Questions tagged [energy-efficiency]
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88
questions
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1answer
37 views
Are AC generators more efficient than DC generators?
I've been doing some research into AC and DC generators, and I was wondering if AC has any advantages in terms of efficiency.
Given that AC generators are usually brushless while DC generators ...
1
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1answer
78 views
What would be a reasonable estimate for the amount of petroleum needed to find, produce and deliver one barrel of petroleum?
A basic "balance sheet" might allocate fuel needed for exploration, well development, production, crude oil transportation, refining, further product transportation and delivery to a ...
0
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2answers
56 views
Why is Carnot Factor defined as 1 - (T(cold) / T(hot))
This is the proof I've found for the Carnot Factor:
$$S = \frac{Q}{T} \qquad \qquad (1)$$
$$S_{in} = S_{out}\qquad \qquad (2)$$
Because entropy stays the same when ...
0
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1answer
40 views
How does the efficiency curve of a well pump shift with speed?
Well pump manufacturers publish "efficiency curves" for well pumps, such as this one (the curve that is most sharply convex down, whose Y axis is read from the "% EFF" scale on the ...
4
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2answers
119 views
More efficient to use LED lighting than to open blinds for light and thereby lose heat when very cold outside?
Currently here it is 9 degrees Farenheit. My home is heated by electric resistance heating (not a heat pump, just plain heating coils). Am I correct in believing that it's more energy efficient to ...
0
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1answer
58 views
Which power plant will generate more electricity in the below discussed scenario?
There are two identical power plants(i.e same turbine dimension and same generator configuration). Both have a hot reservoir. Coal is burnt on both power plant to make the temperature of the hot ...
1
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0answers
43 views
Optimizing flue gas temp for maple syrup evaporator
I have a simple maple syrup evaporator. Fuel is burned in a firebox located under 1mm stainless steel pans containing maple sap--which becomes syrup once enough water is evaporated. After passing ...
0
votes
1answer
26 views
explaining ohmic loss and understanding inverter efficiency curve
I'm trying to understand an efficiency curve from PVsyst, using this documentation
However, I'm not sure what this sentence means:
This production is penalized by an ohmic loss$^1$ of the internal ...
0
votes
1answer
27 views
Where can I find efficiency metrics for diesel engines?
I am doing long term planning for a small fleet of tugboats. A lot of the engines (propulsion, generators, hydraulics) are Detroit Diesels of various sizes (e.g., 4-71, 6-71, 12V-71). Newer engines ...
0
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0answers
9 views
How to calculate the ideal and realistic estimate of thermal efficiency of absorption chiller?
How Can I calculate the ideal and a realistic estimate of the thermal efficiency of the system (thermal, electrical and water) per 1 kWh chilling energy (removed from the chilled water)?
What is the ...
3
votes
2answers
92 views
Natural ways for passively cooling/heating a home?
I always think about how there surely must be natural ways to cool/heat a house, rather than using electricity, like solar panels, heaters, and AC. Does anyone have any good examples of houses/...
2
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0answers
31 views
Optimization: Most efficient way for multiple people to move boxes
We are moving house in a few weeks and have a couple of people helping moving the boxes. My previous experience from moving is of queues building up in small hallways and people getting tired from ...
2
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0answers
54 views
PMDC Motor Characteristic Graph
I am trying create a graph similar to as shown below. However, I am confused as to how the torque is related to the characteristics.
The graph that is to be replicated for certain parameters:
The ...
1
vote
3answers
65 views
Practicality of energy recovery from HVAC systems?
I've been thinking about ways to maximize efficiency in large buildings, and one thing I thought of was to place some sort of turbine in the exhuast vents or smokestacks of factories, power plants, ...
0
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0answers
23 views
at what point is increasing pressure ratio diminishing in returns?
piston engines of ww2 planes had pressure ratio of at least 10, while jet engines were still vastly superior with a pressure ratio of only 3.
Certainly pressure ratio of 1 would bring 0% fuel ...
-1
votes
1answer
62 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 ...
0
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0answers
84 views
Energy Wasted in Electromagnetic Motor Actuator Vs Human Muscle Actuation
I would like to know if the energy utilized by a robotic arm is greater compared to the energy utilized by human arm. Robotic arm is essentially servo motors that use electromagnetic field to create ...
-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
vote
3answers
93 views
Why are some submarines using liquid oxygen for combustion?
I think som submarines like Kockums use liquid oxygen instead of compressed air for driving their combustions engines. Is it more energy efficient to oxygen enrich the air before burning it compared ...
2
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0answers
20 views
One dimensional U-Factor Calculation - How to determine indoor / outdoor film resistances
Can someone clarify the ASHRAE Fundamental 2017 (SI Units) (See Below) Indoor and Outdoor film resistances. The manual states that it comes from Table 3 and in the description of table 3 it states &...
1
vote
1answer
65 views
Laser Power vs Efficiency
Is there some kind of graph or relation between laser power and efficiency. What I'm trying to find out is whether the efficiency of a laser decreases with increase in power or is it that there is no ...
4
votes
1answer
134 views
In a diesel engine, does more heat leave the engine through the tailpipe or the radiator?
Diesel exhaust is hot, and there's a lot of it.
Diesel radiators also get pretty hot.
In a typical diesel engine, which one is dissipating more heat?
EDIT: In response to a request for specificity ...
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2answers
26 views
Relation between engine size and its power to weight ratio
Is there a relation between engine size and its power to weight ratio? For example if you shrink the engine to half the size will it have exactly half the power?
6
votes
3answers
797 views
Three-phase versus single-phase operation of a generator
My generator (a Fermont MEP-803A, 4 cyl diesel, 10kW rated) can run in three distinct modes:
Single-phase 120V, in which one terminal is hot, and another is neutral
Single-phase 120V/240V, in which ...
1
vote
2answers
52 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
32 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
103 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
votes
0answers
23 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
1k 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 ...
0
votes
0answers
59 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
votes
1answer
51 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
votes
2answers
37 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
140 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=...
1
vote
3answers
36 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?
0
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2answers
126 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
votes
3answers
1k 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
952 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
votes
2answers
39 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
votes
1answer
104 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
59 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 ...
2
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1answer
69 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?
1
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1answer
85 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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votes
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
304 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
votes
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
384 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
votes
1answer
249 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
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1answer
717 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
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1answer
277 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
27 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 ...
