Muhammad Yasin Naz

Double and Triple Langmuir Probes Measurements in Inductively Coupled Nitrogen Plasma

The double and triple Langmuir probe diagnostic systems with their necessary driving circuits are developed successfully for the characterization of laboratory built low pressure inductively coupled nitrogen plasma, generated by 13.56MHz radio frequency (RF) power supply along with an automatic impedance matching network. Using the DC properties of these two probes, the discharge plasma parameters like ion saturation current (Iio), electron temperature (kTe) and electron number density (ne) are measured at the input RF power ranging from 250 to 400W and fllling gas pressures ranging from 0.3 to 0.6mbar. An increasing trend is observed in kTe and ne with the increase of input RF power at a flxed fllling gas pressure of 0.3mbar, while a decreasing trend is observed in kTe and ne with the increase of fllling gas pressure at a flxed input RF power of 250W.

Characterization of modified tapioca starch solutions and their sprays for high temperature coating applications.

The objective of the research was to understand and improve the unusual physical and atomization properties of the complexes/adhesives derived from the tapioca starch by addition of borate and urea. The characterization of physical properties of the synthesized adhesives was carried out by determining the effect of temperature, shear rate, and mass concentration of thickener/stabilizer on the complex viscosity, density, and surface tension. In later stage, phenomenological analyses of spray jet breakup of heated complexes were performed in still air. Using a high speed digital camera, the jet breakup dynamics were visualized as a function of the system input parameters. The further analysis of the grabbed images confirmed the strong influence of the input processing parameters on full cone spray patternation. It was also predicted that the heated starch adhesive solutions generate a dispersed spray pattern by utilizing the partial evaporation of the spraying medium. Below 40°C of heating temperature, the radial spray cone width and angle did not vary significantly with increasing Reynolds and Weber numbers at early injection phases leading to increased macroscopic spray propagation. The discharge coefficient, mean flow rate, and mean flow velocity were significantly influenced by the load pressure but less affected by the temperature.

Synthesis and Thermal Degradation Studies of Melamine Formaldehyde Resins

Melamine formaldehyde (MF) resins have been synthesized at different reaction temperature and pH values. Different molar ratios of melamine and formaldehyde were used to synthesize the corresponding resins. The prepared resin samples were characterized by using molecular weight determination viscometry and thermogravimetric analysis (TGA). The maximum percentage of solid content (69.7%) was obtained at pH 8.5 and 75°C temperature. The molecular weight of MF resin was increased with an increase of melamine monomer concentration. The highest residual weight 14.125 wt.% was obtained with sample 10.

Investigation of Vortex Clouds and Droplet Sizes in Heated Water Spray Patterns Generated by Axisymmetric Full Cone Nozzles

The hot water sprays are an important part of many industrial processes, where the detailed knowledge of physical phenomena involved in jet transportation, interaction, secondary breakup, evaporation, and coalescence of droplets is important to reach more efficient processes. The objective of the work was to study the water spray jet breakup dynamics, vortex cloud formation, and droplet size distribution under varying temperature and load pressure. Using a high speed camera, the spray patterns generated by axisymmetric full cone nozzles were visualized as a function water temperature and load pressure. The image analysis confirmed that the spray cone angle and width do not vary significantly with increasing Reynolds and Weber numbers at early injection phases leading to increased macroscopic spray propagation. The formation and decay of semitorus like vortex clouds were also noticed in spray structures generated at near water boiling point temperature. For the nozzle with smallest orifice diameter (1.19 mm), these vortex clouds were very clear at 90°C heating temperature and 1 bar water load pressure. In addition, the sauter mean diameter (SMD) of the spray droplets was also measured by using Phase Doppler Anemometry (PDA) at different locations downstream of the nozzle exit. It was noticed that SMD varies slightly w.r.t. position when measured at room temperature whereas at higher temperature values, it became almost constant at distance of 55 mm downstream of the nozzle exit.

Symmetric and Asymmetric Double Langmuir Probes Characterization of Radio Frequency Inductivley Coupled Nitrogen Plasma

The symmetric and asymmetric double Langmuir probe systems with their necessary driving circuits are developed for characterization of low pressure inductively coupled nitrogen plasma, generated and sustained with 13.56 MHz RF source and an automatic impedance matching network. First of all, the plasma parameters such as ion saturation current, electron temperature and electron number density are determined with symmetric double probe system at different input RF powers, filling gas pressures and radial distance Received 4 March 2011, Accepted 28 March 2011, Scheduled 30 March 2011 Corresponding author: Muhammad Yasin Naz (yasin603@yahoo.com).

