Fast computation of multi-scale combustion systems

In the present work, we illustrate the process of constructing a simplified model for complex multi-scale combustion systems. To this end, reduced models of homogeneous ideal gas mixtures of methane and air are first obtained by the novel Relaxation Redistribution Method (RRM) and thereafter used for the extraction of all the missing variables in a reactive flow simulation with a global reaction mode

Link-wise Artificial Compressibility Method

The Artificial Compressibility Method (ACM) for the incompressible Navier-Stokes equations is (link-wise) reformulated (referred to as LW-ACM) by a finite set of discrete directions (links) on a regular Cartesian mesh, in analogy with the Lattice Boltzmann Method (LBM). The main advantage is the possibility of exploiting well established technologies originally developed for LBM and classical computational fluid dynamics, with special emphasis on finite differences (at least in the present paper), at the cost of minor changes. For instance, wall boundaries not aligned with the background Cartesian mesh can be taken into account by tracing the intersections of each link with the wall (analogously to LBM technology). LW-ACM requires no high-order moments beyond hydrodynamics (often referred to as ghost moments) and no kinetic expansion. Like finite difference schemes, only standard Taylor expansion is needed for analyzing consistency. Preliminary efforts towards optimal implementations have shown that LW-ACM is capable of similar computational speed as optimized (BGK-) LBM. In addition, the memory demand is significantly smaller than (BGK-) LBM. Importantly, with an efficient implementation, this algorithm may be one of the few which is compute-bound and not memory-bound. Two- and three-dimensional benchmarks are investigated, and an extensive comparative study between the present approach and state of the art methods from the literature is carried out. Numerical evidences suggest that LW-ACM represents an excellent alternative in terms of simplicity, stability and accuracy.Comment: 62 pages, 20 figure

CFD MODELING OF SOLAR COLLECTOR WITH NANO-FLUID DIRECT ABSORPTION FOR CIVIL APPLICATION

Direct solar absorption has been considered often in the past as a possible configuration of solar thermal collectors for residential and small commercial applications. Of course, a direct absorption could improve the performance of solar collectors by skipping one step of the heat transfer mechanism of standard devices and by modifying the temperature distribution inside the collector. In fact, classical solar thermal collectors have a metal sheet as absorber, designed such that water has the minimum temperature in each transversal section, in order to collect as much as possible the solar thermal energy. On the other hand, in a direct configuration, the hottest part of the system is the operating fluid and this allows to have a more efficient conversion. Nanofluids, i.e. fluids with a suspension of nano-particles, as carbon nano-horns, could be a good and innovative family of absorbing fluids, for their higher absorption coefficient with respect to the base fluid and stability under moderate temperature gradients. Moreover, carbon nanohorns offer the significant advantage to be non-toxic unlike other carbon nanoparticles (e.g. carbon nanotubes). In this work, an original 3D model of the absorption phenomena in nano-fluids flowing in a cylindrical tube is coupled with a CFD analysis of the flow and temperature field. Recent measurements of the optical properties of nano-fluids with different concentrations have been used for the radiation heat transfer modeling and included in the fluid dynamic modeling as well. Heat losses due to conduction, convection and radiation at the boundaries are included in the model. The results are compared with the typical performance of flat solar collectors present on the marke

Development of a non-radioactive molecular hybridization probe for detecting Strawberry mottle virus in strawberry

