What is Efficiency: Definition and 945 Discussions

Efficiency is the (often measurable) ability to avoid wasting materials, energy, efforts, money, and time in doing something or in producing a desired result. In a more general sense, it is the ability to do things well, successfully, and without waste. "Efficiency is thus not a goal in itself. It is not something we want for its own sake, but rather because it helps us attain more of the things we value". In more mathematical or scientific terms, signifies the level of performance that uses the least amount of inputs to achieve the highest amount of output. It often specifically comprises the capability of a specific application of effort to produce a specific outcome with a minimum amount or quantity of waste, expense, or unnecessary effort. Efficiency refers to very different inputs and outputs in different fields and industries.

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  1. EastWindBreaks

    Heat exchanger - efficiency of the cycle

    Homework Statement Homework EquationsThe Attempt at a Solution Since we want the fluid to be in liquid state before entering a boiler, and super-heated water can only reach 374°C before entering super-critical state, suppose after the expansion, the temperature at point 3 is still higher than...
  2. A

    Does the distance between substations affect the efficiency of electric trains?

    Every time I take a train I sort of think about this, so the electrified overhead wire (DC or AC) and the rails form a transmission line and the train is a load that moves along the transmission line. Let's talk about the DC case as it seems more simple, so when the train is at or near a...
  3. F

    Does a good heat engine make a bad refrigerator?

    Hi all, the efficiency ##\eta## of a generic heat engine working between two temperatures is bound from above by the efficiency ##\eta_{\rm C}## of a Carnot machine working between the same temperatures. That is, if the temperatures are the same, a (ideal) Carnot machine is better than any...
  4. H

    Thermal efficiency of the Rankine cycle

    Homework Statement Calculate thermal efficiency of R-C cycle with saturated steam as shown in the picture. Steam has 4,5MPa when entering into HP part of the turbine (VT in the picture) and expansion on HP is finished at 0,3MPa. Moisture is then removed in the separator and steam is overheated...
  5. YC_128

    Thermal efficiency of the engine in a PV diagram

    A heat engine takes 2.0 moles of an ideal gas through the reversible cycle abca, on the pV diagram shown in the figure. The path bc is an isothermal process. The temperature at c is 820 K, and the volumes at a and c are 0.010 m3 and 0.16 m3, respectively. The molar heat capacity at constant...
  6. A

    Efficiency of an Electric motor pulling a truck up an inclined plane

    Homework Statement See picture. Homework EquationsThe Attempt at a Solution I tried at first just doing (1/3)*(48kJ) to get the energy dissipated, but that would i=give me 16kJ
  7. F

    Do Carnot and Stirling Engines Have the Same Efficiency?

    Hi, I have some doubts and questions about the above thermodynamic cycles. These questions arise from some statements I find in a couple of textbooks: "Physics, 10th edition" by Cutnell et al [A], and the other is "Fundamentals of Physics" by Halliday and Resnick . Actually, I have the versions...
  8. D

    Heating efficiency of a Heat Pump and a Space Heater

    Homework Statement Instead of pumping heat into the cabaret air from the outside air, you could simply put an electric space heater inside the cabaret. A space heater turns electrical energy directly into thermal energy. Why would operating a space heater consume more electric power than...
  9. J

    How Do You Calculate Gear Train Efficiency Based on Load Torque?

    I have been set the following question in my assignment and I have answered all parts with the exception of:- (d) Determine an equation for the efficiency of the gear train in terms of the load (torque) on shaft 2 (all other factors remaining constant). I am struggling here and would appreciate...
  10. C

    I Calculate the Efficiency of a Winston Cone

    How can I calculate radiation transfer efficiency of a Winston cone, assuming a constant efficiency for every reflection at 99% and that the source is perfectly diffuse and covers completely the wider entrance of the cone? Also, are there more efficient non-imaging radiation concentrators with...
  11. E

    Magnet system efficiency made from neodymium magnets

    Me and my friend want to make a strong as possible (made from permanent magnets) homemade metal separator for seeds. We are not good in the physics of such level, so we need consultation. We want to try neodymium magnets for our separator. We learned that magnetic flux density could be reached...
  12. José Ricardo

