Improving the Energy Conversion Efficiency of a Savonius Rotor Using Automatic Valves

2019 ◽  
Vol 141 (3) ◽  
Author(s):  
M. Amiri ◽  
M. Anbarsooz
Keyword(s):  
Low Power ◽  
Energy Conversion ◽  
Conversion Efficiency ◽  
Energy Conversion Efficiency ◽  
Maximum Power ◽  
Power Coefficient ◽  
Speed Ratio ◽  
Tip Speed Ratio ◽  
Savonius Rotor ◽  
Rotor Axis

Savonius wind turbines are popular for their easy fabrication and high starting capabilities. Nevertheless, they suffer from low power coefficients, which are mainly due to a negative torque resulting from the blade moving against the upcoming wind. Numerous methods have been proposed to alleviate the negative torque, among them are modified blade profiles (twisted blades), adding flow deflectors, and valve-aided blades. In this study, the effects of adding automatic valves to a two-bladed Savonius rotor on its energy conversion efficiency are investigated numerically and experimentally. The valves are placed at three different positions: close to the rotor axis, at the blade center, and at the tip of the rotor. Results show that although adding valves can decrease the negative torque of the returning blade, they can also lead to a considerable reduction in the positive torque of the advancing blade. For the rotors in the current study, the maximum power coefficient is increased 20.8% when the valves are at the tip of the blades, while the two other cases have decreased the power coefficient of the rotor. Adding the valves to the blades does not change the tip speed ratio corresponding to the maximum power coefficient of the rotor.

scholarly journals Performance Analysis of a Helical Savonius Rotor with Shaft at 45° Twist Angle Using CFD

2013 ◽  
Vol 3 (1) ◽  
pp. 118 ◽  
Author(s):  
Rajat Gupta ◽  
Bachu Deb ◽  
R. D. Misra
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Twist Angle ◽  
Maximum Power ◽  
Power Coefficient ◽  
Speed Ratio ◽  
Complete Cycle ◽  
Tip Speed Ratio ◽  
Savonius Rotor ◽  
Rotor Angle

Helical Savonius rotor is considered to be superior to conventional Savonius rotor in terms of higher power coefficient (Cp) and better starting characteristic. However studies related to helical Savonius rotors is few. In view of this, in this paper, the performance of a helical Savonius rotor with shaft at 45° bucket twist angle for one complete cycle of rotation was analyzed using Computational Fluid Dynamics. A two-bucket helical Savonius rotor with shaft was designed using GAMBIT, having a height of 60 cm and diameter of 17 cm with 45° bucket twist angle. A three dimensional Computational Fluid Dynamics analysis using Fluent package was done to predict the performance of the rotor. Standard k-? turbulence model with second order upwind discretization scheme and standard wall condition was used. Grid independence test was also conducted to have the best meshing accuracy. Power coefficients (Cp) of the rotor at different tip speed ratios were evaluated for rotor angle variation from 0° to 180°. Cp at each rotor angle increased with increase of tip speed ratio up to an optimum tip speed ratio, but then decreased even if tip speed ratio was further increased. Moreover, the effect of rotor angle on Cp in a complete cycle of rotation was analyzed. Cp was found to be positive at all rotor angles, and higher values of Cp were obtained at rotor angles namely 45°, 90°, 225° and 270°, which would contribute maximum power production by the rotor. In addition to these, flow physics of the rotor was studied using tangential velocity plots w.r.t. rotor angle and path lines across the rotor. It was found that at 45°, 90° and 135° rotor angles, maximum concentration of the path lines near the tip of the blades in the upstream and downstream side of the rotor had occurred, which would be responsible for generation of maximum power coefficient in its clockwise rotation.

Performance of Double Blade Savonius Rotor at Low Rotational Speed

2020 ◽  
Vol 17 (2) ◽  
pp. 729-735 ◽  
Author(s):  
Mohanad Al-Ghriybah ◽  
Mohd Fadhli Zulkafli ◽  
Djamal Hissein Didane ◽  
Sofian Mohd
Keyword(s):  
Turbulence Model ◽  
Rotational Speed ◽  
Maximum Power ◽  
Power Coefficient ◽  
Speed Ratio ◽  
Tip Speed Ratio ◽  
Savonius Rotor ◽  
Maximum Improvement ◽  
Torque Coefficient ◽  
Better Than

