Studies in Ultrafine Particle Production

Ultra fine grinding has attracted many industries for the better product quality. It has been seen that new developments in electronic industries have demand for the desired size distribution (narrow distribution) offine sizes. Attrition mill has specific advantage over other conventional milling equipment such as Ball Mill and fluid energy mill due to the energy saving in the combination process. An attempt has been made to study the performance of grinding in a laboratory Attrition millfor the control of the product size distribution.The experiments were carried in the laboratory Attrition mill and the effect of ball size distribution on product size distribution was studied. The study was concentrated in the estimation of the comm inution functions such as specific rate grinding by experimental techniques. The experimentally estimated breakage distribution functions were used to predict the rate of grinding, and the product size distribution

Synthesis of polythiophene n-type and p-type doping and compensation

The synthesis of pdythiophene leading to the formation of n-type potythiophene, p-type polythiophene and neutral polythiophene has been investigated through electropolymerization with different dopant ions. The influence of doping level over conductivity of the polymer matrix has also been studied which reveals that a preselected room temperature conductivity can easily be imparted to the parent polymer chain. It has also been found that the compensation of one type of conductivity over other occurs during the process of dedoping and redopin

A mean field neural network for hierarchical module placement

This paper proposes a mean field neural network for the two-dimensional module placement problem. An efficient coding scheme with only O(N log N) neurons is employed where N is the number of modules. The neurons are evolved in groups of N in log N iteration steps such that the circuit is recursively partitioned in alternating vertical and horizontal directions. In our simulations, the network was able to find optimal solutions to all test problems with up to 128 modules

Additive Lithography Fabrication And Integration Of Micro Optics

Optical elements are the fundamental components in photonic systems and are used to transform an input optical beam into a desired beam profile or to couple the input beam into waveguides, fibers, or other optical systems or devices. Macroscopic optical elements are easily fabricated using grinding and polishing techniques, but few methods exist for inexpensive fabrication of micro optical elements. In this work we present an innovative technique termed Additive Lithography that makes use of binary masks and controlled partial exposures to sculpt photoresist into the desired optical surface relief profile. We explore various masking schemes for fabricating a variety of optical elements with unprecedented flexibility and precision. These masking schemes used in conjunction with the additive lithographic method allows us to carefully control the photoresist exposure and reflow processes for fabricating complex aspheric lens elements, including aspheric elements whose fabrication often proves highly problematic. It will be demonstrated that employing additive lithography for volume sculpting followed by controlled reflow can also allow us to fabricate refractive beam shaping elements. Finally we will discuss the dry etching techniques used to transfer these optical elements into the glass substrate. Thus the additive lithography technique will be demonstrated as an inexpensive, high throughput and efficient process in the fabrication of micro optical elements

Selective excitation of the LP11 mode in step index fiber using a phase mask

We present a novel mode selective coupling technique for step index fiber. This technique utilizes phase matching for excitation of higher-order modes while suppressing the fundamental mode. Using this technique, a phase element is fabricated and tested to demonstrate the high coupling efficiency to the LP11 mode. In addition, we derive an analytical expression of the coupling efficiency of the LP11 using a single phase element

Mathematical Modelling of Indian Regional Navigation Satellite System Receiver

At present the armoured fighting vehicles are equipped with either global positioning system (GPS) receivers or integrated inertial navigation system (INS)/GPS navigation systems. During hostile situations, the denial/degradation of the GPS satellite signals may happen. This results in the requirement of an indigenous satellite based navigation system. Indian Space Research Organisation has developed an indigenous Indian regional navigation satellite system (IRNSS), with a seven satellite constellation to provide independent position, navigation and timing services over India and its neighbouring regions. In this paper, the development of IRNSS receiver using MATLAB as per IRNSS signal in space interface control document for standard positioning service is discussed. A method for faster IRNSS signal acquisition in frequency domain and delay locked loop code tracking for the acquired satellite signals are used. Models for navigation message decoding and pseudo range/user position calculations are developed using the algorithms provided in IRNSS ICD