La propagación vegetativa del cultivo de frutilla favorece la transmisión de patógenos sistémicos, como es el caso de los virus, que constituyen uno de los principales factores limitantes. Se han descripto más de 20 virus que infectan esta especie; el Strawberry mottle virus (SMoV) es uno de los más frecuentes y responsable de importantes pérdidas económicas. Debido a la falta de antisuero disponible comercialmente para un diagnóstico serológico, el SMoV es detectado fundamentalmente mediante reacción en cadena de la polimerasa con transcripción reversa (RT-PCR). En este estudio se desarrolló una sonda de hibridación molecular no radioactiva para su detección. Se sintetizó cDNA con cebadores específicos diseñados a partir de la región 3’ no codificante del genoma viral. El cDNA obtenido fue clonado, marcado y utilizado como sonda. Se evaluaron seis protocolos de extracción de ARN viral a partir de plantas infectadas, de los cuales el método de bromuro de cetiltrimetilamonio modificado (CTAB) fue el más eficiente. Se evaluaron hojas de diferentes estados fenológicos y pecíolos, y fueron las hojas viejas y los pecíolos los que mostraron mayor reacción.The vegetative propagation of strawberries favors transmission of systemicpathogens, such as viruses, which are one of the main yield-limiting factorsfor this crop. More than 20 viruses have been described as infecting thisspecies; one of the most frequent is the Strawberry mottle virus (SMoV), whichis responsible for significant economic losses. SMoV is usually detected byreverse transcription polymerase chain reaction (RT-PCR), given that serum isnot available for serological tests. In this study, a non-radioactive molecularprobe was developed for SMoV detection. The cDNA was synthesized byRT-PCR using specific primers designed from the 3?UTR region of the viralgenome. The cloned cDNA segment was labeled and used as a probe. Six RNAextraction protocols were evaluated, and the modified cetyltrimethylammoniumbromide (CTAB) method showed the highest sensitivity level. Leaves at differentphenological stages and petioles were evaluated; the highest reaction wasobserved in old leaves and in petioles.Fil: Asinari, Florencia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba; Argentina. Instituto Nacional de Tecnología Agropecuaria. Centro de Investigaciones Agropecuarias. Instituto de Patología Vegetal; ArgentinaFil: Cafrune, Eva Encarnacion. Instituto Nacional de Tecnología Agropecuaria. Centro de Investigaciones Agropecuarias. Instituto de Patología Vegetal; ArgentinaFil: Guzman, F. A.. Instituto Nacional de Tecnología Agropecuaria. Centro de Investigaciones Agropecuarias. Instituto de Patología Vegetal; ArgentinaFil: Conci, Luis Rogelio. Instituto Nacional de Tecnología Agropecuaria. Centro de Investigaciones Agropecuarias. Instituto de Patología Vegetal; ArgentinaFil: Conci, Vilma Cecilia. Instituto Nacional de Tecnología Agropecuaria. Centro de Investigaciones Agropecuarias. Instituto de Patología Vegetal; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba; Argentin

Techno-economic analysis of a solar thermal plant for large-scale water pasteurization

Water pasteurization has the potential to overcome some of the drawbacks of more conventional disinfection techniques such as chlorination, ozonation and ultraviolet radiation treatment. However, the high throughput of community water systems requires energy-intensive processes, and renewable energy sources have the potential to improve the sustainability of water pasteurization plants. In case of water pasteurization by solar thermal treatment, the continuity of operation is limited by the intermittent availability of the solar irradiance. Here we show that this problem can be addressed by a proper design of the plant layout, which includes a thermal energy storage system and an auxiliary gas boiler. Based on a target pasteurization protocol validated by experiments, a complete lumped-component model of the plant is developed and used to determine the operating parameters and size of the components for a given delivery flow rate. Finally, we report an economic analysis of the proposed plant layout, which allows its optimization for different scenarios based on two design variables, namely the solar multiple and the duration of the thermal energy storage. Based on the analyzed cases, it is found that the proposed plant layouts may yield a unit cost of water treatment ranging from ≈32 EUR-cents m−3 to ≈25 EUR-cents m−3

Nanoscale thermal properties of carbon nanotubes/epoxy composites by atomistic simulations

Carbon nanotubes/epoxy composites are increasingly employed in several industrial fields, because of the enhanced material properties provided by the nanofillers. In particular, the thermal conductivity of these nanocomposites is determined by heat transfer mechanisms occurring over multiple scales, thus causing a complex relation between effective response and microscopic characteristics of the material. Here, the thermal properties of epoxy composites reinforced by carbon nanotubes are investigated using atomistic simulations. For a better understanding of how the effective thermal conductivity arises from the characteristics of the composite at the nanoscale, the thermal properties of its constituents are studied separately according to different geometrical, physical and chemical characteristics. The thermal conductivity of carbon nanotubes and epoxy resin alone is first investigated by molecular dynamics; then, the Kapitza resistance at the nanotube–nanotube and nanotube–epoxy interfaces is studied as well. The effective thermal conductivity of the carbon nanotubes/epoxy composite is finally computed and the observed behavior interpreted on the basis of the properties of the nanofillers, matrix and interfaces alone. Results – verified against effective medium theory predictions – show that, for the considered configurations, the effective thermal conductivity of the nanocomposite increases with the nanotube length and volume fraction, with the curing degree of the epoxy and system temperature. In perspective, the presented approach could be employed to investigate other constitutive materials or properties of nanocomposites

