Ashish Alex Sam

Bio: Ashish Alex Sam is an academic researcher from Indian Institute of Technology Kharagpur. The author has contributed to research in topics: Turboexpander & Turbine. The author has an hindex of 5, co-authored 13 publications receiving 63 citations. Previous affiliations of Ashish Alex Sam include VIT University.

Effect of rotation on the flow behaviour in a high-speed cryogenic microturbine used in helium applications.

Abstract: The complex flow characteristics in a high-speed helium microturbine used in cryogenic refrigeration and liquefaction cycles are highly influenced by the effects of rotation In order to enhance the turbine performance and to improve the preliminary design process of the turboexpander, the flow characteristics within the turbine blade passage need to be investigated at different rotational speeds Here, three-dimensional unsteady flow analysis of a high speed cryogenic microturbine used in helium applications was carried out using Ansys CFX® The loss generated by the various secondary and vortical flows for the different cases was quantified in terms of entropy loss coefficient The loss generating mechanism was also assessed by analysing the velocity vectors, entropy contours and the behaviour of the vortex cores With change in speed the influence of scraping flow due to relative casing motion and the blade loading on the flow characteristics was found to vary significantly At lower speeds, the scraping flow decreases and thus augments the tip leakage flow which in turn interacts with the suction side leg of the leading edge vortex to form a single large vortex This combined vortex increases the velocity defect and thus leads to increased loss generation The analysis of the vortex core velocity and the blade loading diagram revealed the need for modifications in blade profile for improved turbine performance Furthermore, the comparison of the CFD results with the Balje's nsds chart showed remarkable variations, the results of which can be used to modify the chart for the design of efficient cryogenic microturbines for helium applications

Conceptual Advanced Transport Aircraft Design Configuration for Sustained Hypersonic Flight

Abstract: The conceptual aircraft design and its integration with a combined cycle engine for hypersonic cruise at Mach 8 is documented in this paper. The paper describes the process taken to develop a hypersonic aircraft from a conceptual approach. The discussion also includes the design and CFD analysis of the integrated combined cycle engine. A final conceptual hypersonic transport aircraft with an integrated combined cycle engine was achieved through this study. According to the analysis carried out, the aircraft is able to take-off and land at the airports it is intended to be used and will be able to generate enough thrust to sustain hypersonic cruise at an altitude of 30 km.

Influence of thermophysical properties of working fluid on the design of cryogenic turboexpanders using nsds diagram

Abstract: Cryogenic turboexpanders are an essential part of liquefaction and refrigeration plants. The thermodynamic efficiency of these plants depends upon the efficiency of the turboexpander, which is the main cold generating component of these plants, and therefore, they should be designed for high thermodynamic efficiencies. Balje's [1] nsdschart, which is a contour of isentropic efficiencies plotted against specific speed and specific diameter, is commonly used for the preliminary design of cryogenic turboexpanders. But, these charts were developed based on calculations for a specific heat ratio (γ) of 1.4, and studies show that care should be taken while implementing the same for gases which have a higher γ of 1.67. Hence there is a need to investigate the extent of applicability of nsds diagram in designing expansion turbines for higher specific heat ratios. In this paper, Computational Fluid Dynamics (CFD) analysis of cryogenic turboexpanders was carried out using Ansys CFX®. The turboexpanders were designed based on the methodologies prescribed by Kun and Sentz [2] following the nsds diagram of Balje and Hasselgruber's technique for generating blade profile. The computational results of the two cases were analysed to investigate the applicability of Balje's nsds diagram for the design of turboexpanders for refrigeration and liquefaction cycles.

A review on expanders and their performance in vapour compression refrigeration systems

Abstract: This paper reviews progress reported in the open literature of the use of expanders to recover expansion power to improve the energy efficiency of vapour compression refrigeration systems. Pioneering works in the field are first discussed, and then a variety of expander mechanisms, including reciprocating piston, rolling piston, rotary vane, scroll, screw and turbine are reviewed together with their reported performance. Most of the reported works have been for transcritical CO2 refrigeration systems, which have reported improvements in the coefficient of performance (COP) of up to 30%. In a non-CO2 system, the maximum reported increase in the COP was 10%. The maximum reported expander efficiency (i.e. the ratio of measured power to the power available from an isentropic expansion) was 83%, obtained with a scroll expander in a CO2 refrigeration cycle. Other expander issues including heat transfer, expansion process, internal leakage, irreversibility, control strategies, installation issues and economic analysis are also reviewed. It is noted that there are a limited number of studies in these areas. Finally, challenges and recommendations for future research in the area of refrigeration expander technology is presented.

Modeling and process optimization of hydrothermal gasification for hydrogen production: A comprehensive review

Abstract: Hydrothermal gasification of biomass is an alternative method of producing hydrogen-rich syngas. Modeling and optimization of hydrothermal processes are important to evaluate the economic feasibility of the process. Furthermore, developing a mathematical model to represent the many underlying mechanisms during hydrothermal gasification could contribute to lower process expenditures, improve efficiency and provide an in-depth understanding of the process. The present study outlines different modeling and optimization strategies for hydrothermal gasification of biomass and waste materials to produce hydrogen-rich syngas. The modeling techniques (e.g. thermodynamic, kinetic and computational fluid dynamic modeling) and process optimization approaches (e.g. univariate, factorial, Taguchi, response surface methodology and mixture design of experiments) are discussed in this review comprehensively together with their merits and limitations. The knowledge gaps and prospects of modeling and optimization of hydrothermal conversion are also elucidated.