What is Efficiency: Definition and 947 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. K

    Efficiency Of Thin Film Solar Cells

    How does the efficiency of a Thin Film solar cell compare to the efficiency of a single crystal solar cell with reference to the 5 main solar cell parameters ( Iopt , Rs, Rsh, Is and n )? I know series resistance( Rs ) will probably increase in thin film cells because of grain boundaries...
  2. mrspeedybob

    The maximum theoretical efficiency of a heat engine

    http://en.wikipedia.org/wiki/Heat_engine This is one of those threads where the OP proposed a device which will not work and hopefully by the end understands why. So here's the device... Air enters through a long intake tube. At the end of the tube it enters a combustion chamber where fuel is...
  3. F

    Thermodynamics Steam Turbine Internal Efficiency Question

    [b]1. Steam into a steam turbine at 7 MPa and 500 deg C. The turbine has an internal efficiency of 90 %. The steam exhausts at 20 kPa. 1) What is the exhaust enthalpy? 2) What is turbine work? 3) What is the quality of the exhaust steam? This is a question I got on a 2nd class boilers...
  4. G

    Energy Efficiency and Transfer

    Hello, First of all this is a fun sidetrack thing. I'm looking for the safest and most efficient molecule that could be split or combined or some way to produce force.Could it be put in a motor-type device and therefore be used as a motor?BTW, this is for like a car.Could Salt Water produce...
  5. N

    What Are Some Hot Topics in Energy Efficiency?

    I need to research something on energy efficiency, but I have no idea what I should do. I've looked at laundry systems, dehumidification in hospitals, textile production. Energy efficiency in residential or commercial settings is paradox because engineers worked to make every component more...
  6. Jalo

    Thermodynamics - Cycle efficiency

    Homework Statement Consider the following reversible cycle: Where S2=S3=(S1+S4)/2 . Prove that the efficiency η is: η= 1 - 2*T6 / (T1+T3) Homework Equations The Attempt at a Solution I know that in a T-S diagram the heat received by the system is equal to the area...
  7. Jalo

    Thermodynamics - Cycle efficiency

    Homework Statement Compute the efficiency of the following cycle: Homework Equations The Attempt at a Solution I know there's an isothermic process between a and b, where heat comes into the system, let's call it Qh. I also know that between b and c heat will leave the...
  8. A

    Carnot Efficiency of a heat engine

    My problem only gives me joules to work with. Is it possible to convert from joules of energy to temperature (Kelvin)?? If so how?
  9. D

    Finding the efficiency of an engine given energy input, energy wasted.

    Homework Statement An inventor claims to have developed an engine which takes in 1.1x108J of heat energy at 400K, and rejects 5.0x107J of heat energy at 200K. Would you advise investing in this project? Explain your answer. Homework Equations W = Q1 – Q2 η = W/Q1 = 1 – Q2/Q1 The...
  10. N

    Electric motor efficiency calculation

    Hello everyone, I am trying to calculate the electric efficiency of some 3 phase electric motors but I am a little confused about the power factor. efficiency=work out/work in work out=rated W of my motor (hp*745.7) work in= V*A*PF*√3 Is the work in correct? Thanks
  11. M

    Why can no other engine be more efficient than a Carnot engine?

    Hello, I am having difficulty understanding the paragraph in my textbook explaining why no other engine can be more efficient than a carnot engine. What does it mean? To prove the validity of this theorem, imagine two heat engines operating between the same energy reservoirs. One is a Carnot...
  12. T

    80W of Power Cannot Be Converted to Energy

    Is this problem as simple as I think it is? Homework Statement A 532 Watt motor is 85% efficient. How much power cannot be converted to energy? Homework Equations The Attempt at a Solution 85\% of 532W\,=\,452.2W 532\,-\,452.2\,=\,80W
  13. L

    How do you show the efficiency of an engine is x?

    Homework Statement A hypothetical engine, with an ideal gas as the working substance, operates in the cycle shown in the diagram, show the efficiency of an engine is : n= 1 - 1/\gamma ((1-(P3\P1))/(1-(V3/V1))) The diagram is basically a section the bottom left quadrant of a circle with an...
  14. C

    Deriving Efficiency of a Diesel Engine Formula

    Homework Statement The Diesel cycle is an idealized representation of the process that occurs in a Diesel combustion engine, as shown in the graph below. Starting at point a, the Diesel cycle consists of an adiabatic compression, an isobaric expansion, and adiabatic expansion and an isochoric...
  15. T

    Efficiency, power, irradiance and speed problem

    Homework Statement I've attached the question Homework Equations The problem is I don't know what equation(s) I have to use. The Attempt at a Solution This question my part of my thermofluid dynamics course but I cannot find a formula in my textbook that uses an irradiance...
  16. T

    Holographic grating - can we calculate efficiency for each order?

