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19 votes
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Could a mainspring be used to generate train acceleration during starting-up from the kinetic energy stored during its slowing down?

I found that on some Spanish lines, the kinetic energy during braking is converted to electricity and used by other trains from the same line (research paper), but why not keeping the mechanical ...
Transistor's user avatar
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19 votes

Can we add treadmill-like structures over the airplane surfaces to reduce friction, decrease drag and producing energy?

You can't reduce friction with machines. The nature of machines is that everything you do adds inefficiency. A moveable wing surface adds weight, complexity, and additional losses. Even if you did it ...
Tiger Guy's user avatar
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11 votes

Could a mainspring be used to generate train acceleration during starting-up from the kinetic energy stored during its slowing down?

On the London Underground, many stations use gravity. The line runs uphill into the station, and then departs downhill. This gives a large amount of energy storage, for free, with no additional moving ...
Neil_UK's user avatar
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10 votes
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Difference in energy consumption between empty fridge and fridge filled with bottles of water

The fridge works by pumping heat from its interior to its exterior. The amount of work it needs to do is proportional to the amount of heat entering the interior (and also the temperature difference ...
Dave Tweed's user avatar
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9 votes
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Is it true that four-wheel drive is less efficient and if so, why?

Simply put, power transmission is not free. Every time you have some energy over here, and you want to move it to over there, you are going to lose some of it in the process. In this case, if your ...
Daniel K's user avatar
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9 votes

Can we add treadmill-like structures over the airplane surfaces to reduce friction, decrease drag and producing energy?

Can you reduce friction by making a surface frictionless? Yes. Will that reduce drag? Most of the drag comes from lift. Without lift, the airplane falls out of the sky. Most of the rest of the drag ...
david's user avatar
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7 votes
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In a diesel engine, does more heat leave the engine through the tailpipe or the radiator?

They are very nearly equal for typical four-stroke non-turbo diesels under load. A turbo diesel under load should have slightly more radiator loss than exhaust loss. At the bottom is a link to the ...
Phil Sweet's user avatar
  • 4,755
7 votes

Could a mainspring be used to generate train acceleration during starting-up from the kinetic energy stored during its slowing down?

Note also that springs are subject to eventual (and very sudden) failure as they develop cracks with age and a very sudden 5.6MJ energy release inside a railroad car would be exceptionally dangerous!
niels nielsen's user avatar
6 votes

Difference in energy consumption between empty fridge and fridge filled with bottles of water

If you have unused space in the fridge, then it's better to fill it with something than to leave it air. This is because every time you open the door, less air will be exchanged with the room, so ...
Olin Lathrop's user avatar
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6 votes

Difference in energy consumption between empty fridge and fridge filled with bottles of water

There are two aspects to this. First if your fridge is filled with anything other than air then you will save the energy associated with cold air escaping whenever you open the door. However if you ...
Chris Johns's user avatar
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6 votes
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Refute my assumption: Bearings Don't Improve Efficiency

Your initial assumption is a bit flawed. You can not just draw the conclusion that all friction is the same. It is like saying all birds i know of can fly thus all birds can fly. Which is obviously ...
joojaa's user avatar
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6 votes
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How Much Efficiency is Lost in a Gear Train

Generally gear trains with lower ratios are more efficient due to reduced amount of sliding action between the gear teeth in mesh, so the compound gear train would probably be a better solution. That ...
jko's user avatar
  • 2,347
6 votes

Three-phase versus single-phase operation of a generator

But I'm thinking it may be better (more efficient maybe? less vibration maybe?) to run it in three-phase mode, with the load balanced among the three hot terminals. Correct. Figure 1. The load is ...
Transistor's user avatar
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6 votes

Can we add treadmill-like structures over the airplane surfaces to reduce friction, decrease drag and producing energy?

Let's be honest here... From an engineering point of view, this is totally impractical and could never work with anything like current technology. Consider that the surface of an aircraft is not a ...
rghome's user avatar
  • 161
5 votes
Accepted

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%...
ericnutsch's user avatar
  • 8,176
5 votes

Can we add treadmill-like structures over the airplane surfaces to reduce friction, decrease drag and producing energy?

Air on a wing or aileron or any airfoil does not slide on the surface of these, a very thin layer of air (boundary layer's contact surface) sticks to the surface and moves at the same speed as the ...
kamran's user avatar
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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 ...
mart's user avatar
  • 4,791
4 votes

What is the difference between Bluetooth Low Energy and Bluetooth BR/EDR in Park mode?

There are many factors that make BLE low power, and I have attempted to address as many of them as possible. In order to better understand the power consumption differences between Bluetooth classic ...
Mahendra Gunawardena's user avatar
4 votes
Accepted

Question about flow temperature and storage temperature in a cogeneration plant

when the cogeneration plant switches of upon reaching 85°C flow and without another heat source, there's no way to reach 95°C. Are you sure the switch-off happens at 85°C flow, and not at 75°C return ...
mart's user avatar
  • 4,791
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, ...
NMech's user avatar
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4 votes
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Natural ways for passively cooling/heating a home?

There are many ways that one can achieve natural cooling and heating. However, the best solutions are very dependent on the situation. Also, the problem with most of these solutions is that you'd need ...
NMech's user avatar
  • 24.4k
4 votes

More efficient to use LED lighting than to open blinds for light and thereby lose heat when very cold outside?

The reason your utility company recommends to let the sunshine in is not to save on lighting energy. it is to take advantage of solar radition energy. a window can let the solar radiation in two ways, ...
kamran's user avatar
  • 22.4k
4 votes

Could a mainspring be used to generate train acceleration during starting-up from the kinetic energy stored during its slowing down?

Mechanical energy recovery has been tried on rapid-transit systems, in the form of flywheel storage. This is known as KERS in the motorsport world, but usage on a railway requires much higher ...
jayben's user avatar
  • 451
4 votes

why can't you hybridise an internal combustion engine with a steam turbine

This is known as a combined cycle implementation. This is extremely common on gas turbine electric generator plants. The exhaust heat goes into a heat recovery steam generator, which makes steam to ...
Tiger Guy's user avatar
  • 6,901
4 votes

Why modern diesel engines have low compression ratio?

Diesel engines with turbos have a lower compression ratio. Also the compression ratio has been lowered generally to help reduce the nitrogen oxide emissions. The better fuel delivery control and spray ...
Solar Mike's user avatar
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3 votes
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Why regenerator "wheels" in a turbine engine?

The main advantage of a rotary regenerator is that you can pack a lot more surface area into a given volume than with a shell and tube type device important for gas-gas heat exchange where heat ...
Chris Johns's user avatar
  • 15.2k
3 votes

How is the energy production of solar and wind compared with the prospect of nuclear fusion?

The reality of generating electricity from nuclear fusion on an industrial scale is still a very long ways off. It is speculative high cost, high risk venture, with a potential high payoff far off ...
Brian Salvatore's user avatar
3 votes

Refute my assumption: Bearings Don't Improve Efficiency

Bearing have rolling elements specifically designed to insulate the two moving surfaces from coming into contact with each other and let the move freely (almost). There are many types of bearings, ...
kamran's user avatar
  • 22.4k
3 votes
Accepted

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 ...
Phil Sweet's user avatar
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