Showing papers by "Ujjwal K. Saha published in 2022"

Experimental Visualization and Analysis of Multiphase Immiscible Flow in Fractured Micromodels Using Micro-Particle Image Velocimetry

Abstract: The study of fluid flow through fractured porous media has drawn immense interest in the fields of soil hydrology, enhanced oil recovery (EOR) and others. In this work, a low cost fractured micromodel with regular pore geometry is fabricated and visualization experiments are performed to study the flow field produced by single-phase and two-phase immiscible flow. The fractured micromodel is fabricated using Polydimethylsiloxane (PDMS) substrate. The micro-PIV method is applied to map the flow velocity, both at the throat and near the fracture region of micromodel. In two-phase flow, imbibition flow experiments are performed to investigate the effects of fracture on the front migration caused by the trapping mechanism of residual fluid (displaced phase). The velocity distribution obtained for the two-phase flow revealed many peculiarities that are completely different from the single-phase flow pattern. These peculiarities create instabilities that yield random preferential flow paths near the pockets of stagnant fluid. Such dynamic events are quantified by mapping the velocity magnitude of flow fields. No effects of fracture are seen in the single-phase flow where uniform flow patterns are observed in the porous region. However, for the two-phase flow, more pockets of trapped fluids are found at the junction of two fractures.

Aerodynamic Design and Wind Tunnel Tests of Small-scale Horizontal-axis Wind Turbines for Low Tip Speed Ratio Applications

Abstract: In recent times, the application of small-scale horizontal axis wind turbines (SHAWTs) has drawn interest in certain areas where the energy demand is minimal. These turbines, operating mostly at low Reynolds number (Re) and low tip speed ratio (λ) applications, can be used as stand-alone systems. The present study aims at the design, development, and testing of a series of SHAWT models. On the basis of aerodynamic characteristics, four SHAWT models viz., M1, M2, M3, and M4 composed of E216, SG6043, NACA63415, and NACA0012 airfoils, respectively have been developed. Initially, the rotors are designed through blade element momentum theory (BEMT), and their power coefficient have been evaluated. Thence, the developed rotors are tested in a low-speed wind tunnel to find their rotational frequency, power and power coefficient at design and off-design conditions. From BEMT analysis, M1 shows a maximum power coefficient (Cpmax) of 0.37 at λ = 2.5. The subsequent wind tunnel tests on M1, M2, M3, and M4 at 9 m/s show the Cpmax values to be 0.34, 0.30, 0.28, and 0.156, respectively. Thus, from the experiments, the M1 rotor is found to be favourable than the other three rotors, and its Cpmax value is found to be about 92% of BEMT prediction. Further, the effect of pitch angle (θp) on Cp of the model rotors is also examined, where M1 is found to produce a satisfactory performance within ±5° from the design pitch angle (θp, design).

Changing landscape of India's renewable energy and the contribution of wind energy

Abstract: A country of billion people, India has witnessed a sharp increase in its economic activities in the past few decades, fulfilling the needs of its ever-growing population, which has come at the expense of a considerable sum of energy and carbon emission. With rising global concern on climate change and India's commitment toward reducing carbon emission, the country is gradually shifting towards harnessing energy through renewable energy (RE), and in recent times, the electricity generation via RE covers about 20%. The road towards RE comes with many challenges, especially when most of its economic activities heavily rely on conventional energy sources. The article highlights the ever-increasing energy requirements of India and the contributions that the RE is making. Being the most contributor among all the RE in India, wind energy has a significant role. This paper presents some of the critical aspects of wind power development, current statistics, potential, and challenges. There upon, it provides some essential recommendations for wind power development, market value addition, tariff regulation, grid connectivity, research and development, and future scope of offshore wind farms in India.

