Yogeshwar Sahai

Chitosan biopolymer for fuel cell applications.

Fuel cell is an electrochemical device which converts chemical energy stored in a fuel into electrical energy. Fuel cells have been receiving attention due to its potential applicability as a good alternative power source. Recently, cost-effective and eco-friendly biopolymer chitosan has been extensively studied as a material for membrane electrolytes and electrodes in low to intermediate temperature hydrogen polymer electrolyte fuel cell, direct methanol fuel cell, alkaline fuel cell, and biofuel cell. This paper reviews structure and property of chitosan with respect to its applications in fuel cells. Recent achievements and prospect of its applications have also been included.

The effect of tundish wall inclination on the fluid flow and mixing: A modeling study

A mathematical model to represent turbulent fluid flow and mixing in continuous casting tundishes has been developed. The model involves solution of the three-dimensional turbulent Navier-Stokes equation, turbulence being modeled by the so-calledK-ε, two-equation model. Fluid flow parameters and residence time distribution has been predicted in a tundish of rectangular cross section. The model is later extended to predict fluid flow in typical industrial tundishes where walls are not vertical, but rather slightly inclined from the vertical. This results in an interresting variation in fluid flow, which may have important technological implications. The theoretical predictions are compared with measurements obtained in water models. The detailed understanding of the hydrodynamics of the tundish flow can be used to optimize their design for steel cleanliness.

Effect of holding time and surface cover in ladles on liquid steel flow in continuous casting tundishes

Mathematical modeling of fluid flow and heat transfer of melt in a typical two-strand slab caster tundish has been done for a complete casting sequence. The complete casting sequence consists of 1 minute of tundish emptying period during the ladle transfer operation followed by 1 minute of tundish filling period by the new ladle and pouring at the normal operating level of the tundish for 46 minutes. The effect of varying ladle stream temperature conditions on the melt flow and heat transfer in the continuous casting tundish has been studied. When the ladle stream temperature decreases appreciably over the casting period, corresponding to heat loss of the melt in the ladle from the top free surface, the incoming melt temperature becomes lower than that of the melt in the bulk of the tundish after about 30 minutes from the start of teeming. This results in melt flow along the bottom of the tundish instead of the normal free surface directed flow. The ladle melt stream temperature shows little variability when the ladle has an insulated top. Corresponding to this situation, the temperature of the incoming melt remains higher than that of the melt in the bulk of the tundish and the normal free surface directed flow is maintained throughout the casting period. The product cast under such condition is expected to have a uniformly low inclusion content. The heat loss condition from the top of the ladle has been shown to be the dominant factor in determining fluid flow and heat-transfer characteristics of the melt in the tundish rather than the holding time of the melt in the ladle.

Modeling of fixed bed heat storage units utilizing phase change materials

A computer model has been developed for the calculation of the heat exchanged and temperature profiles in a packed bed containing a phase change material. The packed bed is intended as a heat storage unit in which an inert fluid flowing through the bed exchanges heat with an encapsulated spherical shot of the phase change (melting and freezing) material. Examples of predicted bed temperature profiles during heat storage and utilization cycles are given. For A1-12 wt pct Si and Al-30 wt pct Si shot, a sequence of storage and utilization cycles with cyclic cocurrent fluid flow was found to utilize the high latent heat of fusion of the shot efficiently and permit the utilization of the bed as a near isothermal (577°C) heat recuperator.

Tundish Technology for Casting Clean Steel: A Review

With increasing demand of high-quality clean steel, cleanliness is of paramount importance in steel production and casting. Tundish plays an important role in controlling the continuously cast steel quality as it links a batch vessel, ladle, to a continuous casting mold. Tundish is also the last vessel in which metal flows before solidifying in mold. For controlling the quality of steel, flow and temperature control of the melt are critical, and these are presented in this paper. Use of proper flux, design of flow control devices, and gas injection in tundish become important factors in casting clean steel. Recycling of hot tundish, centrifugal flow tundish, H-shaped tundish, etc. are some of the developments which were implemented to cast clean steel and these are discussed.

Role of near-wall node location on the prediction of melt flow and residence time distribution in tundishes by mathematical modeling

Several researchers have been engaged in three-dimensional (3-D), mathematical modeling of melt flow in tundishes using finite difference techniques over the past 10 to 15 years. Most of these computational schemes employ thek-ε model of turbulence and are capable of predicting the general flow pattern in different flow systems. However, detailed comparison of computed results with water-model experiments in the tundish system has shown that the finite difference grid spacing has an influence on the predicted fluid flow and the residence time distribution of the melt. In the present work, the effect of variation in the grid spacing on the flow predictions is presented. Further, guidelines are presented for proper spacing of grids to enhance the predictive capabilities of such models.

