Analysis of the Mechanism of Counter-current Spray Drying

Results of experimental investigations of the effect of drying and atomization parameters on counter-current spray drying are discussed. Based on 96 experimental tests, the local and global distributions of velocity, temperature, drying air humidity and moisture content of material dried in the drying tower were determined. Analysis of the results showed that the process of agglomeration during counter-current spray drying depended mainly on air temperature in the atomization zone.     

Light intensity and image visualization of GDI injector sprays according to nozzle hole arrangements

The light intensity measurement and image visualization of multi-hole injection spray due to different hole arrangements and hole numbers were investigated. The light intensities and behavior characteristics of the GDI spray were analyzed through the axial and diagonal spray penetration, cone angle, and spray area from the spray images by using the image visualization system and image analysis system. The atomization performance of GDI injectors was analyzed by the local and overall Sauter mean diameter (SMD) measurement.     

The atomization current and droplet size of ethanol in two different small-scale electro-spraying systems

An experimental study on electro-spraying from small-scale combustors is carried out using liquid ethanol as fuel. Two systems of electro-spraying are employed in the present study; one is a nozzle system (without a ring electrode) and the other is a nozzle-ring system (with a ring electrode). The photos of electro-spraying at the cone-jet mode are taken by a digital camera. The voltage drop across the resistance in the loop is measured by a data acquisition instrument, and the atomization current is calculated according to Ohm's Law. The size and velocity of electro-spraying droplets are measured by a Phase Doppler Anemometer. A non-dimensional analysis on atomization current is completed to explain the electro-spraying phenomena of liquid at the stable cone-jet mode. The results show that, the lower atomization current and droplet velocity corresponds to smaller size of droplet. Based on the results of non-dimensional analysis, it is found that the dimensionless atomization current in both the nozzle system and nozzle-ring system obeys the scaling law as square root of the dimensionless flow rate. The charge density is of a −1.5 power dependence on droplet diameter. Both of the nozzle and the nozzle-ring systems show a good agreement with Rayleigh instability.     

Polycarbonate nanoparticles spray coated on silicon substrate using micro-electromechanical-systems-based high-frequency ultrasonic nozzle

Mono-disperse polycarbonate (PC) nanoparticles 20 nm in diameter was spray coated on silicon substrate using a novel high-frequency ultrasonic nozzle. Specifically, Bisphenol-A polycarbonate with a molecular weight (M_w) of approximately 6.4 × 10⁴ g/mol was first dissolved in pyridine. The resulting solution was sprayed into surfactant-containing de-ionized (DI) water using a 300 kHz silicon-based multiple-Fourier horn nozzle (MFHN). As pyridine was extracted into the water, PC nanoparticles formed but remained dispersed. This suspension of PC nanoparticles was then sprayed onto a silicon substrate using a 500 kHz 3-Fourier horn nozzle. Scanning electron microscopy (SEM) of the dried substrate revealed that PC nanoparticles were spread uniformly with no aggregation.     

Comparison of theoretical methods for assessing the heat of formation of C1 and C2 chlorofluorocarbons and hydrochlorofluorocarbons

The heat of formation of a number of key C₁ and C₂ chlorofluorocarbons and hydrochlorofluorocarbons have been calculated by G3, G3MP2, G3MP2B3 and G3B3 methods. Based on the results of the atomization approach, it was found that the errors are approximately dependent upon the number of C-F or C-Cl bonds. Moreover, the bond additive correction (BAC) procedure and isodesmic reactions approach improved the accuracy and decreased these system errors significantly. The extended comparison between the BAC procedure and isodesmic reaction approaches had been made; the latter yielded the best results and showed broader applicability.     