Hydrodynamics of multi-sized particles in stable regime of a swirling bed

Using particle imaging velocimetry (PIV), we observed particle motion within the stable operating regime of a swirling fluidized bed with an annular blade distributor. This paper presents velocity profiles of particle flow in an effort to determine effects from blade angle, particle size and shape and bed weight on characteristics of a swirling fluidized bed. Generally, particle velocity increased with airflow rate and shallow bed height, but decreased with bed weight. A 3° increase in blade angle reduced particle velocity by approximately 18%. In addition, particle shape, size and bed weight affected various characteristics of the swirling regime. Swirling began soon after incipience in the form of a supra-linear curve, which is the characteristic of a swirling regime. The relationship between particle and gas velocities enabled us to predict heat and mass transfer rates between gas and particles.

Effect of ferrocene concentration on the quality of multiwalled CNTs grown by floating catalytic chemical vapor deposition technique

Controllable synthesis of quality carbon nanotubes is a precondition for their broad applications. The objective of the work was to study the effect of catalyst concentration on the quality, diameter, length, alignment and crystallinity of the grown multiwalled carbon nanotubes (MWCNTs). To meet the stated objective, MWCNTs were successfully synthesized by using floating catalytic chemical vapor deposition technique. The ferrocene concentration was varied from 0.1 to 0.2 g and MWCNTs were synthesized with ethylene as a carbon precursor at reaction temperature of 850 ◦ C. The grown MWCNTs were characterized by using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Raman spectroscopy. The obtained data revealed that an increase in concentration of the ferrocene significantly affects the diameter, crystallinity and growth of nanotubes, however, negligible effect on the CNTs forest length was noticed. The dense, uniform and meadow like patterns of grown CNTs were observed for 0.15 g ferrocene. The average diameter of the grown CNTs was ranged from 32-75 nm. Above 0.15 g ferrocene, some of the grown CNTs were found defective and few black spots were also appeared in TEM images.

SCATTERING OF A RADIALLY ORIENTED HERTZ DIPOLE FIELD BY A PERFECT ELECTROMAGNETIC CONDUCTOR (PEMC) SPHERE

PEMC medium is a special type of metamaterial which generalizes the pre-existing concepts of perfect electric conductor (PEC) and perfect magnetic conductor (PMC). PEMC medium is described by a special parameter named as admittance which decides the nature of medium as PEC or PMC. Electromagnetic flelds scattered by a PEMC sphere are investigated theoretically. A Hertz dipole as a source of excitation is considered. Co-polarized and cross-polarized components of the scattered flelds are taken into consideration. A general solution of flelds scattered by the PEMC sphere has been sought.

Effect of pre-coat solution temperature on fluidized bed urea coatings

Abstract In this study, coating properties of the native cassava starch were improved by reacting it with urea and di-sodium tetraborate. The FTIR spectroscopy was used to study the possible reaction mechanism of the coating formulation. The prepared starch dispersions were used to coat 3·45 mm urea granules in a swirling fluidised bed reactor. An in-house built fluidised bed with an intermittent top spraying facility was used to coat the urea beds fluidised above their minimum level of fluidisation. The pre-coat solution temperature was varied from 50 to 80°C and the corresponding coated urea samples were further characterised for their surface morphology, coating hardness and nitrogen release time. The SEM images revealed that the surface of the coated urea was harder, denser and smoother as compared to the uncoated urea. Significant improvements in mechanical parameters of coated urea were seen with an increase in solution temperature and mass of the di-sodium tetraborate. The overall nutrients release time of the coated urea in water was increased from 63·33 to 209 s. The surface hardness and coating thickness of coated urea was also increased with an increase in pre-coat solution temperature and di-sodium tetraborate mass in the coating composition.

Experimental Study of Airless Spray Jet Breakup at Elevated Temperature and Pressure

The presented research work was focused onto the understanding of the jet behavior of the sprays of heated water during the low pressure atomization process. This task was accomplished using an in-house built intermittently forced liquid spraying system capable of lowering the liquid viscosity and surface tension to a desired value and then atomizing it into a full cone spray patterns in the ambient air surrounding. Using a high speed camera, the jet breakup dynamics were visualized as a function of system input parameters. The analysis of the grabbed images confirmed the strong influence of these processing parameters on full cone spray characteristics. It was also predicted that heated liquids generate a dispersed spray pattern by utilizing the partial evaporation of the spraying medium that is the induction of thermal energy enhances the jet disintegration ability. The spray cone width and angle did not vary significantly whereas the Weber and Reynolds numbers along with other nozzle flow parameters showed an appreciable response to the load pressure and temperature at early stages of water injection. The ultimate objective of the work was to understand and control the airless spray jet breakup mechanism under reduced load pressure and high water temperature.