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Renewable Energy
Published in Chitrarekha Kabre, Synergistic Design of Sustainable Built Environments, 2020
Tides are the result of gravitational forces of the sun and the moon onto the earth’s oceans. The tidal energy has the advantage that low and high tides can be precisely calculated and predetermined, in contrast to solar and wind power, tides are entirely independent of outside influences. The technology to harness the kinetic energy of the water flow and convert into electricity includes an axial flow turbine, a cross-flow turbine, and a reciprocating device. Axial flow turbines look similar to HAWT, and cross-flow turbines are like VAWT. They can be placed on the seafloor where there is strong tidal flow. Because water is about 800 times denser than air, tidal turbines have to be much sturdier and heavier than wind turbines. Tidal turbines are more expensive to build than wind turbines but capture more energy with the same-size blades. Figure 5.27 illustrates an axial flow turbine.
Hydropower and Marine Energy
Published in Radian Belu, Fundamentals and Source Characteristics of Renewable Energy Systems, 2019
The cross-flow turbine has a drum-like rotor with a solid disk at each end and gutter-shaped “slats” joining the two disks. A jet of water enters the top of the rotor through the curved blades, emerging on the far side of the rotor by passing through the blades a second time. The shape of the blades is such that on each passage through the periphery of the rotor the water transfers some of its momentum, before falling away with little residual energy. A cross-flow turbine has a drum-like rotor and uses an elongated, rectangular-section nozzle which is directed against curved vanes on a cylindrically shaped runner. Cross-flow turbines are less efficient than the modern-day turbines, but can accommodate larger water flows and lower heads. A jet of water enters the turbine, thus gets directed through the guide-vanes at a transition piece upstream on the runner which is built from two or more parallel disks connected near their rims by a series of curved blades. The flow is directed to a limited portion of the runner by the guide vane at the entrance to the turbine. The turbine allows water to flow twice through the blades. In the first stage, water flows from the outside of the blades to the inside; in the second stage, the water passes from the inside back out. The flow leaves the first stage attempts to cross the open center of the turbine but as the flow enters the second stage, a compromise direction is achieved which causes significant shock losses.
Power and Energy Directly from Water
Published in Yatish T. Shah, Water for Energy and Fuel Production, 2014
These are designed for use in river and ocean currents with a horizontal-axis turbine in which a vertically submerged blade has performance characteristics similar to a horizontally mounted cross-flow turbine [52]. The turbine blades are concave such that the leading edge offers reduced resistance while the trailing edge is aerodynamically optimized to reduce the flat dynamic effect. The rotational speed of turbine is low. Since hydrokinetic power is proportional to the cube of velocity, turbine blade can be designed to accommodate flow rate; it could be long and broad for slow-moving deep currents or it could be short and thin for fast-moving shallow currents.
Numerical investigations on performance improvement of cross flow hydro turbine having guide vane mechanism
Published in Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 2022
Gaurav Saini, R. P. Saini, S. K. Singal
The simplicity in construction, low investment, and maintenance leads to develop an efficient cross-flow turbine. The poor performance of turbine under off-design conditions discourages its usage for micro-hydro power sites. Based on the literature studies, laboratory testing, and field installations, it has been experienced that the water flow within the rotor is the cause of lower efficiency. By keeping in view, the present study is carried out to develop an efficient and simple mechanism to direct the unguided flow inside the runner cavity (open space between the two runner stages) of CFT. Two (symmetrical and unsymmetrical) types of guide vanes were analyzed computationally and the results of the present study have been validated with experiments in the laboratory. To obtain the better performance of turbine, best positions and placement angles of different guide vanes were analyzed. In order to operate the turbine under part load, overload, and design load conditions, five variable discharge conditions were simulated. Based on the extensive experimental and numerical investigations, the following key conclusions have been obtained: The optimum guide vane placement inside the runner cavity directs the water and creates a defined path for smooth entry of water in the second stage of blades with less turbulence and vortices.The performance of the cross-flow turbine with guide vane was compared with the turbine having no guide vane under similar operating conditions.CFT with symmetrical and unsymmetrical guide vane yields the maximum efficiency at 55° and 45° placement angle, respectively, for all positions of guide vane. Further, the right position of guide vane (symmetrical and unsymmetrical) creates a smooth flow with less turbulence in water flow and hence better performance under similar operating conditions.The right position of unsymmetrical guide vane yields a maximum efficiency of 79.9% under design discharge conditions.Cross-flow turbine experiences a maximum enhancement in turbine efficiency as 5.2% for right position of unsymmetrical guide vane under 50% discharge conditions.