Questions tagged [efficient-energy-use]

Use the tag *Efficient Energy Use* in questions having to do with processes or engines or constructions where energy is spent or transferred and the efficiency thereof. Efficiency means both the measurement and the techniques and principles for its optimization.

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Why the efficiency of air standard cycle is above 50% while the efficient of an otto cycle (real engine) is below 35%?

I want to know the reason behind why the efficiency of otto cycle (real engine) is less than air standard cycle
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56 views

Cutting down on power by bypassing mechanical to electrical conversions: Why not? [closed]

The only answer to this I can think of is energy portability issues. Another modern-world insanity is converting mechanical energy to electrical, only to turn it back into mechanical. The example I ...
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Lighter car vs heavier car, energy efficiency

I typically assumed in vehicle energy efficiency debates, the importance always in propulsion- to reduce vehicle mass. This usually implies high energy mass density fuel, like hydrogen fuel cells, ...
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Will water pump efficiency change if water is pumpted into air versus underwater?

I have a water pump. It pumps water from a low spot to a higher spot. The manufacturer only recommends the motor is kept underwater at all times, and to attach a pipe size that won't slow the ...
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PMDC Motor Characteristic Graph for Given Parameters

TL;DR Need to make a graph which showcases all parameters of a PMDC motor against the torque input. I am trying create a graph similar to as shown below. However, I am confused as to how the torque is ...
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23 views

Energy Utilization in Electromagnetic Actuator Vs Piezo-electric Actuator

Electromagnetic actuators are quite common in almost all industrial and household applicatons. I was wondering that the motion produced by the electromagnetic actuators are the side product of the ...
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46 views

Nuclear Reactor's Heat Engine's Thermal Efficiency

Nuclear reactor has to convert its heat into mechanical energy and to electric energy with its turbine heat engine. I learned the heat engine of a common PWR nuclear reactor is around 33%. The ...
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1answer
48 views

How to find efficiency of a cycle thats not Carnot Cycle?

Here is the Full Question: A monoatomic gas is expanded adiabatically from volume $V_0$ to $2V_0$ and then is brought back to the initial state through an isothermal and isochoric process respectively....
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58 views

Efficiency of engine with two isotherms one isochor and one isobar

I was creating a hypothetical engine for fun and trying to calculate the thermal efficiency. The engine which I was trying to calculate consisted of: Isothermal compression, Isobaric expansion, ...
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22 views

Does incoming light polarization and phase effect the efficiency of photovoltaic cells?

As I understand it, standard photovoltaic cells depend on both the creation of electron-hole pairs and those pairs being created in the depletion zone in a P-N junction. Is seems like the production ...
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999 views

Can regular air conditioner be used as heater? [closed]

In winter season, the normal room temperature is generally 6 to 10 degree Celsius, if the air conditioner is working at 25 degree Celsius will it be working as a heater, making the room warm (relative ...
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43 views

Maximum possible fuel efficiency at a given altitude

What's the maximum physically or technically possible fuel efficiency (considering common fuels like gasoline or diesel) that can be reached for a 1 ton vehicle at sea level? Can this be calculated? ...
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1answer
53 views

Heater efficiency on maintaining temperature?

I have a central heating system with natural gas (atmospheric) heater warming the water going through the closed loop to radiators. I can set the temperature of the hot water in a fairly broad range, ...
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173 views

What is the maximum theoretical efficiency of conversion of potential energy to kinetic energy and vice-versa?

Am looking at different techniques available for identifying sources of energy. As part of it, have the following question : What is the maximum theoretical efficiency of conversion of potential ...
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1answer
45 views

Calculating output of a solar cell

If we are given a particular solar panel with some semiconductor tabs in it, How can I calculate the output of the Solar panel per metre square With the values of ( average hours of sun everyday, ...
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1answer
216 views

How does the Carnot Cycle work?

