Questions tagged [energy-efficiency]
The energy-efficiency tag has no usage guidance.
65
questions
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1answer
18 views
How much weight has weight in fuel efficiency?
Comparing the official fuel efficiency figures for several cars, I was surprised to discover that the Smart Fortwo has a weight between 750 to 800 kg and needs 4.3 L/100 km, but the VW Polo with a ...
3
votes
1answer
30 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
69 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 ...
2
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0answers
15 views
Energy/Efficiency Calculations for Large Multi-stage Package HVAC
I frequently use the Equivalent Full Load Hour (EFLH) estimation method to calculate the expected energy usage for commercial HVAC equipment. While not ideal, it works well enough to given an order ...
6
votes
3answers
572 views
How Much Efficiency is Lost in a Gear Train
I want to get a rough estimate for the transmission efficiency of two different gear trains. One is a one-stage gear train with 11.67:1 ratio (140/12 teeth) and the other is a compound two-stage gear ...
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0answers
18 views
How to know which efficiencies to take into account when calculating power of a certain part of a power transmission system?
I have an example which I am not certain about:
So It consists of a friction wheel, whose power $P_{fw}$ we know. The power is used to power the driven machine $Dm$ on a shaft that lies on 2 bearings,...
0
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0answers
39 views
Most efficient turbine for harnessing energy from bidirectional air flow?
I am currently working on designing an oscillating water column as part of a project. In summary:
OWC are devices with a semi-submerged chamber or hollow open to the
sea below, keeping a trapped ...
2
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1answer
34 views
Effect of Pressure on Combustion efficiency (of hydrogen) in excess air
Can somebody explain relation between combustion efficiency and pressure in lean mixtures using any kind of chart or mathematical equations?
At first glance I thought, combustion efficiency increases ...
-1
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2answers
32 views
Does utilizing exhaust energy to supercharge (“turbocharging”) increase the thermal efficiency of a gasoline internal combustion engine?
The work done by a turbocharger increases the inlet charge without much of a burden to the exhaust flow. This increases the amount of air (and fuel) that flows into the engine. How does this affect ...
4
votes
2answers
116 views
Do 3 blade wind turbines generate more power than a 9 blade, all else being equal?
After doing some research, I have come to the realization that 3 blade design horizontal turbines have the greatest maximum coefficient of performance. Most sources seem to agree a Cp of ~0.45 at TSR=...
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3answers
31 views
Efficiency of an engine
What is meant by thermodynamic efficiency of an engine?
and what are the factors that affect the thermodynamic efficiency of a diesel engine?
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2answers
88 views
Refute my assumption: Bearings Don't Improve Efficiency
If two surfaces rub together with a normal force between them, friction is generated. You could add lubrication between those two surfaces and reduce that friction.
Bearings essentially consist of ...
5
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3answers
985 views
Is it true that four-wheel drive is less efficient and if so, why?
I have heard many times that four-wheel drive is less efficient than two-wheel drive. Many car producers have a normal drive mode where only two wheels are powered, and turn the four-wheel drive on ...
0
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1answer
204 views
calculating the efficiency of a microwave oven
If I want to calculate the efficiency of a microwave oven, I have the input Energy (= power (watts) x time (s)) and the output which I measured using temperature difference (q=mct).
So do I divide ...
0
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2answers
36 views
Would some manufacturing processes be more efficient if driven differentially by a single motor, up to ~150 kW, than multiple lower-rated motors?
I'm writing a discussion paper on the potential energy efficiency benefits of integrating different manufacturing processes by co-location on the same site. One possible field for integration is in ...
3
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1answer
69 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 ...
1
vote
1answer
48 views
Calculate Efficiency Loss of a Leak in a Hydraulic Cylinder
I am trying to figure out what the efficiency loss of a leaking hydraulic cylinder is. This master's thesis found that a controllable pitch propeller (essentially a hydraulic cylinder inside a ...
1
vote
1answer
45 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?
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1answer
78 views
how would one calculate the % of heat not absorbed by a heat sink?
