Satyanarayanan Seshadri

Bio: Satyanarayanan Seshadri is an academic researcher from Indian Institute of Technology Madras. The author has contributed to research in topic(s): Laser-induced breakdown spectroscopy & Organic Rankine cycle. The author has an hindex of 3, co-authored 15 publication(s) receiving 33 citation(s).

Performance investigation of two stage Organic Rankine Cycle (ORC) architectures using induction turbine layouts in dual source waste heat recovery

Abstract: Improvement in performance of Organic Rankine Cycle (ORC) systems, particularly in the context of dual heat sources such as IC engines, leads to better return on investments. However, the choice of architecture to achieve the best performance is not evident from available literature. When two separate heat sources are present concurrently at different temperature levels with heat contents such as in IC engines, single stage pre-heated ORC and dual loop ORC are the two commonly deployed ORC architectures. In this study, two stage architectures: Series two stage ORC (STORC) and Parallel two stage ORC (PTORC) are analysed and their performance is compared against a single stage pre-heated ORC at sub-critical conditions in the utilization of high temperature (primary) exhaust gases (573–773 K) and low temperature (secondary) jacket water (353–393 K) representing IC engine waste heat conditions. Results show that STORC and PTORC are able to achieve the maximum net power output for an intermediate utilization of secondary heat source. The power output gains from two stage layouts improves significantly with a reduction in heat source temperature difference and for lower ratios of the heat available between the primary to secondary heat source. For a 2.9 MW natural gas IC engine operating at its design point, STORC delivers 8.5% more power output whereas PTORC delivers 0.3% less power output than pre-heated ORC. Compared to a dual–loop ORC, STORC presents a less complex and improved cycle architecture with a 13.1% increased power output and a 27.9% reduced heat exchanger requirements.

Effect of ambiance on the coal characterization using laser-induced breakdown spectroscopy (LIBS)

Abstract: The influence of surrounding gases, such as He, N2, atmospheric air, and Ar, and gas flow rate on the laser-induced breakdown spectroscopy (LIBS) characterization of coals in free space is studied. The atomic and molecular carbon (C2 and CN) emission intensities are observed to be higher in Ar and N2 ambiance. Quantitative analysis of carbon and ash content in different coal samples is carried out using the carbon bound atomic and molecular emission signals and the ash forming elements (Si, Fe, Mg, Al, Ca, Na, and K) signals. The sum of the LIBS emission of the all and major ash forming elements increased linearly with an increase in the ash content. Similarly, the ratio between the carbon signals (C I, CN, and C2) and the sum of major ash forming elements (Si, Al, Fe, and Ca) also showed a linear increase with the increase in carbon content in coal samples. The linear coefficient of regression, R2, was estimated to be 0.67, 0.58, and 0.85, and the root mean square of calibration samples was estimated to be 5.71, 5.82, and 5.57 wt% using the partial least square regression (PLSR) method for air (no flow), N2, and Ar atmosphere, respectively. The precision and accuracy of the carbon measurement in coal samples by the LIBS technique using the PLSR method were higher in the presence of Ar than air or N2 atmosphere due to the plasma shielding effect.

Design and performance analysis of a novel Transcritical Regenerative Series Two stage Organic Rankine Cycle for dual source waste heat recovery

Abstract: A Transcritical Regenerative Series Two stage Organic Rankine Cycle (TR-STORC) is proposed to improve the efficiency of existing Series Two stage ORC (STORC) architecture by combining supercritical heating in the high pressure (HP) stage and partial evaporation with regeneration in the low pressure (LP) stage. Exhaust gas and jacket water from a stationary IC engine is used as the primary and secondary heat source respectively. Using cyclopentane as working fluid, system exergy performance is analysed for a range of heat source temperatures and for different ratios of heat available between the heat sources. At lower HP evaporator pressures, lower values of vapour outlet temperatures lead to maximum power output. For a wide range of heat ratios and temperatures, TR-STORC delivers improved exergetic performance over STORC and pre-heated ORC. It is the recommended choice for all scenarios of dual source heat recovery. For the engine design point, TR-STORC delivers increased power output by up to16% and 23% than STORC and pre-heated ORC respectively. TR-STORC maintains exergetic superiority for all the working fluids investigated with maximum net power outputs exceeding STORC by15–34% and preheated ORC by 15–52%.