    Hi, I'm new to working with gratings. From using the basic grating eqn., I'm able to model the diffraction angles for each order with different angles of incidence upon the grating and I can calculate the dispersion given a broadband source with known minimum and maximum wavelength...
  17. P

    Optimizing for cost efficiency

    Homework Statement The cost of fuel to propel a boat through the water (in dollars per hour) is proportional to the cube of the speed v. A certain ferry boat uses $100 worth of fuel per hour when cruising at 10 miles per hour. Apart from fuel, the cost of running this ferry (labor...
  18. A

    How Does Increasing Compression Ratio Affect CO2 Emission in Otto Cycle Engines?

    Homework Statement Estimate the change in volume of carbon dioxide if 'r' is increased from 10 to 11 (10% increase). Assume 30 million cars, all use 1m^3 of fuel each year Homework Equations Efficiency of an Otto Cycle η=1-r^(1-gamma) The Attempt at a Solution Original...
  19. P

    Oil pressure as it relates to efficiency

    I know a guy that is really big into hot rods. He's got a late 80's model firebird with a custom engine in it. Dudes got probably got between $15-20k in the engine alone. It puts out somewhere just over 1000 hp, and he's done all the work on his own, so I feel inclined to believe the guy. But I...
  20. B

    Efficiency map of the drive train of a car

    Hi there, I'm reading a report about the efficiency of the drive train of an electric car. The author recorded the speed and acceleration of the car over a period of time and created the graph below to illustrate the efficiency. Could anybody tell me what the relationship is between the...
  21. K

    Propulsive Efficiency: Understanding Jet Engines

    Hello everyone, Long time follower, first time user here. I have got a Q about propulsive efficiency. My understanding of the jet engine in a nutshell is that air is compressed in the compressor (pressure and temp go up), energy added in the combustor (large increase in temp), work...
  22. G

    Aerodynamic efficiency and static longitudinal stability

    Hello, I am looking for research results, report etc. dealing with -aerodynamic efficiency and static longitudinal stability- Couldn´t find anything useful yet! Any ideas would be very much appreciated. Best Regards, granby
  23. O

    Muscles opperating with efficiency of 18%

    Homework Statement Muscles operate with an efficiency of about 18.0 percent in converting stored chemical energy into work. How much chemical energy will be expended by a 63.6 kg person in the process of ascending several flights of stairs to a height of 21.0m? Homework Equations pe=...
  24. T

    What is the efficiency of the cycle

    Question is attached Thanks!
  25. J

    Electron/Hole Effective Mass vs Solar Cell efficiency

    Hi. I'm doing research relating to solar cells and came about the topic related to effective masses. The wiki article stated how effective mass (solid state materials) influences the efficiency of solar cells, but doing more research I couldn't find any solid examples of an effective mass vs...
  26. S

    Basic thermo question: heat engine efficiency

    Is it strictly true that an engine will be more efficient if operating in a hotter environment... e.g. your car is more efficient in the summer than the winter? Just going through thermo 1, not a HW question, but it just seems to be true to me because the simple Newton's law of cooling says...
  27. P

    How to calculate the efficiency of a trebuchet?

    Homework Statement Hi, VERY URGENT and I am so confused Find the efficiency of the optimum trebuchet. Optimum trebuchet Specs: Counterweight= 5kg Sling Length= 78cm (laid out fully) Length from fulcrum to load= 44cm Length from fulcrum to counterweight=16cm Height the weight drops...
  28. S

    Exploring the Mysteries of Antenna Efficiency

    I understand a changing current in a wire gives way to an opposite magnetic field that resists the induced magnetic field, until there is no change in magnetic field, then you're left with a constant induced magnetic field. So my confusion with the antenna is when an electron rapidly...
  29. N

    Does Increasing ICE Engine Efficiency Lower Exhaust Temperatures Proportionally?

    So the current estimate is that an ICE engine is about 20%. If we were able to increase the efficiency of a given engine, would that result in a proportional decrease in exhaust temperatures? (Given that driveline loss to friction is constant)
  30. C

    Why does gas turbine efficiency increase with size?

    Thank you Regards
  31. N

    AC motor vs. DC motor efficiency

    I am currently using a 600HP DC motor for an extruder application and I am exploring the idea of switching to a 600HP AC motor. What kind of energy savings/efficiency can I expect if any?
  32. K

    Efficiency of Low-Speed vs. High-Speed Chairlifts

    Homework Statement The energy lost operating a low-speed chairlift is the same as the energy lost operating a high-speed lift of equal path length. What happens to the efficiency when you change from a low speed to a high speed chairlift? Homework Equations We know that high speed...
  33. K

    Wind turbine efficiency question

    If we look at wind turbines used for power generation, they typically have 3 blades, and the blades are very slender compared to the blades of a house fan. I don't understand how such a slender blade can capture a significant amount of the wind's energy. The energy available in the wind is...
  34. Drakkith

    Solar Panel Efficiency and Temperature

    What affect does the temperature of a solar panel have on it's efficiency? I know they become less efficient at higher temperatures, but is this effect linear? Would decreasing the temperature sub-freezing temperatures do anything? On a related note, apparently they have invented a transparent...
  35. F

    Process of increasing solar cell efficiency- what's it like?

