Industrial Engineering

Detection and characterisation of voids in heavy liquid metals (HLM) is required for next generation nuclear reactor systems. However, its determination presents a challenge owing to their opaque nature and the high temperatures involved. Therefore, tools are needed that can be used to capture local, quantitative information at relevant nuclear operating conditions. In this work, the feasibility of using optical fibre sensors for the measurement of void fractions in liquid metals is presented. Since the functioning of optical probes is usually explained by a crude on-off model, the complexity of both the optical response and the hydrodynamic tip-interface interactions often remain hidden to new users. To clarify this point, well-controlled lab-scale experiments dealing with the response of three concept probe tip geometries are presented. Analysis of the obtained signal transients is used to provide guidelines for effective data processing. To conclusively demonstrate the principle, an optimal prototype system successfully determined the local void fraction and frequency in a pilot-scale reactor using liquid lead bismuth eutectic (LBE) as working fluid. The information obtained by the optical sensor allows for validation of computational fluid dynamics (CFD) models to aid the design of LBE-based nuclear reactors, as well as for other liquid metal-gas systems in general.

By using a counter rotating plate-plate device, single droplets in shear flow have been microscopically studied at confinement ratios ranging from 0.1 to 0.75. The droplet-to-matrix viscosity ratio was fixed at 0.45 and 1.5. Results are presented for systems with a viscoelastic Boger fluid matrix or a viscoelastic Boger fluid droplet, at a Deborah number of 1. Although the separate effects of confinement and component viscoelasticity on droplet dynamics in shear flow are widely studied, we present the first systematic experimental results on confined droplet deformation and orientation in systems with viscoelastic components. Above a confinement ratio of 0.3, wall effects cause an increase in droplet deformation and orientation, similar to fully Newtonian systems. To describe the experimental data, the Shapira-Haber theory ͓Shapira, M., and S. Haber, Int. J. Multiph. Flow 16, 305-321 ͑1990͔͒ for confined slightly deformed droplets in Newtonian-Newtonian systems is combined with phenomenological bulk models for systems containing viscoelastic components ͓Maffettone,

Numerical simulations and experimental data are compared for the investigation of the influence of viscoelasticity on drop deformation in shear A viscoelastic drop suspended in a Newtonian liquid, or a Newtonian drop suspended in a viscoelastic liquid, is sheared and investigated for transients, relaxation after cessation of shear flow, and step-up in shear rate. The numerical simulations are conducted at parameters chosen to model the experiments. We use the volume of fluid (VOF) continuum surface force (CSF) algorithm for situations dominated by shear For drop relaxation experiments, we use the paraboloid representation of the interface in the surface tension force (PROST) algorithm. The Oldroyd-B and Giesekus constitutive models are implemented. An interesting result is that by stepping up in the capillary number gradually, a stationary states is achieved at higher capillary numbers than without the graduated steps. The experimental work is described in Verhulst, Moldenaers and Cardinaels [1]. We present a summary of the numerical approach here. The reader is referred to [2] for details.

An experimental study of drop dynamics under shear is conducted for five fluid pairs: a reference Newtonian system, two systems with a viscoelastic drop in a Newtonian matrix, one with a Newtonian drop in a viscoelastic matrix, all at drop to matrix viscosity ratio λ = 1.5, and a separate case at λ = 0.75. The viscoelastic liquids are either a Boger fluid or a shear-thinning viscoelastic fluid satisfying an Ellis model. Deborah numbers in the range 1 to 2 and a range of capillary numbers from low to above breakup conditions are addressed. The results focus on three aspects: relaxation after cessation of shear, a new viscoelastic drop breakup scenario, and the effect of shear flow history on drop breakup. Numerical simulations with the 3D volume-of-fluid PROST method complement the experimental results.

As agricultural companies encounter number of risks in their business, it is very important to control the risks for their stable management. So we examine the agricultural business risks and propose the risk management strategies for the agricultural companies.