Overview of the factors affecting the performance of vanadium redox flow batteries

Abstract: Redox flow batteries are being utilised as an attractive electrochemical energy storage technology for electricity from renewable generation. At present, the global installed capacity of redox flow battery is 1100 MWh. There are several parameters that significantly govern redox flow battery performance amongst which electrode activation, electrode material, felt compression, electrolyte additive, electrolyte temperature, membrane, and flow field design are notable. This review article presents an overview of the influence of individual components by comparing the performance of a parametrically modified cell with a default cell, which has 0% felt compression, inactivated electrode, zero electrolyte additives, and ambient condition operation. From the reviewed studies, electrode activation (thermal, chemical, laser perforation) and felt compression were identified as the most significant parameters. Electrolyte additive and flow field design were identified to be reasonably significant. Electrolyte temperature and membrane type were identified as the least significant amongst all the parameters. Based on this survey, a parametric matrix has been outlined that will aid researchers to identify appropriate parameters to focus research efforts onto improved redox flow battery performance.

Laser-Induced Breakdown Spectroscopy Combined with Temporal Plasma Analysis of C2 Molecular Emission for Carbon Analysis in Coal.

Abstract: A benchtop laser-induced breakdown spectroscopy is demonstrated to determine the elemental carbon content present in raw coal used for combustion in power plants. The spectral intensities of molecular CN and C2 emission are measured together with the atomic carbon (C) and other inorganic elements (Si, Fe, Mg, Al, Ca, Na, and K) in the laser-induced breakdown spectroscopy spectrum of coal. The emission persistence time of C2 molecule emission is measured from the coal plasma generated by a nanosecond laser ablation with a wavelength of 266 nm in the Ar atmosphere. The emission persistence time of molecular C2 emission along with the spectral intensities of major ash elements (Fe, Si, Al, and Ca) and carbon emissions (atomic C, molecular CN, and C2) shows a better relationship with the carbon wt% of different coal samples. The calibration model to measure elemental carbon (wt%) is developed by combining the spectral characteristics (spectral intensity) and the temporal characteristics (emission persistence time of C2 molecule emission). The temporal characteristic studies combined with the spectroscopic data in the partial least square regression model have resulted in an improvement in the root mean square error of validation, and the relative standard deviation is reduced from 10.8% to 4.1% and from 11.3% to 6.0%, respectively.

A review of laser-induced breakdown spectroscopy for plastic analysis

Abstract: With massive coal consumption in the industry, the increasing requirements for improving combustion efficiency and environmental protection raise widespread interests. Laser-induced breakdown spectroscopy (LIBS) shows the merits of high-speed, minimally destructive, simple preparation, etc. Combining it with the analytical chemistry methods have become a promising way for coal analysis. In this work, LIBS instruments for collecting coal spectra, pretreatment methods for coal samples, preprocessing of coal data, and analytical chemistry methods for coal analysis were summarized. Moreover, LIBS applications, including coal ranks, combustion efficiency, and environmental protection, are provided. Finally, this review proposes a description of limitations and the potential developing trend for this topic.

Evaluation and optimization of a novel geothermal-driven hydrogen production system using an electrolyser fed by a two-stage organic Rankine cycle with different working fluids

Abstract: In this study, a novel system comprising of a two-stage organic Rankine cycle, driven by geothermal energy and coupled with a proton exchange membrane electrolyser, is investigated and optimized from thermodynamic and exergoeconomic viewpoints. Various working fluids are considered so as to ascertain the effects of thermophysical properties on the performance of the system. The electricity output from the two-stage organic Rankine cycle is employed to produce hydrogen through electrochemical reactions in the proton exchange membrane electrolyser. The effects are assessed on key parameters of variations in geothermal water temperature and the pressure ratio of high-pressure organic Rankine cycle turbine. Considering three distinct cases, a thorough optimization is performed utilizing a genetic algorithm. It is concluded that a 2-3 percent-point improvement in energy efficiency, as well as a 35% to 41% increase in hydrogen production and a 9.5% to 12% reduction in cost per unit exergy of hydrogen can be achieved via optimization. R123 is shown in the optimization to perform the best among the considered working fluids, with isopentane performing second best.