    About the efficiency of engines

    if we had an entire car made of Starlite (a material that was created resistant to 18032 °F). Would the efficiency of the combustion engine be close to that of the electric and that of the electric would be almost 100% efficient? https://en.wikipedia.org/wiki/Starlite
  13. bgm

    Efficiency of Base Load Power Plants

    interested in efficiency metrics with regard to our base-load infrastructure... this information is not readily available. I think that renewable stuff has its place only after we make the most of our base plants with load shifting. The base plants exist, and they waste energy. I simply do not...
  14. T

    Thermodynamic cycle efficiency

    Homework Statement n moles of gas, that follow van der Waals equation are to be employed as the auxiliary system in a circular cycle(parameterized using T_h and T_c as shown on the TS diagram. Calculate the efficiency of the cycle. Homework Equations , , Q = TdS The Attempt at a Solution...
  15. C

    Electrical How to maximize the efficiency of the corona discharge generator

    Hi, I have a wirmhurst electrostatic generator and I want to use it to create a corona discharge. My common sense tells me that the metal "shaft", which connects to the metal spheres should lead to significant (electron) leak, since it has a much smaller radius of curvature than said spheres. If...
  16. T

    Carnot Cycle efficiency, temperature dependency

    Hi, We know that a heat engine working on a Carnot Cycle the efficiency is: 1 - QL/QH = 1 - TL/TH where T is in Kelvin. But if we use a different absolute temperature scale whose values at TH and TL are different, then the value of efficiency also changes. I am confused about this issue...
  17. S

    Is there a way to increase the efficiency of spdc?

    Can a setup be made such that the efficiency of spontaneous parametric downconversion approaches 100%? From what I have been told, this would be possible using classical input fields matching both the pump and output frequencies, but I am unsure if one could simply use laser of both frequencies...
  18. Gregs6799

    Calculate the efficiency of a furnace’s heat transfer process

    Homework Statement [/B] Hi guys. Been looking at this question for a while and can't figure it out. An aluminium furnace is fuelled with propane gas. The furnace is loaded up with 4 aluminium ingots each of mass 22.5 kg. The question is: If 2.1 kg of propane is used to complete the melting...
  19. V

    Increasing Diesel Engine Efficiency with Retractable Plates

    In case of diesel cycle thermal efficiency is low, because heat addition takes place at constant pressure.so can we introduce some retractable plate which sits below the piston during end of compression stroke,and retracts back after heat addition,thus providing constant volume heat addition and...
  20. R

    I Efficiency prediction (minimum versus average)

    I am trying to determine the efficiency of a light source for treating plants. When using the light source, there is an equal probability of encountering two different plant species. The light source has a certain electro-optical efficiency ##\eta_{\text{eo}}##. And each plant type has a...
  21. Edemardil

    How Many Food Calories with Efficiency %

    I figured out (a) but I am having trouble with (b): (a) What is the efficiency of an out of condition professor who 2.10e5 J of useful work while metabolizing 500 kcal of food energy? (b) How many food calories would a well-conditioned athlete metabolize in doing the same work with an efficiency...
  22. R

    Solar PV:What happens to the lost energy?inductive recovery?

    Hi there, I am new in here, thanks for any reply. I took same title of a previous closed 3D by pranj5. As understood main part of the energy absorbed by PV panels goes in reflection and heat. The heat origins mainly in electrons that are excited but not enough to jump or they jump but they...
  23. G

    What factors affect the efficiency of a DC motor?

