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Showing papers by "Ujjwal K. Saha published in 2013"


Journal ArticleDOI
TL;DR: In this paper, a detailed review of various computational methods addressing the influence of various operating parameters and augmentation techniques has been reported from this review study, it is observed that with the selection of a proper computational methodology, the design, performance, and efficiency of a Savonius rotor can be enhanced significantly.
Abstract: In recent era, research and development activities in the field of renewable energy, especially wind and solar, have been considerably increased, due to the worldwide energy crisis and high global emission However, the available technical designs are not yet adequate to develop a reliable distributed wind energy converter for low wind speed conditions The Savonius rotor appears to be particularly promising for such conditions, but suffers from a low efficiency Till now, a number of experimentations have been carried out in the area of Savonius rotor to increase its efficiency These large-scale experimentations involve massive costs and hazards In this context, computational studies have shown a significant importance to carry out the research with large number of physical designs and parameters Over the past four decades, investigations have been carried out with various computational methodologies and turbulence models to optimize the different parameters and hence the efficiency of these rotors In the present paper, a detailed review of various computational methods addressing the influence of various operating parameters and augmentation techniques has been reported From this review study, it is observed that with the selection of a proper computational methodology, the design, performance, and efficiency of a Savonius rotor can be enhanced significantly

147 citations


Journal ArticleDOI
21 May 2013
TL;DR: The Savonius rotor is a drag-based vertical axis wind turbine and is used as an alternative source in small-scale energy generation as mentioned in this paper, which is a very simple design, low-cost, easy installation, and good starting point.
Abstract: The Savonius rotor is a drag-based vertical axis wind turbine and is used as an alternative source in small-scale energy generation. Design simplicity, low-cost, easy installation, good starting ab...

99 citations


Journal ArticleDOI
TL;DR: In this paper, the performance, combustion and emission characteristics of emulsified biodiesel in a diesel engine at an elevated compression ratio (CR) and retarded injection timing (IT) were investigated.

85 citations



Journal ArticleDOI
TL;DR: In this paper, the effect of overlap ratios on static torque characteristics of a vertical axis wind turbine was analyzed with the help of a finite volume based computational fluid dynamics (CFD) software package Fluent 6.3.

60 citations


Journal ArticleDOI
TL;DR: In this paper, the effects of particle size, solid inventory and operating pressure on bed hydrodynamics and heat transfer in a pressurized circulating fluidized bed has been studied.

49 citations


Journal ArticleDOI
TL;DR: In this paper, the hydrodynamic and heat transfer characteristics at four different % mixing of biomass in sand (2.5, 7.5%, 12.5% and 20%) have been investigated in a pressurized circulating fluidized bed.

26 citations


Proceedings ArticleDOI
15 Nov 2013
TL;DR: In this paper, a computational study has been performed to simulate the air-flow over different blade profiles using shear stress transport (SST) k-ω turbulence model and the results obtained are validated with the available experimental data.
Abstract: Rapid depletion rate of fossil fuels with an increasing energy demand and their high emission are imposing the evolution activities in the arena of renewable energy To meet the future demands of renewable energy sources, wind energy is a very promising concept In this feature, the drag based vertical axis wind turbines (VAWTs) are suitable for small scale wind energy generation for decentralized locations However, these turbines have low power and torque coefficients as compared to other wind turbines Numerous blade shapes have been proposed till now to improve the performance of these turbines In the present paper, a computational study has been performed to simulate the air-flow over different blade profiles using shear stress transport (SST) k–ω turbulence model The results obtained are validated with the available experimental data In the dynamic simulations, the power and torque coefficients are calculated considering the blade arc angle as the variable shape parameter The effects of drag and lift forces on the variable blade shapes are also studied in static simulations at various angular positions The present paper tries to demonstrate an effective computational methodology to predict the flow behavior around a drag based VAWT Through this study, it has been found possible to select an optimal blade shape from the point of its aerodynamic performanceCopyright © 2013 by ASME

23 citations


Journal ArticleDOI
22 Mar 2013
TL;DR: In this article, the use of bio-origin fuels as renewable and environmentally benign sources of diesel fuel has been discussed, and concerns over environmental pollution are leading to the usage of bio origin fuels.
Abstract: Diesel fuel has a limited resource, and concerns over environmental pollution are leading to the use of ‘bio-origin fuels’ as they are renewable and environmentally benign. Palm oil methyl ester, a...

