Shireesh B. Kedare

Experimental Investigations on the Effect of Overlap Ratio and Blade Edge Conditions on the Performance of Conventional Savonius Rotor

The torque of a conventional Savonius rotor is studied experimentally for overlap ratio from 0.10 to 0.70, blade edge condition (flat and round) and the change in Reynolds number. The results indicate that the coefficient of static torque improves marginally for round edged rotors for rotor angles up to 45°. The coefficient of static torque decreases as the overlap ratio is increased to 0.70 from 0.50 and is independent of the Reynolds numbers studied in the range between 120000 to 200000. Wind tunnel blockage ratio is studied. The power coefficient increases with the increase in the Reynolds number, whereas the coefficient of static torque is independent of the Reynolds number in the range studied. The coefficient of power, torque coefficient and coefficient static torque are independent of blockage ratios at a given Reynolds number.

Model Testing of Single- and Three-Stage Modified Savonius Rotors and Viability Study of Modified Savonius Pump Rotor Systems

The suitability of modified Savonius wind rotors for water-pumping application is studied with a mathematical model developed for estimating the discharge over a period of time. Single- and three-stage modified Savonius rotors, which are extensively tested in an open jet wind tunnel, are chosen. The best geometrical configuration for a single-stage rotor has shown a maximum coefficient of power of 19% at a Reynolds number of 120000, which increases with the increase in the Reynolds number. The coefficient of power at a higher Reynolds number experienced in the field trials is estimated by extrapolating the results at a lower Reynolds number. The discharge for these modified Savonius rotors is estimated from the mathematical models developed for roto-dynamic and piston pumps at design wind velocities of 6 and 8.5 m/sec. The estimated discharges for a single-stage rotor of 3 m diameter at design wind velocities of 6 and 8.5 m/sec are 5000 and 6000 m3/month for roto-dynamic pumps. The estimated discharge is substantially higher for roto-dynamic pumps than for piston pumps.

High-Temperature Receiver Designs for Supercritical CO2 Closed-Loop Brayton Cycles

High-temperature receiver designs for solar powered supercritical CO2 Brayton cycles that can produce ∼1 MW of electricity are being investigated. Advantages of a supercritical CO2 closed-loop Brayton cycle with recuperation include high efficiency (∼50%) and a small footprint relative to equivalent systems employing steam Rankine power cycles. Heating for the supercritical CO2 system occurs in a high-temperature solar receiver that can produce temperatures of at least 700 °C. Depending on whether the CO2 is heated directly or indirectly, the receiver may need to withstand pressures up to 20 MPa (200 bar). This paper reviews several high-temperature receiver designs that have been investigated as part of the SERIIUS program. Designs for direct heating of CO2 include volumetric receivers and tubular receivers, while designs for indirect heating include volumetric air receivers, molten-salt and liquid-metal tubular receivers, and falling particle receivers. Indirect receiver designs also allow storage of thermal energy for dispatchable electricity generation. Advantages and disadvantages of alternative designs are presented. Current results show that the most viable options include tubular receiver designs for direct and indirect heating of CO2 and falling particle receiver designs for indirect heating and storage.Copyright

Physical design space for isolated wind-battery system incorporating resource uncertainty

The physical design space of a wind-battery system enables a system designer to understand the trade-offs between different system design variables, the physical limits of the major decision variables, and arrive at an optimum solution subject to an appropriate design objective. An improved methodology for design of isolated wind-battery systems by accounting for the uncertainty associated with wind speed is proposed in this article. Chance-constraint programming technique is used to incorporate resource uncertainty in system sizing; thereby, facilitating system design corresponding to a specified reliability requirement. It is found that the cut-in speed of the wind turbine plays a critical role in delivering desired power supply reliability. A feasible design solution is obtained only when the probabilities associated with the cut-in and the cut-off wind speeds are accounted for along with the specified system reliability requirement. All feasible combination of system variables generated through a time-series simulation are represented on a rotor diameter versus generator rating diagram with minimum battery bank size as parameter. Solutions obtained by the proposed method are validated by sequential Monte Carlo simulations. Optimum system configuration for a given reliability requirement is determined based on minimum cost of energy (US

Review on Savonius Rotor for Harnessing Wind Energy

/kWh). It is shown that wind-battery systems cannot be designed to provide power supply reliability beyond a maximum value.

