Spatial and time evolution of non linear waves in falling liquid films by the harmonic expansion method with predictor-corrector integration

Falling film flows in vertical or inclined planes, and pipes, are present in the energy and chemical industry (Chemical reactors, evaporators, condensers…). The occurrence of waves in these falling films is of relevance because it enhances the heat and mass transfer in comparison with a flat film. Perturbation theory can be applied to the Navier-Stokes (NS) equations expressing the velocity and the pressure in terms of an order formal parameter representing the smallness of the stream wise spatial derivative. Normally good results are obtained for this kind of problems solving the first order NS equations. In the present work we use the integral approach method and we expand the velocity profile of the falling liquid in a complete orthogonal set of harmonic functions satisfying the boundary conditions of the NS problem in first order approximation of the formal expansion. The present model does not assume self-similar profile of the velocity and its convergence to the solution is good with few harmonics. The problem is discretized by means of a uniform grid. Then the partial differential equations are integrated over the length of an arbitrary node. Proceeding in this way we have obtained a set of coupled ordinary differential equation system (ODES) for the harmonics of the flow rate and the film thickness at each grid node The resulting coupled ODES is integrated by a semi-implicit predictor-corrector method of the Adams-Moulton type that converges, with one iteration, at each time step. The method predicts well the experimental data on the evolution of the waves with time, the height of the waves, the wave separation, and the wave profiles for different experimental conditions. Providing a physical understanding of the non-linear wave phenomena produced in falling films.Papers presented to the 12th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Costa de Sol, Spain on 11-13 July 2016

Estudio del comportamiento de la película de líquido en flujo anular aire-agua vertical ascendente al variar la tensión superficial mediante mezclas agua-1-butanol

[ES] El documento recoge el estudio llevado a cabo en la instalación VAFF (Vertical Anular Flow Facility) donde se estudia el comportamiento del régimen de flujo anular vertical ascendente aireagua. Se han llevado a cabo un conjunto de tests con un rango de caudales de aire de 2000 ¿ 3500 l/min y de agua de 4 ¿ 7 l/min. Estos tests se han repetido un total de cuatro veces variando la proporción de 1-butanol que se le adiciona al agua con objeto de variar su tensión superficial manteniendo prácticamente inalteradas el resto de propiedades. De esta forma las tensiones superficiales obtenidas fueron de 72·10-3 , 68.5·10-3 , 55·10-3 y 45·10-3 N/m. En el documento se muestran algunos de los resultados, así como el error cometido.Los autores quieren agradecer el apoyo de la Agencia Nacional de Investigación de España al proyecto EXMOTRANSIN, ENE2016-79489-C2-1-P.Rivera-Durán, Y.; Muñoz-Cobo, JL.; Cuadros, J.; Berna, C.; Escrivá, A.; Iglesias, SM.; Domínguez, DS. (2019). Estudio del comportamiento de la película de líquido en flujo anular aire-agua vertical ascendente al variar la tensión superficial mediante mezclas agua-1-butanol. Sociedad Nuclear Española. 1-8. http://hdl.handle.net/10251/180951S1

Impact of liver tumour burden, alkaline phosphatase elevation, and target lesion size on treatment outcomes with 177Lu-Dotatate: an analysis of the NETTER-1 study

Purpose: To assess the impact of baseline liver tumour burden, alkaline phosphatase (ALP) elevation, and target lesion size on treatment outcomes with 177Lu-Dotatate. Methods: In the phase 3 NETTER-1 trial, patients with advanced, progressive midgut neuroendocrine tumours (NET) were randomised to 177Lu-Dotatate (every 8 weeks, four cycles) plus octreotide long-acting release (LAR) or to octreotide LAR 60 mg. Primary endpoint was progression-free survival (PFS). Analyses of PFS by baseline factors, including liver tumour burden, ALP elevation, and target lesion size, were performed using Kaplan-Meier estimates; hazard ratios (HRs) with corresponding 95% CIs were estimated using Cox regression. Results: Significantly prolonged median PFS occurred with 177Lu-Dotatate versus octreotide LAR 60 mg in patients with low ( 50%) liver tumour burden (HR 0.187, 0.216, 0.145), and normal or elevated ALP (HR 0.153, 0.177), and in the presence or absence of a large target lesion (diameter > 30 mm; HR, 0.213, 0.063). Within the 177Lu-Dotatate arm, no significant difference in PFS was observed amongst patients with low/moderate/high liver tumour burden (P = 0.7225) or with normal/elevated baseline ALP (P = 0.3532), but absence of a large target lesion was associated with improved PFS (P = 0.0222). Grade 3 and 4 liver function abnormalities were rare and did not appear to be associated with high baseline liver tumour burden. Conclusions: 177Lu-Dotatate demonstrated significant prolongation in PFS versus high-dose octreotide LAR in patients with advanced, progressive midgut NET, regardless of baseline liver tumour burden, elevated ALP, or the presence of a large target lesion. Clinicaltrials.gov: NCT01578239, EudraCT: 2011-005049-11