The performance of the single and double blade Savonius rotors are numerically analyzed using the K-ε/realizable turbulence model. The computations are implemented at different values of tipspeed ratio from 0.2 to 0.4 with a step of 0.05. Both rotors have the same dimensions with an external overlap between their blades equals 0.02 m. The results indicate that the double blade rotor performs better than the single blade rotor in terms of power coefficient. In addition, the torque coefficient is improved at all tested values of tip-speed ratio. Furthermore, the results of the simulation show that the maximum power coefficient was 0.163 at tip-speed ratio = 0.4 for the double blade rotor, whereas the maximum improvement of the double blade rotor occurs at tipspeed ratio = 0.2 with a percentage of 11.86% compared to the single blade rotor. Moreover, the highest value of the torque coefficient was 0.524 at tip-speed ratio = 0.2 for the double blade rotor.

Numerical Modeling of Vertical Axis Wind Turbines

2014 ◽  
Author(s):  
Teresa Parra-Santos ◽  
Armando Gallegos-Muñoz ◽  
Miguel A. Rodriguez-Beneite ◽  
Cristobal Uzarraga-Rodriguez ◽  
Francisco Castro-Ruiz
Keyword(s):  
Mechanical Energy ◽  
Vertical Axis ◽  
The Self ◽  
Power Coefficient ◽  
Speed Ratio ◽  
Vertical Axis Wind Turbine ◽  
Tip Speed Ratio ◽  
Vertical Axis Wind Turbines ◽  
Selection Of ◽  
Rotor Axis

This paper aims to predict the performance of Vertical Axis Wind Turbine (VAWT), hence the modeling of kinetic energy extraction from wind and its conversion to mechanical energy at the rotor axis, is carried out. The H-type Darrieus turbine consists of three straight blades with shape of aerofoil attached to a rotating vertical shaft. The criterion on the selection of this kind of turbines, despite its reduced efficiency, is the easy manufacture in workshops. A parametric study has been carried out to analyze the camber effect on the non dimensional curves of power coefficient so that the self starting features as well as the range of tip speed ratio of operation could be predicted.

Study on Performance and Flow Condition of a Cross-Flow Wind Turbine With a Symmetrical Casing

2011 ◽  
Vol 133 (5) ◽  
Author(s):  
Junichiro Fukutomi ◽  
Toru Shigemitsu ◽  
Hiroki Daito
Keyword(s):  
Wind Turbine ◽  
Rotational Speed ◽  
Flow Condition ◽  
Cross Flow ◽  
Low Noise ◽  
Maximum Power ◽  
Power Coefficient ◽  
Speed Ratio ◽  
Tip Speed Ratio ◽  
The Cross

A cross-flow wind turbine has a high torque coefficient at a low tip speed ratio. Therefore, it is a good candidate for use as a self-starting turbine. Furthermore, it has low noise and excellent stability; therefore, it has attracted attention from the viewpoint of applications as a small wind turbine for an urban district. However, its maximum power coefficient is extremely low (10%) as compared to that of other small wind turbines. Prevailing winds in two directions often blow in urban and coastal regions. Therefore, in order to improve the performance and the flow condition of the cross-flow rotor, a casing suitable for this sort of prevailing wind conditions is designed in this research and the effect of the casing is investigated by experimental and numerical analysis. In the experiment, a wind tunnel with a square discharge is used and main flow velocity is set as 20 m/s. A torque meter, a rotational speed pickup, and a motor are assembled with the same axis as the test wind turbine and the tip speed ratio is changeable by a rotational speed controller. The casing is set around the cross-flow rotor and flow distribution at the rotor inlet and the outlet is measured by a one-hole pitot tube. The maximum power coefficient is obtained as Cpmax = 0.19 with the casing, however Cpmax = 0.098 without the casing. It is clear that the inlet and the outlet flow condition is improved by the casing. In the present paper, in order to improve the performance of a cross-flow wind turbine, a symmetrical casing suitable for prevailing winds in two directions is proposed. Then, the performance and the internal flow condition of the cross-flow wind turbine with the casing are clarified. Furthermore, the influence of the symmetrical casing on performance is discussed and the relation between the flow condition and performance is considered.