    Hi forum, I've been thinking about efficiency factors, I've read that they are more efficient at higher loads? I was wondering why this is... On the one hand at higher loads (maybe lifting a heavier mass) the rotation rate is reduced so this reduces energy losses due to friction? (so goes with...
  24. V

    Automotive Calculation of the efficiency of an engine

    We know efficiency (η) = Woutput/Winput Now in any cycle, for instance, the Otto cycle, let the total work output be WO, total heat added be WH & the total work done on the gas to compress it be WC. Then, will efficiency be equal to (η) = (WO-WC)/WH ? Or will it be equal to (η) = WO/(WH+WC) ?
  25. Benhur

    The entropy of a Carnot cycle and the efficiency equation

    I have my first question. It's about entropy in the Carnot cycle and I'll try to be direct. The equal sign in the Carnot cycle efficiency equation is related to the fact that the total entropy doesn't change at the end of the whole cycle (being related to the fact that the heat exchanges occur...
  26. Alexandre Ricardo

    Efficiency in a thermodynamic cycle

    I have to calculate the efficiency of the above cycle for an ideal gas, that goes at the order a-b-c-a: I know that the answer is 16/97 but I can't calculate the heat in the a-b stage.
  27. C

    What is the combustion efficiency of liquid fuel rockets?

    How efficiently is the fuel burned in a typical liquid fuel rocket engine? I've heard numbers ranging from 95% to below 50%.
  28. lc99

    Carnot Engines Question -- Composite Configuration Efficiency

    Homework Statement Homework EquationsThe Attempt at a Solution Trying to figure this out. So, I'm thinking that adding a extra resevoir for another engine will not add efficiency. It will should split up the W done by the heat reservoir. It just seems to make sense that way. So would the...
  29. UMath1

    Heat Engine Efficiency and Entropy

    In deriving the Carnot Efficiency, the assumption is made that theoretically most efficient engine will generate no net entropy, meaning that the entropy that enters the system during heat absorption must equal the entropy that leaves the engine during heat rejection. Why is the case? Why would...
  30. Rafe Zayed

    Second law efficiency of Rankine cycle

    Can you provide me any source from where I can learn about the overall second law efficiency calculation of a simple Rankine cycle?
  31. D

    Question about the efficiency of a generator

    Using a certain kinetic energy, does a generator produce the same amount of electric energy even if I change the rpm by gearing? Also, does a generator produce energy in proportion to the number of rotation? I mean, does a generator create the same amount of energy between when it's rotated 10...
  32. GANESH SHETTI

    One 160 kW motor vs two 129 kW motors

    This is related to steel wire pulling machine. I have 2 cases. In CASE-1: ONE MOTOR 160 kW AND CASE-2: TWO MOTORS 129 kW Each. i.e 2x129 kW Which case would have an efficient pulling force and efficiency Case 1 or Case 2.
  33. Rasta philosophy

    Car randament (engine efficiency)

    Diesel and otto car cannot have randament of 100 per cent, practically. But teoretically they could have?
  34. N

    MHB Optimizing Process Efficiency for 25% Sales Increase

    I've been stuck on this for hours, can someone pleas Current = 1 Sub p/ 600 Seconds | 1 Sub p/ 10 Minutes | 6 Sub p/ 1 Hour | 60 Subs @ 10 Hours Need = 1 Sub p/ 500 Seconds | 1 Sub p/ 8.33333 Minutes | 7.2 p/ 1 Hour | 72 Subs @ 10 Hours So I figure I need to shave off 100 seconds to meet the...
  35. Ranku

    I Energy efficiency of nuclear and fossil fuel

    Can anyone give a percentage comparision of efficiency of energy conversion in nuclear fuel and fossil fuels like oil and coal?
  36. jdawg

    Efficiency Associated with Cost

    Homework Statement The concrete slab of a basement is 11m long, 8m wide, and 0.20m thick. During the winter, temperatures are nominally% °C and 10°C at the top and bottom surfaces, respectively. If the concrete has a thermal conductivity of 1.4W/m*K, what is the rate of heat loss through the...
  37. O

    Nearly Perfect Efficiency - 2nd Law of Thermodynamics

    Recently read this article on Physorg: https://phys.org/news/2018-01-efficiency.html My questions are: 1. If "converting" information into energy requires a system (the demon I suppose) having a photodiode, processor, laser (light trap) all expending energy in order to cause the conversion...
  38. X

