A. Toutant

Université de Perpignan | UPVD · PROMES Laboratory of Processes, Materials and Solar Energy

The concept of solar receiver using fluidized particles as heat transfer fluid is attractive from the point of view of its performance but also of the material used. In this concept, the receiver is composed of tubes subjected to concentrated solar radiation in which the fluidized particles circulate vertically. Circulation in the tubes, immersed i...

Les énergies renouvelables font partie intégrante de la stratégie énergétique de la plupart des pays. Ce contexte engage à considérer avec attention toutes les solutions qui peuvent contribuer à l’émergence d’un monde décarboné. Parmi ces solutions, le solaire occupe une position de choix avec ses modes de conversion photovoltaïque et thermique, do...

Thermal Large-Eddy Simulations (T-LES) of highly anisothermal and turbulent channel flows are assessed using Direct Numerical Simulations (DNS). The investigated conditions are representative of solar receivers used in concentrated solar power towers. Four thermal operating conditions are considered. They aim to study several locations in the solar...

A numerical approach was implemented, to study a boiling flow in a horizontal serpentine tube. A NEPTUNE_CFD two-fluid model was used, to study the behavior of the refrigerant R141b in diabatic cases. The model was based on the Euler–Euler formalism of the Navier–Stokes equations, in which governing equations are solved for both phases of the fluid...

Solar receiver flows are very complex since the heating fluid is strongly turbulent and asymmetrically heated at high temperature levels. To deepen the understanding of these flows, four DNS have been performed in different fluid heating configurations. The Navier-Stokes and the energy equations are solved under the low Mach approximation and the c...

Fluidization regimes were studied in numerous papers with applications in risers in which gas velocity is the main driving force. The situation is different when a tube is immersed in a fluidized bed vessel in which a pressure is imposed to move the particle upward. The particle-in-tube solar receiver concept is based on this latter operation mode...

Concentrating solar power plants with direct steam generation have the possibility to store the generated energy in thermal form very easily. This is achieved by using two-phase accumulators in which the heat is stored directly in tanks filled with water and steam in a saturated state. The Llo solar power plant, owned by SUNCNIM in France, has nine...

This chapter focuses on the necessity to understand anisothermal turbulent flows inside gas solar receivers. It presents various modeling approaches starting with complex numerical modeling and simulations, and then simplified models and simulations. The chapter provides detailed presentations of fine models and simulations taking into account the...

In this study based on direct numerical simulations (DNS) of homogeneous bubbly flows, an analysis of velocity fluctuations is performed and a methodology for the development of a bubble-induced agitation (or pseudoturbulence) model is described. This process is based on the separation of two phenomena causing velocity fluctuations in the liquid: t...

The fluidized particle-in-tube solar receiver concept is promoted as an attractive solution for heating particles at high temperature in the context of the next generation of solar power tower. Similar to most existing central solar receivers, the irradiated part of the system, the absorber, is composed of tubes in which circulate the fluidized par...

Direct Numerical Simulations are performed to analyze the influence of key boundary conditions and flow characteristics on entropy generation rate statistics in a highly anisothermal forced convective turbulent channel flow of a thermo-dependent fluid submitted to asymmetrical heating. Each parameter is varied separately to quantify its influence c...

Uncertainties may skew the understanding of experiments or numerical simulations results. The impact of the flow parameters uncertainties of measurement on wall heat flux is investigated in a non-isothermal turbulent channel flow. A heat transfer correlation dedicated to gas-pressurized solar receivers of concentrated solar tower power is used. Bot...

Thermal large-eddy simulations (T-LES) and a direct numerical simulation are carried out in a bi-periodical channel with hot and cold wall temperatures of, respectively, 900 and 1300 K. The mean fluid temperature is lowered below the cold wall temperature thanks to a heat source, resulting in a both walls heating of the fluid. The hot and cold wall...

This study deals with thermal large-eddy simulation (T-LES) of anisothermal turbulent channel flow in the working conditions of solar receivers used in concentrated solar power towers. The flow is characterized by high-temperature levels and strong heat fluxes. The hot and cold friction Reynolds numbers of the simulations are, respectively, 630 and...

Artificial compressibility methods aim to reduce the stiffness of the compressible Navier-Stokes equations by artificially decreasing the velocity of acoustic waves in the fluid. This approach has originally been developed as an alternative to the incompressible Navier-Stokes equations as this avoids the resolution of a Poisson equation. This paper...

This study deals with forced convective heat transfer. It is divided into two parts. Firstly, a review of heat transfer involving forced convection in tubes and channels is proposed. In the case of channel geometry, studies dealing with symmetrically and asymmetrically heated flows as well as one side heated flows are reported. Then, a new correlat...

