31 votes

Why don't hydroelectric plants use cascades of turbines instead of single turbines?

The exhaust gasses are compressible fluids, whereas liquid water is not. Here's an animation of how a gas turbine works: https://www.youtube.com/watch?v=gqNtoy2x5bU At the combustion stage, the gas ...
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  • 5,940
19 votes

Why do hydroelectric plants use turbines instead of an efficient 'water wheel' configuration?

Actually the turbine method is very efficient. The Turgo turbine is up to 90% efficient at extracting the energy from the water. Large-scale hydro plants using Francis Turbines can be as high as 95% ...
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  • 5,940
14 votes

Why do hydroelectric plants use turbines instead of an efficient 'water wheel' configuration?

There are two different ways for the water flow to transmit energy. One is the pressure difference between the water entering and leaving the turbine. The other the kinetic energy change of fast ...
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12 votes
Accepted

Why is using steam to rotate a turbine more efficient?

The main reason is that a turbine requires a pressure drop to extract energy from the working fluid. The drop in temperature that is observed in a turbine is a result of the expansion of the fluid; ...
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  • 2,989
7 votes

What is a tesla turbine and how is it different from other turbines(like pelton or francis turbine)?

While "conventional turbines operate by imparting impulse or reaction energy from an incoming fluid using "buckets" or spiral surfaces on the turbine "runner", a "Tesla ...
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6 votes

efficiency and flow separation

You are describing a very interesting engineering problem. The requirement of a turbine is to convert fluid-energy into mechanical energy over a range conditions. Since the flow around the airfoils ...
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  • 1,202
6 votes

Why don't hydroelectric plants use cascades of turbines instead of single turbines?

What's missing so far is an explanation why you can't expand from high pressure to atmospheric in a single stage gas turbine. There are two types of gas turbines - impulse and reaction turbines. Both ...
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  • 1,600
5 votes

To what degree are wind and water turbines exchangeable?

Given that water is roughly 1000× as dense as air, and incompressible besides, it should be fairly obvious: A wind turbine would be destroyed by the forces that water would put on it, and a ...
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  • 6,759
5 votes

What is the Boussinesq approach?

To take into account the effect of turbulent fluctuations on a flow field, the Navier-Stokes equations are modified to include such effects. The obtained equations are called Reynolds-averaged Navier-...
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  • 2,149
5 votes
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What prevents the use of electric engines to assist with spacecraft launches? (Space Shuttle Booster Supplement)

Electric turbine engines First off, "electric turbine engines" don't really exist. What you're probably thinking of is an electric version of the jet turbine engine, which is a type of ...
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5 votes
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What is the theoretical maximum energy efficiency of hydro turbines?

Something can only be 100% efficient when a lot of generous assumptions are taken into account. If you assume: No friction (turbine surface, turbulence, nozzle, or bearings) Perfect cup design (100%...
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  • 7,489
4 votes

Fan Sensors (Tachometer vs Locked Rotor)

It's a trade-off between the simplicity of the sensor and how comprehensive the reported data is. The locked rotor sensor only reports whether or not the motor is spinning, not how fast it's spinning ...
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  • 2,989
4 votes

Why is using steam to rotate a turbine more efficient?

Heating water to make steam is not necessarily more efficient, but a lot more practical. What you describe is how internal combustion engines work, for example, so it's a valid concept. However, ...
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4 votes

Question about bounday layer thickness?

The greater the length of the flat plate, the more contact area there is with the fluid. Consequently, the fluid near the start of the plate has had less viscous friction forces acting on it than the ...
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  • 2,579
4 votes

Why is more steam required to turn a steam turbine when electric power consumption is higher

Because you can't get something for nothing? If the generator is generating more electrical power then that energy has to come from somewhere. The more power you try to pull from a generator the ...
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  • 766
4 votes
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Can combined cycle turbines be small enough for trains?

We can try to answer this question by looking at existing equipment in terms of size and weight and make an educated guess from there if all this fits on a train. Our CC will consist of: Gas turbine ...
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  • 4,653
4 votes

Practicality of energy recovery from HVAC systems?

So, if I understand correctly you are proposing to use a turbine in the exhaust vents in order to reclaim the energy from the flowing air. However, in most cases the air is flowing due to forced flow, ...
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3 votes
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Why does my model of a wind turbine show high RPM with low power output?

I don't think you really designed a 1300 W wind turbine. You assumed your generator would be able to produce the necessary current but to be able to produce 1300 W you have to build a wind turbine big ...
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  • 181
3 votes

Why is using steam to rotate a turbine more efficient?

You are almost describing a gas turbine engine. These are used to generate electrical power, and also to power aircraft. But, in a gas turbine the output of the combustor is at high pressure, and ...
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  • 247
3 votes

Identifying category of wind turbine

The design looks like a Savonius turbine, but horizontally mounted, instead of the typical vertical mounting that you see with this design. I'm really not sure why this would be mounted this way ...
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3 votes

Is the concept IC Engine a viable concept?

Reading through the site I would say no. Using the exhaust gas as input for the turbine will have horrible efficiencies for powering everything he listed. Also, on the "How turbochargers work" page he ...
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3 votes

Why don't hydroelectric plants use cascades of turbines instead of single turbines?

The reason why a hydroelectric generator is fundamentally different to a gas turbine is because water under pressure is not a gas, and does not change size significantly as energy is extracted from it....
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3 votes

Why don't hydroelectric plants use cascades of turbines instead of single turbines?

Water turbines are a major source of electric power. A water turbine generally has only one rotor disk. (from Old Moonraker at Wikipedia) Gas turbines are used in natural gas electric power ...
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3 votes

Why don't hydroelectric plants use cascades of turbines instead of single turbines?

Water is going to have to leave the turbine at a speed. That what you've referred to as its residual mechanical power. The thing is, the turbine has already slowed down the water as much as can ...
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  • 3,701
3 votes

Why not design a Wind Turbine like an Anemometer?

Because the back of the cups create a lot of drag thereby reducing the power produced. The blade profile used in classic 3-bladed HAWTs is also used in VAWTs and they look like "egg beaters" needing ...
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3 votes

Why not design a Wind Turbine like an Anemometer?

One other reason is that the propeller-type turbine allows it to be rotated to avoid damage in high winds. When the air is flowing transverse to the axis of the propeller it encounters relatively ...
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3 votes

When were airfoil cross-sections first used in turbine blades?

Good description in the link, but curved surfaces were in use as sails around 800 years ago and Bernoulli came up with his formula , Ludwig Prandtl was testing sections in 1017 in his large wind ...
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3 votes

Generating practical power without an iron core, but with high RPM

the iron structure(s) inside a generator serve the purpose of minimizing flux leakage, which maximizes the utilization of the magnetic field in generating electricity. One of the ways in which they ...
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3 votes

What determines the cost of the wind turbines?

Where does the power for a wind turbine come from? Answer - the wind. So how do you get 15kW from the wind rather than 11kW? Answer - you either need a location with a higher wind speed, or you need ...
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  • 3,135
3 votes
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Do 3 blade wind turbines generate more power than a 9 blade, all else being equal?

Because in the real world, all else is never equal, but let's start there analytically. What does "all else being equal" actually mean? With respect to a flat swept disk perpendicular to an ideal ...
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