This paper presents an analysis of the gas-jet wiping process in hot-dip galvanization. This technique consists of reducing the liquid film thickness on a moving substrate by applying gas slot jets. A theoretical development allows the computation of the film thickness evolution in the wiping zone. It is further simplified to an engineering model which predicts directly the final coating thickness, in good agreement with wiping experiments. The limit of applicability of jet wiping is due to the occurence of a violent film instability, called splashing, which takes the form of a liquid droplet emission just upstream the nozzle. An experimental investigation of this phenomenon is conducted on a water-model facility. Two nozzle designs are tested. The effect of process parameters such as the strip speed, the nozzle pressure, the standoff distance, and the tilt angle of the nozzle on splashing is emphasized. A dimensionless correlation is established to predict the operating conditions leading to splashing occurence. It is successfully confronted to observations made on galvanization lines.

The use of relief valves is crucial for the safety of power plants. Indeed, these valves, simple but robust in their design, provide the ultimate protection when all other safety systems are inadequate. This study is focused on valve opening characteristics which can be studied through the determination of flowforces applied on the valve disk. A spring-loaded safety relief valve (SRV) (1½ in. G 3 in.) and its transparent model are tested under static conditions. The spring is removed and the forces, exerted at the valve disk for different inlet pressures and lift positions, are measured in compressible, incompressible, and two-phase flows. Results indicate that even for relatively small qualities (i.e., 5–10%), two-phase mixtures approach compressible flow behavior (especially for the higher lifts) in terms of disk force. Additionally, an inverse flowforce of air and water is noticed above a certain value of valve lift. Numerical simulations with a commercial computation fluid dynamics (CFD) code are performed in a 2D axisymmetric model of the valve for validation purposes. The main motivation of these computations is to obtain the qualitative physical explanation of this phenomenon revealing the displacement of the sonic line which occurs in air flow simulations. Finally, the importance of precise adjustment of the valve ring (in the smallest valve opening) for its optimal use is stressed by quantitative analysis using CFD simulations.

A flashing phenomenon is often met in liquid propulsion of safety fields in industrial environments. This violent evaporation occurs when a liquid finds itself suddenly in a thermodynamic non-equilibrium and becomes superheated. To investigate theoretically the source processes and validate models for design and safety assessments, knowledge of accurate and reliable data such as distribution of droplet size, velocity and temperature in the closest field of flashing occurrence is mandatory. In this present work, an experimental study is undertaken in order to characterize the two-phase jet after a sudden accidental release and aims to quantify the effects of initial conditions such as initial storage pressure, temperature, geometrical effects of the release points etc on the spray characteristics. To fulfil this goal, a laser-based optical technique like Phase Doppler Anemometry (PDA) is used to obtain information for particle diameter and velocity evolution in this harsh environment. Cases for different initial pressures, temperatures and orifice diameters are studied and the droplet size and velocity evolution are presented in function of initial parameters.

This paper presents an experimental characterization of the jet wiping process, used in continuous coating applications to control the thickness of a liquid coat using an impinging gas jet. Time Resolved Particle Image Velocimetry (TR-PIV) is used to characterize the impinging gas flow, while an automatic interface detection algorithm is developed to track the liquid interface at the impact. The study of the flow interaction is combined with time resolved 3D thickness measurements of the liquid film remaining after the wiping, via Time Resolved Light Absorption (TR-LAbs). The simultaneous frequency analysis of liquid and gas flows allows to correlate their respective instability, provide an experimental data set for the validation of numerical studies and allows for formulating a working hypothesis on the origin of the coat non-uniformity encountered in many jet wiping processes.

The Belgian nuclear research institute (SCK•CEN) is developing MYRRHA. MYRRHA is a flexible fast spectrum research reactor, conceived as an accelerator driven system (ADS). The configuration of the primary loop is pool-type: the primary coolant and all the primary system components (core and heat exchangers) are contained within the reactor vessel, while the secondary fluid is circulating in the heat exchangers. The primary coolant is Lead Bismuth Eutectic (LBE). The recent nuclear accident of Fukushima in 2011 changed the requirements for the design of new reactors, which should include the possibility to remove the residual decay heat through passive primary and secondary systems, i.e. natural convection (NC). After the reactor shut down, in the unlucky event of propeller failures, the primary and secondary loops should be able to remove the decay heat in passive way (Natural Convection). The present study analyses the flow and the temperature distribution in the upper plenum by applying laser imaging techniques in a laboratory scaled water model. A parametric study is proposed to study stratification mitigation strategies by varying the geometry of the buffer tank simulating the upper plenum.

A single-phase Large Eddy Simulation is performed in a simplified cowl-box model and compared to PIV data. Indeed, prior to the analysis of the interaction between a turbulent air flow and an interface of liquid, the most accurate description of the 3D flow field is required. Although the qualitative phenomena are correctly rendered (flapping motion of impinging inlet jets), quantitative differences are noticed, mainly due to non satisfactory turbulent boundary condition, which induces an overestimation of the jets core length, and modifies its interaction with the cowl box walls. Nevertheless, a qualitative analysis of the instantaneous flow shows the generation of large coherent vortical structures due to the oscillation of the impinging jets at the bottom wall. The advection of these structures in the cowl-box generates large oscillations of wall shear stress and pressure distribution, which are thought to be of great importance for further two-phase flow simulations.