A sensitivity analysis of heat transfers in an asymmetrically heated turbulent channel flow is performed using a dedicated heat transfer correlation. The investigated correlation is developed to study the heat transfers between the fluid and the wall in gas-pressurized solar receivers of concentrated solar power tower. The working conditions corres...

Variational methods are used to optimize convective heat transfer in a channel gas flow. The minimization of a functional objective combining the rate of total entropy generation in the channel on the one hand and the total viscous dissipation on the other hand results in velocity and temperature fields. A weighting factor allows varying the relati...

Spatial and spectral energy exchanges associated with the turbulence kinetic energy per unit mass, or half-trace of the velocity covariance tensor, are studied in an anisothermal low Mach number turbulent channel flow. The temperatures of the two channel walls are 293 K and 586 K. This generates a strong temperature gradient in the wall-normal dire...

This paper studies the large-eddy simulation (LES) of isothermal turbulent channel flows. We investigate zero-equation algebraic models without wall function or wall model: functional models, structural models and mixed models. In addition to models from the literature, new models are proposed and their relevance is examined. Dynamic versions of ea...

The subgrid-scale modelling of a low Mach number strongly anisothermal turbulent flow is investigated using direct numerical simulations. The study is based on the filtering of the low Mach number equations, suited to low Mach number flows with highly variable fluid properties. The results are relevant to formulations of the filtered low Mach numbe...

In fluid dynamics, an important problem is linked to the knowledge of the fluid pressure. Recently, another approach to study incompressible fluid flow was suggested. It consists in using a general pressure equation (GPE) derived from compressible Navier-Stokes equation. In this paper, GPE is considered and compared with the Chorin's artificial com...

A crucial issue in fluid dynamics is related to the knowledge of the fluid pressure. A new general pressure equation is derived from compressible Navier-Stokes equation. It is argued that this new pressure equation allows unifying compressible, low-Mach and incompressible approaches. Moreover, this equation should be able to replace the Poisson equ...

Recently, several methods have been proposed to simulate incompressible fluid flows using an artificial pressure evolution equation, avoiding the resolution of a Poisson equation. These methods can be seen as various levels of approximation of the compressible Navier–Stokes equation in the low Mach number limit. We study the simulation of incompres...

Heat and mass transfer enhancement in a convective flow is studied using a variational optimization technique. Entropy generation rate is minimized while allowing to vary the relative weight of the total viscous dissipation in the objective functional to determine optimized velocity and scalar field patterns. The resulting velocity, thermal and mas...

On bubble forces in turbulent channel flows from direct numerical simulations - Volume 882 - A. du Cluzeau, G. Bois, A. Toutant, J.-M. Martinez

In a previous study, we have shown that the momentum transfer between phases, which requires modeling in two-fluid models, is partly comprised of a laminar dispersion force connected to surface tension and pressure effects. This dispersion force, which is obtained by stepping away from the particle hypothesis, is important for the prediction of the...

Materials for solar receivers in concentrated solar power plants are subjected to harsh working conditions including high temperatures, thermal shocks, and cycling, which cause high thermal and mechanical stresses in the materials. Ceramics are, therefore, excellent candidates as solar receiver materials for their high thermal, chemical, and mechan...

The subgrid-scale modelling of a low Mach number strongly anisothermal turbulent flow is investigated using direct numerical simulations. The study is based on the filtering of the low Mach number equations, suited to low Mach number flows with highly variable fluid properties. The results are relevant to formulations of the filtered low Mach numbe...

Entropy generation rates have been computed and analyzed in a fluid heated and sheared by a flat plate for isothermal and isoflux thermal boundary conditions, with and without fixing the total heat exchange power. To address a large number of situations, the plate/fluid temperature gap is allowed to vary up to large values. Thermal boundary conditi...

This paper studies the large-eddy simulation of anisothermal low Mach number turbulent channel flows. We consider the large-eddy simulations of the low Mach number equations in two formulations, the velocity formulation and the Favre formulation. In both formulations, we investigate the subgrid-scale modeling of the two most significant subgrid ter...

Direct Numerical Simulations have been performed for a fully-developed low Mach turbulent flow of an ideal gas with thermo-dependent viscosity and thermal conductivity in a flat channel at mean friction Reynolds number Reτ=180 submitted to asymmetric heating with a wall temperature ratio T2/T1=2. Mean and turbulent statistics of the flow have been...

Two-phase bubbly flows are found in many industrial applications. These flows involve complex local phenomena that are still poorly understood. For instance, two-phase turbulence modelling is still commonly based on single-phase flow analyses. A direct numerical simulation (DNS) database is described here to improve the understanding of two-phase t...

This paper studies the large-eddy simulation (LES) of isothermal turbulent channel flows. We investigate zero-equation algebraic models without wall function or wall model: functional models, structural models, and mixed models. In addition to models from the literature, new models are proposed and their relevance is examined. Dynamic versions of e...

