Department of Mechanical Engineering

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IIT Jodhpur

The present work aims to develop a model of a new electrochemical CO2 separation and release technology. We present a one-dimensional transient model of an electrochemical cell for point source CO2 capture and release, which mainly focuses on the simultaneous mass transport and complex chemical reactions associated with the separation process. For concreteness, we use an ionic liquid (IL) with 2 M thiolate anion (RS−) in 1 M disulfide (RSSR) as an electrolyte in the electrochemical cell to capture, transport and release CO2 under standard operating conditions. We computationally solved the model to analyze the time-dependent behavior of CO2 capture and electro-migration transport across the cell length. Given high nonlinearity of the system, we used a finite element method (FEM) to numerically solve the coupled mass transport equations. The model describes the concentration profiles by taking into account the individual transport of all participating species, charged as well as neutral. The model predicts performance characteristics of electrochemically assisted CO2 capture and release in terms of faradaic efficiency and cell current density as the cell dynamics evolves and approaches the steady state. The model provides an opportunity to better understand electrochemically assisted CO2 capture and release, and when coupled with experimental results will provide an early assessment of feasibility for large-scale application in realistic conditions. © 2017 Elsevier B.V.

World University root node

Journal of Electroanalytical Chemistry

Transient modeling of electrochemically assisted CO2 capture and release

In the present study, we construct a nonlinear whistler wave model to explain the magnetic field spectra observed for lion roars in the Earth’s magnetosheath region. We use two-fluid theory and semi-analytical approach to derive the dynamical equation of whistler wave propagating along the ambient magnetic field. We examine the magnetic field localization of parallel propagating whistler wave in the intermediate beta plasma applicable to the Earth’s magnetosheath. In addition, we investigate spectral features of the magnetic field fluctuations and the spectral slope value. The magnetic field spectrum obtained by semi-analytical approach shows a spectral break point and becomes steeper at higher wave numbers. The observations of IMP6 plasma waves and magnetometer experiment reveal the existence of short period magnetic field fluctuations in the magnetosheath. The observation shows the broadband spectrum with a spectral slope of −4.5 superimposed with a narrow band peak. The broadband fluctuations appear due to the energy cascades attributed by low-frequency magnetohydrodynamic modes, whereas, a narrow band peak is observed due to the short period lion roars bursts. The energy spectrum predicted by the present theoretical model shows a similar broadband spectrum in the wave number domain with a spectral slope of −3.2, however, it does not show any narrow band peak. Further, we present a comparison between theoretical energy spectrum and the observed spectral slope in the frequency domain. The present semi-analytical model provides exposure to the whistler wave turbulence in the Earth’s magnetosheath. © 2017, Springer Science+Business Media B.V.

Fulltext

Astrophysics and Space Science

Nonlinear whistler wave model for lion roars in the Earth’s magnetosheath

Waste heat recovery combined with exhaust gas recirculation is a promising technology that can address both the issue of NOx (nitrogen oxides) reduction and fuel savings by including a pressurized boiler. In the present study, a theoretical optimization of the performance of two different configurations of steam Rankine cycles, with integrated exhaust gas recirculation for a marine diesel engine, is presented. The first configuration employs two pressure levels and the second is configured with three-pressure levels. The models are developed in MATLAB based on the typical data of a large two-stroke marine diesel engine. A turbocharger model together with a blower, a pre-scrubber and a cooler for the exhaust gas recirculation line, are included. The steam turbine, depending on the configuration, is modeled as either a dual or triple pressure level turbine. The condensation and pre-heating process is optimized to utilize the maximum waste heat recovery. The Genetic algorithm and fmincon active-set algorithm are used to optimize the design and operation parameters for the two steam cycles. The optimization aims to find the theoretically optimal combination of the pressure levels and pinch-point temperatures to maximize the power production. Results show that the two-pressure level steam cycle produces 1577 kW of net power; whereas the three-pressure level cycle produces 1641 kW at full load operation. The optimum pressure levels for the two-pressure level configuration are found to be 33.4/4.7 bara. For the three-pressure level configuration, the optimum pressure levels are found to be 33.5/10.5/4.7 bara. The amount of waste heat recovery from the pressurized boiler is significantly higher than from the main boiler for both cycles. It is, therefore, concluded that the three-pressure level steam cycle (configuration 2) is more efficient than the two pressure level cycle (configuration 1). At the same time, the engine equipped with waste heat recovery with a three-pressure level steam cycle is simpler to operate in Tier II operation. However, the two-pressure level steam cycle is a simpler configuration. © 2017 Elsevier Ltd