Optimal temperature and current cycles for curing of composites using embedded resistive heating elements

Curing is an important and time consuming step in the fabrication of thermosettingmatrix composite products. The use of embedded resistive heating elements providing supplemental heating from within the material being cured has been shown in previous studies (Ramakrishnan, Zhu, and Pitchumani, 2000, J. Manuf. Sci. Eng., 122, pp. 124-131;, Compos. Sci. Technol., 60, 2699-271

EFFECT OF MEMBRANE PROPERTIES ON DYNAMIC BEHAVIOR OF POLYMER ELECTROLYTE MEMBRANE FUEL CELLS

ABSTRACT Understanding the performance of proton exchange membrane (PEM) fuel cells is critical to the water management in the fuel cell system. Low-humidity operating conditions present a complex interaction between dynamic behavior and water transport owing to different time scales of water transport mechanisms in the transient process. Toward understanding the effects of membrane properties on the dynamic behavior, this paper presents numerical simulations for a single channel PEM fuel cell undergoing changes in load, by subjecting the unit cell to step change in current. The objective is to elucidate the complex interaction between cell voltage response and water transport dynamics for various membrane properties, where the performance is critically related water content of the membrane. Detailed computational fluid dynamics (CFD) simulations are carried out to show that step increase in current density leads to anode dryout due to electro-osmotic drag, and investigate its dependence on variations in membrane properties. INTRODUCTION The need for energy efficient, clean and quiet, energy conversion devices for mobile and stationary applications has presented proton exchange membrane (PEM) fuel cells as a potential energy source for mobile and stationary applications. Due to major improvements in catalyst loading and membrane technology, PEM fuel cells have seen increased usage in various applications. A further reduction in cost can be achieved through better design, improved performance and durability of the fuel cells. This objective has generated lot of interest for research in control and optimization of transport and electrochemical processes of fuel cells A PEM fuel cell is composed of membrane electrode assembly (MEA), sandwiched between porous gas diffusio

COMPUTATIONAL MODELING OF LATENT THERMAL ENERGY STORAGE SYSTEM WITH EMBEDDED HEAT PIPES

ABSTRACT: Due to the intermittent nature of solar energy availability, storing sun's energy in the form of latent thermal energy of a phase change material (PCM) is an effective technique that is widely used in energy storage and load management applications. In a Latent Thermal Energy Storage System (LTES), a heat transfer fluid (HTF) exchanges energy with a PCM. The advantages of an LTES include its isothermal operation and high energy storage density. However, the low thermal conductivity of PCM poses a significant disadvantage due to reduction in the rate at which the PCM can be melted (charging) or solidified (discharging). This paper explores an approach to reducing the thermal resistance of PCM in a LTES through embedded heat pipes. A heat pipe is a passive heat transfer device that efficiently transfers large amount of energy between the PCM and HTF thus indirectly amplifying the effective thermal conductivity of PCM. A transient computational analysis of a shell and tube LTES embedded with heat pipes is performed for charging to determine the position of melt front and energy stored as a function of time. The influence of the number and orientation of heat pipes and design configuration of the system is analyzed to identify configurations that lead to improved effectiveness. INTRODUCTION: Fossil fueled power plants are detrimental to the environment and efforts are underway to replace fossil fuels with renewable energy sources including solar energy. Concentrated solar power plants (CSP) capture the solar energy and store as heat which can be used to drive a turbine and produce electricity. CSP thus provide low-cost energy generation and have the potential to become the leading source of renewable energy for future power generation. But, due to the intermittent nature of solar energy availability, it is often desirable to store energy for use on demand including times when solar energy is unavailable. Energy can be stored either as sensible heat or latent heat of which latent heat storage is more advantageous due to its high volumetric energy density and high Rankine cycle efficiency owing to their isothermal operation. In the LTES system, HTF exchanges energy with a PCM. The operation of LTES constitutes two cycles namely, charging and discharging. During charging, hot HTF obtained b