Questions tagged [energy]
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106
questions
0
votes
1answer
69 views
What is the maximum distance for eavesdropping? [closed]
There is a closed question
https://physics.stackexchange.com/questions/276667/what-is-the-maximum-distance-for-eavesdropping-sound-waves
on Physics Stack Exchange and I thought this might fit better ...
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 $h$...
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 ...
0
votes
3answers
51 views
How to convert car power into energy (MJ) used per km?
I am currently attempting to do an energy audit regarding how much energy my car uses per kilometer. I am not sure whether my approach to this is right, and it feels like I have made too many ...
0
votes
1answer
41 views
Understanding "total primary energy supply"
I am trying to wrap my head around the diagram and explanation here but can not understand completely how it is computed.
https://energyeducation.ca/encyclopedia/Total_primary_energy_supply
For ...
2
votes
1answer
58 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
1answer
93 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 ...
0
votes
3answers
86 views
If the developing countries consumed as much energy per capita as China how much the current energy need would grow?
I recently saw this question and I immediately thought that the discussion was too limited to current energy production, it simply assumes that the amount of energy we use today is the amount of ...
2
votes
2answers
140 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 ...
1
vote
0answers
29 views
Equations of motion in matrix form and energy consumption
I am working on Lagrangian derived high-dimensional motion equations for a robot in matrix form. The structure of such an equation is known:
$M(q)\ddot{q}+C(q,\dot{q})\dot{q}+G(q)=0$
In here, $M(q)$, $...
3
votes
2answers
64 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 ...
4
votes
1answer
243 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
97 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?
1
vote
0answers
48 views
Why do solar cells need to be square-shaped?
There were circular solar cells 30 years ago. Why do we have square-shaped solar cells now? Why square?
Furthermore,
Why do monocrystalline solar cells have rounded/cropped edges?
1
vote
0answers
50 views
Why does a system with zero resultant moment turn after temporarily force-tilted?
Say a beam, 3m long from end to end, has a pivot placed at its centre of mass, at half its length i.e. 1.5m. Objects with weight 200N each are placed on both ends of the beam. The system is in ...
1
vote
0answers
21 views
Why doesn't the Stress Power in the theorem of the expended mechanical power contribute to the kinetic energy?
The following is the formula of the expended mechanical power:
$P(t)$ $=$ $\frac{d}{dt}$ $\int \frac{1}{2} \rho\ v^2 dV$ $+$ $\int \sigma \colon d\ dV$
where $P(t)$ is the mechanical power entering ...
0
votes
1answer
35 views
Half-life Unit Notations
I was looking for some element's half-life, on the following website:
http://nucleardata.nuclear.lu.se/toi/listnuc.asp?sql=&A1=214&A2=214&Z=88
For 214,88-Ra, the half-life is shown to be: ...
1
vote
2answers
45 views
How to determine energy dissipated from work applied on a load cell
I am using a load cell to see how much force people can apply on it, to help determine their health.
I am integrating the force applied on the bracket in Newtons in relationship to time, giving me the ...
1
vote
1answer
27 views
Weibull distribution Units - ENGIEQSOL
I am using Engineering Equation Solver, and it has been telling me the units of my distribution are inconsistent.
According to a the book I am reading, I think it should be unitless (as it is a ...
1
vote
2answers
70 views
Bernoulli equation on moving cart
Let’s say I have moving cart with velocity U .
And water from pipe flows at velocity V with respect to ground
The question asks to use Bernoulli equation , pressure is atmospheric in the top
If I use ...
0
votes
1answer
50 views
Why am I getting wrong value here?
A man threw a ball with force 10 N to two displacement of 5 m and 10 m.
F = ma, so let mass be 2 kg.
a = 5 m/s2.
Work done = 10 × 5 and 10 × 10 = 50 Nm and 100 Nm.
Now, since a = 5, I assumed that ...
1
vote
1answer
46 views
Can we say kinetic energy is tangential K.E?
I saw this in my textbook that
$\dfrac{\text{d}K}{\text{d}t} = \dfrac{\text{d}(1/2mv^2)}{\text{d}t}= F_t v$ where $F_t$ is the resultant tangential force on the body.
Now, let $F_t= F\cos\theta$
$$\...
0
votes
1answer
37 views
What does the author mean? Turbomachinery - Reaction
I am reading a book of Fundamental Energy Systems.
The author describes the rate of change in head for a turbomachine as:
$$ \frac{1}{2}[(V_1^2-V_2^2)+(U_1^2-U_2^2)+(V_{R2}^2-V_{R1}^2)] = H =U_1V_{u1} ...
1
vote
1answer
28 views
Statistics on energy mix in Europe [closed]
Does anybody know where to find statistics on the energy mix in Europe (preferred by country)? I can only find the share of renewables.