    I've recently gained an interest in solar cells and it's development. I know the basic working principle of solar cells, but other than that I'm quite clueless about the field. I was wondering, what is the process of increasing solar cell efficiency like? Are there analytical ways of...
  36. M

    DC Motor Efficiency: Does It Change With Voltage?

    Hello, I would like to know if the motor efficiency is changing with respect to applied voltage or it doesn't change. What I do mean. The efficiency=(V*I)/(Torque*velocity) and the power losses= I^2*R. Can I say that mechanical power ( Torque*speed)=V*I-I^2*R If so, can I say that the...
  37. L

    Which Door Type Uses Less Energy: Hinged or Sliding?

    To understand, in a specific case, which motion spends less energy - angular or linear - I want to ask an unusual question. Which kind of door - hinged or sliding door - needs less energy to change its state from closed to fully opened, in a specific interval of time "t"? If I want to close...
  38. D

    Steam Heat Exchanger Efficiency

    Heya, id like a little help calculating the efficiency of some steam heat exchangers. They are used in industrial dryers, steam goes through the radiator and then air is blowed to it in order to heat the fabric. Currently my radiators are made from carbon steel tubes and fins, it has 78 flat...
  39. P

    Can superheating of steam increases efficiency and output of thermal power plants?

    I just want to ask a simple question to experts here. Can superheating of steam increases efficiency and output of thermal power plants?
  40. O

    Why Is My Calculation of Carnot Engine Efficiency Incorrect?

    Homework Statement A Carnot engine operates between 230°C and 120°C, absorbing 6.30*10^4 J per cycle at the higher temperature. What is the efficiency of the engine? Homework Equations eff = 1 - (Tcold/Thot) The Attempt at a Solution Using this equation, I get 47.83 percent...
  41. A

    How Many Joules Can Be Extracted from Piezoelectric Quartz When Struck with a Hammer?

    Lets say I have a hammer, and a piece of piezoelectric quartz. If I hit the quartz with the hammer with the kinetic energy of 100 joules, how many joules can I get out of the quartz?
  42. J

    I.C. Engine Question. Solve for: Mean Effective Pressure & Volumetric Efficiency

    Hello all. I am new to the forums. I am having trouble solving a couple of questions. Maybe some of you can help me out. Thanks in advance! Homework Statement Number of cylinders 4 Stroke cycle 4 running at 4400 rpm Volume...
  43. M

    How Is Solar Panel Efficiency Calculated?

    Sorry I was unsure where to submit this thread. I am doing a school project on designing a solar system for my home and I was wondering how the efficiency of a cell is calculated. The way I calculated it, which i read of a website is... 1. calculate area of cell (in meters) 2. divide watt...
  44. A

    Poisson distribution with efficiency problem

    Hi, I have a problem with determining the probability distribution function of the number n of detector counts in a given time t. I am assuming the events follow exponential distribution ε(t,λ) = λexp(-λt). Now if that was everything it would simply be a Poisson distribution, however, what I...
  45. M

    Is the Carnot efficiency valid for fuel cells?

    So, I've read in books and on Wikipedia (see for instance http://en.wikipedia.org/wiki/Carnot%27s_theorem_%28thermodynamics%29#Applicability_to_fuel_cells_and_batteries) that the Carnot efficiency cannot be applied to a fuel cell because it is not a heat engine that produces work, operating...
  46. M

    How the efficiency of transformer affects turn ratio

    A secondary textbook said that if there is no flux leakage, Vp/Vs=Np/Ns, no matter what is the efficiency of the transformer. May I know will the ohmic loss and eddy current contribute to the loss and modify the voltage ratio? thanks!
  47. D

    Physics Assignment - Efficiency of an Electrical Appliance - Kettle.

    Homework Statement Hey physicists. I have a problem. My assignment this term for physics is to test the efficiency of an electrical appliance, and to make suggestions on how to improve the efficiency for the future. I conducted a number of experiments on the kettle, using 2 different kettles...
  48. R

    Need help with a tricky thermodynamics question involving isentropic efficiency

    Homework Statement An engine operates on an air cycle consisting of the following non-flow processes in succession: 1-2 isentropic compression from an initial state of 80 kPa, 27°C and the volume of 0.071 m 3 through the volume compression ratio of 17.75; 2-3 reversible heat...
  49. K

    Pyhton data's structural size and loop efficiency

    While programming to find the largest prime factor for a composite number i came across a problem that if the number taken as input exceeds a certain limit, the loop time turns out to be a very long one and some times even resembling the time taken by an infinite loop.The method used for finding...
  50. F

    Energy, temperatures and efficiency

    Hi all Working through a past paper as I have an exam tomorrow and can't quite see where to start with the following question. Homework Statement A steam engine produces 2.4 kJ of work per cycle for a heat input of 6 kJ. If the temperature of the hot source for the engine is 600 °C and...
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