José Gonzalez-Aguilar

Carbon nanostructures production by gas-phase plasma processes at atmospheric pressure

Carbon nanostructures have received much attention for a wide range of applications. This paper reviews the historical role of plasmas in the gas-phase synthesis of carbon nanostructures and the present plasma technologies for industrial production purposes. It enumerates the advantages and disadvantages with respect to concurrent technologies commonly employed nowadays. Finally, some carbon nanostructures produced in our laboratory will serve as examples of the plasma processes potential.

Design and electrical charaterization of a low current–high voltage compact arc plasma torch

A new compact plasma torch associated with a resonance power supply allows the generation of low power discharges (typically 100 W–1 kW) under high voltage (>1 kV) low current (<1 A) conditions. The resonance power supply allows continuous control of the discharge current, which is a major improvement with respect to the traditional dc power source based on a high voltage transformer. In addition, this system is characterized by a high conversion efficiency that is crucial when it comes to industrial applications. It has been shown that different regimes ranging from streamer over gliding arc to continuous discharges were obtained depending on the operating conditions. The objective of this paper is a better understanding of the different observed behaviour through the determination of the main torch and power supply parameters.

Production of Carbon Nanotubes and Other Nanostructures Via Continuous 3‐Phase AC Plasma Processing

Abstract The highly flexible plasma system allows the independent flow control of plasma gas, carbonaceous feedstock and metal catalyst. Further important control parameters include current intensity and product quenching rate yielding in an excellent control of the thermal history of the carbon products. Temperature profiles measured along the reactive flow of carbon particles are presented, mapping time–temperature relations for typical operating conditions. In addition, the principle product families are presented. From the characteristics observed and NT product analysis, it is concluded that the AC plasma technology shows a significant potential for the continuous production of bulk quantities of carbon‐based nanotubes of controlled properties and novel tube‐like nanostructures.

Synthesis of Titania Nanoparticles Using a Compact Nonequilibrium Plasma Torch

A compact plasma torch has been developed to synthesize titania nanoparticles at atmospheric pressure. It is operated at high-voltage (>700 V) and low-current (<0.4 A) conditions, and its typical discharge power is in the range 200–500 W. Titania nanoparticles were synthesized by oxidizing titanium tetraisopropoxide vapor in the plasma torch. The synthesized titania particles are a mixture of rutile and anatase with a mean crystallite size between 30 and 50 nm. This plasma torch can be used to generate atmospheric nonequilibrium plasmas for facile and environmental friendly synthesis of various nanoparticles.

Theoretical and experimental study of an argon free burning arc dicharge at very high-pressure and low-intensity

This paper deals to study a low current intensity, very high-pressure (PGt105 Pa) free-burning argon arc discharge in a tip-tip configuration. A 2D axisymmetric two-temperature fluids model has been developed. The model contains three chemical species (e, Ar, Ar+), the appropriated thermodynamics and transport properties expressed as a function of electron and heavy temperatures and pressure, and the electrodes sheath submodel. Theoretical results were compared with experimental data obtained under pressure comprised between 0,1 to 10 MPa and 0.1 to 500 mA. Highest voltages are obtained at very high pressures and low current intensities. Theoretical model indicates that pressure increment causes an arc diameter reduction. This is due to the augmentation of radial heat losses by natural convection at arc fringes and by conduction due to a better energy transfer by neutral- electrons collisions. Surprisingly, the very high-pressure conditions seems having a stabilizing effect on the arc discharge.

Electrode sheath model for an argon free burning arc discharge at very high pressure and low intensity

In this paper, a two-temperatures model has been applied to the near cathode and anode layers for a very high- pressure (>>105 Pa), low-current (< 1 A) argon free burning arc discharge in a tip-tip configuration. Different theories that has been proposed in the literature regarding cathode and anode phenomena were reviewed first. The model behavior has been studied in different pressure and current conditions and the results were compared to the model proposed in the literature. Typical results obtained from this model show that the voltage drop in the cathode layer varies between 1 to 150 V for cathode temperatures of 5000 and 3000 K, respectively. For the anode layer, typical 3-14 V voltage drops were observed. Very high pressure influence on the voltage drop clearly appear for pressures up to 10 MPa on the cathode layer. In the anode layer, high pressure seems to not have a relevant role. A 9 and 6 V maximal voltage drop at the near- cathode zone has been obtained for pressures equal to 0.1 MPa and 10 MPa respectively (electrode wall temperature, 4000 K). In the anode layer, maximal total voltage drop was estimated around 5 V.

Continuous production of Fullerenes and other carbon nanomaterials on a semi-industrial scale using plasma technology

A new production method is presented allowing the production of bulk quantities of fullerenes and other carbon nanomaterials using a 3‐phase thermal plasma (260 kW). The main characteristics of this method lie in the independent control of the carbon throughput by injection of a solid carbon feedstock, and the immediate extraction of the synthesised product from the reactor, allowing production on a continuous basis. The currently investigated plasma facility is of an intermediate scale between lab‐size and an industrial pilot plant, ready for further up scaling to an industrial size. The influence of a large number of different carbon precursors, plasma gases and operating conditions on the fullerene yield has been studied. At this state, quantities of up to 1 kg of carbon can be processed per hour with further scope for increase, leading to production rates for this type of materials not achievable with any other technology at present.

Tailor-made carbon nanomaterials for bulk applications via high-intensity arc plasma

Abstract Different families of carbon nanostructures produced by a continuous plasma process are presented. Due to the flexibility of this original technology, properties of classical carbon black products can be adjusted more freely during synthesis and an even wider range of parameters is accessible. Novel products with distinctive characteristics are observed when treating nanostructured material in the high‐temperature plasma. Evaluation of the application properties of selected materials indicates in certain cases an excellent performance. Plasma‐synthesised or plasma‐treated carbon nanomaterials have an important potential to improve the performance of carbon‐black‐containing materials.

A parametric experimental study of aerothermal performance and efficiency in monolithic volumetric absorbers

This paper presents experimental thermal efficiency measurements conducted on nine monolithic absorbers manufactured in siliconized silicon carbide with square flow channels. The effects of two geometric parameters on efficiency have been investigated: flow channel width and absorber length. Experiments have been conducted in the test bench for optical and thermal absorber characterizations at the IMDEA Energy Institute, which employs a 7 kWe (1.2 kWth) high flux solar simulator. The facility is modular in design and allows for a rapid interchangeability of the test components. Experimental measurements are benchmarked against on-sun tests conducted in a pilot deployment with a similar monolithic configuration. The effects of absorber cross-sectional geometry on thermal efficiency are discussed. It is generally concluded that a significantly larger effect of the forced convection heat transfer mechanism with respect to the radiative mode is necessary in order to achieve the volumetric effect in this type ...

Heat exchanger modelling in central receiver solar power plant using dense particle suspension

In this paper, a detailed thermodynamic model for a heat exchanger (HX) working with a dense particle suspension (DPS) as heat transfer fluid (HTF) in the solar loop and water-steam as working fluid is presented. HX modelling is based on fluidized bed (FB) technology and its design has been conceived to couple solar plant using DPS as HTF and storage media with Rankine cycle for power generation. Using DPS as heat transfer fluid allows extending operating temperature range what will help to reduce thermal energy storage costs favoring higher energy densities but will also allow running power cycle at higher temperature what will increase its efficiency. Besides HX modelling description, this model will be used to reproduce solar plant performance under steady state and transient conditions.