I am learning the Carnot cycle, which consists of four transformations for a fluid. In the first two transformations the volume of the fluid expands, generating work. This happens in two steps: ...
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37 views

Sound from a rocket

I have been watching programmes commemorating the Apollo 11 mission. One obvious feature of the launch is the sound. It was mentioned that water was sprayed into the pit below the rocket not (...
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1answer
138 views

Why does intercooling improve the efficiency of a Brayton Cycle?

I've read in numerous sources that intercooling improves the efficiency of a Brayton cycle. The explanation given is that it decreases the compression work by minimizing the temperature during the ...
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179 views

Why a reversible engine's efficiency must be equal to that of a Carnot engine

Apparently, in order to prove that an engine must be as efficient as a Carnot engine if reversible is because apparently for its efficiency in either direction: $\eta_E \le (1-T_2/T_1)$ $\eta_R \ge (...
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90 views

Can two quasi-static adiabates intersect? [closed]

I saw a question in my physics book that I've been trying to understand lately. The question is simple: given two quasi-static adiabatic curves, could you find a point of their intersection? Also, ...
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80 views

Is it possible to transform energy stored in anti-matter into coherent radiation?

In Travellers, a sci-fi show on netflix, they have 10g of some form of anti-matter floating around. A quick $mc^2$ calculation gives a quantity of $E = 10^{15} J$. For reference, Little Boy released $...
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465 views

How to calculate the power required by a fountain pump?

How can I calculate the power required by a fountain pump, if just the efficiency of the pump, the height of the fountain and the diameter of the water jet is given?
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Should we take the elevator instead of the stairs to save energy?

In our university there's a posted sign that encourages students to take the stairs instead of the elevator to save the university electricity during the hot NYC summers. When you climb the stairs ...
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Is it more efficient to drive fast uphill?

I know that for a rocket escaping the atmosphere, it's not efficient to travel slowly because even staying stationary consumes a lot of fuel. Does the same apply to a vehicle traveling uphill? In ...
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303 views

Natural gas furnace vs. power plant efficiency

In the USA, residential heaters often use a measurement called AFUE, which is supposed to be a percentage of input energy to output energy. It is typical for a two-stage natural gas furnace to achieve ...
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3answers
266 views

Is the “efficiency” of car brake affected by how much force is applied by the brake?

Someone argues with me that stepping on a car's brakes for long periods of time will wear out the brakes faster than applying the brakes for short periods of time. We were talking about stepping on ...
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Why is it so inefficient to generate electricity by absorbing heat?

When I turn on a heater, it's supposed to be roughly 100% efficient. So it converts electricity to heat with great efficiency, but why can't we do the reverse: generate electricity by absorbing heat? ...
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265 views

Efficiency of any machine

Why cant the efficiency of a machine be 100%? We always see that there is some energy that is lost, mostly in the form of heat. But why is it so? Is it impossible to create a machine with 100% ...
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86 views

How can I calculate the efficiency of an air-powered car?

An air-powered car is powered using high pressure compressed air stored in a tank. The pressurized tank is connected to an air-powered engine. The volume of the tank is 0.3 m3, and the initial ...
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1answer
41 views

would heating a stove to 400 degrees be more or less energy efficient if done more quickly?

Would heating a stove to say 400 degrees be more or less energy efficient if done over a shorter or longer period of time? say 5 vs 10 minutes. Which would cost more on the electricity bill?
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50 views

Efficiency given two temperatures

Not sure what formula to use for this question? I am new to physics and the regular efficiency formula doesn't seem like the one I should be using. I was thinking the carnot efficiency, since it ...
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875 views

Stacking thermoelectric generators for a better efficiency

As far as I know, a thermoelectric generator has about 5-8% of efficiency. That means it uses 5% of the heat and converts them to electricity. Rest 95% is dissipated through the other side. So I can ...
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1answer
95 views

How can energy of petrol be compared to electricity?

