19
votes
Accepted
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 ...
- 10.4k
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 ...
- 6,544
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 ...
- 405
10
votes
Accepted
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 ...
- 6,874
9
votes
Accepted
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 ...
- 2,646
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 ...
- 633
7
votes
Accepted
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 ...
- 4,607
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!
- 14.3k
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 ...
- 11.4k
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 ...
- 15.2k
6
votes
Accepted
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 ...
- 3,597
6
votes
Accepted
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 ...
- 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 ...
- 10.4k
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 ...
- 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%...
- 7,904
5
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 ...
- 15.5k
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 ...
- 22.1k
4
votes
Accepted
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
...
- 4,772
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 ...
- 7,125
4
votes
Accepted
Third Rail vs Overhead Cable: which is more efficient in terms of electricity consumption?
Your "Bonus question" holds the answer here. Assuming that the two trains are perfectly identical, and that the power consumption is identical (which, if you have the same weight, motor, and size, it ...
- 236
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 ...
- 4,772
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, ...
- 24.3k
4
votes
Accepted
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 ...
- 24.3k
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, ...
- 22.1k
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 ...
- 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 ...
- 6,544
3
votes
Accepted
What theoretical efficiencies can wind / hydro turbines achieve?
The theoretical maximum efficiency of a wind turbine is the Betz Limit, which is $\frac{16}{27}$ ( ~ 59.3%).
The result dates back to 1919.
The Betz limit is, as you note, speed invariant. To get an ...
- 3,751
3
votes
Why are freezerless refrigerators more efficient?
Heat flux is directly proportional to gradient of temperature - in other words, if you have an imperfect insulation wall, it will pass the more heat the higher the temperature difference between its ...
- 6,125
3
votes
Accepted
Are there any methods to work out what appliances are running in my home from an aggregate power consumption sampled 6 times a minute?
The word that will unlock your searching is disaggregation - there's quite a lot of research going on right now into energy disaggregation.
These generally involve some kind of learning algorithm, ...
- 3,751
Only top scored, non community-wiki answers of a minimum length are eligible