Questions tagged [energy]

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20
votes
4answers
4k views

How does turning off electric appliances save energy

We all know if we use less electricity we save energy. But the energy we're getting is result of burning (not necessarily the literal meaning) the fuel. Even if we don't use that energy that fuel is ...
17
votes
3answers
7k views

What is the most efficient means of warming a building with a high ceiling?

Consider a large auditorium, a church, or some other very large, essentially one roomed building with a high ceiling. Suppose that the building has many entrances which enable cold air in/hot air out ...
13
votes
1answer
827 views

What causes rechargeable batteries to age? What can be done to extend life of these batteries?

These days most of modern electronics use rechargeable batteries as a power source. Also, these days most modern rechargeable batteries are Lithium Ion or Lithium Polymer based. Like any other devices,...
9
votes
5answers
3k views

How can one calculate the change in heat energy when the specific heat varies with temperature?

Many materials have a specific heat which varies with temperature, especially as the temperature change grows large. How does one calculate the heat energy that an object receives in this case? Can ...
8
votes
4answers
5k views

Why does "potential energy" have the word "potential" in it?

Imagine a block of mass $m$ placed on the ground. I slowly lift it up to height $h$. The work done by me on the block is $mgh$. This amount of energy is now stored in the block when it is at height $h$...
7
votes
5answers
9k views

Is compressed air energy storage economically viable in the home?

If I install a small air compressor/engine, generator, and tank in my garage, and I charge it up at night when electricity costs $\frac{5.4p}{kWh}$ and use it during the day to power my house when ...
7
votes
1answer
400 views

Energy of a 3D Timoshenko beam

I am interested in the kinetic energy T and the potential energy U of a three dimensional Timoshenko beam. For a 2D Timoshenko beam the energies read: $$ T = \dfrac{1}{2} \int\limits_o^l \left( \rho ...
7
votes
2answers
801 views

Calculation of the stored energy for a heat storage tank

There is a heat storage tank that is directly loaded from the top and the heat is also taken from the top. The colder water from the heating circuit return flow enters the heat storage tank at the ...
6
votes
2answers
977 views

Can the Sabatier reaction power a vehicle?

The Sabatier reaction converts CO2 to methane. Can a vehicle that burns methane recover it (at least some part) from the exhaust gases via the Sabatier reaction? I am interested to know how this would ...
5
votes
2answers
11k views

Calculating torque needed to climb a graded hill

I've been designing an electric skateboard which is driven by only one of the rear wheels (for the moment). As I was picking out motors for the board, I soon realized I would need to find a balance ...
5
votes
3answers
4k views

Relationship between wind velocity, turbine rotor diameter, and power output

I'm trying to understand and identify the equations to use in defining the relationship between wind velocity, turbine rotor diameter, and power output for a wind turbine. To simplify my question, ...
5
votes
1answer
523 views

How could we possibly harness the energy from the Earth's negative charge?

I've been reading the Feynman lectures, and in this lecture about lightning, he describes how the Earth is negatively charged, and how there is thus an electric field of about $100\ \tfrac{\text{V}}{\...
5
votes
1answer
150 views

Calculation of the specific CO2 emission of a cogeneration plant for the produced electricity

Suppose I have a cogeneration plant that runs on natural gas and produces heat and electricity. The heat effeicieny is $\eta_{th} = 0.4$ and the electricity efficiency is $\eta_{el} = 0.4$. The ...
4
votes
2answers
399 views

Turning an engine over with engine compression

When you compress a bicycle pump and seal the opening, the pump will automatically return to it's initial position when you release it. I suppose this is how air suspension works as well? if you have ...
4
votes
1answer
257 views

What does MM prefix mean in MMtoe?

I was reading documents about energy importation and came across the following: The import was of 5,915.87 MMtoe I wonder if MMtoe = $10^6*10^6$ toe = $10^{12}$ toe. First time coming across a ...
4
votes
1answer
236 views

Does The W*nkBand Work?

A certain product (link: Metro, somewhat safe for work) is currently trending on social media, that allows men to convert the kinetic energy of their more vigorous personal activities into electrical ...
4
votes
1answer
110 views

Why do monocrystalline solar cells have rounded/cropped edges?

