Engineering Stack Exchange
Engineering Stack Exchange

Questions tagged [energy]

136 questions
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4 answers

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 gone forever. (Except saving money on bills) My…
ShivCK
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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 and traffic in and out of the building is…
Paul
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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, over time these rechargeable batteries lose the…
Mahendra Gunawardena
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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 we simply use the specific heat capacity at the…
Max Ning
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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 $h$. This energy is called the potential energy of…
Harshit Rajput
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5 answers

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 electricity costs $\frac{12.5p}{kWh}$ would this be…
jhabbott
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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 A \left( \dfrac{\partial w}{\partial t} \right)^2…
Ferdi811
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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 bottom. This creates a layered water temperature in…
Emma
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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 be implemented, and whether such a vehicle has…
sloupioc
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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 between torque needed to climb hills, and RPM to…
Satchel
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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, let's use the following assumptions: Average wind…
Dwiparna Datta
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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 $100\ \tfrac{\text{V}}{\text{m}}$ near the surface of the earth. To me,…
QCD_IS_GOOD
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What happens to generated electricity if it is not used?

Let's take for example hydroelectricity produced at a dam and not consumed by any household or industry... Will the electricity need to be stored? What will happen if it is not stored? Does it flow like water and get wasted back to the earth? What…
Nagendra
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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 burning of natural gas produces 215 g/kWh of CO2. For…
Emma
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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 and friction; are these kinds of speeds possible…
Thomas
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