Francesco D'Annibale

Bio: Francesco D'Annibale is an academic researcher from ENEA. The author has contributed to research in topics: Boiling & Bubble. The author has an hindex of 12, co-authored 23 publications receiving 433 citations.

Experimental results of nanofluids flow effects on metal surfaces

Abstract: The results of an experimental study on the effects of the flow of nanofluids (water-based suspensions of nanometer-sized solid particles) on metal surfaces are presented. Either different nanofluids (containing TiO2, Al2O3, ZrO2, and SiC, respectively) and different target materials (aluminum, copper, stainless steel) have been investigated, under similar operating conditions. Different behaviors were observed depending on the specific combination nanofluid-target material, which in some cases led to severe damaging of the tested target, thus highlighting the need for an adequate preliminary investigation of the possible interactions between the selected nanofluid and the apparatus materials, before its adoption as heat transfer fluid.

Experimental analysis of corrosion and erosion phenomena on metal surfaces by nanofluids

Abstract: In the present work an analysis of experimental data obtained exposing metallic targets to the flow of a number of nanofluids has been carried out. The investigated suspensions were composed of typical nanometer-sized solid particles, such as TiO 2 , Al 2 O 3 , SiC, and ZrO 2 at different concentrations, suspended in different base fluids. The effects of the flow of these nano-materials on three reference targets made of commercial metals (aluminum, copper, and stainless steel) have been assessed. An accurate analysis of the results showed that, where present, the observed damages are caused by chemical corrosion rather than by mechanical erosion, the pH of the suspension being the most important parameter. Conversely, no influence of the particles’ nature and content was found, even at high concentrations of nanoparticles (up to 20% by weight). This is believed to be a useful information about the practical feasibility of advanced systems, like in heat transfer applications, based on the use of these relatively new fluids.

A Benchmark Study on the Thermal Conductivity of Nanofluids

Abstract: This article reports on the International Nanofluid Property Benchmark Exercise, or INPBE, in which the thermal conductivity of identical samples of colloidally stable dispersions of nanoparticles or “nanofluids,” was measured by over 30 organizations worldwide, using a variety of experimental approaches, including the transient hot wire method, steady-state methods, and optical methods. The nanofluids tested in the exercise were comprised of aqueous and nonaqueous basefluids, metal and metal oxide particles, near-spherical and elongated particles, at low and high particle concentrations. The data analysis reveals that the data from most organizations lie within a relatively narrow band (±10% or less) about the sample average with only few outliers. The thermal conductivity of the nanofluids was found to increase with particle concentration and aspect ratio, as expected from classical theory. There are (small) systematic differences in the absolute values of the nanofluid thermal conductivity among the various experimental approaches; however, such differences tend to disappear when the data are normalized to the measured thermal conductivity of the basefluid. The effective medium theory developed for dispersed particles by Maxwell in 1881 and recently generalized by Nan et al. [J. Appl. Phys. 81, 6692 (1997)], was found to be in good agreement with the experimental data, suggesting that no anomalous enhancement of thermal conductivity was achieved in the nanofluids tested in this exercise.

Two-phase flow, boiling and condensation in conventional and miniature systems

Abstract: Providing a comprehensive introduction to the fundamentals and applications of flow and heat transfer in conventional and miniature systems, this fully enhanced and updated edition covers all the topics essential for graduate courses on two-phase flow, boiling, and condensation. Beginning with a concise review of single-phase flow fundamentals and interfacial phenomena, detailed and clear discussion is provided on a range of topics, including two-phase hydrodynamics and flow regimes, mathematical modeling of gas-liquid two-phase flows, pool and flow boiling, flow and boiling in mini and microchannels, external and internal-flow condensation with and without noncondensables, condensation in small flow passages, and two-phase choked flow. Numerous solved examples and end-of-chapter problems that include many common design problems likely to be encountered by students, make this an essential text for graduate students. With up-to-date detail on the most recent research trends and practical applications, it is also an ideal reference for professionals and researchers in mechanical, nuclear, and chemical engineering.

A review on optical properties and application of nanofluids in direct absorption solar collectors (DASCs)

Abstract: As an abundant, cheap and pollution-free renewable energy resource, solar energy offers a great alternative to conventional fossil resources and is expected to play an increasingly significant role in our global energy future. Solar thermal collectors are conventional devices for capturing solar radiation. Direct absorption solar collector (DASC) is a new generation of solar thermal collectors in which the transport medium is directly exposed to the incident solar radiation. To improve direct absorption collectors absorption and heat transfer capabilities, molecular-level additives are added to their working fluids. As a production of the emerging world of nanotechnology, nanofluids – which are engineered suspensions of nanoscale materials in host fluids – have shown remarkable improvement in thermo-physical and optical properties of conventional heat transfer fluids. This review presents a comprehensive survey of the recent studies on optical characterization, relevant equations and theoretical modeling approaches, and application of nanofluids in direct absorption solar collectors. Possible issues and challenges encountered in potential exploitation of nanofluids in DASCs are addressed as well.