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. W

    Wankel/rotary engine efficiency

    I was just wondering how we can find out the efficiency of a rotary engine? Obvious, it is more efficient than a gasoline/diesel engine.For example the RX8 on 1.3 L in 2 rotors get 250 hp which is quite impressive for that capacity,also it works in 4 stroke,and the power to weight ratio is...
  2. P

    Calculating Otto Engine Clearance w/ Efficiency 46.4% & k=1.3

    Homework Statement What is the clearance of an ideal otto engine if the efficiency is 46.4% and k=1.3 Homework Equations efficiency = Worknet/Heat Added k=1.3 hot air T= 1900kThe Attempt at a Solution i don't know how to start
  3. T

    Effeciency and Current Relationship

    Homework Statement I'm doing an investigation for my physics class, where we were told to investigate the relationship between current flowing through and the efficiency of an immersion heater. My hypothesis was that as current increased, the efficiency would decrease due to the relationship...
  4. T

    Carnot Cycle with negative temperatures

    Homework Statement Heat engines at negative temperatures. Consider using two heat reservoirs to run an engine (analogous to the Carnot cycle of chapter 3), but specify that both temperatures, T_hot and T_cold, are negative temperatures. The engine is to run reversibly. (a) If the engine is to...
  5. T

    What is the efficiency and power loss of electric vehicle motors?

    I'm looking for a good figure out there like this to describe electrical vehicles. I know EV's are on average 60% efficient but I'm looking to discuss the losses and percentage loss at the systems in an EV. Anyone have any insight?
  6. S

    Water injection improves or reduces gas turbine power?

    Hello, I am currently working on a storage project which allows me to decouple the compressor from the expander of a gas turbine. (see image link below) The reason I use a gas turbine is to reheat the air which was cooled after being compressed. As you can imagine there is a efficiency loss...
  7. N

    Turbomachines and efficiency

    can anyone please explain difference between polytropic efficiency and stage efficiency in turbomachines
  8. Zack K

    Efficiency of Ramp: Solving Box Push Up Problem

    Homework Statement A 7.0 kg box is pushed up the ramp (height is 6 m and hypo is 12 m) in 3.25 s. If it requires a force of 40 N to push at a constant velocity, what is the efficiency of the ramp? Homework Equations Eff=(Wout/Win) x100 W= Fxd F=ma The Attempt at a Solution The problem I have...
  9. U

    Why the efficiency of air core transformer changes (up and down)

    The graph below shows the efficiency of an AIR CORE transformer at different voltages (from MAINS). At low voltages, it has high efficiency and gets lowers because of high magnetising current causing heat loss. But why is it higher at some points again? I do not understand this pattern. Please...
  10. S

    Does efficiency always depend on reversibility of the engine?

    I'm confused on the efficiency of a Thermal engine in the case it is reversible or not reversible, in particular where the ideal gas follows isochoric or isobaric processes. Infact during isochoric and isobaric processes $$Q_{isochoric}=n c_v \Delta T$$ $$Q_{isobaric}=n c_p \Delta T$$ So the...
  11. S

    Efficiency of engine when non-boundary work done is done?

    The thermal engine efficiency is defined as $$\eta = \frac{W_{\mathrm{produced}}}{Q_{\mathrm{absorbed}}}\tag{1}$$ A more general definition of efficiency (not only for thermal machines is) $$\eta = \frac{\mathrm{Work \, produced}}{\mathrm{Energy \, absorbed}}\tag{2}$$ But suppose that, in one...
  12. Joyal Babu

    On the possibility of making an engine with efficiency 1

    https://www.researchgate.net/post/Gibbs_free_energy_U-TS_PVIn_a_high_pressure_environment_when_PV_equals_TS_can_we_actually_use_the_entire_internal_energy_of_a_system_to_do_work?_iepl%5BviewId%5D=EMvZ8y3kBTyHiPzK6A8YVYvn&_iepl%5BsingleItemViewId%5D=erF86LeZ0BmbObFXKscz92Ib&_iepl%5BactivityId%5D=7...
  13. ChrisVer

    A What is the significance of a slow turn-on curve in trigger efficiency plots?

