We report on the superhydrophobicity of self-organized surfaces of polyethylene (PE) nanowire arrays that are fabricated by a nano-injection moulding technique. The highly-aligned PE nanofibers with high aspect ratio are formed after the infiltration of polymer melts into the alumina nanopores by wetting action and fluid vibrational perturbation. The self-organized surfaces of polymer nanowire arrays are found to have micro-to-nanoscale hierarchical nanostructures, and have superhydrophobicity of >150° contact angles. The present superhydrophobic surfaces may be quite promising due to its simple but massive production with high quality.
A numerical simulation on a segmented arc heater which is used to generate high thermal flow environments for the test of heat shield materials, were carried out. In this numerical prediction work, targets level of input power class, minimum enthalpy at the exit of the heater, and maximum pressure inside the heater were set up as 400 kW, 20 MJ/kg, and 4 bar, respectively. In order to produce uniform temperature and velocity characteristics of thermal flow for a successful test, effects of design and operation variables on the thermal plasma characteristics were analyzed. Number of the segments packs and diameter of the constrictor were changed 1 ∼ 3 (105 ∼ 315 mm) and 12 ∼ 20 mm, respectively. As the torch operating variables, arc current was changed from 300 A to 500 A and plasma forming gas flow rate was varied from 6 g/s to 14 g/s. Arc current was adjusted to achieve about 400 kW according to constrictor geometry at fixed gas flow rate of 10 g/s, and optimal design conditions for uniform radial temperature and low pressure profiles with Mach number 1 at the supersonic throat were expected when the constrictor length and diameter were 315 mm and 16 mm, respectively. From the numerical results, diameters of the supersonic nozzle exit which determines test target size were calculated as 55.5 mm and 82.4 mm in the cases of Mach number 2 and 3, respectively.
Present paper considers processes of production and treatment of hollow particles in plasma flows. Specifics of agglomerated powders treatment and expansion of hollow droplets are analyzed theoretically. Experimental results on production of hollow micro particles of ZrO2, Ni, CoNiCrAlY alloy, SiO2 are shown here.
An attempt to form a “tiny” spherical flame over the small jet burner (so called microflame) as a model of a tiny droplet flame was made experimentally without any assistance brought by large facilities which could eliminate/minimize buoyancy effect. Using ceramic burner and high-temperature air effectively suppresses the quenching distance and such “super-stabilized” micro-jet flame would be fairly close to 1-D (droplet) flame. The temperature of air (up to 770 K) and the fuel (methane) flow rate were varied as experimental parameters. Fundamental characteristics of limiting and near-extinction behavior of methane-air microflame in high-temperature air are investigated. Results show that the flame shape under high-temperature air condition is hardly affected by the external disturbance and the quenching distance is minimized due to the increase of the temperature at burner tip. It is found that the theory developed by Kuwana et al., to predict the limiting behavior of small-scale flame would be applicable even for the one formed in high-temperature air. Minimum flame size achieved in high-temperature air is predicted as an order of hundreds micron; interestingly, this is identical to what is predicted with ideal adiabatic burner (i.e., no conductive and radiative heat loss to/from the burner) in our previous numerical work.
The effects of the structural geometry at the nanometer scale on the thermal resistance at a liquid molecule-solid interface, as well as the interfacial energy transport mechanism of liquid molecules, were investigated directly by the nonequilibrium classical molecular dynamics simulations. The 12-6 Lennard-Jones potential energy functions for liquid molecules and the channel structure at the nanometer scale are employed so as to discuss the effects of the surface geometry at the nanometer scale on the interfacial thermal resistance in comparison with a flat surface. The thermal resistance between solid and liquid molecules was calculated by the temperature discontinuity at the liquid-solid interface and the energy flux that was added or subtracted by the Langevin method per unit area so as to maintain a constant boundary temperature of solid walls. The substantial interfacial thermal resistance reduction depending on the interaction parameters between solids and liquid molecules was observed in the case of the nanostructure surface in comparison with the flat surface. The liquid-solid interfacial thermal resistance reduction in the case of nanostructure surface relates to the energy transport mechanism change at the liquid-solid interface and the surface area magnification.
Carbon nanotubes possess outstanding properties such as high thermal conductivity, ultra-high physical strength, and durability. With regard to applications, a single-walled carbon nanotube (SWCNT) is a great candidate for a new material. Furthermore, a metal-coated SWCNT has been experimentally developed and its properties have attracted much attention. In this study, we simulated the deposition process of metal species onto an SWCNT to estimate its resulting physical strength and thermal diffusivity using a classical molecular dynamics method. Consequently, we found that the physical strength of the metal-coated SWCNT was similar to that of an uncoated SWCNT, whereas its thermal diffusivity showed a decrease of 90%.
