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The energy efficiency of the water turbine is higher than that of the wind turbine
Author: source: date: 2019-02-23 14:21:56
The water turbine's energy efficiency is as high as 80% to more than 90%，but the best wind turbine energy efficiency is only 40 points. They are all fluids, the principle is the same, but the effect is so much worse.
First of all, we need to be clear about what the efficiency definitions of these two machines are:
Wind turbine efficiency: Refers to the ability of the impeller to capture the kinetic energy of free flow, without mechanical and power electronic systems efficiency. The upper limit of this efficiency (~0.59) is determined by Betz
theory, the optimal cp of modern wind turbines can reach ~0.50.
The efficiency of the turbine unit, Is the ratio of the total energy that can be captured in the kinetic energy + potential energy of a high water level flow, Not the kinetic energy capture efficiency of the turbine impeller system
alone for free flow (The impeller of the turbine is operated in a closed system, and the flow energy conversion efficiency is not bound by Betz theory). In fact, the energy in the high-water flow accounts for a large part of the
energy. After the water flows through the turbine, the speed and kinetic energy do not change significantly. The main potential energy has been transformed, so it is so efficient.
The density of water and the energy density it brings are helpful. Wind turbines and hydro turbines are direct conversion of mechanical energy to mechanical energy at the front end of the power generation. High density fluids
push heavy machinery more efficiently: The machine itself can be made smaller. The fluid itself is sticky, Small contact area reduces friction loss; Large-scale fan blades have significant aerodynamic drag such as tip-induced
resistance; The friction loss of the machine itself accounts for a smaller proportion of the captured energy.
The density of water is large, and the air density and water are three orders of magnitude different; The upstream of the turbine is the high water level of the dam, Water has a lot of potential energy that can be used to
convert; The wind turbine is facing free flow, what needs to be captured is the kinetic energy of the air. Due to the density gap, this energy gap is very large, wind energy can be said to be relatively thin. The most important is,
the impeller of the turbine runs in a closed system, can maintain the pressure of the incoming flow, but the blades of the wind turbine operate in an open system.
l In conclusion, that’s why The energy efficiency of the turbine is higher than that of the wind turbine.