    I am trying to understand how a Trigger efficiency plot should be interpreted in the scenario of an analysis that is using that trigger. What does a turn-on curve tell us about events that pass the trigger? One example (I think it's PUBLIC so it's accessible)...
  14. Dusan Stan

    One big propeller vs. multiple smaller propellers....

    The question is which is better from the efficiency point of view: One big propeller or multiple smaller ones? Or are they the same? My general impression is that a bigger one will have much more better efficiency as if you consider the following points: 1. lift is proportional to the area of...
  15. S

    Problem with refrigerator and radiator

    Homework Statement The following data refer to an electrically operated refrigerator: - Efficiency : ## \xi = 2.4## - Temperature inside: ##T_i = -9 ° C ## - Temperature of the radiator ## T_r = 40 °C ## - Room temperature: ## T_s = 35 °C## - Total surface of walls: ## A = 3.2 m ^ 2 ## -...
  16. S

    What is the effect of efficiency on the cost of electricity?

    I'm having trouble understanding the effect of efficiency on the cost of electricity for a PV system. By the graph I've uploaded, as the efficiency of a PV system goes up, the cost of electricity goes up. But the equation in the other photo has efficiency in the denominator of the equation...
  17. Fizzics

    Is it Possible to get over 90% efficiency from a servo motor

    ...If so what would the highest figure be whilst running a 1kw (single or 3 phase) motor under normal conditions also would using a 10:1 Gearbox change that efficiency level?
  18. B

    I Geometric efficiency and CTDI(vol)

    Is there a relationship between the geometric efficiency of the scanner and computer tomography dose index of a scanner? I expect the relationship would be inverse but I wanted to check (i.e: if I half the geometric efficency I would double the CTDI(vol). Is this correct thanks
  19. B

    Water pump (centrifugal) efficiency, does placement height mater?

    I am pumping water out of a pond that is being dug with a 30 h.p. centrifugal water pump. I am lifting the water about fifteen feet and discharging it at the same level as the pump. I feel lowering the pump near the water level and pushing the water up the fifteen feet would be more efficient...
  20. S

    Decoupling Compression and Expansion of a turbine

    Hi, I just want to double check something: My understanding is that the higher the compression pressure the higher the amount of energy per unit mass it will take to compress a given mass of gas. So my question is, would a decoupled system where the compression can take place over a longer...
  21. MattRob

    Reduced Efficiency at Sea Level

    Liquid-fueled rocket engines almost always seem to have lower specific impulse at sea level than in a vacuum. I know of one reason: 1. Nozzle expansion. Many engines are optimized for higher-altitude performance, so their nozzle is over-expanded for lower altitudes. I would say more, but I...
  22. DevonZA

    Power output/input, energy input, efficiency of engine & generator

    Homework Statement Homework Equations P=2piNT/60 P=I^2R Pin=Pout/efficieny E=P/t The Attempt at a Solution 2.1 P=I^2R = (5)^2x48 = 1200W 2.2 Pin=Pout/efficiency = 1200/0.86 = 1395.35W 2.3 P=2piNT/60 *3100.78=2pi(500)T/60...
  23. S

    Efficiency of a PV module and solar thermal collector

    Does the efficiency of a PV module and solar thermal collector go down as ambient temperature (outside temperature) increases? I know there are other factors that influence efficiency, but I'm only considering the one parameter of temperature on a PV module and solar thermal collector.
  24. A

    Magnetism, electricity, and photons

    If photons are part of a magnetic field like electrons, which electrons can be read with an amp meter, what can measure or count photons? Electrons are not counted but the magnetic field changes when more current flows and the ammeter reads a change in the magnetic field. What type of light are...
  25. U

    Is it more efficient to eject burnt fuel as reaction mass in rockets?