Polyvinyl Alcohol Chemical Hydrogel Electrode Binder for Direct Borohydride Fuel Cells

A novel and cost-effective electrode binder consisting of polyvinyl alcohol (PVA) chemical hydrogel is reported for direct borohydride fuel cells (DBFCs). In this work, DBFCs have been assembled with Misch-metal-based AB 5 alloy as anode, carbon-supported palladium (Pd/C) as cathode, and PVA hydrogel membrane electrolyte (PHME) as well as Nafion-117 membrane electrolyte (NME) as separators. All the DBFCs reported here were studied using an aqueous alkaline solution of sodium borohydride as fuel and an aqueous acidified solution of hydrogen peroxide as oxidant in passive mode and under ambient conditions of temperature as well as pressure. PVA chemical hydrogel (PCH) binder-based electrodes and MEAs have been fabricated using a novel, simple, and time-effective technique. Effectiveness of PCH as electrode binder in comparison to commercial Nafion electrode binder has been evaluated by studying electrochemical performances of DBFCs employing PCH as well as Nafion as electrode binders. The DBFCs employing PCH binder-based electrodes and PHME as well as NME as electrolytes exhibited peak power density values of about 69 and 75 mW cm ―2 at corresponding current density values of about 71 and 75 mA cm ―2 , respectively. PCH electrode binder is a less expensive alternative to the Nafion electrode binder, which is traditionally used in fuel cells.

Non-Metallic Inclusions

It is evident that molten steel and liquid oxide inclusions are in equilibrium state or in a motion to equilibrium. At the same time each procedure during secondary steelmaking (e. g. changing of steel composition by adding of ferroalloys, deoxidizers, slag-making additions, or changing of temperature and pressure over the melt) drifts an equilibrium point of ―steel – inclusions‖ system. Because that the transformation of nonmetallic inclusions takes place during secondary steelmaking. ―Non-metallic inclusions‖ software is designed for simulation of liquid oxide inclusions transformation which follows after change of oxidation level, chemistry, or temperature of liquid steel. Herein, transformation means a change of inclusions mass and chemistry. The program gives clear understanding of the internal dependencies in liquid steel – oxide inclusions system and the effect of some parameters on transformation processes. The simulation of the ex-solution of solid phases into liquid inclusions and the change of its aggregative state is not provided in the current program version. This obstacle can be compensated by complex analysis of computation results and appropriate phase diagrams. The model doesn’t take into account influence of slag on metal chemistry, but it is possible to calculate it by means of ―Slag – steel‖ software on www.steelmaker.ru . The model assumes that liquid metal initially contains some quantity of oxide inclusions (entrapped slag is a main cause of its origin). Three types of initial inclusions can be used in the current program version:

Effect of transverse distribution of secondary cooling water on corner cracks in wide thick slab continuous casting process

Abstract In the present work, a two-dimensional heat transfer model to describe the thermal behaviour of the wide thick slab during continuous casting process was developed, in which the boundary conditions for secondary cooling zone were calculated from the realistic water flux along the transverse surface of slab. The accuracy of the model calculation results were verified and calibrated by infrared thermography and nail shooting results. Furthermore, the slab temperature distribution under typical casting conditions were investigated numerically, and based on the hot ductility of microalloyed steel, the different arrangements of nozzles were optimized and designed to reduce the slab transverse corner cracks. The plant results showed that the defect rate of rolled plate corner and edge cracks were reduced from 12·6 to 3·5% with the optimised nozzles configurations.

Fluid dynamics in channel reactors stirred by submerged gas injection

This work describes the fluid flow and associated local and longitudinal mixing phenomena which influence the behavior and characteristics of continuous flow reactors, such as the Noranda reactor and the Q-S process. In the present work, mixing in channel reactors agitated by submerged gas injection along the length has been studied using a water model. The effects of gas injector separation, gas flow rate, depth of water, lateral configuration of injectors, submersion depth of gas injectors, and width of the channel have been investigated. It has been found that the longitudinal mixing depended significantly on the locations of the gas injectors. For constant values of other variables, there existed an optimum injector separation at which maximum longitudinal mixing was found. Industrial applications of this study are described.