21 citations


Proceedings ArticleDOI
05 Dec 2013
TL;DR: In this article, a number of rotor models with different aspect ratios were tested in a low speed wind tunnel with open test section facility, and the effects of overlap ratio and gap ratio were also studied keeping the rotor height to be the same.
Abstract: With the rapid execution in the renewable energy field, vertical axis wind turbines are finding its application in the small-scale distributed wind energy generation, particularly in rural areas. The Savonius rotor is a drag based vertical axis wind turbine and is used as a small-scale wind energy converter with low installation and maintenance cost. These rotors are simple in design, easy to assemble and can be operated at low-speed wind from any direction. However, these rotors are not gaining popularity because of its low efficiency and improper design. The aspect ratio (height to diameter of the rotor) is one of the very important factors for designing a suitable small-scale wind turbine. The other important factors include overlap ratio, gap ratio and blade profile of the rotor. In the present investigation, a number of rotor models with different aspect ratios are tested in a low speed wind tunnel with open test section facility. The effects of overlap ratio and gap ratio are also studied keeping the rotor height to be the same. The wind speed is varied from 5–10 m/s. To estimate the performance of these rotors, electrical loads are given with respect to different wind speeds and the power output is calculated in terms of voltage and current. The results depicted an optimum aspect ratio of 0.80, which can be used to improve the performance of Savonius rotors.Copyright © 2013 by ASME

18 citations


Journal ArticleDOI
TL;DR: In this article, a pressurized circulating fluidized bed (PCFB) unit of 54 mm inner diameter and riser height of 2000 mm has been fabricated to investigate the effect of pressure on suspension density and heat transfer.

Journal ArticleDOI
TL;DR: In this paper, a modified σ-transformation was used to solve 2D and 3D nonlinear liquid sloshing problems in vertically excited containers with a grid independence study.
Abstract: In this paper, various aspects of the 2D and 3D nonlinear liquid sloshing problems in vertically excited containers have been studied numerically along with the help of a modified σ-transformation. Based on this new numerical algorithm, a numerical study on a regularly and randomly excited container in vertical direction was conducted utilizing four different cases: The first case was performed utilizing a 2D container with regular excitations. The next case examined a regularly excited 3D container with two different initial conditions for the liquid free surface, and finally, 3D container with random excitation in the vertical direction. A grid independence study was performed along with a series of validation tests. An iteration error estimation method was used to stop the iterative solver (used for solving the discretized governing equations in the computational domain) upon reaching steady state of results at each time step. In the present case, this method was found to produce quite accurate results and to be more time efficient as compared to other conventional stopping procedures for iterative solvers. The results were validated with benchmark results. The wave elevation time history, phase plane diagram and surface plots represent the wave nonlinearity during its motion.

Journal ArticleDOI
TL;DR: In this paper, both the thermogravimetric (TG) analysis and differential scanning calorimetry were used to study the influence of heating rate on the degradation of rice husk.
Abstract: Present study involves characterisation and thermal analysis of rice husk as a potential source for gasification. Both the thermogravimetric (TG) analysis and differential scanning calorimetry were used to study the influence of heating rate on the degradation of rice husk. Experiments were carried out at three different heating rates of 10, 30, and 80 K min−1. The kinetic parameters, viz. pre-exponential factor, activation energy, and order of reaction were evaluated for both first and second reaction zones, which are categorized based on the degradation of cellulose, hemicelluloses, and lignin content present in the biomass. The degradation of mass with temperature obtained from TG curve was validated numerically. The thermal response of rice husk undergoing decomposition has also been modelled by using a one dimensional (1-D) transient thermal model with an nth order approximation for the rate of decomposition. Kinetic parameters, heat of decomposition, and thermal properties are taken as input to the model. The model was validated by measuring the transient temperature profiles during decomposition using Heisler chart at heat transfer coefficient of 20 W/m2 K. The data for specific heat and thermal conductivity of the biomass were taken from the literature and the values of heat of decomposition and kinetic parameters were taken from the experiments. Model results were compared well with the result obtained by using Heisler chart.

01 Feb 2013
TL;DR: In this paper, the free surface elevation during liquid sloshing at low excitation frequency was found by using a video camera and free surface oscillations of liquid at different excitation frequencies calculated by the image processing technique.
Abstract: This paper pays attention to finding the free surface elevation during liquid sloshing at low excitation frequency. Experiments have been conducted at low frequency ratios to find the free surface elevation and the obtained results are reported here. The liquid behavior is captured by means of a video camera and the free surface oscillations of liquid at different excitation frequencies calculated by the image processing technique. The liquid height is observed by the intensity variation of the interface between the air and liquid. The location of maximum gradient has been considered as interface. The effects of excitation amplitude, frequency and liquid fill level have been studied.

01 Aug 2013
TL;DR: In this paper, a novel feeding system has been designed and fabricated in order to provide an uniform and continuous flow of low bulk density biomass in a circulating fluidized bed (CFB) unit, which removes the difficulties associated with the various existing biomass feeding system such as bridge formation in the feeder and chocking.
Abstract: A novel feeding system has been designed and fabricated in order to provide an uniform and continuous flow of low bulk density biomass in a circulating fluidized bed (CFB) unit. The novel feeding system removes the difficulties associated with the various existing biomass feeding system such as bridge formation in the feeder and chocking. In the novel design, a hollow pipe with holes at its surface has been installed at the core of the hopper to provide the aeration effect. The experiments were carried out at four different inventories of 250, 500, 750 and 1000 gm and at three different sawdust particle sizes of mean diameter 732, 853 and 921 µm. Results of the experiment show that, the developed feeding system is suitable for supplying biomass without chocking to a CFB reactor to generate power for more than 5 kW-hr.