What is the meaning of this croped part? Why do they crop it, rather than let it be full square?
4
votes
1answer
586 views

Getting high RPM out of a low RPM motor

I'm trying to use a 1500 RPM-rated electric motor to accelerate a (light, 25kg) shaft up to 50 000 RPM. At these speeds I figure using a belt system or roller chains is out of the question due to wear ...
3
votes
6answers
3k views

Working hours of power plant generators

My question might seem a simple one, but it has been troubling me for a while. How many hours in a day do conventional electrical generators work (the ones in large power plants)? Do they by any ...
3
votes
2answers
160 views

How high will a flywheel catapult launch a payload?

First off, this is not a homework question or anything like that. I'm trying to build a catapult to launch a payload using a flywheel as an energy device! It goes like this: The flywheel spins up to ...
3
votes
1answer
36 views

Question about flow temperature and storage temperature in a cogeneration plant

Let's assume I have a cogeneration plant that produces heat with a nominal output. The heat is given into a heat storage tank, which is filled from above. The maximum flow temperature of the ...
3
votes
1answer
49 views

Clutch role in a micro hydropower

I've recently visited an old (about 60 years old) micro hydroelectric standalone installation. Total electric power is about 3 kW A/C. A local told me between generator + fly-wheel and turbine there ...
3
votes
1answer
59 views

Trying to understand how much it costs to run my clothes dryer

I am trying to calculate the running cost of my clothes dryer and have bought myself an energy meter to check its usage. I plugged the meter in, reset it, and then turned it over to the aggregate kWh ...
3
votes
2answers
67 views

What are some technical problems with generating electricity using a gas turbine or combustible engine at a gas flaring site?

Numerous oil and gas exploration sites practice flaring for safety and disposal of unwanted low calorific gases. However, instead of just standalone burning the gas, why can't a gas turbine or ...
3
votes
1answer
116 views

What is the difference between a diffuser and a duct in turbines?

I have been reading this paper, which addresses the advantages of diffusers in cross flow turbines. The abstract says (emphasis is mine): A CP’s extraordinary improving resulted when yaw increased ...
3
votes
2answers
259 views

How to automatically process energy meter data considering outliers and meter reset?

I want to algorithmically process energy meter data. The energy meter measures a heat or power producer or a heat or power consumer (but not both, so the measured energy will always have a positive ...
3
votes
2answers
87 views

Compressed air energy storage?

I'm wondering, if you put an air compressor pipe into a micro turbine, lets say something like that attached to a motor, does air that get out of the turbine have the same energy as when it gets in ? ...
2
votes
1answer
208 views

How to convert Joules(kinetic energy) plot chart into watts?

How to convert Joules(kinetic energy) plot chart into watts? Anyone know how?
2
votes
3answers
199 views

Gasturbine energy balance

I have a question regarding gasturbine energy balance, the total energy that flows into the gasturbine is given 12 MW and the power needed for the compressor is 4.4 MW and the turbine power is 9.3 MW....
2
votes
1answer
6k views

Specific energy vs Specific power in batteries

When looking at the Wikipedia page for Lithium-ion batteries, one can see that there are some technical details such as Specific Energy and Specific Power, but I don't know how to connect them. For ...
2
votes
2answers
88 views

Can we make significant energy from human waste? [closed]

I am trying to find if making energy from human waste (excrement, sewage) is profitable? Lets say I live in a city of 16 million people which does not put waste into use. What could be the ...
2
votes
1answer
60 views

Converting between MMBTU and MWh

a quick question: I want to convert between MMBTU and MWh to get at emission factors from energy. I have the following information: I use the data given in 40 CFR 98 (see EPA source here) by the EPA ...
2
votes
2answers
148 views

How do 3 blade turbines come so close to the Betz Limit?

I have seen many diagrams (see attached) that indicate that modern 3 blade turbines are nearly 50% efficient, which is about 80% of the Betz limit. Betz calculated his limit based on a theoretical ...
2
votes
1answer
985 views

How do I calculate the additional energy required to pump fluid through a restriction?