Influence of the spacer location and the direct heating in the single and two phase region on the development of in-phase instabilities of boiling water reactors

The dynamic of boiling flows can be considered as a complex problem where generally more than one instability mechanism is present. This problem of two-phase flow instabilities is found in a big variety of energy and chemical engineering systems such as the channels of Boiling Water Reactors (BWR), conventional steam boilers, and phase change heat exchangers used in the chemical industry. Among the different instability types, one of the most important for the nuclear engineering field is the in-phase instability that appears in boiling water reactors (BWR). In this instability type a synchronized oscillation of the power and the thermal-hydraulic variables is produced in all the channels of the reactor. This paper study the influence of the spacer location and the direct heating i.e. the heating of the boiling channels by neutron and gamma rays on the in-phase instabilities BWRs.Papers presented to the 12th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Costa de Sol, Spain on 11-13 July 2016

Type II instabilities in advanced heavy water natural circulation reactors: Application to the AHWR

[EN] This paper deals with the instabilities in advanced heavy water reactors driven by natural circulation at high pressure and power conditions. This paper also study which are the design and operating parameters that have more influence on the appearance of type II instabilities. Some of the results are compared with usual BWR reactors to stablish which are the differences between both types of reactors in the development of limit cycle oscillations and the maximum amplitude values of these oscillations when some of the influential parameters on the stability are changed. This paper also explains the main characteristics of the modelling used to simulate the fuel channels, the risers or outlet feeders, the recirculation loop of this reactor, and the kinetic and heat transfer models. In addition, we compare the closure relations used in this model with the experimental correlations for the AHWR, to know the applicability of the correlations for the AHWR under natural circulation conditions. Finally, we study in this paper the influence on the decay ratio (DR) and the limit cycle amplitude of a set of design and operational parameters. Some of these parameters are: the amount of coolant direct heating by neutrons and gamma-rays, the form loss coefficient at the channel inlet, the form loss coefficient in the spacers, the phase change number No, the characteristic natural circulation time and the effective inertia of the recirculation loop.The authors of this paper are indebted to the help received for the MINECO grant ENE2016-79489-C2-1-P and to the Bhabba Atomic Center, specially to Dr Vijayan for give us the opportunity to review the PH.D. Thesis of Mr. Sapna Singh.Muñoz-Cobo, J.; Escrivá, A.; Berna, C. (2019). Type II instabilities in advanced heavy water natural circulation reactors: Application to the AHWR. Progress in Nuclear Energy. 117:1-13. https://doi.org/10.1016/j.pnucene.2019.103056S11311

Comparison of polynomial chaos expansion methods for uncertainty quantification in computational fluid dynamics simulations

Computational Fluid Dynamics (CFD) computer codes have proven to be a powerful tool in the analysis of all kinds of fluid systems. However, there is still a lack of practical methods for determining the uncertainty of their results, as most current techniques require performing too many simulations to be affordable in industrial-scale situations. One of the most promising methods for uncertainty quantification in computational fluid dynamics is Polynomial Chaos Expansion, a name that includes a variety of techniques, all based on the same mathematical background: projecting the system’s response into a basis of orthogonal polynomials. This paper discusses the main advantages and drawbacks of three of these techniques, namely random sampling, Gaussian quadrature and linear regression, in terms of reliability, ease of use and computational costs. All three techniques were applied to simulations of the turbulent mixing of two streams of water inside a Y-shaped channel, and the results compared with experimental data. Results show that, in this test case, quadrature method provides more reliable results than the other two techniques, with a lower computational cost. Due to its robustness and low number of simulations required, Polynomial Chaos Expansion via quadrature methods might be suitable for most industrial CFD simulations.Papers presented to the 12th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Costa de Sol, Spain on 11-13 July 2016