I'm planning on building a plant growth chamber inside a sealed/insulated 55 g rain barrel, and I'm trying to figure out how much of the heat from my lights will enter the chamber, and how much ...
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1answer
32 views
How is the Ampyx Power plain generating energy? [closed]
This is what I'm talking about:
Wikipedia
Youtube video 1
Youtube video 2
Official site
Can you please explain me on how this plane is generating energy? Reeling back the aircraft should consume the ...
0
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1answer
243 views
How to calculate actual efficiency of a steam turbine
What are the parameters required to calculate the overall efficiency of a steam turbine and how to calculate. Is there are certain assumptions to be made while calculating the overall efficiency of a ...
0
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2answers
49 views
Should I run 2-wheeler at constant speed?
I have been recommended not to run the two-wheeler (Suzuki Access) at a constant speed (I give a constant throttle in a way that I run essentially at a constant speed of about 40-45 kmph). In fact, I ...
3
votes
1answer
221 views
Efficiency and NOx emission of lean burn gas engines
I have a question regarding the efficiency of lean burn gas engines. Maybe it is just a confusion concerning the terminology of "thermal efficiency", "brake mean pressure", "brake thermal efficiency" ...
0
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1answer
135 views
Why regenerator “wheels” in a turbine engine?
Back in the early 60s, Chrysler built a turbine car powered by a turbine engine it had under development.
An interesting feature of the engine was a regenerator system to recover heat from the gases ...
2
votes
1answer
416 views
What are the limiting factors on diesel engine compression ratios?
Higher compression ratios in internal combustion engines generally improve the engine's fuel efficiency. But diesel engines don't seem to go above a ratio of 25 or so. What is the limiting factor for ...
1
vote
1answer
239 views
Energy consumption of a boiler
I have a question that maybe will be very easy for you.
I am working on a district heating model using Dymola, and now I have to incorporate a boiler into my model, such as this one.
I was asked to ...
0
votes
1answer
25 views
What is the fraction of power transmitted to the generator in full-hybrid cars?
In full-hybrid cars like the Toyota Prius, usually both internal combustion engine (ICE) and electric motor produces mechanical power to the wheels at cruise. But some of the mechanical power produced ...
0
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2answers
50 views
Thermal efficiency affected by hertz (Gas turbine)
Take the LMS100 gas turbine for example. Why does the efficiency change when generating power in 50 or 60hz waveform?
0
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1answer
70 views
What is the explanation why Pulse and Glide is more energy-efficient for trains [closed]
I read that trains in pratice instead of acceleration to a certain speed level and holding the speed, they accelerate and then cost, accelerate again, und keep this pattern. This was shown by ...
0
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1answer
61 views
Natural gas boiler Vs. Electric Heater efficiency
If a facility buys natural gas at 8 dollars/Mcf to provide heating from an 85% efficient natural gas boiler, what is the equivalent cost of electricity ($/kWh) for a 95% efficient electric heater?
I'...
0
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2answers
458 views
How is the energy production of solar and wind compared with the prospect of nuclear fusion? [closed]
I am trying to find reliable information and comparisons about the energy production of renewable energy technologies, specifically, how solar and wind alternatives compare to nuclear fusion.
Why is ...
0
votes
1answer
511 views
What is the maximum efficiency of a mechanical electric generator?
If we apply a simple push to rotate a system of gears to generate electricity, what is the maximum practical and theoretical power efficiency of the system, assuming the push as the only source of ...
0
votes
1answer
46 views
Has anyone achieved significant energy savings by increasing the cooling setpoints in retrofit office buildings, in practice?
I have a simulation based research vs. practical experience type question:
There are a number of academic research papers available which claim 20% to 40% cooling energy savings by increasing the ...
0
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1answer
54 views
How the COP differs for a Vapor Compression Chiller without the U*A values of Evaporator/Condenser?
I am trying to find the COP of a VCR system. I can reach the COP with using the EES(Engineering Equation Solver), without dealing with the UA values, i.e. just with the energy balances for the cycle. ...