    Thermal efficiency of a Diesel engine

    Hi, i’m learning about the thermal efficiency of a diesel cycle at university and I'm trying to understand the equation. The first law of thermodynamics states Wnet + Qnet = 0, but one of the attachments below says Qnet - Wnet = 0 and I don't understand how this is the case. Also, for process...
  39. A

    Percent power and Efficiency

    Hello all, I need to know what is the difference between the percent power and efficiency for air compressor. Is it the same or what is the relationship between them. Thanks
  40. W

    Internal quantum efficiency (IQE)

    Homework Statement The IQE is defined as (photons emitted from active region ##s^{-1}##) / electrons injected across the junction. Derive an expression for this quantity, then find the injected electron concentration ##n## which maximises it. Homework EquationsThe Attempt at a Solution We've...
  41. MarkFL

    MHB Firefox Revamped: Update Brings Speed & Efficiency Boost!

    Earlier today, when I saw that Firefox was installing an update when I fired it up, I did my usual groaning facepalm and wondered what I might find broken this time. I've been a faithful Firefox user since 2004, shortly after it appeared on the market. But in recent years, my loyalty has been...
  42. J

    Engineering Transformer -- find equivalent circuit from efficiency and V.R

    Homework Statement For 200 KVA, 4000/1000 V transformer. 1 phase. Efficiency is 0.97 at full load and 60% load at unity power factor. No load pf = 0.25 Full load Voltage regulation at 0.8 pf lag is 5% Find transformer ckt parameters for referred to lv side Homework Equations efficiency is...
  43. patrickmoloney

    Why can the efficiency of a refrigerator (heat pump) be greater than one?

    In a heat engine thermal energy is converted into mechanic energy. In a heat pump or refrigeration cycle - fluid is being circulated between hot and cold wells. But how can the efficiency be greater than 1? Is it because COP_{\text{heating}}>COP_{\text{cooling}}
  44. I

    How to calculate the efficiency of a fuel engine

    Homework Statement [/B] Im trying to find the efficiency of a gasoline engine regarded as a control volume. Am I right to use the HV as total energy input into the system? Assuming the enthalpy of formation of the fuel can't be found. I am really wondering if enthalpy of formation equals the...
  45. L

    Please check my math about this engine efficiency calculation

    Hello. I wanted to see how much more efficient a car would be if hydrogen and oxygen (created through electrolysis of water) were injected into the engine alongside gasoline. I got lost when I found out that I would need 241.8 kJ/mol of water to electrolyze it...
  46. D

    Does the volume of water affect efficiency of heater?

    Ok, so i did a physics experiment a few days ago and now i have to do a write up. The question is does the volume of water in the calorimeter affect the efficiency of the immersion heater? Could someone pls explain to me what happens & y? My results showed that as you increase the volume, the...
  47. unseeingdog

    Multiple rotors on a wind turbine

    Could multiple, smaller rotors on a wind turbine (on the same shaft) be more effective than a single, larger rotor? Why do most wind turbines have only one big rotor? I was thinking about doing a science fair project on this topic, but I have been unable to find a conclusive answer to this...
  48. mfb

    Just add poison: Bacteria outperform plants in efficiency

    The authors call them "cyborg bacteria", but as far as I can see they didn't change the bacteria artificially, they just put them in unusual conditions, including poison. They used bacteria that get rid of poisonous substances (such as cadmium) by forming crystals out of them. Under the right...
  49. S

    Proper calculation of the efficiency

    Homework Statement Hello! This is actually a computational-statistics problem in data analysis, and I got a bit stuck. I have several events from a Monte Carlo simulation from 2 particles collision and for each event I have the primary vertex and the tracks associated to it. I wrote an...
  50. Domenico94

    Electric cars -- Does periodic coasting help efficiency?

    Hi. I'm a student of electrical engineering, and I've always been interested in the idea of electrical cars, so I came up with a question: let's suppose we want to have a normal trip with car, and then we're not interested in going so fast with it. When we are driving in this condition, it isn't...
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