    Is it more energy efficient to throw a large object slower than a slower object faster? For example, suppose a 100kg person out in space threw a 10 kg object away from themselves at 1 m/s. that means that the 100 kg person would move in the opposite direction at .1 m/s. And this should take...
  26. K

    Find the maximum thermodynamic efficiency

    Homework Statement If an engine operates between 250°C and 25°C, what is its maximum thermodynamic efficiency?Homework Equations Ec=1-Tc/Th The Attempt at a Solution 1-25/250 =90% or 1-(25+273)/(250+273) =43% In this question,which one should I use K or ºC ? thank you
  27. S

    Help to understand polytropic exponent and efficiency

    Hello all, I am new to thermodynamics applied to turbines and compressors and I am trying to get my head around what is represented when calculating the work of a compression/expansion process using the polytropic exponent as oppose to the specific heat ratio of 1.4 (I'm working with air). The...
  28. S

    Efficiency of Electrical Conversion

    I completed a solar energy lab, where we looked at power flows, which were represented through different parts of a circuit measured with 3 separate ammeters. We used four different modes and varied the irradiance and load. only charging = energy from solar panel to circuit without battery...
  29. P

    Light Collection Efficiency for Liquid Scintillation Detecto

    How do I calculate the light yield and light collection efficiency of a liquid scintillation detector? Couls someone give me a formula for that? What data do I need to calculate it? THanks a bunch!
  30. S

    How Does a Heat Engine's Efficiency Affect Final Temperature and Work Output?

    Homework Statement Two identical tanks of water are at absolute temperatures ##T_A## and ##T_B## respectively, where ##T_{A} > T_{B}##. The tanks each have a heat capacity ##C##, and they are thermally isolated from their environment. Suppose that a heat engine is installed in contact with the...
  31. B

    Transformer Efficiency Problems

    Hello, My friend designs a special transformer, believing that its efficiency will rise and voltage regulation will fall compared to an ordinary one . He did a test with the same resistive load and got results below: T1(ordinary) Vp=220V 50Hz AC Vs(nl) = 99.8V Vs(fl) = 92.8V Pin = 129W...
  32. S

    Question about Reversible Engines and Carnot Efficiency

    Homework Statement I have a question regarding heat engines that cropped up whilst I was doing a practice question. I will summarise the results I obtained for the previous parts of the question so as to save your time. The highlighted parts of the image are where I am having some issues. I...
  33. A

    Small diameter water nozzle efficiency versus nozzle length

    Hello! We are 3 students working on a bachelor thesis rigth now, with the purpose to determine the efficiency for different nozzle designs. We have done several practical tests, where we have logged the water pressure and the flow out from the nozzle, and calculated the nozzle efficiency based...
  34. Passionate Eng

    Transformer Efficiency - Max & Calculation

    hello there i have some confusion about transformer efficiency when it is max? and how it is calculated in different loading conditions e.g. at 80% of full load or at given PF
  35. John Pang

    Carnot Efficiency: Qh/Ql=Th/Tl Explained

    Another question, according to catnot efficiency, Qh/Ql=Th/Tl .Can anyone help explain how is this equation derived? It is really frustrating as my textbook doesn't explain this.
  36. S

    Is the movement of a turbine itself a loss of efficiency?

    Someone please help me understand this concept that has always confused me: Is the movement of the turbine itself a loss of efficiency since that is energy that is not being converted into other (e.g., electrical) energy? For example, if a wind turbine is not hooked up to anything, it will...
  37. Mingsliced

    Centrifugal/Reciprocating Pump Efficiency

    Homework Statement It is proposed to pump 1500 m3 of a liquid (density 1100 kg m–3) each day through a total head of 10 m (including all losses) by using either a centrifugal pump or a reciprocating pump. The centrifugal pump discharges 2.0 m3 min–1 when driven by an electric motor supplying...
  38. S

