Questions tagged [energy-efficiency]

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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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/...
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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 ...
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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 ...
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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, ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 &...
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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 ...
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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?
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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=...
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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?
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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?
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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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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
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 ...
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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
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" ...
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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 ...
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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 ...
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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 ...
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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 ...