Acoustic resonance and atomization for gas-liquid systems in microreactors

It is shown that a liquid slug in gas–liquid segmented flow in microchannels can act as an acoustic resonator to disperse large amounts of small liquid droplets, commonly referred to as atomization, into the gas phase. We investigate the principles of acoustic resonance within a liquid slug through experimental analysis and numerical simulation. A mechanism of atomization in the confined channels and a hypothesis based on high-speed image analysis that links acoustic resonance within a liquid slug with the observed atomization is proposed. The observed phenomenon provides a novel source of confined micro sprays and could be an avenue, amongst others, to overcome mass transfer limitations for gas–liquid processes in flow.     

Effect of the area of a lithium niobate transducer on the efficiency of ultrasonic atomization driven by resonance vibration

In recent years, individual control of one’s personal environment has been drawing increasing attention due to the growing interest in health care. Wearable devices are especially useful because of their controllability regardless of location. Humidity is one of the inevitable factors in the personal environment as a preventive against infectious diseases. Although atomization devices are commonly used as a method of humidity control, at present, there are no wearable humidity control devices. Vibration of a lithium niobate (LN) device in the thickness mode is a promising piezoelectric method for miniaturization of atomization devices for humidity control. To miniaturize the atomization device, the transducer size needs to be small not so much as to decrease the atomization efficiency. However, the effect of the device area on the atomization efficiency of LN at a size suitable for mounting in wearable devices has not been studied. Here, we conducted an atomization demonstration of LN devices with different sizes to evaluate particle size and atomization efficiency. Furthermore, to reveal the relationship between vibration behavior and atomization efficiency, resonance vibration in the MHz frequency band was evaluated by the finite element method and an impedance analyzer. The results showed that the peak size of water particles atomized by each device was in the range of 3.2 to 4.2 µm, which is smaller than particles produced by typical piezoelectric ceramics. Moreover, the best LN size for efficient atomization was found to be 8 mm × 10 mm among the five LN device sizes used in experiments. From the relationship between vibration behavior and atomization efficiency, the size of the transducer was suggested to affect the vibration mode. The obtained result suggested that the LN device is suitable for small wearable nebulizer devices.     

电热原子吸收光谱法中原子化过程动力学研究的最新进展

本文评述了1994－2000年年间电热原子吸收光谱法中原子化过程动力学研究的最新进展,内容包括升温原子化过程动力学参数测定方法、等温原子化过程动力学参数测定方法、动力学参数测定方法的比较、双先导物升温原子化过程的动力学模型、考虑原子蒸气再沉积过程的升温原子化过程的动力学模型以及原子化器表面、基体改进剂及干扰物对分析物原子化过程的影响。引用文献31篇。     

Kinetic Approach to the Interpretation of Analyte Losses During the Preatomization Thermal Treatment in Electrothermal Atomization Atomic Absorption Spectrometry

A method for evaluating E_a(loss), the apparent activation energy of the analyte loss process during the high-temperature thermal pretreatment stage in electrothermal atomization atomic absorption spectrometry (ETA-AAS) has been developed. The method is based on extracting information from the declining portion of thermal pretreatment curves (in this case presented as absorbance vs pyrolysis time at various fixed temperatures). Five volatile analytes (As, Pb, Sb, Se, and Sn) have been studied in the presence of tungsten chemical modifier (20 μg of W in H₂O₂).

The data on E_a (loss) have been utilized together with those obtained from treating the atomization peaks E_a and with literature data on known values of bond energies and enthalpies of certain chemical reactions. Possible mechanisms of analyte losses and atomization are discussed.     

Palladium Release in Electrothermal Atomic Absorption Spectrometry

The absorbance signal in electrothermal atomic absorption spectrometry is a result of the processes of atom formation and dissipation and first of all depends on the initial generation of atoms from the surface. The rising part of the absorbance time profiles can be used for characterization of the release of the metals like Pd, Ag, Au etc. The method is applied to investigate the palladium release from a pyrocoated graphite support at different initial masses of the Pd. The kinetic parameters are evaluated and conclusions about the distribution of palladium on the graphite surface are made. The estimated values of apparent activation energies depend on the initial mass of analyte. The advantages and limitations of the present approach are discussed.