Jinkai Li

Effect of characterization of powder on particle velocity in dense-phase pneumatic conveying

Particle velocity is an important characteristic parameter in the process of evaluating dense-phase pneumatic conveying system. It relates to the properties of conveying materiel, system performance, operating conditions, physical properties of conveying gas etc, and has some noticeable effect on the conveying capacity, energy consumption, wear between particles and pipe. Of all influencing factors, characterization of powder is crucial to impact particle velocity. In this paper, pneumatic conveying experiments of four kinds of powdery material whose different solid physical properties are tested and taken are carried out using compress air in long distance pipe. The trend of particle velocity was achieved by the experimental data gained from Groups of differential pressure transmitters. Dimension analysis and mathematical analysis were adopted to obtain a theoretical correlation equation of particle velocity versus solid characteristics:And this equation can be used to predict the tendency of particle velocity for different kind of solid precisely.

Controlling the morphology and size of (Gd 0.98− x Tb 0.02 Eu x ) 2 O 3 phosphors presenting tunable emission: formation process and luminescent properties

AbstractnThe (Gd0.98−xTb0.02Eux)2O3 phosphors have been successfully obtained using the urea-based homogeneous precipitation method in the present work. The particle growth of the precursors with mono-dispersion spherical morphology is surface-diffusion controlled and precipitated in the order of the Tb(OH)CO3u2009>u2009Gd(OH)CO3u2009>u2009Eu(OH)CO3, and the formation process has been also studied in detail. Partially replacing the pure water with ethylene glycol (EG) can control the particle size and morphology owing to its lower permittivity constant and interface energy. By monitoring the excitation at 314xa0nm (4f8u2009→u20094f75d1 transition of Tb3+), the (Gd0.98−xTb0.02Eux)2O3 phosphors exhibit both Tb3+ (green) and Eu3+ (red) emissions at 547 and 613xa0nm, respectively. The presence of Gd3+ and Tb3+ excitation bands on the PLE spectra by monitoring the Eu3+ emission directly provides an evidence of the Tb3+u2009→u2009Eu3+ and Gd3+u2009→u2009Eu3+ energy transfer, respectively. The quenching concentration is determined to be 2.0xa0at.%, and the quenching mechanism is determined to be the exchange reaction between Eu3+. The emission color can be readily tuned from approximately green to red via adjusting the Eu3+ content. The temperature-dependent analysis has been performed, and the results indicate that the (Gd0.98−xTb0.02Eux)2O3 samples possess good thermal stability. Owing to the Tb3+u2009→u2009Eu3+ energy transfer, the lifetime for the Tb3+ emission rapidly decreases, and the energy transfer efficiency has been calculated. The EG addition does not bring appreciable changes to the lifetime values for the both Tb3+ and Eu3+ emissions, but enhances remarkably the luminescent intensity which confirms the variation of the particle morphology/size, and the reason can be explained by the scattering of the light. The (Gd0.98−xTb0.02Eux)2O3 phosphors developed in this work hopefully meet the requirements of various lighting and optical display applications.

Thermal Conductivities and Viscosities of Al

Al2 O3 -water nanofluids containing low volume concentrations (0.1–0.5 vol. %) of Al2 O3 nanoparticles with 40nm and 65nm average particle size were produced using a two-step method with ultrasonication and without any surfactant. The thermal conductivities and viscosities were evaluated by KD2-pro thermal property meter and rotational viscometer respectively at different temperature. Thermal conductivities measurements show that the thermal conductivities of Al2 O3 -water nanofluids are higher than water. The thermal conductivities with average particle size of 40nm and 65nm are respectively enhanced by 17.9% and 11.2% when approximately 0.5vol.% of Al2 O3 nanoparticles are added. Furthermore, the experimental results show the thermal conductivities increased nearly linearly with the nanoparticle volume concentration increasing, and significantly increased with the temperature increasing. Comparison between the experiments and the theoretical models shows that the measured thermal conductivities are much higher than the values calculated from theoretical models, indicating new heat transport mechanisms included in nanofluids. In the contrast to thermal conductivities, the viscosities measurements show that the viscosities of the Al2 O3 -water nanofluids significantly decrease with increasing temperature, and increased nonlinearly with the nanoparticle volume concentration. As the volume concentration of nanoparticles is increased up to 0.5%, the viscosities of Al2 O3 -water nanofluids with average particle size of 40nm and 65nm are respectively increased nonlinearly up to 28.3% and 17.5%, which exceed the Einstein model predictions.Copyright