38
votes
Accepted
Why does it take so long to restart a nuclear power plant?
When a reactor is shut down the core produces much less heat, but they do still produce heat through a mechanism known as decay heat. The fact that the core is producing less heat means that the ...
- 3,575
36
votes
Accepted
How does turning off electric appliances save energy
Electricity production optimization is a very complex subject. It is also affected by many parameters , which I will try to outline below.
TL;DR: Demand is constantly monitored and supply is ...
- 24.3k
20
votes
How does turning off electric appliances save energy
Timescales on the grid
Power demand fluctations can be broken into timescales from micro-seconds to decades. On the "decades" end of the scale, the power industry and utility regulators work ...
- 449
13
votes
Why does it take so long to restart a nuclear power plant?
Xenon is a result of the nuclear reaction and a neutron poison. If you don't wait for the xenon to decay, it eats up too many neutrons and you can't go critical. They always say "there are not ...
- 1,000
10
votes
How does turning off electric appliances save energy
Yes, they monitor demand and due to differences in how different power stations are controlled they can increase or reduce output to match demand.
Some power plants like nuclear run at full output as ...
- 15.5k
9
votes
Relationship between wind velocity, turbine rotor diameter, and power output
It's not a simple relationship.
First let's deal with the kinetic energy of the wind passing through the rotor.
The mass of air passing through it in one second, $m$, is equal to the the density of ...
- 3,751
7
votes
Why does it take so long to restart a nuclear power plant?
The answer really boils down to two factors: safety and testing. I'm going to give a generic summary of these two things below, but the real answer is quite complicated.
The crux of nuclear plant ...
- 3,587
7
votes
How much power does it take to supply a laser which delivers 100 watts?
The total electrical to optical power efficiency of a laser system is sometimes termed wall-plug efficiency. It is the ratio of
$$\eta = \frac{\text{optical output power}}{\text{consumed electrical ...
- 24.3k
7
votes
Alcohol as a working fluid?
Yes - for certain applications. Low-energy, low-temperature, small installations, possibly 'accessory' power where providing a bit of weak rotary power to some point of machinery would be difficult ...
- 6,125
6
votes
Accepted
What is the difference between shaft power and brake power?
The short answer is these terms are defined by standards organizations based on specific test methods. These methods specify the engine condition, environmental factors, fuel chemistry, inlet and ...
- 4,617
6
votes
How does turning off electric appliances save energy
Peak Demand
One of the biggest issues in the electricity business is managing peak demand. This is the maximum amount of electricity needed at any one time. Typically this will be the middle of the ...
6
votes
Accepted
Why do kWh (smart) meters have a maximum operating altitude?
Electronic components are rated for altitude because:
Air density affects convective cooling, both forced and natural, meaning the cooling is reduced at altitude.
Air density affects air's dielectric ...
- 6,544
5
votes
Accepted
Why there is no piston style pedal bicycle?
The biggest problem with a "two cylinder" crankshaft is that there is a dead spot in the torque curve whenever either "piston" is at TDC or BDC.
When you have your feet directly on the pedals of a ...
- 6,874
5
votes
Generating power from fruit
You seem to be asking about using fruit juice as the electrolyte of a battery. Yes, that's possible, but you don't get a lot of power that way. The power also doesn't just come from the fruit juice. ...
- 11.4k
4
votes
Accepted
Having three heaters on single PCB
Increasing the insulation between the heat sources there is quite difficult.
Instead, you can sink the heat away:
Add a full copper fill on the backside of the PCB and connect that into a heat sink ...
- 1,943
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
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
Why is electricity used for powering our device?
Electricity is a convenient way to generate power centrally and distribute it to where it is needed according to demand. Central power generation by technologies like steam and gas turbines means that ...
- 15.2k
4
votes
substituting power supplies safe?
If you get lucky, the power supply will either shut down because it is overloaded, or deliver a very reduced voltage. Either way, the keyboard won't work properly, or won't work at all.
If you get ...
- 12.5k
4
votes
How to calculate hydropower in kW without water head
If you have horizontal water flow (no head) you are extracting its kinetic energy (from its velocity) not its potential energy (from its head).
So you need to know the velocity of that flow as well ...
- 1,620
4
votes
Accepted
Intuitive explanation for why doubling max speed is proportional to eightfold power
Think of it as the volume of water you're displacing per second - the area multiplied by the distance moved.
So intuitive I hope I can get away without an equation, but there's some good stuff in the ...
4
votes
Intuitive explanation for why doubling max speed is proportional to eightfold power
It's a pretty rough approximation, and only holds where skin friction is the dominant source of drag throughout the speed range considered. Skin friction increases about as speed ^2. So for double ...
- 4,617
4
votes
Specific energy vs Specific power in batteries
Batteries can't deliver unlimited current. Internal resistance, and limitations of the chemical reaction within the battery make that it can only deliver so much current. And the more current is drawn,...
- 1,174
4
votes
Accepted
Power systems unclear voltages
Note the problem specifies the load is "delta connected". There is no neutral connection to measure phase voltage ($V_{LN}$) against.
Also note the supply frequency is 60 Hz. 208 V is a ...
- 361
4
votes
Accepted
Torque Problems vs Motor Problem?
The motors have a rated speed of 2750rpm. It doesn't look like there's much of a gear ratio, so at the moment the motors spin at the same speed as the wheels. With 16" wheels, 2750rpm is about ...
- 156
3
votes
Accepted
Relationship between output mechanical power and max pressure for a pump?
Generally speaking, for fluid systems the mechanical power can be computed as the product of pressure and volumetric flow rate:
$\dot{E} = P\dot{V}$
where $\dot{E}$ is the power, $P$ is the pressure ...
- 1,220
3
votes
What happens if current provided to mono phase motor is less than rated power
Torque is proportional to current. If you can't supply the full current, then the torque will be lower than it would be otherwise.
The highest current draw is at startup when the motor is not ...
- 11.4k
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
3
votes
Having three heaters on single PCB
Well, air has worse thermal conductivity than practically any solid, so chances are that a hole will decrease the heat transmission. There are however solids with thermal conductivity very close to ...
- 453
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