Questions tagged [energy-efficiency]

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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 ...
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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 ...
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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 ...
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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 ...
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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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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,...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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" ...
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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 ...
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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 ...
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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 ...
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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 ...
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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?
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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 ...
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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'...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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%. ...
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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 / ...
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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 ...
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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 ...
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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 ...
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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 $...
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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.
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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/...
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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 "...
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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 ...
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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 ...
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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 ...
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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?