In order to clarify flame behavior in the combustion chamber of swirling-oxidizer-flow-type hybrid rocket engines, a small hybrid rocket engine with a large quartz glass window was fabricated to observe the inside of the combustion chamber from the front directly. PP and PMMA fuel grains were burned under the swirling and non-swirling oxygen flow conditions. For both PP and PMMA combustion, the disturbed swirling flames were found to develop closer to the grain surface than those without swirl, resulting in an increase of the fuel regression rates. The swirling flames consisted of not a single large flame but an annular aggregate of small striated flames on the grain surface. Emission spectra of counter-diffusion flames over the PP and PMMA rods showed that the strong continuum due to hot carbon particles in the flames, and the weak C2 and CH emissions were also visible. The filtered photographs which took the continuum and C2 emissions in the hybrid rocket combustion chamber suggested that the gas-phase reactions of PMMA with oxygen substantially occurred not in the center region of the combustion chamber, but near the PMMA gain surface. For PP combustion, the gas-phase reactions with oxygen may also occur in some degree near the central region.
In order to prevent pulverization and fracture of metallurgical coke, control of gasification reaction part in coke lump and embrittlement behavior is important. Addition of catalyst particle is an effective and a simple method for enhancement of the CO2 gasification reactivity. However, the effect of the catalyst particle on coke-matrix and gasification part of coke lump after gasification reaction has not been investigated. In this study, the effect of iron particles on coke-matrix state after gasification reaction is investigated experimentally. Coke-matrix vanishing is evaluated by spatial distribution of lump porosity and microscopic observation. Elastic modulus of coke-matrix is evaluated by nano-indentation method. Coke lumps with and without iron-particles (ferrous coke and formed coke, respectively) were used. These coke lumps were gasified by CO2-containing gas. Reaction temperature was set at 1173 K. Reaction gas compositions were set at 100/0 and 50/50 in ratio of CO2/CO. In each reaction gas composition, in ferrous coke, a decrease in the elastic modulus of coke-matrix with progress of gasification is smaller than that in formed coke and coke-matrix vanishing occurred. It is suggested that the iron particle promotes gasification reaction of coke-matrix selectively around itself (and coke-matrix in that part is rapidly vanished). It is also suggested that this reaction mechanism maintains elastic modulus of coke-matrix because of the local rapid gasification reaction around the iron particle.
To estimate the enthalpy effects of test gas in a direct-connect dual-mode combustor, an experimental study was conducted. Wall pressures were compared under two cases with different types of air heater (combustion heater and electric heater) at various H2 fuel equivalence ratios. Considering flame holding, dual-mode transition and wall pressure value, matching total enthalpy was found to be more effective than matching total temperature in terms of mitigating vitiation effects in the case of a combustion heater. On the other hand, for vitiation flow, matching total temperature is more effective than matching total enthalpy for ignition to duplicate that of clean air flow. Therefore, flow total condition (total temperature or total enthalpy) should be selected according to experimental candidates.
Recently, the spectral properties of thermal radiation have been controlled by surface gratings having a size in the optical wavelength range, and this technique has been applied to improve the efficiency of energy systems, e.g., thermophotovoltaic generators and sky radiators. In this paper, the technique was applied to an advanced cooling system for electronic devices. In general, electronic devices are packaged in resin to protect them from damage; however, resin prevents heat from escaping from the package because of resin's strong absorption of thermal radiation in the infrared range and low thermal conductivity. By controlling the spectral property of thermal radiation from electronic devices, the thermal radiation absorbed by resin can be decreased. As a result, a cooling system for electronic devices is possible. At first, we performed a numerical simulation to design the optimal surface gratings to cool electronic devices packaged in epoxy resin. The surface gratings were fabricated using a MEMS process. The performance of the fabricated emitter was evaluated experimentally. In conclusion, we confirmed that this new cooling technique will be effective for electronic devices.
The radio frequency (RF) inductively coupled plasma technique is a new and promising synthesis method of single-walled carbon nanotubes (SWCNTs) at large scales, for industrial and commercial applications. In this method, a mixture of carbon black and metal catalysts is directly vaporized by the RF plasma. Subsequently, inside the reactor chamber and under a controlled temperature gradient, carbon-metal clusters are formed and become the potential sites for nucleation and growth of SWCNTs. In this process, the local plasma properties and the thermo-fluid field in the system affect the yield rate of SWCNTs, and therefore it is important to find an appropriate operating condition, which maximizes the yield rate. Numerical modeling in conjunction with experimental studies can help investigate the contribution of the thermo-fluid field and process parameters to the formation of catalyst nanoparticles and carbon nanotubes in the induction thermal plasma system. The goal of this research is to carry numerical study of SWCNT growth in a RF induction thermal plasma system with a suitable chemistry model. This model is employed to investigate the influence of the thermo-fluid field and gas-phase reactions on carbon nanotube growth and to predict the SWCNT yield rate as a function of operating conditions.