Finite Time Thermodynamics: Realizability Domain of Heat to Work Converters

2019 ◽  
Vol 44 (2) ◽  
pp. 181-191 ◽  
Author(s):  
M. A. Zaeva ◽  
A. M. Tsirlin ◽  
O. V. Didina
Keyword(s):  
Heat Transfer ◽  
Heat Exchange ◽  
Energy Conversion ◽  
Conversion Efficiency ◽  
Finite Time ◽  
Heat Engine ◽  
Energy Conversion Efficiency ◽  
Maximum Power ◽  
Working Fluid ◽  
Finite Time Thermodynamics

Abstract From the point of view of finite time thermodynamics, the performance boundaries of thermal machines are considered, taking into account the irreversibility of the heat exchange processes of the working fluid with hot and cold sources. It is shown how the kinetics of heat exchange affects the shape of the optimal cycle of a heat engine and its performance, with a focus on the energy conversion efficiency in the maximum power mode. This energy conversion efficiency can depend only on the ratio of the heat transfer coefficients to the sources or not depend on them at all. A class of kinetic functions corresponding to “natural” requirements is introduced and it is shown that for any kinetics from this class the optimal cycle consists of two isotherms and two adiabats, not only for the maximum power problem, but also for the problem of maximum energy conversion efficiency at a given power. Examples are given for calculating the parameters of the optimal cycle for the case when the heat transfer coefficient to the cold source is arbitrarily large and for kinetics in the form of a Fourier law.

scholarly journals A Variable Fractional Order Fuzzy Logic Control Based MPPT Technique for Improving Energy Conversion Efficiency of Thermoelectric Power Generator

Energies ◽  
2020 ◽  
Vol 13 (17) ◽  
pp. 4531
Author(s):  
N. Kanagaraj ◽  
Hegazy Rezk ◽  
Mohamed R. Gomaa
Keyword(s):  
Fuzzy Logic ◽  
Steady State ◽  
Energy Conversion ◽  
Fractional Order ◽  
Conversion Efficiency ◽  
Fuzzy Logic Controller ◽  
Energy Conversion Efficiency ◽  
Maximum Power ◽  
Maximum Power Point ◽  
Power Point

Thermoelectric generation technology is considered to be one of the viable methods to convert waste heat energy directly into electricity. The utilization of this technology has been impeded due to low energy conversion efficiency. This paper aims to improve the energy conversion efficiency of the thermoelectric generator (TEG) model with a novel maximum power point tracking (MPPT) technique. A variable fractional order fuzzy logic controller (VFOFLC)-based MPPT technique is proposed in the present work in which the operating point of the TEG is moved quickly towards an optimal position to increase the energy harvesting. The fraction order term α, introduced in the MPPT algorithm, will expand or contract the input domain of the fuzzy logic controller (FLC to shorten the tracking time and maintain a steady-state output around the maximum power point (MPP). The performance of the proposed MPPT technique was verified with the TEG model by simulation using MATLAB /SIMULINK software. Then, the overall performance of the VFOFLC-based MPPT technique was analyzed and compared with Perturb and observe (P&O) and incremental resistance (INR)-based MPPT techniques. The obtained results confirm that the proposed MPPT technique can improve the energy conversion efficiency of the TEG by harvesting the maximum power within a shorter time and maintaining a steady-state output when compared to other techniques.

scholarly journals On the Impact of the Dynamics of Heat Transfer of the Thermal Machine Working Fluid and Heat Sources on the Shape of the Boundary of the Set of Realizable Regimes

2019 ◽  
Vol 3 (2) ◽  
pp. 36
Author(s):  
Margarita Zaeva ◽  
Anatoly Tsirlin ◽  
Olga Didina
Keyword(s):  
Heat Transfer ◽  
Heat Exchange ◽  
Energy Conversion ◽  
Conversion Efficiency ◽  
Heat Engine ◽  
Energy Conversion Efficiency ◽  
Maximum Power ◽  
Working Fluid ◽  
Transfer Coefficients ◽  
The Impact

From the point of view of finite time thermodynamics, the performance boundaries of thermal machines are considered, taking into account the irreversibility of the heat exchange processes of the working fluid with hot and cold sources. We show how the dynamics of heat exchange affects the shape of the optimal cycle of a heat engine and its performance, in particular, energy conversion efficiency in the maximum power mode. This energy conversion efficiency can depend only on the ratio of the heat transfer coefficients to the sources, or not depend on them at all. A class of dynamic functions corresponding to “natural” requirements is introduced and it is shown that, for any dynamics from this class, the optimal cycle consists of two isotherms and two adiabats, not only for the maximum power problem, but also for the problem of maximum energy conversion efficiency at a given power. Examples are given for calculating the parameters of the optimal cycle for the cases when the heat transfer coefficient to the cold source is arbitrarily large, and for dynamics in the form of a linear phenomenological (Fourier heat transfer) law.