Energy Conversion and Management

Modeling and optimization of integrated exhaust gas recirculation and multi-stage waste heat recovery in marine engines

For performance improvement and noise reduction, swept and anhedral tips have been incorporated in advanced-geometry rotor blades. While there are aerodynamic benefits to these advanced tip geometries, they come at the cost of complicated structural design and weight penalties. The effect of these tip shapes on loads, vibration and aeroelastic response are also unclear. In this study, a comprehensive helicopter aeroelastic analysis which includes rotor-fuselage coupling shall be described and the analysis results for rotor blades with straight tip, tip sweep and tip anhedral shall be presented and compared. The helicopter modelled is a conventional one with a hingeless single main rotor and single tail rotor. The blade undergoes flap, lag, torsion and axial deformations. Tip sweep, pretwist, precone, predroop, torque offset and root offset are included in the model. Aerodynamic model includes Peters-He dynamic wake theory for inflow and the modified ONERA dynamic stall theory for airloads calculations. The complete 6-dof nonlinear equilibrium equations of the fuselage are solved for analysing any general flight condition. Response to pilot control inputs is determined by integrating the full set of nonlinear equations of motion with respect to time. The effects of tip sweep and tip anhedral on structural dynamics, trim characteristics and vehicle response to pilot inputs are presented. It is shown that for blades with tip sweep and tip anhedral/dihedral, the 1/rev harmonics of the root loads reduce while the 4/rev harmonics of the hub loads increase in magnitude. Tip dihedral is shown to induce a reversal of yaw rate for lateral and longitudinal cyclic input. © 2017 Royal Aeronautical Society.

Aeronautical Journal

Effects of rotor blade-tip geometry on helicopter trim and control response

The present work simulates the transformation of austenite to ferrite with mixed-mode in a simplified austenitic grain geometry. The quantitative phase-field model, developed on the basis of non-local equilibrium at the interface, simulates the transformation. The present work reveals that the soft-impingement takes place much earlier than has been so far considered. The accumulation of carbon in and around the meeting point of the diffusion layers is not continuous, and a detailed mechanism of soft-impingement is presented here. The growth of ferrite under mixed-mode of transformation is analyzed and found to be consistent with the theory. © 2017, The Minerals, Metals & Materials Society and ASM International.

Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science

A Quantitative Phase-Field Simulation of Soft-Impingement in Austenite to Ferrite Transformation with Mixed-Mode

The objective of the present work is to measure the heat transfer and pressure drop in flow boiling with refrigerant R123 as the working medium. Local heat transfer coefficient along the axial length of tube and overall averaged heat transfer coefficient are compared with available correlations. In the present study, spatial variation in heat transfer coefficient along the axial length of tube is analysed with the increase of quality. Variation in heat transfer coefficient in different flow boiling region i.e. subcooled, nucleate and convective is studied. The experiments are conducted with seven test sections made of SS304 having four different tube diameters 5.5 mm, 7.5 mm, 9.5 mm and 12.0 mm with two different heated lengths 500 mm and 1000 mm. The system pressure is varying from 1.3 bar to 3.2 bar. The experimental data of two-phase pressure drop and critical heat flux are compared with available correlations. Correlations are suggested to measure the local heat transfer coefficient during boiling process, two-phase pressure drop and critical heat flux. Data of critical heat flux are published to contribute in the data bank for horizontal straight tubes. © 2017 Elsevier Ltd