When driving my car, which is powered by an electrical engine, I'm consuming between 10 and 17 kWh per 100 km (measured at the charging outlet). The car I had before consumed between 5 and 8 litres ...
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173 views

How much extra fuel is needed to transport a 1kg object over a distance of 10,000 miles? [closed]

I propose the scenario: a 1,300-kilogram, base weight, vehicle is carrying a 1-kilogram textbook with a 35% efficient engine over a distance of 10,000 miles. How much fuel is being burned to carry ...
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87 views

How to prove that an arbitrary cycle in the PV diagram has an efficiency less or equal than Carnot's Cycle? [duplicate]

The statement is: Consider an ideal gas with constant number of particles (N is constant), and an arbitrary thermodynamic cycle (closed curve with no self-interesections) in the PV diagram. Show that ...
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1answer
289 views

Understanding efficiency

This is a repost of a previous question, following the advice of an experienced user. I was told that reversible processes are more efficient than irreversible ones, and that this fact is expressed ...
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633 views

Understanding entropy and efficiency

A few years have passed since the last time I studied thermodynamics, and I'd like to give me a chance of asking some questions, maybe trivial, I don't know, but I want to clear matters up. Since my ...
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1answer
59 views

Is it correct to find ideal engine's efficiency using celsius scale?

I am solving a problem from my book which asks to calculate the maximum efficiency of an engine whose hot body is at temperature 300°C and cold body is at 25°C. Using 1- Tc/Th, I got efficiency equals ...
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380 views

Water turbine power generation for large and small turbines

If you have a small water turbine and a larger water turbine in a river, would the larger turbine produce more power or would they produce the same because of the equal speed of the river?
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3k views

What is the average range of voltage of lightning in sky?

I wondered how much energy is required to produce , such a loud sound? What is the average range of voltage in sky? Is there any possible way to store it ,and use when needed?
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Why is the efficiency of human cells less than the efficiency of an Otto engine?

I always used to think (I don’t know why!) that the efficiency of human (and animal and plant) cells should be equal to or near the efficiency of a Carnot engine or at least should be the highest ...
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1answer
320 views

How is the energy efficiency in bicycles accounted for? [duplicate]

Bikes are more efficient than walking, but that's only because roads are flat so wheels make sense, right? Does it make sense to say that this fact is simply gained by putting a lot of energy into ...
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1answer
73 views

How much realistically usable energy can be obtained from matter/antimatter interaction?

The high energy density of a matter/antimatter system is well known. However, depending on the nature of the material, most of the energy from the interaction is released in the form of photons (...
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3answers
703 views

Calculating the electrical power generated from a wind turbine [closed]

Heres the question: A wind turbine has blades that sweep an area of 2000 m^2. It convrts the power available in the wind to electrical power with a efficiency of 50%. What is the electrical power ...
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2answers
215 views

Are all heaters exactly as energy efficient as each other?

I many applications, efficiency is measured in terms of how much of the input energy is wasted generating heat instead of the actual type of energy you want. For example, lightbulbs generating heat ...
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120 views

How can I get 100% fuel efficiency from an IC Engine in a car?

I understand that the current technology of internal combustion (IC) engines gives about 20% for a normal car. I want to understand what I can do to achieve 100% or near 100% efficiency in the same ...
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4answers
4k views

Why does heat engine need to reject energy to environment?

The most efficient thermodynamics cycle is the Carnot cycle, it involves 1/ Receiving heat from hot source, expanding and doing work on the surround 2/ Receiving work from environment, being ...
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234 views

How much money can I save on gas by losing weight?

I read somewhere that if you carried around a penny in your car, over the lifetime of the car, you would end up paying an extra penny in gas than if you weren't carrying that penny. I was wondering ...
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Do you know the principle which says that connecting two sources of similar kind produces a waste and destruction? [closed]

There is a great article, called commutation cells, which states that you cannot transfer kinetic energy from one container to another immediately, bypassing the potential energy storage. Otherwise, ...
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3k views

Which is more mechanically efficient, a bicycle or a unicycle?

Human physiology aside, I wonder which device is more mechanically efficient, a bicycle or a unicycle?