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Pressure swirl nozzles are widely used in industries due to their good atomization quality at relatively low operating pressure. This paper experimentally investigates the thermal effects on the spray cone formation of a pressure swirl nozzle in spray cooling. Particle image velocimetry (PIV) is used to reflect the thermal effects on global spray behaviour of the spray cone impinging on a heated surface, while Phase-Doppler Interferometry (PDI) is used to investigate the thermal effects on droplet sizes, droplet velocity and flux distributions. It is found that temperature of the impinged surface plays an important role in the formation of spray cone in spray cooling. The spray cone expands under impinging on a heated surface with high surface temperatures, which consequently influences the spatial distributions of the droplet flux and velocity, as well as the probability density distributions of the diameter and velocity of the impinging droplets and secondary droplets. The heat transfer experiments reveal that the expansion of spray cone under impinging on the surface with difference temperatures have significant effects on the surface temperature non-uniformity and heat transfer coefficient in spray cooling.

Non-invasive laser detective techniques, Phase Doppler Anemometry (PDA), were used to measure solids holdup and velocity profiles in a three-phase gas–liquid–solid bubble column. The cylindrical bubble column was driven by a point air source made of a 30-mm diameter perforated air stone centrally mounted at the bottom. It had an inner diameter of 152 mm and was filled with liquid up to 1 m above the point source. Monosized acrylic beads with a nominal diameter of 3 mm were used as the solid phase. With added salt, the liquid density was adjusted to 1.0485 kg/m3 for matching the density of the solid phase which was 1.05 kg/m3. The bubble diameters generated were within the range of 600–2400 μm. The turbulent characteristics of the bubbles and the solid phase were measured at five different air rates, namely 0.4, 0.6, 0.8, 1.0 and 1.2 L/min (corresponding to the superficial gas velocities of 0.375, 0.549, 0.752, 0.919 and 1.128 mm/s, respectively). The time averaged velocity measurements indicated tProd. Type: FTPhat a large circulation flow pattern exist in the column. Driven by the bubbles, the solid motion was upward in the center region and downward near the walls in the bubble column. The solid holdup values decrease slightly along the radial position in the lower part of the bubble column, and it became uniform in the upper part. The mean solid phase concentration is exponential decay with the height z. The solids velocity and holdup distribution presented here can improve the understanding of the flow behavior in a three-phase bubble column.

Phase Doppler anemometry was used to quantify the flow characteristic of a three phases (liquid, solid, and bubbles) cylindrical bubble column driven by a point air source made of a 30-mm diameter perforated air stone centrally mounted at the bottom. The cylindrical bubble column had an inner diameter of 152 mm and was filled with liquid up to 1 m above the point source. Acrylic beads with a nominal diameter of 3 mm were used as the solid phase. To match the density of the solid phase which was 1.05 kg/m3, the liquid density was raised to about 1.0485 kg/m3 by added salt. The bubble diameters generated were within the range of 600–2400 µm. The detailed turbulent characteristics of the liquid-phase velocity, bubble diameter, bubble velocity, and solid velocity were measured at three different air rates, namely 0.4, 0.8, and 1.2 L/min (corresponding to average gas volume fraction of 0.0084, 0.0168, and 0.0258, respectively) for the homogeneous bubble column regime. With the addition of the solid phase, the flow field was found to be relatively steady compared to the two-phase column referencing the probability density functions for both the liquid and bubble velocities. An analysis based on the determination of the drag forces and transversal lift forces was performed to examine the flow stability in the three-phase bubble column. The analysis illustrated that how the added solid phase effectively stabilized the flow field to achieve a steady circulation in the bubble column and a generalized criterion for the flow stability in the three-phase bubble column was derived. Further investigation for the transition and the heterogeneous bubble column regime with air rates at 2.0 and 4.0 L/min shown that this criterion can also be used as a general prediction of flow stability in this three-phase bubble column. © 2013 American Institute of Chemical Engineers AIChE J, 59: 2286–2307, 2013