Implementation of Soft Computing Techniques in Predicting and Optimizing the Operating Parameters of Compression Ignition Diesel Engines: State-of-the-Art Review, Challenges, and Future Outlook

Abstract: Fossil fuels being the primary source of energy to global industrialization and rapid development are being consumed at an alarming rate, thus creating a dire need to search for alternative fuels and optimise the internal combustion (IC) engine performance parameters. Traditional methods of testing and optimising the performances of IC engine are complex, time consuming and expensive. This has led the researchers to shift their focus to faster and inexpensive techniques like soft computing (SC), which predict the optimum performance with a substantial accuracy. The SC techniques commonly used are Artificial Neural Network (ANN), Fuzzy Logic, Adaptive Neuro Fuzzy Inference System (ANFIS), Genetic Algorithm (GA), Particle Swarm Optimization (PSO) and hybrid techniques like ANN-GA, ANN-PSO and others. The data of engine parameters predicted with these models have been found to be in very close indices with the experimented values making them a reliable predicting tool. The ANN, fuzzy logic, and ANFIS models have been found to have a correlation coefficient (R) above 0.9 suggesting a good level of agreement between experimented and predicted values of several engine-out parameters. In the present review article, the application of various SC techniques in the prediction and the optimization of output parameters of compression ignition (CI) diesel engines are thoroughly reviewed along with their future prospects and challenges. This review work highlights the implication of these SC techniques in CI diesel engines run on both conventional fuel as well as biodiesels.

A Comprehensive Review on Analytical Formulations of Wind Turbine Wake Models and Future Scope in the Development of Wind Farms of Assorted Configurations

Abstract: Of late, the design and development of large and small wind farms are gaining importance to meet the growing energy demand. In this aspect, several wind turbine wake models have been proposed over the years, some of which are the legacy of Jensen, Larsen, Lissaman, Frandsen, and Ainslie wake models. Despite their robustness, the analytical formulations of these models are widely explored as research tools for estimating the performance of wind farms. However, because of several limitations and assumptions like top-hat shape, Gaussian profile, axisymmetric, negligible atmospheric boundary layer effect, and others, these models often overestimate the flow characteristics. In view of this, there is always a scope for developing better correlations to predict the performance of wind farms more accurately. This article gives a conspectus of various wind turbine wake models that have evolved over the years and then recommends some conceptual wind farm designs of assorted configurations.

Experimental Probe Into a Biogas Run Dual Fuel Diesel Engine Using Oxygenated Ternary Blends at Optimum Equivalence Ratio and Under the Effect of Intake Charge Preheating

Abstract: The key challenge of dual fuel mode (DFM) of a compression ignition (CI) diesel engine is to improve the engine overall performance, and to reduce the carbon monoxide (CO) and unburnt hydrocarbon (HC) emissions. The gaining popularity of DFM lies with its inherent ability to curb harmful pollutants nitrogen oxides (NOx) and smoke, besides offering operational flexibility to use gaseous and liquids fuels simultaneously. In addition, the use of renewable fuels in DFM is found to be the highly suitable to achieve the optimum engine overall performance. In this DFM study, biogas as the primary gaseous fuel is used in a diesel engine in conjunction with ternary blends of diesel-biodiesel-ethanol (TB-E), diesel-biodiesel-butanol (TB-BT) and diesel-biodiesel-diethyl ether (TB-DEE) as the renewable pilot fuels. For each combination, the experiments are conducted at the optimum global fuel-air equivalence ratio (?global) and with intake charge preheating to analyze the performance, combustion and emission characteristics of the engine. The important parameters such as brake thermal efficiency, actual diesel replacement, coefficient of variation of indicated mean effective pressure, relative cycle efficiency, cylinder mean gas temperature, ignition delay, combustion duration are investigated. The study demonstrates the optimum performance of the DFM engine with TB-DEE.

