Preheated Nitrogen Research Articles

Experimental study on laminar lifted flames of pre-vaporized palm oil biodiesel

Characteristics of laminar lifted flame of pre-vaporized palm oil biodiesel have been experimentally investigated by varying fuel mole fraction at elevated unburnt gas temperatures. The biodiesel fuel was pre-vaporized and mixed with pre-heated nitrogen at a range of fuel mole fractions of 0.01 – 0.02. The unburnt gas temperature was varied from 500 K to 650 K. The results showed that the increase in jet flow velocity influenced the liftoff of the laminar non-premixed flame. Furthermore, the higher fuel mole fractions and the elevated unburnt gas temperatures led to a reduction in the liftoff height of the flame. Hence, a limited range of conditions, where the lifted flame occurred was determined for a given unburnt gas temperature and fuel mole fraction. At some of the experimental conditions such as 500 K and 550 K, the flames still experienced liftoff even at smaller jet velocities compared to stoichiometric laminar burning velocity of the same mixture. This behavior was believed to associate with the buoyant force produced at the nozzle of the rim, causing secondary entrainment of the mixture flow at relatively low jet flow velocities. The results suggested a correlation between the liftoff height and jet flow velocity, with the inclusion of the stoichiometric laminar burning velocity, regardless of the unburnt gas temperature and fuel mole fraction in the mixture. The adaptation of the buoyancy-induced velocity to the liftoff velocity correlated well with the stoichiometric laminar burning velocity, showing the significance of the buoyant force near the nozzle exit.

Corrosion Performance of Laser Posttreated Cold Sprayed Titanium Coatings

The recent development of cold spray technology has made possible the deposition of highly reactive, oxygen sensitive materials, such as titanium, without significant chemical reaction of the powder, modification of particle microstructure and with minimal heating of the substrate. However, the presence of interconnected pathways (microscale porosity) within the deposit limits the performance of the metallic coating as an effective barrier to corrosion and substrate attack by corrosive media is usually inevitable. The aim of the present study was to investigate the effects of processing, including a postspray laser treatment, on the deposit microstructure and corrosion behavior. Commercially pure titanium (CP Ti) was deposited onto a carbon steel substrate, using a commercial cold spray system (CGTTM Kinetiks® 4000) with preheated nitrogen as both the main process gas and the powder carrier gas. Selected coatings were given a surface melting treatment using a commercial 2 kW CO2 laser (505 Trumpf DMD). The effect of postdeposition laser treatment on corrosion behavior was analyzed in terms of pore structure evolution and microstructural changes. Optical microscopy, scanning electron microscopy, and x-ray diffraction were employed to examine the microstructural characteristics of the coatings. Their corrosion performance was investigated using electrochemical methods in 3.5 wt.% NaCl (ASTM G5-94 (2004)). As-sprayed titanium coatings could not provide favorable protection to the carbon steel substrate in the aerated NaCl solution, whereas the coatings with laser-treated surfaces provided barrier-like properties.

Thermochemical treatment of E-waste from small household appliances using highly pre-heated nitrogen-thermogravimetric investigation and pyrolysis kinetics

The EU directive on waste of electrical and electronic equipment (WEEE) 2002/96/EC has set a goal of recovering 70–80% in terms of materials and energy. Nowadays, thermal cracking (pyrolysis) of such waste streams is receiving renewed attention, due to the energy and material recovery that can be achieved and therefore the sustainable waste management. However, it still lacks the kinetic background which is of great importance for a successful design of thermochemical processes. In this study the kinetic parameters of WEEE (originating from small household appliances) pyrolysis using highly pre-heated nitrogen under six different heating rates (1–2.5 K/s) have been estimated using a combination of model-free and model fitted methods. Even though WEEE is heterogeneous material, similar behavior at each of the six different heating rates applied was observed. The activation energy of the pyrolysis process determined with two different model-free methods gave comparable results. Pre-exponential factor and reaction order were determined using the Coats-Redfern method. The estimated kinetic parameters for the WEEE pyrolysis are: E = 95.54 kJ/mol, A = 1.06 × 10 8 and n = 3.38.

