Sreenivas Jayanti

Bio: Sreenivas Jayanti is an academic researcher from Indian Institute of Technology Madras. The author has contributed to research in topics: Pressure drop & Combustion. The author has an hindex of 37, co-authored 142 publications receiving 3884 citations. Previous affiliations of Sreenivas Jayanti include Ohio State University & Imperial College London.

CFD Study of Power and Mixing Time for Paddle Mixing in Unbaffled Vessels

Abstract: CFD-based computations of the flow field, power consumption and mixing time are presented for a mechanically stirred eight-blade paddle impeller in an unbaffled vessel over a range of Reynolds numbers covering laminar, transitional and turbulent flow regimes. The flow field calculations were performed using the sliding mesh technique to account for the motion of the impeller, and mixing time studies were done using a simulated tracer injection experiment. The effect of grid density and the choice of the turbulence model were investigated. The results are compared with flow field data from Dong et al . 1 , and power and mixing time correlations from the literature and show satisfactory agreement. It is shown that the product of mixing time and rotational speed remains constant for paddle impellers for laminar flow and that the use of a low Reynolds number turbulence model is necessary for good prediction of mixing time in the transitional flow.

A detailed kinetic model for biogas steam reforming on Ni and catalyst deactivation due to sulfur poisoning

Abstract: This paper deals with the development and validation of a detailed kinetic model for steam reforming of biogas with and without H 2 S. The model has 68 reactions among 8 gasphase species and 18 surface adsorbed species including the catalytic surface. The activation energies for various reactions are calculated based on unity bond index-quadratic exponential potential (UBI-QEP) method. The whole mechanism is made thermodynamically consistent by using a previously published algorithm. Sensitivity analysis is carried out to understand the influence of reaction parameters on surface coverage of sulfur. The parameters describing sticking and desorption reactions of H 2 S are the most sensitive ones for the formation of adsorbed sulfur. The mechanism is validated in the temperature range of 873–1200 K for biogas free from H 2 S and 973–1173 K for biogas containing 20–108 ppm H 2 S. The model predicts that during the initial stages of poisoning sulfur coverages are high near the reactor inlet; however, as the reaction proceeds further sulfur coverages increase towards the reactor exit. In the absence of sulfur, CO and elemental hydrogen are the dominant surface adsorbed species. High temperature operation can significantly mitigate sulfur adsorption and hence the saturation sulfur coverages are lower compared to low temperature operation. Low temperature operation can lead to full deactivation of the catalyst. The model predicts saturation coverages that are comparable to experimental observation.

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

Abstract: 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.

A review of flow and heat transfer characteristics in curved tubes

Abstract: 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.