Evolving a Bio-Inspired Blade Shape of the Drag-based Vertical-axis Wind Rotor Derived from Orange Sea-pen (Ptilosarcus Gurneyi)

Abstract: Inspired by the polyp leaf of the Orange sea-pen (Ptilosarcus gurneyi), a novel blade shape of the Savonius vertical-axis wind rotor is developed. The similarities between the aerodynamic and the hydrodynamic aspects of the Savonius rotor blade profile and the sea-pen leaf are reviewed, and an appropriate analogy is thereby established. The shape of the sea-pen leaf is then extracted to fabricate the rotor blades. The performance of this sea-pen bladed rotor is evaluated in a low-speed subsonic wind tunnel at different wind velocities. The two-dimensional (2D) numerical analysis is also performed to support the experimental findings and to study the influence of blade shape on the pressure and the torque distributions of the rotor. The novel sea-pen bladed rotor, having lesser material requirements, is seen to demonstrate higher performance than that of the conventional semicircular bladed rotor in the tested range of low tip-speed ratio.

Blade Design Considerations of Small Wind Turbines: From Classical to Emerging Bio-inspired Profiles/Shapes

Abstract: The utility of small wind turbines (SWTs) covering horizontal and vertical-axis types as off-grid, standalone, and decentralized energy supplement systems has gained market attention. Such turbines primarily operate at low Reynolds number ( Re) and low tip speed ratio ( λ) conditions. Under such circumstances, the design, development, and testing of SWTs have become a tedious task, mainly due to the lack of precise aerodynamic knowledge of SWT. The present article reviews the fundamental aspects of SWT, including airfoil selection criteria, blade design, and aerodynamic improvement through passive flow control and augmentation techniques. The article also reports several classes of potential airfoils that can be employed in the design of SWTs. The airfoils considered operate mainly in the range of Re = 0.3 x 105 to 3 x 105 and λ = 0.5 to 6. Besides the classical approach, the article showcases the prospects of several bioinspired profiles/shapes that are meant for SWTs operating at low Re and λ conditions. Towards the end, various design constraints and applicability of SWTs are summarized.

An exploratory experimental study of a single-cylinder diesel engine run on diesel–Mesua ferrea Linn oil–diethyl ether ternary blends

Abstract: A small compression ignition (CI) diesel engine was run with different concentrations of diethyl ether (DEE) in Mesua ferrea Linn oil (MLO, 80% by volume)-diesel (20% by volume) blend (M20). DEE was mixed volumetrically by 5 and 10% with M20 to form ternary fuel blends M20D05 and M20D10 respectively. The results revealed an enhancement of 4.4% brake thermal efficiency (BTE) with a 5% DEE ternary blend when compared to M20 fuel at lower loads. At maximum output condition, the BTE of ternary blends M20D05 and M20D10 were found lowered by 5.1% and 6.8% respectively to the diesel mode. Brake specific fuel consumption increased with an increase in the amount of DEE in the M20 as compared to the neat M20. An elongated ignition delay period and decelerated combustion process were attained by DEE ternary blends. A maximum reduction of 13.6% CO and 25.6% NOx emissions was achieved with 10% DEE ternary blend as compared to M20 fuel. The HC emissions were increased with the increase of DEE in the blend to the neat M20 fuel. The study suggests that the ternary blends can replace the fossil diesel fuel by 25–30% in CI engines without making any engine modification.

Predicting the Optimum Performance of a Vertical-Axis Savonius Wind Rotor With Parametric Modeling Using Artificial Neural Network and Golden Section Method

Abstract: This paper explores the function approximation characteristics of Artificial Neural Network (ANN) by implementing it on the vertical-axis Savonius wind rotor technology. In this regard, a suitable experimental dataset documented in literature is exploited to train the ANN comprising the rotor performance as output and 11 different design and operating parameters as input with the help of MATLAB R2020b software. Multiple ANN models are trained by varying the number of hidden neurons which are then evaluated based on their estimation error and correlation coefficient (R) as decision criteria. The optimum ANN architecture demonstrates R ≈ 98 0.96 and 0.98 for the testing and training datasets, respectively. Further, in the quest of finding the optimum performance from the entire power curve of the rotor, the Golden Section Method (GSM) is linked with the trained ANN model. Using these soft computing techniques, a parametric study is carried out to understand the dependency of rotor performance on their design and operating parameters. At the end, a graphical interface is developed as a product so as to allow the user to predict the performance of the new rotor designs intuitively.