Synthesis of Composite Microparticles with a Mixing Cross

Fine particles of pharmaceuticals and other materials can be rapidly made by a patented drying process known as CO 2 -Assisted Nebulization with a Bubble-Dryer (CAN-BD), by aerosolization from a low-volume mixing device (e.g., a tee or cross). The compounds of interest are dissolved in water or an appropriate organic solvent and mixed intimately with supercritical or near-critical CO 2 by pumping the fluids through a mixing device at room temperature and about 83 bar. The mixture is then decompressed through a capillary tube flow restrictor into a drying chamber maintained at near atmospheric pressure. The aerosol plume is mixed with preheated nitrogen in the drying chamber and is dried in less than 5 s at temperatures between 0 and 60° C. The dry powders (hollow, porous, or solid) collected from the chamber can usually be in the particle size range (1-5 μm) optimum for pulmonary drug delivery. The use of a cross as a mixing device permits solutes or suspensions in two liquid streams and a nebulizing fluid (e.g., supercritical CO 2 ) to be mixed and desolvated to form heterogeneous microparticles. If one solid in the heterogeneous particles is a slowly dissolving coating material, the heterogeneous particles can release the second solid at a slower rate. If one solid is leached, a large porous particle with a high surface area can be obtained, yet its mean aerodynamic diameter is in the particle size optimum for pulmonary delivery. The primary advantages of this process are that (1) solids soluble in water and solids soluble in organic solvents can be micronized in a single-step process to generate heterogeneous particles, and (2) it facilitates drying of microbubbles and microdroplets at lower temperatures than those used in traditional spray drying processes.

Nitridation of iron by CW-CO 2 laser nitriding technologies

Laser nitriding is an attractive method to improve metal surface properties, such as hardness, wear, and corrosion resistance, with the advantage of simple experimental setup, rapid treatment, and precise process control. Here, iron nitride (Fe x N) is obtained by the mixing technology with laser and pre-heated nitrogen (LHN) or nitrogen plasma (LPN) beams on the surface of pure iron in atmosphere ambient. In these two technologies, laser provides heat, pre-heated nitrogen provides help for nitrogen activity, and nitrogen plasma provides nitrogen ions, respectively. The two technologies are superior to the previous laser nitriding (LN) methods. However, iron nitride more difficult was obtained by the mixing technology with laser and pre-heated nitrogen than by the mixing technology with laser and plasma, and iron oxide was not observed in the sample treated by the latter. The feasibility of the technologies is analyzed in theory. X-ray diffraction measurements reveal formation of iron nitride in the as-treated sample by these technologies. Moreover, the concentration and phase formation of iron nitride were given at different laser power densities and different scanning velocities with emphasis on the mixing technology with laser and plasma.

Prehated, Combustion-Driven Gasdynamic Lasers

The effect of preheated nitrogen on the available laser specific energy is examined for two classes of combustion-driven gasdynamic lasers (GDLs). The analysis combines a nonequilibrium model of the relevant GDL processes with a simplified nondissociating combustion model handling a variety of candidate GDL fuels. For a more comprehensive evaluation of the capabilities of preheating, an optimization routine is added to the combined laser/combustion models. The effectiveness of preheating to enhance laser specific energy is demonstrated, although preheating may impose unacceptable hardware requirements. The application of numerical optimization techniques appears to offer a means to improve laser design.

Heat transfer between dispersed liquid metals and gases in packed beds

The rates of heat transfer occurring during the counter-current contacting of dispersed liquid metals and gases in towers packed with ring and spherical packings are examined. Using mercury and air as the heat exchange fluids, heat transfer studies at room temperature are described and the heat transfer mechanisms examined. Heat transfer data are also presented for the contacting of molten lead with preheated nitrogen in a pilot plant scale apparatus. Utilizing the mercury irrigated tower as a room temperature analogue of the high temperature apparatus, the mechanisms operating at high temperature (400° to 600°C) are examined. Two basic heat transfer mechanisms operate below about 400°C: the direct mechanism, which refers to convective heat transfer across the gas/liquid metal interface, and the indirect mechanism, a complex process involving conduction and convection in a sequence such as liquid metal-solid packing-gas phase. Above about 400°C, another mechanism, radiation heat transfer between the liquid metal and its environment, is thought to become significant, but experimental errors masked its detection in the present study.