Effect of temperature on the characteristics of ZnO nanoparticles produced by laser ablation in water

Effect of the water temperature on the characteristics of zinc oxide nanoparticles (NPs) produced by laser ablation process is investigated experimentally. The fundamental wavelength of a Q-switched Nd:YAG laser was employed to irradiate a high-purity zinc plate in distilled water at different temperatures of 0, 20, 40 and 60^°C. The produced NPs were diagnosed by UV–vis–NIR spectroscopy, X-ray diffraction method, transmission electron microscopy and scanning electron microscopy. Results show that with increase in the water temperature from 20 to 60^°C, size of NPs decreases while their bandgap energy increases. Maximum ablation rate occurs at the highest temperature. Crystalinity also increases with increase in the water temperature. The abnormal behaviour of water at 0–4^°C affects the NPs characteristics.     

MEASUREMENT TECHNIQUES AND DATA INTERPRETATIONS FOR VALIDATING CFD MULTI PHASE REACTOR MODELS

One problem associated with the use of Computational Fluid Dynamics(CFD) in reactor modeling is the proper validation of the models. Proper validation in this context means that the physical fluid dynamic model, the mathematical implementation and the data used for validation must be consistent. The present paper addresses this issue and to provide appropriate relations between experimental method and modeling approach

A critical review of currently used measurement techniques for characterizing multiphase now systems is presented. The interpretation of the data obtained from the various techniques is discussed as well as how these data can be used for validation of various CFD model formulations

Steady state models can be validated using time averaged data, making sure that the averaging time for the experimental data is long enough so that low frequency periodic oscillations also are evened out. If homogeneous systems are considered, then a volume average approach may be used for modeling, If the system cannot be considered homogeneous and steady, as is the most common case, then a dynamic ensemble averaging technique should be preferred. The validation of such models must be done with methods fast enough to resolve periodic fluctuating structures of interest. These methods are cumbersome and tedious to operate and the ergodic hypothesis may be invoked enabling the use of volume or time averaged data for the validation of ensemble averaged models.     

Surface modified Al 2 O 3 in fluorinated polyimide/Al 2 O 3 nanocomposites: Synthesis and characterization

Organic–inorganic hybrid materials consisting of inorganic materials and organic polymers are a new class of materials, which have received much attention in recent years. In the present investigation, at first, the surface of nano-alumina (Al ₂ O ₃ ) was treated with a silane coupling agent of $\boldsymbol{\gamma} $ -aminopropyltriethoxysilane (KH550), which introduces organic functional groups on the surface of Al ₂ O ₃ nanoparticles. Then fluorinated polyimide (PI) was synthesized from 4,4 ^′ -(hexafluoroisopropylidene) diphthalic anhydride and 4,4 ^′ -diaminodiphenylsulfone. Finally, PI/modified Al ₂ O ₃ nanocomposite films having 3, 5, 7 and 10% of Al ₂ O ₃ were successfully prepared by an in situ polymerization reaction through thermal imidization. The obtained nanocomposites were characterized by fourier transform infrared spectroscopy, thermogravimetry analysis, X-ray powder diffraction, UV-Vis spectroscopy, field emission scanning electron microscopy and transmission electron microscopy. The results show that the Al ₂ O ₃ nanoparticles were dispersed homogeneously in PI matrix. According to thermogravimetry analysis results, the addition of these nanoparticles improved thermal stability of the obtained hybrid materials.