Constructal thermodynamic optimization for dual-pressure organic Rankine cycle in waste heat utilization system

Abstract: Dual-pressure organic Rankine cycle (DPORC) is a technology with great potential to solve energy problems. This paper performs constructal thermodynamic optimization (CTO) for the DPORC based on a combination of constructal theory and finite-time thermodynamics. The tube outside diameters of the heat exchangers, such as high- and low-temperature evaporators (HTE and LTE) and condenser, and the volume ratio of the high-pressure turbine are the design variables, the system net power output (POW) is the optimization function, and the total volume of the turbines and total heat transfer area (HTA) of the heat exchangers are the constraints. The influences of some parameters, such as the HTA ratios of the HTE and LTE, and the total mass flow rate (MFR) of the working medium on the CTO results are studied. The performance comparison between the DPORC and single-pressure ORC (SPORC) is carried out under the same conditions. The results demonstrate that the system net POWs after the four stepwise CTOs are improved by 1.70%, 3.01%, 5.80% and 8.84% over against the initial system net POW, respectively. Reducing the HTA ratios of the HTE and LTE and increasing the total MFR of the working medium can increase the system net POW. Compared with the performance of the SPORC, the system net POW and system net thermal efficiency of the DPORC are increased by 4.91% and 5.51%, respectively. The optimization results can be used to guide the optimal designs of the low-temperature waste heat utilization systems.

Pathways to Low Cost Electrochemical Energy Storage: A Comparison of Aqueous and Nonaqueous Flow Batteries

Abstract: Energy storage is increasingly seen as a valuable asset for electricity grids composed of high fractions of intermittent sources, such as wind power or, in developing economies, unreliable generation and transmission services. However, the potential of batteries to meet the stringent cost and durability requirements for grid applications is largely unquantified. We investigate electrochemical systems capable of economically storing energy for hours and present an analysis of the relationships among technological performance characteristics, component cost factors, and system price for established and conceptual aqueous and nonaqueous batteries. We identified potential advantages of nonaqueous flow batteries over those based on aqueous electrolytes; however, new challenging constraints burden the nonaqueous approach, including the solubility of the active material in the electrolyte. Requirements in harmony with economically effective energy storage are derived for aqueous and nonaqueous systems. The attributes of flow batteries are compared to those of aqueous and nonaqueous enclosed and hybrid (semi-flow) batteries. Flow batteries are a promising technology for reaching these challenging energy storage targets owing to their independent power and energy scaling, reliance on facile and reversible reactants, and potentially simpler manufacture as compared to established enclosed batteries such as lead–acid or lithium-ion.

Analysis and optimization of a fuel cell integrated with series two-stage organic Rankine cycle with zeotropic mixtures

Abstract: In this article, thermodynamic modeling of a cogeneration system consisting of a series two-stage organic Rankine cycle (STORC) and a proton exchange membrane (PEM) fuel cell is conducted. The fuel cell dissipated heat is utilized as STORC plant input. In order to gain a higher efficiency for the proposed cogeneration system, the condenser of the organic Rankin cycle is replaced by a thermoelectric generator (TEG) to minimize heat loss. Moreover, zeotropic mixtures have been employed due to their lower irreversibility compared to single working fluid. Simulation code is developed in MATLAB software linked with the REFPROP software to extract the thermodynamic properties. This simulation code calculates the exergy efficiency and system's total cost rate. Since the performance of the system is affected by the working fluid, three zeotropic mixtures are compared with R123. The parametric study shows that high pressure (HP) and low pressure (LP) evaporator temperature, current density, and PEM operating pressure significantly affect the total cost rate and the second law efficiency. The results indicate that Ipentane-cis Butane has better efficiency among the selected zeotropic mixtures. Furthermore, the genetic algorithm multi-objective optimization is applied to determine the optimal design parameters of the system in a scatter distribution schematic. Finally, the normalized Pareto frontier of Ipentane-cis Butane is given and the related best point of working as a higher exergy efficiency and lower cost rate are specified. Eventually, it is concluded that the integration of STORC with primary PEM fuel cell improves overall exergy efficiency by 1.9%. The total cost rate for optimum point can be in a range of 1.36–14.94 ($/h), depending on the hydrogen production process.