Study of pool scrubbing events under jet injection regime

Submerged jet hydrodynamics might have a significant role in the attenuation of radioactivity releases during nuclear power plant accidents. In particular, these studies are important in Steam Generator Tube Rupture accidents (SGTR accident) for Pressurized Water Reactors (PWRs), Station Black-Out (SBO events) in Boiling Water Reactors (BWRs) or in severe accidents, like the one occurred at the Fukushima Daiichi Nuclear Power Plant. Pool scrubbing has been habitually associated with globular discharges, i.e. at low injection velocities. Following this tradition, the SPARC90 code was developed to determine the trapping of fission products in pools during severe accidents, but only under these low injection velocity conditions. SPARC90 code assumes that the carrier gas enters the water pond at low or moderate velocities, forming a big bubble that eventually detaches from the injection pipe. However, there are a number of possible scenarios in which the capture of fission products in aqueous ponds might also occur under the jet injection regime, in which particle laden gases may enter the water at very high velocities resulting in a submerged gas jet. The present paper introduces the fundamentals, major hypotheses and code modifications developed in order to estimate particle removal during gas injection in pools under jet regimes. A simplified, yet reliable, approach to the submerged jet hydrodynamics was implemented based upon updated equations of jet hydrodynamics and aerosol removal, ensuring that both gas-liquid and droplet-particle interactions are correctly accounted for. The resultant code modifications were validated as far as possible, however, no suitable hydrodynamic tests were found in the literature. Hence, an indirect validation approach, based on data from pool scrubbing experiments, had to be employed. Moreover, validation was further limited by the scarcity of pool scrubbing tests under jet regimes (e., g., ACE, LACE, POSEIDON II and RCA experiments). This confrontation has been satisfactory, the experimental data and the simulations follow the same trends. We must highlight some main points, such as the capability of SPARC90-Jet to capture the increasing tendency of DF with both, aerosol diameter and pressure-submergency, catching not only the experimental trend but also the magnitude. Finally, emphasize the substantial improvement achieved with regard to the old SPARC90 code version, which has been clearly shown when comparing the SPARC90 and the SPARC90-Jet results against the available experimental data. But nevertheless, the work presented along this paper should be considered as a step towards an effective comprehension of the jet injection regime.Papers presented to the 12th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Costa de Sol, Spain on 11-13 July 2016

Experimental characterization of the entrained droplet velocities into a submerged gaseous jet

The study of submerged gaseous jets injected into stagnant water pools began in the 70s caused by the fact that they are commonly found in many industrial processes and engineering applications, such as underwater propulsion, metallurgical and chemical processes or nuclear reactors. Consequently it is important to be able to characterize these processes. The low air-water density ratio and the aggressiveness of the pool discharge process result in very complicated flow structures, which are inherently unsteady and turbulent. This poses a major challenge for the measurement of the various parameters involved in the discharge of gaseous submerged jets. Experimental studies of round turbulent air jets submerged in stagnant water are described in this paper. In particular, the entrained droplet velocity, which is crucial for the characterization of the jet, was determined. The experiments were performed using a water tank equipped with an air injector. A high speed camera in conjunction with Particle Image Velocimetry (PIV) techniques was used to measure the velocity of the entrained droplets during jet spreading. Results indicate that the droplet velocity distribution follows a decreasing exponential function. Moreover, the Reynolds number at the injector nozzle was used to develop a correlation linking the initial jet properties and the mean velocity of the entrained droplets. This work represents a new step towards a better understanding of the behavior of submerged gas jets injected into aqueous mediums. The velocity of the entrained droplets was determined, both its mean and distribution function. The extension of the present work to different nozzle diameters and aqueous mediums properties will be addressed in an upcoming paper.Papers presented to the 12th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Costa de Sol, Spain on 11-13 July 2016