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3answers
82 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 ...
0
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2answers
100 views
Can you use the kinetic energy of air to power a car?
In my fluid mechanics class, I've learned that a fluid traveling in a pipe will generate a force when the exit area is smaller then the entrance area. Suppose a pipe is attached to a car that will use ...
3
votes
1answer
174 views
Can combined cycle turbines be small enough for trains?
Combined Cycle Turbines are a gas turbine whose exhaust heat powers a second turbine running on steam. These can get thermal efficiencies greater than 50%, whereas a plain turbine would get 30 to 35%. ...
0
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1answer
71 views
cycle efficiency for (otto -diesel -dual) at constant Pr & Temp
It's written that at constant pressure & temperature for Otto & Diesel cycles
the efficiency of diesel is more than efficiency of Otto.
Efficiency = Work / Heat added = 1- (Heat rejected / ...
1
vote
1answer
314 views
What is the difference (if any) in capacity factors and efficiency between reservoir hydropower and run-of-river power plants?
My question is about differences between reservoir-hydropower and run-of-river power plants. Are run-of-river plants less efficient? what would be an approximate guess of the differences? (assuming ...
0
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1answer
40 views
Efficiency of off road vehicles [closed]
Im working on efficienxy of heavy vehicle. Since i never had any experience with this kimd of things ( cars ) i dont have so much insight in what kind of efficiencys are important in vehicle. I have ...
8
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1answer
3k views
What is the difference between Bluetooth Low Energy and Bluetooth BR/EDR in Park mode?
It is known that Bluetooth Low Energy transmits data only during short time intervals called Connection Events. Connection events occur regullary with predefined period. The rest of the time Bluetooth ...
0
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1answer
43 views
Power/Efficiency of expanding air-flow
Assuming, I've got a machine, that runs with pressurized air and provides the following measurements:
$\dot m$ - mass-flow through the machine (same for input and output)
$p_{1}$ - input pressure
$...
2
votes
4answers
2k views
What is the theoretical maximum energy efficiency of hydro turbines?
From what I've read it seems that hydro turbines can theoretically achieve 100% energy conversion from kinetic to electrical energy. However, I just wanted to double check if this was true.
0
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1answer
139 views
Best fuel for supercar engines
To experienced supercar owners/engineers:
What is the best fuel for a turbocharged 6 liter V8, 7.6 liter V10, or 9.2 liter V12 (Audi R8 or Lamborghini Aventador type cars) in terms of speed/...
5
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2answers
92 views
What's more energy efficient: fewer air conditioners working at max capacity or more working at part capacity?
The central heat and air in the house I'm renting is unable to keep the house below 80 °F during the hot summer here (100 °F days). We've had 3 HVAC techs out to look at it and they all say there's "...
0
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2answers
132 views
Calculate efficiency of water heating
I have a heating system with which I heat up 10 liters of water by 24.2°C in 610 seconds.
My system consumed 0.5 KW of electric energy in this time.
Now I used this formula:
Specific heat ...
2
votes
2answers
373 views
Transporting water uphill at the highest efficiency possible?
I have a passing interest in water desalination projects. One of the challenges of desalination is simply moving the water from the ocean to the desalination plant. Typically the plant is built above ...
0
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1answer
1k views
Relationship Between Gear Ratio and DC Motor Power Consumption
In my class, we are currently trying to understand the relationship between gear ratio and motor power consumption.
Given two gears, one attached to a motor, and the other attached to a string ...
0
votes
1answer
49 views
Daylighting, how to improve coverage
I am doing this daylighting project for which we must bring the light far down into a bunker. I have found .
I have heard and read that the quantity of light that you bring in a cable decreases, 60% ...
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5answers
2k views
Difference in energy consumption between empty fridge and fridge filled with bottles of water
I have about 12 bottles of water. If I want to minimize the energy consumption of my refrigerator, should I put these bottles in the fridge or leave them out?