Bubble column is widely used in both industrial and environmental applications. In this study, we examine the flow dynamics and stability of a bubble column driven by a point air source centrally mounted at the bottom using Phase Doppler anemometry (PDA). The model cylindrical bubble column had an inner diameter of 152 mm and was filled with the liquid to about 1 m height, above the point air source, which was made of a 30-mm diameter perforated air stone. The bubble diameters were within the range of 400–1300 μm. A customized setup was developed for accurate PDA measurements of the two phases, and detailed turbulent characteristics of the liquid phase velocity, bubble diameter, bubble velocity and the slip velocity were collected throughout the column. The comprehensiveness of the data set enabled a close examination of the hydrodynamic stability inside the column. Measurements were taken at three different air rates, namely 0.13, 0.25 and 0.38 L/min (corresponding to average gas volume fractions of 0.0065, 0.0138 and 0.0197, respectively). The results illustrated a large-scale coherent liquid circulation pattern inside the column. The circulation pattern in the upper column was relatively steady, while the pattern in the lower column was strongly unsteady with the probability density functions (pdf) for both the liquid and bubble velocities showing distinct twin peaks. An analysis based on the determination of the bubble drag forces and transversal lift forces is performed by decomposing the twin-peaked pdfs into two separated Gaussian distributions, one for the upward flow due to the bubble rises and the other for the downward flow due to circulation. Through the decomposition, a stability criterion can then be established by choosing the local bubble size as the representative length scale for the turbulent eddies inside the column. The analysis with the criterion illustrates why a steady circulation pattern was achieved in the upper column, and at the same time shows that the instability at the bottom column was induced by the low frequency meandering of the bubble swarm.

Gallium borate nanowires have been synthesized using a simple and readily scaleable solid-state reaction among boron, boron oxide and gallium oxide. The GaBO 3 nanowires have diameters ranging from 90 to 150 nm and lengths of several hundreds nanometer, exhibiting a poor crystallization. After a nanoscale support catalyst Fe 2 O 3 /Al 2 O 3 was used as additive in the reaction, the diameters, lengths and crystallization were effectively improved. The nanowires exhibit a well-crystallized one-dimensional single-crystal structure with diameters ranging from 20 to 60 nm and lengths up to several micrometers. The growth mechanism was also presented in this letter.

Nanobamboo and nanotube structures of BN have been controllably synthesized by reaction of barium metaborate with ammonia. The gallium addition plays an important role in the formation of nanotubes. The experimental results indicate that, without the gallium additive, the reaction results in the growth of nanobamboo structure. Gallium addition, probably as a catalyst within the framework of vapor–liquid–solid growth, promotes the growth of nanotubes. High-solution transmission electron microscopy research indicates that rhombohedral stacking order is the dominant atomic arrangement for BN nanobamboos; whereas hexagonal stacking is the dominant arrangement for BN nanotubes.

The effect of reaction temperature of carbon nanotube-confined reaction was discussed by demonstrating the synthesis of Ge nanostructures. The mixture of Ge and GeO 2 is used as Ge vapor source. The noticeably different morphology could be observed when the different reaction temperatures were used. Ge quantum dots and their arrangement based on the trace of the starting carbon nanotubes were formed when 1000°C of reaction temperature and 1 h of duration time were adopted. The diameter of the quantum dots were found to be strongly depend on the used reaction temperatures and the time duration .

An effective route of growing boron nitride nanotubes was developed. By reacting boron, silica and iron oxide catalysts supported on alumina, gas-phase reactants and liquid-phase catalyst could be generated in-situ. When ammonia was then introduced, boron nitride nanotubes could be formed by the reaction of boron oxide and ammonia inside the liquid-phase catalysts. The synthesized boron nitride nanotubes are highly-crystallized and multi-walled structures with 10–30 nm in diameter. The growth process was explained based on vapor–liquid–solid wire-like growth mechanism.

A simple method for synthesizing titanium carbide (TiC) nanowires is demonstrated. TiC nanowires with a covered layer of graphite can be synthesized by the reaction of TiO gas with methane in the presence of a catalyst containing Fe. This graphite layer can be effectively removed by heating as-synthesized samples to 600°C in air. The length of TiC nanowires is several hundreds of microns and their diameters range from 30 to 100 nm. A growth mechanism of TiC nanowires involves vapor–liquid–solid reaction.

A novel method was demonstrated to fabricate boron nitride nanotube films on silicon substrate in a location-controlled fashion. The pre-deposited SiO2 layer on the substrate controls the growth space of BN nanotubes synthesized by an ammonothermal reaction of boron and its oxide.