Numerical Simulation on 2D Savonius Rotor in Ground Effect

2014 ◽  
Vol 953-954 ◽  
pp. 424-427
Author(s):  
Jian Yong Zhu ◽  
Kai Wang ◽  
Hai Bin Ruan
Keyword(s):  
Numerical Simulation ◽  
Power Output ◽  
Ground Effect ◽  
Aerodynamic Performance ◽  
Power Coefficient ◽  
Speed Ratio ◽  
Tip Speed Ratio ◽  
Savonius Rotor ◽  
Calculation Results ◽  
Torque Values

The Aerodynamic Performance of 2D Savonius Rotor in Ground Effect is Numerically Simulated through Solving Unsteady Compressible RANS Equations and the Standard k-ε Turbulence Model. the Calculation Results Indicate that the Ground Effect Influences the Starting Performance and the Power Output. the Optimal Height between the Ground to the Lowest Part of the Rotor is 0.4 Times Rotation Diameter, at which the Starting Performance is Optimal. the Ground Effect also Increases the Power Coefficient and the Tip Speed Ratio Corresponding to the Maximum Power Coefficient. when Determining the Rated Tip Speed Ratio, the Fluctuation of the Torque Values and the Power Coefficient with Different Tip Speed Ratio should be Synthesized.

scholarly journals PERFORMANCE ANALYSIS OF A HELICAL SAVONIUS ROTOR WITHOUT SHAFT AT 45° TWIST ANGLE USING CFD

2013 ◽  
pp. 126-133 ◽  
Author(s):  
Bachu Deb ◽  
Rajat Gupta ◽  
R.D. Misra
Keyword(s):  
Twist Angle ◽  
Three Dimensional ◽  
Power Coefficient ◽  
Speed Ratio ◽  
Complete Cycle ◽  
Tip Speed Ratio ◽  
Savonius Rotor ◽  
Velocity Magnitude ◽  
Computational Fluid Dynamics Analysis ◽  
Upwind Discretization

Helical Savonius rotor exhibits better performance characteristics at all the rotor angles compared to conventional Savonius rotor. However studies related to the performance measurement and flow physics of such rotor are very scarce. Keeping this in view, in this paper, a three dimensional Computational Fluid Dynamics analysis using commercial Fluent 6.2 software was done to predict the performance of a two-bucket helical Savonius rotor without shaft and with end plates in a complete cycle of rotation. A two-bucket helical Savonius rotor having height of 60 cm and diameter of 17 cm with 45° bucket twist angle was designed using Gambit. The buckets were connected at the top and bottom circular end plates, which are 1.1 times the rotor diameter. The k-ε turbulence model with second order upwind discretization scheme was adopted with standard wall condition. Power coefficients (Cp) and torque coefficients (Ct) at different tip speed ratios were evaluated at different rotor angles. From the investigation, it was observed that power coefficient increased with increase of tip speed ratio up to an optimum limit, but then decreased even further tip speed ratio was increased. Further investigation was done on the variations of Cp & Ct in a complete cycle of rotation from 0° to 360° in a step of 45° rotor corresponding to the optimum tip speed ratio. The value of Cp at all the rotor angles is positive. Moreover, velocity magnitude contours were analyzed for each rotor angle and it could be concluded that high aerodynamic torque and power can be expected when the rotor is positioned at 45º & 90º with respect to incoming flow.

A ruthenium complex as a single-component redox shuttle for electrochemical photovoltaics

2015 ◽  
Vol 51 (36) ◽  
pp. 7745-7748 ◽  
Author(s):  
Jeung Yoon Kim ◽  
Won Seok Yun ◽  
Ho-Jin Son ◽  
JaeDong Lee ◽  
Nak Cheon Jeong
Keyword(s):  
Low Power ◽  
Energy Conversion ◽  
Conversion Efficiency ◽  
Ruthenium Complex ◽  
Energy Conversion Efficiency ◽  
Illumination Level ◽  
Single Component ◽  
Large Enhancement ◽  
Redox Shuttle

A new conceptual “single-component redox shuttle” led to a large enhancement of VOC (∼940 mV) and also greatly boosted the energy conversion efficiency under low-power illumination level by a factor of ca. 5.6.

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