Spatial and spectral energy exchanges associated with the turbulence kinetic energy per unit mass, or the half-trace of the velocity covariance tensor, are studied in an anisothermal low Mach number turbulent channel flow. The temperatures of the two channel walls are 293 K and 586 K. This generates a strong temperature gradient in the wall-normal...

The subgrid terms of the low Mach number equations are investigated in a strongly anisothermal low Mach number flow. The filtered low Mach number equations are established in three formulations in order to compare the unweighted classical filter and the density-weighted Favre filter on the one hand, and the filtering of the momentum conservation eq...

In fluid dynamics, an important problem is linked to the knowledge of the fluid pressure. Recently, another approach to study incompressible fluid flow was suggested. It consists in using a general pressure equation (GPE) derived from compressible Navier–Stokes equation. In this paper, GPE is considered and compared with the Chorin's artificial com...

This work proposes a new empirical direct methodology to estimate both the solar flux distribution and intensity on the surface of central receivers. In solar power tower plants with deteriorated heliostats, the numerical simulations to estimate the incident solar flux are not precise. Hence the thermal behaviour of the receivers cannot be determin...

This paper investigates the energy exchanges associated with the half-trace of the velocity fluctuation correlation tensor in a strongly anisothermal low Mach fully developed turbulent channel flow. The study is based on direct numerical simulations of the channel within the low Mach number hypothesis and without gravity. The overall flow behaviour...

This paper establishes a new formulation of the energy exchanges between the different parts of total energy. The decomposition uses the Reynolds averaging. This leads to a ternary decomposition of kinetic energy into the turbulence kinetic energy, the mean kinetic energy and the mixed kinetic energy, acting as an exchange term between the mean and...

A crucial issue in fluid dynamics is related to the knowledge of the fluid pressure. A new general pressure equation is derived from compressible Navier–Stokes equation. This new pressure equation is valid for all real dense fluids for which the pressure tensor is isotropic. It is argued that this new pressure equation allows unifying compressible,...

Hybrid low pressure air extractors are an economic way to enhance indoor air quality. The evaluation of their energetic performances needs the analysis of flow parameters that is typically done with wind tunnel data and numerical simulations. The purpose of this study is to analyze, numerically and experimentally, the flow and the energetic perform...

Hybrid solar gas-turbine (HSGT) is an attractive technology to foster market penetration of CSP. HSGT offers some major advantages like for example high solar-to-electric conversion efficiency, reduced water requirement and low capital cost. A very high temperature solar receiver is needed when elevated solar share is claimed. A few research works,...

The thermal boundary layer spatial developments in a turbulent open channel flow are studied by Large Eddy Simulations. The channel flow is submitted to an asymmetrical heating: the upper and lower walls have imposed non-uniform temperatures of about 590 K and 380 K respectively, while the fluid enters at 288 K. A fully-developed channel flow inlet...

In very anisothermal turbulent flows, the temperature gradient and turbulence are strongly coupled. The impact of the temperature gradient on turbulent kinetic energy (TKE) balance terms is of particular importance. It is investigated using direct numerical simulations and large eddy simulations of a fully developed anisothermal channel flow. A low...

On se propose dans cet article d’exprimer la demi-trace du tenseur de corrélations de vitesse pour les écoulements turbulent fortement anisotherme. Le nombre de Reynolds turbulent moyen est égal à 180. Les différents termes sont décomposés de manière à retrouver ceux présents dans le cas incompressible. Cela permet de se rapprocher, à des fins de v...

The effect of flow dynamics on the discharge mode is studied in order to design a technical solution for thin film coating on large surfaces. The configuration consists in two atmospheric pressure helium plasma jets impacting a surface and confined in a tube. This system operates in open air. It has been studied by short exposure time pictures, cur...

Strong temperature gradients introduce a major external agency into the wall-bounded turbulent flows. In these flows, the temperature field and the turbulent velocity field are highly correlated. In fact, standard RANS turbulent models are not able to accurately reproduce these flows. In order to improve the performance of the models, we need to un...

The thermomechanical behavior of a plate solar receiver with asymmetric heating is studied in this paper. The large-scale absorber/exchanger module is made of silicon carbide. It is irradiated by concentrated solar energy and heats pressurized air flowing inside textured channels up to high temperature. We look for the best compromise in terms of t...

This paper reports on the study of confined jets and jets interaction in terms of increasing chemical transport. The context of this study is the atmospheric pressure plasma-enhanced chemical vapor deposition, higher thin film growth rate being desired, while maintaining total flow rate as low as possible. Turbulence mixing and enhanced heat transf...

This work focuses on the simulation of the internal structure of a plate solar receiver with asymmetrical heating. The receiver examined in this paper is irradiated by concentrated sunlight and heats up pressurised air to high temperature. Solar receivers, in the same way as some other industrial heat exchangers, are heated asymmetrically due to on...