I'd like to see the whole mix with a split into energy sources (...
1
vote
2answers
43 views
Hydraulic energy recovery for high-pressure, low flow (non-steady state) conditions
What would be the best way to implement hydraulic energy recovery while de-pressurizing a pressurized volume of silicone oil initially at 1500 bar. Can a piston pump be concievably repurposed as a ...
0
votes
1answer
55 views
Is oil collapsing [closed]
Oil industry in permain basin is collapsing.
Also, no new technology or anything to save it this time.
Is this the beginning of the end for oil?
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 ...
0
votes
0answers
31 views
How energy intensive is creating artificial islands in the IJsselmeer?
The City of Amsterdam is building a series of artificial islands for new housing. One of them is Centrumeiland. Its size is 13 ha. (130,000 m2). Its creation requires 800,000 m3 of sand (Source), i.e. ...
0
votes
2answers
73 views
Why do some metals with bcc structure show ductile-brittle transition in charpy impact test?
I was learning about the charpy impact test and came across the graph on this webiste that shows the impact energy for bcc and fcc structures as a function of temperature. I tried searching for an ...
3
votes
2answers
149 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 ...
0
votes
0answers
28 views
Determine Heating costs in $/kWh for a specific location
Suppose I wanted to find the average heating price for a specific location in the US, where:
heating_price: The price of equivalent unit energy intensity of heating energy source (e.g. natural gas), ...
-1
votes
1answer
112 views
Capacity credit vs capacity factor
What is the difference between capacity factor and capacity credit? I know that capacity factor = annual generation / (installed capacity * 8760) but I don't understand how capacity credit is ...
-1
votes
1answer
53 views
Fluid Mechanics Question
I am preparing for GATE(Chemical). I need the answer of this question part 2 (question 54) as I am not able to find the mistake in my logic.
I have applied the logic here as:
Initial energy stored in ...
-1
votes
1answer
81 views
How much time to melt marshmallow under heat lamp?
Using the Specific Heat Formula, I found that I need to apply 612J of heat to melt 18g of marshmallow. Marshmallow has a specific heat of 2 J/(g*C), melting point of 98.6°F, and a starting room ...
-1
votes
1answer
32 views
Why Do Airborne Wind Energy Systems Use Kites And Not Balloons?
Title says it all,
Why are AWE-companies like Makani spending years and millions of dollars developing drones, rather than simply using a balloon-based design?
Wouldn't it be easier and faster to get ...
-1
votes
2answers
61 views
Kinetic energy of a rigid body
A homogeneous disk with radius $R$ and mass $m$ rolls without sliding on a horizontal fixed plane. Peripheral point $A$ has velocity $v$. Determine the kinetic force of the disk.
In my textbook they ...
0
votes
1answer
32 views
Clothoid Curve / Euler Spiral Energy Transfer
I've seen in an advertisement that Clothoid curves–also known as Euler Spirals–"transfer maximum energy" to a ball bearing that is rolled down it. Firstly, I was wondering if that might be ...
-1
votes
1answer
59 views
calculating energy usage with measuring the temperature
I am an electrical engineer working on a project. My goal of this project is to make an IoT solution where I continuously measure the temperature of room in a building. I want to calculate the amount ...
0
votes
0answers
32 views
Why is the functional of an elastic system equal to it's total potential energy and why is it stationary at it's minimum?
Okay this was even quite difficult to formulate but let's start with some statement's in my FEM book:
Elastic continuum has a functional which is equal to it's total potential energy
Elastic system ...
2
votes
1answer
64 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 ...
1
vote
0answers
24 views
How do I correctly model this system of torsion springs?
I am currently designing a symmetric parallel mechanism that can be modeled as follows:
Here, $\tau^j$ denotes actuator moments and $k_i$ are torsion springs constants. For a specific point in the ...
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 ...
7
votes
2answers
715 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 ...
3
votes
1answer
33 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 ...
5
votes
1answer
132 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 ...
-1
votes
2answers
33 views
Uses of orifice in Water Jet Cutting?
I wonder whats the usage of orifice/orifice plate in Water Jet Cutting Machines. To increase pressure(due to a smaller diameter with respect to the entrance cross-sectional area) or to convert to ...
1
vote
1answer
49 views
How to estimate wind generation using power curve?
I am trying to verify windfarmer generation estimates manually. To do so I am trying to manually calculate the estimated energy production (kWh) of a wind turbine. The information I have available is ...
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 ...
2
votes
3answers
190 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....
1
vote
0answers
52 views
Enthalpy vs Heat
If we have a closed cylinder filled with a gas and we heat it, by $1^{st}$ law we have: $\Delta q=\Delta U$ (?) since $\Delta V$ = 0. But $\Delta H= \Delta U+ V. \Delta P$.
What does that difference ...