Let's say I have a pump pushing fluid through a 250 ft pipe, 1.5'' diameter, at a rate of 20 gallons per minute. I would like to calculate the delta in energy required to pump this fluid with and ...
2
votes
1answer
71 views

Understanding the total energy in a AA battery

AA batteries have about 4 watt-hours (14400 joules, 10620.9 pound-feet). Ignoring losses, does that mean a AA battery could theoretically lift 10,620.9 pounds, 1 foot high? You'd need an electric ...
2
votes
2answers
2k views

How much braking force do cars generate?

I've been trying to find actual figures for the braking power of cars (in order to determine things like stopping time). As I understand it this comes in two parts: the maximum force that the brakes ...
2
votes
1answer
2k views

What kind of signal is the signum function? A power signal or an energy signal?

I'm studying "signals and systems". We can indentify two kinds of signals: power signal and energy signal. The definitions are: Energy of a time-continous signal $$ E_x = \int_{-\infty}^{+\infty}{|x(...
2
votes
1answer
97 views

Dehumidification calculations

I'm looking at options for DIY dehumidification and am hoping to get a sanity check on some calculations, and verification that I'm using the right factors in the right way. As a reference point, I ...
2
votes
1answer
48 views

What are the key technical challenges to development of traveling wave reactors?

I recently learned about traveling wave reactors (TWRs) on the Netflix Bill Gates special, as an example of a cutting-edge technology Gates is funding which has the potential solve several ...
2
votes
1answer
25 views

What are the necessary qualitative criteria for the existence of limit cycles

The literature on the existence of limit cycles is replete with complex and abstract mathematical analysis. Or for specific systems of specific structure, specific mathematical criteria that determine ...
2
votes
1answer
74 views

Converting grams of fuel per kWh of energy

Is there a database showing how many grams of a particular fuel generates how many Kilowatt hours of electricity?
2
votes
1answer
379 views

How do you calculate the Enthalpy of a geothermal resource?

Enthalpy seems to be commonly used to characterize geothermal reservoirs, but how is it calculated? I have an example here where the enthalpy is cited as 800 $kJ kg^{-1}$ for a reservoir with a ...
2
votes
1answer
1k views

Why use different specific heat capacities in the energy equations for incompressible and compressible fluid flow?

Background: I notice that there is quite a bit of similarity between the standard heat equation and the energy equation (from the navier stokes equations). The heat equation is given as $$\frac{\...
2
votes
1answer
96 views

Short power outage, deliberate?

The power went out in my block just now, so I got in my car and drove around and found a utility truck next to a pole that is at the junction between the block circuit and an adjoining circuit (which ...
2
votes
0answers
34 views

How do you estimate the energy of an impact?

I am trying to determine the energy of elastic stress waves generated in a solid by an impact. I have a time domain waveform from a piezoelectric transducer that was placed next to the impact site, as ...
2
votes
1answer
800 views

What are the differences between compressor stations, pump stations, and booster stations?

I am doing some research on impacts related to natural gas compressor stations. In some states, I've received data for compressor stations alongside other facilities in the oil and gas world. These ...
2
votes
1answer
103 views

How do generators in space transmit/ deposit energy back to Earth? [closed]

I've read about the idea of putting solar panels in space, or the already used electrodynamic tethers which gain energy as they move through Earth's magnetic field. The question I have is: How do ...
1
vote
4answers
3k views

Why can't energy be entirely recovered from a moving car's rotating wheels?

I have a friend who isn't properly visualizing energy loss in a moving car. His idea: Cars that can run forever without being recharged - - > while the engine rotates the front wheels the move the ...
1
vote
3answers
89 views

Radioactive Materials to Energy AT HOME

Is there a way to use a radioactive elements (Americium in my case, but for demo, any radioactive material) to create a usable amount of energy (Power small LED?) AT HOME! Using materials that can be ...
1
vote
2answers
124 views

Light bulbs with highest energy efficiency [closed]

Most specs for light bulbs list luminous efficiency (or, more accurately sometimes, luminous efficacy) but not energy efficiency. Luminous efficacy tells you how bright the light is as observed by a ...