    Generator efficiency in a vacuum

    If you had a generator in a vacuum with a magnetically levitated rotor and power was drawn from the system by induction, use your imagination on the design of the device, but my question is: Where are the flaws in this concept? (Since perpetual machines are theoretically impossible). In other...
  39. Physicist50

    Solar Cells & Refractive Index

    Hi there, I have recently been researching in depth solar cells/panels, the parameters of their efficiency and the photoelectric effect in general, specifically how different wavelengths of light affect it. My research has yielded a few facts; that the efficiency of standard silicon solar cells...
  40. srinaath

    Why efficiency of induction motor is low for low HP?

    why there is a decrease in efficiency of induction motor when power rating is low? example 1 HP motor efficiency is say 85% then 1/4HP motor efficiency is less than 85%? please clear me this doubt?
  41. C

    Why is the efficiency of a rubber band slingshot constant

    Homework Statement I need to explain for a lab, why the efficiency of a rubber band slingshot constant for different stretch lengths. I don't need math, just a general explanation of why kinetic energy of projectile/elastic potential energy in rubber band is constant. Homework EquationsThe...
  42. N

    Thermal efficiency of reciprocating engines

    In a perfect, ideal world with constant specific heats the thermal efficiency of an otto cycle is dependent on its pressure ratio and a diesel cycle is dependent on its pressure ratio and cut off ratio. But since in the real world the equations with these terms do not hold since specific heats...
  43. A

    Efficiency of Irreversible Engine

    I have a small confusion that can an irreversible engine have greater efficiency than reversible engine if both have different source and sink temperatures?I know that under same conditions reversible engines are more efficient but what can be concluded under different conditions like both...
  44. J

    Efficiency of an electric motor

    The motor runs on dc current. I understand efficiency is useful work/work input. It is attached to the pulley. I think efficiency will remain constant as long as voltage of mains and vertical height remain constant. Am I wrong? Other people claim efficiency increases with load
  45. Marcin H

    Heat Cycles, Work, and Efficiency

    Homework Statement Homework Equations W=-∫PdV ε=W/Q PV=nRT COP=Q/W The Attempt at a Solution Using the first equation for work, I got W=-nrT*ln(3V1/V1) but I don't think that is right. Is this the wrong formula to use for this problem? My answer should be in terms of P1 and V1.
  46. jdawg

    Isentropic efficiency of a pump

    Homework Statement Find the isentropic efficiency of the pump: effpump=(h4s-h3)/(h4-h3) state 3: p3=1.5 bar, h3=467.11, x3=0, v3=1.0528/1000 m3/kg ,s3=1.4336 kJ/kg*K, T3=111.4 deg C state 4: p4=60 bar, h4=474.14, compressed liquid state 4s: p4=60 bar, s3=s4s The values in red are the ones I...
  47. duran9987

    Compute work in Carnot Refrigerator

    Homework Statement The temperature inside the room ##T_I= 25 C ## and the temperature outside the house is ##T_O = 32C##. The temperature difference causes energy to flow into the room (by conduction through the walls and window glass) at the rate 3,000 J/s. To return this energy to the...
  48. y2j

    Calculate Isentropic Efficiency: Tips & Tricks

    Hi can anyone help me about the following ? if I have the experimental data of inlet and outlet of expander (temperature and pressure) working in ORC. Now if I want to find the Isentropic efficiencie : the Isentropic expansion can be found by (entropy in = entropy out) but how to find the...
  49. A

    How much current does the elevator consume?

    Homework Statement Energy conversion efficiency of the elevator is 80%, it is working from 220 volts. How much current does the electro motor consume while it is constantly lifting the 500 kg cabin at 2 m/s. The attempt at a solution I=P/U, so I figured I need to know the power. P=F*v. I...
  50. A

    Electrical Efficiency Calculations HVAC

    Hi, I am trying to do a comparison of electrical efficiencies between 2 HVAC compressors but struggling to find formulas or calculations to figure it out. Can anyone help me?
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