Investigations on Performance of Stirling Engine Regenerator Matrix

Wind machines convert kinetic energy of the wind into usable form of mechanical energy or electrical energy. The Savonius rotor is a vertical axis wind machine which is simple in design. High starting torque characteristics make it suitable for standalone power generation as well as water pumping applications. This paper reviews the literature on the performance characteristics of the Savonius rotor. Multi-bladed rotor, multistage rotor, shape of the blade, use of deflecting plate, guide vanes and nozzle augmentation are several ways to enhance the performance characteristics. This review would help an engineer in building an improved Savonius rotor for a given application.

Performance characteristics of a reciprocating wind machine

Stirling engine technology has attracted attention due to recent environmental and energy problems. The regenerator is the main component in high efficiency Stirling engines. A suitable regenerator must be designed for each Stirling machine to provide high performance. The aim of the present work is to find a feasible number of screens in regenerator by taking into account the pressure drop, dead volume, the thermal penetration depth and geometry of regenerator. The second order cyclic analysis with realistic assumptions is carried out for a single cylinder, beta Stirling engine with rhombic drive for predecided operating conditions, such as pressure of 30 bar, hot side temperature of 750 K, speed of 1440 rpm and hydrogen as the working fluid. It is intended to design and develop the Stirling engine with capacity ≥ 1.5 kWe and the efficiency of drive mechanism and alternator is assumed as 85% each. Miyabe’s and Martini’s approaches are used to simulate regenerator performance considering non-sinusoidal motion of displacer and piston. The results reveal that the flow loss increases remarkably to attain higher value of regenerator effectiveness. However, increase in the speed results into an increase in the mass flow rate of the working fluid. It is observed that regenerator effectiveness decreases only marginally over the range of speeds considered. It is also ensured for selected regenerator screen that the thermal penetration depth (239 μm) should be greater than wire radius of mesh (20.5 μm). For present set of operating and geometrical parameters, length of regenerator is fixed as 22 mm which gives regenerator effectiveness as 0.965. Further, the practice to fill more screens than the designed number of screens in the regenerator, while assembling is not advantageous. It increases pressure drop which results in reduced power output. These are some of the important conclusions.Copyright

Numerical investigations on the Dish–Stirling engine system

Abstract This paper presents theoretically determined C P − λ characteristics of a wind machine which produces slow reciprocations in a vertical plane. The characteristics are derived by developing and solving the equation of motion of the wind machine under steady wind, and it is shown that they are governed by eight dimensionless parameters. Comparisons with earlier investigations are reported, and, based on the numerical analysis, suggestions for improving the performance of the wind machine are made. Finally, the wind machine is shown to be particularly suitable for adaptation to bore wells fitted with reciprocating pumps, where water must be pumped from depths in excess of 30 m and where a multiblade horizontal-axis wind machine cannot be used because of the starting torque constraint.

Experimental Investigations on Two and Three Stage Modified Savonius Rotor

ABSTRACT The Stirling engine is an environmentally friendly external combustion heat engine and reduces the complexities of the combustion process, and indirectly helps in reduction of CO2 emission. Modelling based on cyclic analysis is performed for a Beta configuration Stirling engine of 1.5 kWe capacity using a rhombic drive for the solar-dish-supported Stirling engine. The analysis helps in estimating the overall efficiency of the system using the experimental correlation of the solar concentrator ARUN160 at the engine operating temperature. The analysis shows that the system will have overall efficiency around 25% in the range of 750–1050 K at the expansion space. The degradation of performance compared to that at an operating temperature of 1025 K is only marginal and makes 750 K a more preferred temperature. The present study evaluates a range of possible design goals and provides suitable alternatives and thus provides a clear understanding of the system design considerations.

On the Existence of Non-Convexities in the Design Space of Isolated Wind-Battery Systems

Single stage modified Savonius rotor (without shaft) is having higher coefficient of power (0.21) compared to single stage conventional Savonius rotor (0.17). Coefficient of static torque is negative for a 1/6th of a cycle from rotor angle 135° to 165° and from 315° to 345°. There is a large variation in the coefficient of static torque in a cycle of 180° from a peak of 0.44 at 30° to a lowest value of −0.21 at 165°. Multi-staging provides positive coefficient of static torque at all rotor angles and reduces large variations in a cycle. Wind tunnel tests were conducted to assess the aerodynamic performance of two and three stage modified Savonius rotors without shaft in between the end plates at different rotor aspect ratios and stage aspect ratios. The coefficient of static torque variations decrease with the increase in the number of stages. However, the coefficient of power decreases with the increase in the number of stages. The effect of intermediate plates on the performance of rotors is also studied. Correlations are developed for all the modified Savonius rotors tested for a range of Reynolds numbers.