3D printed lattice metal structures for enhanced heat transfer in latent heat storage systems

The low thermal conductivity of Phase Change Materials (PCMs), e.g., paraffin waxes, is one of the main drawbacks of latent heat storage, especially when fast charging and discharging cycles are required. The introduction of highly conductive fillers in the PCM matrix may be an effective solution; however, it is difficult to grant their stable and homogeneous dispersion, which therefore limits the resulting enhancement of the overall thermal conductivity. Metal 3D printing or additive manufacturing, instead, allows to manufacture complex geometries with precise patterns, therefore allowing the design of optimal paths for heat conduction within the PCM. In this work, a device-scale latent heat storage system operating at medium temperatures (similar to 90 celcius) was manufactured and characterized. Its innovative design relies on a 3D Cartesian metal lattice, fabricated via laser powder bed fusion, to achieve higher specific power densities. Numerical and experimental tests demonstrated remarkable specific power (approximately 714 +/- 17 W kg-1 and 1310 +/- 48 W kg-1 during heat charge and discharge, respectively). Moreover, the device performance remained stable over multiple charging and discharging cycles. Finally, simulation results were used to infer general design guidelines to further enhance the device performance. This work aims at promoting the use of metal additive manufacturing to design efficient and responsive thermal energy storage units for medium-sized applications, such as in the automotive sector (e.g. speed up of the engine warm up or as an auxiliary for other enhanced thermal management strategies)

Techno-economic analysis of a solar thermal plant for large-scale water pasteurization

Water pasteurization has the potential to overcome some of the drawbacks of more conventional disinfection techniques such as chlorination, ozonation and ultraviolet radiation treatment. However, the high throughput of community water systems requires energy-intensive processes, and renewable energy sources have the potential to improve the sustainability of water pasteurization plants. In case of water pasteurization by solar thermal treatment, the continuity of operation is limited by the intermittent availability of the solar irradiance. Here we show that this problem can be addressed by a proper design of the plant layout, which includes a thermal energy storage system and an auxiliary gas boiler. Based on a target pasteurization protocol validated by experiments, a complete lumped-component model of the plant is developed and used to determine the operating parameters and size of the components for a given delivery flow rate. Finally, we report an economic analysis of the proposed plant layout, which allows its optimization for different scenarios based on two design variables, namely the solar multiple and the duration of the thermal energy storage. Based on the analyzed cases, it is found that the proposed plant layouts may yield a unit cost of water treatment ranging from ≈32 EUR-cents m-3 to ≈25 EUR-cents m-3

Thermal transport across nanoparticle-fluid interfaces: the interplay of interfacial curvature and nanoparticle-fluid interactions

We investigate the general dependence of the thermal transport across nanoparticle–fluid interfaces using molecular dynamics computations. We show that the thermal conductance depends strongly both on the wetting characteristics of the nanoparticle–fluid interface and on the nanoparticle size. Strong nanoparticle–fluid interactions, leading to full wetting states in the host fluid, result in high thermal conductances and efficient interfacial transport of heat. Weak interactions result in partial drying or full drying states, and low thermal conductances. The variation of the thermal conductance with particle size is found to depend on the fluid–nanoparticle interactions. Strong interactions coupled with large interfacial curvatures lead to optimum interfacial heat transport. This complex dependence can be modelled using an equation that includes the interfacial curvature as a parameter. In this way, we rationalise the existing experimental and computer simulation results and show that the thermal transport across nanoscale interfaces is determined by the correlations of both interfacial curvature and nanoparticle–fluid interactions