Direct numerical simulations of a turbulent channel flow submitted to a high temperature gradient are performed. The temperatures of the channel walls are imposed to 293 K for the cold one and 586 K for the hot one. In this configuration, the flow is subsonic, while temperature variations can be strong and induce significant variations of the fluid...

The modeling of the lift force in high shear rate pipe flow is an essential issue for the estimation of the droplet dispersion. The analytical models used in most CFD softwares, such as the popular models of Auton or Saffman, overestimate the intensity of the lift force for inertial particles at high particle Reynolds number. In this paper, after a...

The focus of this paper is on the characteristics (in terms of pressure loss and heat transfer) of an isothermal turbulent flow inside the absorber of a solar receiver. After a short description of the receiver and the power plant, we will focus on a certain kind of internal geometry: straight fins. A preliminary study based on correlations will be...

La présente invention concerne un module de récepteur surfacique solaire fonctionnant à haute température, traversé d'un canal (101) le long duquel s'effectue un transfert thermique entre un fluide (liquide ou gaz) en mouvement dans ledit canal (101) et au moins une paroi (104) du récepteur exposée au rayonnement solaire concentré, caractérisé en c...

This work focuses on the thermal performance enhancement of fluid heat exchanger with asymmetrical heating. Industrial heat exchangers such as solar receivers often have asymmetrical heating. The forced internal convective heat transfer and friction loss behaviours are studied for turbulent flows promoted by a combination of delta winglet vortex ge...

This article presents Large Eddy Simulations of thermal boundary layer spatial development in a low-Mach number turbulent channel flow. A coupling between isothermal biperiodic channel and anisothermal open channel is done to obtain a fully developed turbulent inlet. The interaction between a high temperature gradient and a turbulent flow is studie...

Thermal striping is one of the possible initiator of pipe rupture. In this framework, thermal fluctuations in a heated periodic channel have been calculated using Large Eddy Simulation (LES). The fluid Prandtl number is set to 0.01 and the friction Reynolds number to 395. The Werner and Wengle Wall Function is used with the Navier-Stokes equations...

In this Letter, we find that the Kolmogorov scaling law is no longer valid when the flow is submitted to strong dilatational effects caused by high temperature gradients. As a result, in addition to the nonlinear time scale, there is a much shorter “temperature gradients” time scale. We propose a model that estimates the time scale of the triple de...

Among the various direct numerical simulation (DNS) methods dedicated to multiphase flow, the front-tracking methods that use a Lagrangian mesh to describe explicitly the interfaces are generally considered as a very accurate and complex method. In this family of methods, while a fine Lagrangian mesh is desirable for a better representation of the...

In this study the Stereoscopic Particle Image Velocimetry (S-PIV) technique was used to analyze the aerodynamic behavior of a textured surface. This textured surface is supposed to cover the inside of the hot wall of asymmetric heat exchangers. A high heat transfer coefficient and a low pressure drop are desired for the studied module receiver. The...

This paper studied nonisothermal plane channel flows using themethod of thermal largeeddy simulations (TLES). Several temperature ratios (TR = TH/TC) were investigated, where TC and TH are the temperatures of the cold and hot sides, respectively. Each TR case is further considered for two wall Reynolds numbers (Reτm), 180 and 395, where the wall Re...

Thermal fatigue is a major problem for liquid metal fast reactors due to the high temperature differences of the coolant in the circuits and because liquid metals efficiently transmit thermal fluctuations to walls. Detailed thermal hydraulic investigations have been carried out to quantify the amplitudes and frequencies of the temperature fluctuati...

Thermal large eddy simulations are carried out in order to study the convective flow in a solar receiver. We investigate the impact of thermal gradients on a turbulent channel flow with imposed wall temperatures for two turbulent Reynolds numbers based on the friction velocity (180 and 395). In this configuration, the flow is subsonic, while temper...

In the quest for a better description of the thermal-hydraulics of a PWR sub-channel by using DNS results to upscale valuable information towards higher scale industrial models, two main tasks have been identified and tackled separately. The first one is dedicated to the simulation of adiabatic turbulent two-phase flows in a sub-channel. The second...

In this paper, we study turbulent two-phase flow. We consider the level of description where only the large scales of turbulence and the large deformations of bubbles are explicitly described:•the small scale of turbulence are not represented and we are close to the Large Eddy Simulation concept,•the mean geometry of each bubble is explicitly descr...

In order to study and validate the jump conditions established in part 1, we realize a priori tests thanks to the data of a 3D Direct Numerical Simulation (DNS) of a strongly deformable bubble in a spatially decaying turbulence. The complex interactions between interface and turbulence are fully resolved. An explicit filtering of the DNS has been e...