International Journal of Heat and Mass Transfer

Boiling pressure drop, local heat transfer distribution and critical heat flux in horizontal straight tubes

In this paper, we present a method that focuses on posture correction for stable quadruped locomotion over un- even terrain. Stability is ensured by switching to stable postures during gait transitions, where the posture is selected based on the terrain, foothold reachability and gait sequence. For fast and efficient posture evaluation, we use value functions that approximate stability and kinematic parameters. Learning using regression methods is used to create the value functions, which eliminates the need for additional sensors and computation for posture evaluation. This approach has been verified both numerically and experimentally. © 2017 ACM.

ACM International Conference Proceeding Series

Terrain adaptive posture correction in quadruped for locomotion on unstructured terrain

Evaporation rate of water is strongly influenced by energy barrier due to molecular collision and heat transfer limitations. The evaporation coefficient, defined as the ratio of experimentally measured evaporation rate to that maximum possible theoretical limit, varies over a conflicting three orders of magnitude. In the present work, a semi-analytical transient heat diffusion model of droplet evaporation is developed considering the effect of change in droplet size due to evaporation from its surface, when the droplet is injected into vacuum. Negligible effect of droplet size reduction due to evaporation on cooling rate is found to be true. However, the evaporation coefficient is found to approach theoretical limit of unity, when the droplet radius is less than that of mean free path of vapor molecules on droplet surface contrary to the reported theoretical predictions. Evaporation coefficient was found to reduce rapidly when the droplet under consideration has a radius larger than the mean free path of evaporating molecules, confirming the molecular collision barrier to evaporation rate. The trend of change in evaporation coefficient with increasing droplet size predicted by the proposed model will facilitate obtaining functional relation of evaporation coefficient with droplet size, and can be used for benchmarking the interaction between multiple droplets during evaporation in vacuum. © 2016 Elsevier B.V.

Department of Mathematics

Physics Letters, Section A: General, Atomic and Solid State Physics

Evaluation of evaporation coefficient for micro-droplets exposed to low pressure: A semi-analytical approach

The Glass-Metal Joints play an indispensable role in many applications such as, in concentrating solar power, nuclear and electronics industry. The aim of the present work is the fabrication of glass-metal joints using borosilicate glass with austenitic stainless steel and copper. The joints were fabricated using resistance heating and mechanical behavior of these fabricated joints was determined. Single lap joint between glass and metal was used in order to measure the strength of glass-metal joint. The micro-hardness evaluation of these fabricated joints was also carried out. Oxidation studies were also conducted to examine the role of oxide formation in the joints using X- Ray Diffraction measurements. The mechanical behavior and microstructure evolution of austenitic stainless steel to borosilicate glass joint and copper to borosilicate glass joint were analyzed and it was found that bonding characteristic of different glasses with copper was poor, because of its poor thermal stability at higher sealing temperature. Out of different composition glasses, G6 glass resulted shear strength around 0.124MPa which was the maximum among all joints. © 2018 by World Scientific Publishing Europe Ltd.

Mechanical Properties and Performance of Engineering Ceramics and Composites XI

An experimental study on fabrication, mechanical behavior characterization and micro structural evolution in glass-metal joints

This paper proposes a kinematically redundant planar manipulator for lower limb rehabilitation application, having configuration 4PRP. The challenges in the existing mechanisms has been analyzed and a new configuration is proposed. This configuration helps to improve the effective workspace of the lower limb rehabilitation robot. The lower limb rehabilitation systems are used to treat the post stroke patients and limb injured patients by providing rigorous exercises through the motor nerves recovery. This paper shows the advantages of the proposed 4-PRP kinematically redundant planar manipulator over existing 2PRP-2PPR in providing higher effective workspace with same capability in performing lower limb rehabilitation tasks. © Springer Nature Singapore Pte Ltd. 2016.