.

SCWR Rod Bundle Thermal Analysis by a CFD Code

The present paper describes the results of the application of the FLUENT code in the analysis of rod bundle configurations proposed for high pressure supercritical water reactors. The model considers a 1/8 slice of a rod bundle. The details from CFD calculations offer predictions of the circumferential clad surface temperature and of the effect of axial power distribution on the mass exchange between subchannels and on the maximum surface rod temperature. Geometry and boundary conditions are adopted from a previous work that made use of subchannel programs, allowing for a direct comparison between the two techniques. Both the standard k-e model and the Reynolds stress transport model are used. Conclusions are drawn about the present capabilities in predicting heat transfer behavior in fuel rod bundles proposed for supercritical water reactors.Copyright

STH-CFD Codes Coupled Calculations Applied to HLM Loop and Pool Systems

This work describes the coupling methodology between a modified version of RELAP5/Mod3.3 and ANSYS Fluent CFD code developed at the University of Pisa. The described coupling procedure can be classified as “two-way,” nonoverlapping, “online” coupling. In this work, a semi-implicit numerical scheme has been implemented, giving greater stability to the simulations. A MATLAB script manages both the codes, oversees the reading and writing of the boundary conditions at the interfaces, and handles the exchange of data. A new tool was used to control the Fluent session, allowing a reduction of the time required for the exchange of data. The coupling tool was used to simulate a loop system (NACIE facility) and a pool system (CIRCE facility), both working with Lead Bismuth Eutectic and located at ENEA Brasimone Research Centre. Some modifications in the coupling procedure turned out to be necessary to apply the methodology in the pool system. In this paper, the comparison between the obtained coupled numerical results and the experimental data is presented. The good agreement between experiments and calculations evinces the capability of the coupled calculation to model correctly the involved phenomena.

Natural and Gas Enhanced Circulation Tests in the NACIE Heavy Liquid Metal Loop

The paper reports on the results carried out from the natural circulation and gas-injection enhanced circulation tests performed on a heavy liquid metal loop, named NACIE, and located by the Brasimone ENEA Research Centre. The work is aimed at providing information on the characterization and interpretation of the basic mechanisms proposed in the design of future reactor relying on these circulation mechanisms. The results discussed in the present work concern the experiments performed using Lead Bismuth Eutectic (LBE) as coolant. Both natural circulation and gas-injection enhanced have been addressed, drawing conclusions about the observed phenomena. Numerical simulations have been performed in collaboration with the University of Pisa, adopting the RELAP5/Mod3.3 system code modified to allow for LBE as a cooling fluid. Post-test calculations have been performed to compare the code response with the experimental results under the natural circulation and gas enhanced circulation flow regime, allowing to qualify the adopted nodalisation as well as the performance of the code when employed on HLM loop. The available data will allow to validate and qualify numerical tools for engineering application, establishing a reference experiment for the benchmark of commercial codes when employed in HLM loop.Copyright

Water/Pb-Bi Interaction Experiments in LIFUS5/Mod2 Facility Modelled by SIMMER Code

The new generation Heavy Liquid Metal Reactors (HLMRs) are characterized by a pool type configuration having high pressure steam generators set inside the reactor vessel. The primary (hot low pressure LBE melt) and secondary (high pressure sub-cooled water) coolant could come into contact as consequence of Steam Generator Tube Rupture (SGTR) phenomenon, that cannot be considered negligible. The structural integrity of the reactor internals, steam generators in particular, could be affected by the SGTR scenario consequences. The pressure wave propagation, cover gas pressurization, domino effect on the surrounding tubes, reactivity feedback due to steam dragged into the core, primary system pollution and slug formation constitute the most hazardous effects of the SGTR accident. Therefore, this accidental scenario constitutes a safety issue in the design and in the preliminary safety analysis. A key issue in the SGTR analysis for HLMRs is constituted by the availability of qualified experimental data, suitable to be extrapolated to full scale plant and to support the computer code development and demonstrating the code reliability in the phenomena prediction (qualified code).In this paper, part of the experimental campaign performed in the LIFUS5/Mod2 facility at ENEA CR Brasimone (in the frame of the THINS project), investigating the water-LBE interaction, is reported. The experimental activity aimed to provide high-quality measurement data for supporting the development and validation phase of computer codes for SGTR numerical simulation. The reported experimental test has been numerically simulated by SIMMER III code. The pressure, temperature and injected water mass flow rate time trends have been computed during the water-LBE interaction in the reaction vessel. The work aims to evaluate the prediction capability of the two-dimensional SIMMER III code and to determine the suitability of the SIMMER code physical models.Copyright

Fuel Dispersion and Flow Blockage Analyses for the Myrrha-Fastef Reactor by Simmer Code

This work illustrates the 3D set up model and the results concerning the recent analysis of fuel dispersion in the MYRRHA-FASTEF reactor performed with SIMMER code within the EU-FP7 SEARCH Project. Under severe accidental conditions, the release of fuel in the primary system can occur in case of fuel rod clad failure and degradation. Two cases were therefore taken into account, an imposed fuel release to study key parameters which influence the dispersion phenomenon and a coolant flow blockage in a fuel assembly.The reactor was simulated by a 3D Cartesian geometry with 65×63×42 cell mesh. Steady-state and transient analyses were performed by SIMMER-IV. Steady-state analysis was performed in order to assess the correct operability of the code and of the model. The results were compared with the design values. The most significant results obtained for temperature trends and profiles, velocity and mass flow rate trends are reported. Transient results were also analysed, i.e. fuel dispersion transients were simulated, comparing the effect of fuel porosity on the fuel dispersion inside the pool. In addition, the effects of the release position and the fuel particle dimension on the dispersion phenomenon were also investigated.The final section of the paper describes the effects of a flow blockage on the core degradation and dispersion of fuel particles in the primary circuit of the MYRRHA reactor. This simulation, with fuel porosity equal to 5%, started after a preliminary steady state condition. The mass flow rate in one of the inner fuel assemblies was then reduced to about 10% of the initial value.The results show that the SIMMER-IV code is capable of predicting steady-state results in good agreement with the nominal values, also confirming the correctness of the set up model.Copyright

Experimental and Computational Analysis of Steam Condensation in the Presence of Air and Helium

Abstract This paper discusses the results of investigations devoted to the study of steam condensation in the presence of air and a light noncondensable gas. A double strategy has been adopted, including complementary experimental and computational activities. Novel data have been made available by the CONAN (CONdensation with Aerosols and Noncondensable gases) facility, investigating the effects induced by light noncondensable gases in experimental configurations that were scarcely investigated in past studies. Computational fluid dynamics condensation models have been developed and validated. The suitability of helium as a substitute for hydrogen in experimental activities has been investigated by theoretical and computational analyses that allow establishing simple criteria for the scaling of condensation tests in the presence of a light noncondensable gas.