Oxy-fuel combustion of pulverized coal: Characterization, fundamentals, stabilization and CFD modeling

The possible role of ammonia in a future energy infrastructure is discussed. The review is focused on the catalytic decomposition of ammonia as a key step. Other aspects, such as the catalytic removal of ammonia from gasification product gas or direct ammonia fuel cells, are highlighted as well. The more general question of the integration of ammonia in an infrastructure is also covered.

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Ammonia as a possible element in an energy infrastructure: catalysts for ammonia decomposition

Review: Direct ethanol fuel cells

The performance of heat exchangers can be improved to perform a certain heat-transfer duty by heat transfer enhancement techniques. In general, these techniques can be divided into two groups: active and passive techniques. The active techniques require external forces, e.g. electric field, acoustic or surface vibration, etc. The passive techniques require fluid additives or special surface geometries. Curved tubes have been used as one of the passive heat transfer enhancement techniques and are the most widely used tubes in several heat transfer applications. This article provides a literature review on heat transfer and flow characteristics of single-phase and two-phase flow in curved tubes. Three main categories of curved tubes; helically coiled tubes, spirally coiled tubes, and other coiled tubes, are described. A review of published relevant correlations of single-phase heat transfer coefficients and single-phase, two-phase friction factors are presented.

A review of flow and heat transfer characteristics in curved tubes

A review of high-temperature proton exchange membrane fuel cell (HT-PEMFC) system

The present work investigates utilization of ultrasound in reagent-based coal de-ashing and de-sulfurization. The coal under study was received from Girald mine, Rajasthan, India. Three different ultrasonic frequencies (25 kHz, Dual (58/192 kHz) and 430 kHz) and three reagents (HCl, HNO 3 and H 2 O 2 ) were used. The study employed a Taguchi fractional-factorial L 27 DOE. Experimental data were used to derive an empirical model for the prediction of total sulfur removal. The model incorporates cavitational intensity, reagent concentration, sonication time, coal particle size and coal concentration as key parameters. Effects of above factors on reagent-based ultrasonic coal-desulfurization are presented here. An optimum set of process parameters are identified and validated. Larger-scale trial with high-ash and high-sulfur coals is strongly recommended.

Feasibility of using ultrasound-assisted process for sulfur and ash removal from coal

A conceptual model of a high-efficiency, stand-alone power unit based on a fuel cell stack with an integrated auto-thermal ethanol reformer

In 1957 Metzner and Otto proposed a simplified way of calculating the power consumption in impeller-driven systems for power-law type of fluids. Assuming a proportionality between the shear rate and rotational speed of the impeller, they reported that the proportionality constant was independent of the geometric and fluid properties of the mixing system. This was later contested by a number of researchers, and different correlations have been given to evaluate the proportionality constant. An in-depth investigation of the Metzner–Otto concept is discussed with the help of computational fluid dynamics (CFD) techniques to calculate the flow field created by an anchor impeller. Fundamentally, both of the assumptions are broadly valid for typical operating parameters used in anchor-driven impeller systems. A new correlation, based on the Metzner–Otto concept and making use of the present CFD simulations, was developed to calculate power consumption in anchor-driven mixing systems.

Mixing of power-law fluids using anchors: Metzner-Otto concept revisited

Effect of electrode intrusion on pressure drop and electrochemical performance of an all-vanadium redox flow battery

For high current density operation of redox flow batteries, proper circulation of the electrolytes over the active area of the cell is important. In the present paper, we study experimentally the effect of channel dimensions of a serpentine flow field for vanadium redox flow battery applications. The study encompasses three aspects: effect on the extent of felt intrusion into the flow channels, effect on the pressure drop over a cell for a given electrolyte circulation rate, and effect on the electrochemical performance characterized by a number of parameters. Eight variants of channel and/or rib dimensions in serpentine flow fields have been studied in cells of 400 cm2 and 900 cm2 active area. A lumped parameter model, validated with water and electrolyte circulation data, has been developed to predict the pressure loss and flow apportionment in the cell. The results show that sensitivity to channel dimensions is more keenly felt in the larger cell with noticeable improvements in pressure drop, peak power density and discharge energy density. Increasing channel width and decreasing rib width is recommended as the ideal strategy to improve the overall performance of the cell.

Sreenivas Jayanti

Papers

Feasibility of using ultrasound-assisted process for sulfur and ash removal from coal

A conceptual model of a high-efficiency, stand-alone power unit based on a fuel cell stack with an integrated auto-thermal ethanol reformer

Mixing of power-law fluids using anchors: Metzner-Otto concept revisited

Effect of electrode intrusion on pressure drop and electrochemical performance of an all-vanadium redox flow battery

Effect of channel dimensions of serpentine flow fields on the performance of a vanadium redox flow battery