What is Adiabatic: Definition and 494 Discussions

In thermodynamics, an adiabatic process (from the Greek adiábatos, meaning “impassable”) is a type of thermodynamic process which occurs without transferring heat or mass between the system and its surroundings. Unlike an isothermal process, an adiabatic process transfers energy to the surroundings only as work. It also conceptually supports the theory used to explain the first law of thermodynamics and is therefore a key thermodynamic concept.
Some chemical and physical processes occur too rapidly for energy to enter or leave the system as heat, allowing a convenient "adiabatic approximation". For example, the adiabatic flame temperature uses this approximation to calculate the upper limit of flame temperature by assuming combustion loses no heat to its surroundings.
In meteorology and oceanography, adiabatic cooling produces condensation of moisture or salinity, oversaturating the parcel. Therefore, the excess must be removed. There, the process becomes a pseudo-adiabatic process whereby the liquid water or salt that condenses is assumed to be removed upon formation by idealized instantaneous precipitation. The pseudoadiabatic process is only defined for expansion because a compressed parcel becomes warmer and remains undersaturated.

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  1. C

    Work Required for Adiabatic Compression

    Homework Statement One mole of gas compressed to half of its original volume adiabatically, what is the work done? Homework Equations dE= dW + dQ (the d one the w and q should have the line though it) pV^ α= constant = k The Attempt at a Solution As it is adiabatic dQ = 0...
  2. A

    Ideal Gases under Adiabatic Compression

    I'm having trouble understanding what happens to the internal energy of an ideal gas being compressed adiabatically. If DU = DQ + DW, then as we do work PdV compressing the gas, since in adiabatic processes DQ=0, W the change in internal energy is non-zero, so U must increase. But if...
  3. A

    (Thermodynamics) Express adiabatic bulk modulus in terms of

    Homework Statement The adiabatic bulk modulus is defined as: \beta_s=-V(\frac{∂P}{∂V})_sExpress it in terms of experimental variables: C_p, C_v, \alpha, \beta Homework Equations Heat capacity at constant pressure:C_P=(\frac{∂Q}{∂T})_P Heat capacity at constant volume:C_V=(\frac{∂Q}{∂T})_V...
  4. B

    Entropy change in a reversible adiabatic process

    For a reversible process, I imagine it is correct to say that dS = \frac{dq}{T} where all quantities refer to system quantities (not the surrounding). However, for an adiabatic process, dq = 0 . Thus, should it be the case that for an adiabatic reversible process, dS =...
  5. A

    (Thermo) Show that in a Reversible Adiabatic process

    Homework Statement Show that in a reversible adiabatic process, for 1 mole of ideal gas P1V1γ=P2V2γ Where, γ=CP/CVHomework Equations Listed above.The Attempt at a Solution Frankly, I don't really understand what I'm being asked to do.
  6. B

    Isothermal vs Adiabatic expansion

    http://www.pichem.net/images//reversible-adiabatic//adiabatic-expansion-2.jpg Evidently the adiabatic curve is steeper than the isothermal curve. How can I prove this mathematically using the following facts: P_{1}V_{1} = P_{2}V_{2} for a reversible isothermal process...
  7. J

    Reversible Adiabatic Compression: Enthaply Calc

    Homework Statement a fluid undergoes a reversible adiabatic compression from .5 MPa, .2 m3 to .05 m3 according to the law PV1.3 = constant. determine the change in enthalpy, internal energy and work transfer during the process. Homework Equations P1V11.3 = P2V21.3 dH = T dS + V dP dS = 0...
  8. S

    Meaning of the adiabatic constant

    Hello for adiabatic process, pVγ=const What is the physical meaning of the constant at the Rhs of this equality? Many thanks.
  9. D

    Adiabatic Availability and Changing States

    1) What is adiabatic availability? 2) How can the state of a system change without changing amounts of constituents or without changing parameters? 3) Does anyone really use the concept of "adiabatic availability" other than Gyftoppoulas and Paolo? I am reading the book, "Thermodynamics...
  10. P

    Is Work Done During Adiabatic Compression of a Quantum State?

    Is work done by the external agency when an adiabatic change in the Hamiltonian is performed on some State ψ?
  11. M

    Solving Adiabatic Process in Diesel Engine: Final Temp of Air-Fuel Mixture

    Homework Statement In a diesel engine, the piston compresses the air-fuel mixture from an initial volume of 630 cm^3 to a final volume of 30cm^3. If the initial temperature of the air-fuel mixture is 45 degrees C and the process is occurring adiabatically, determine the final temperature...
  12. M

    What is the calculation for work in an adiabatic process?

    Homework Statement My textbook says that W = i/2Δ(pV) for an adiabatic process. I don't understand :S Homework Equations W=∫pdV The Attempt at a Solution
  13. M

    Adiabatic Process: Burst Tire & Cloud Formation

    how is the rapid escape of air from a burst tyre and cloud formation in atmosphere an example of adiabatic process? please explain
  14. P

    Derivation of Adiabatic Lapse Rate

    In the derivation of the adiabatic lapse rate, upon using the 1st law of thermodynamics: Why is potential energy neglected? The parcel of air is doing work PdV which is balanced by the internal energy term, cvdT. I can't think of a reason to neglect gravitational potential energy here. Thanks.
  15. C

    Adiabatic Expansion - proof of PV^(gamma) = constant

    Hi, I was looking at the proof for the derivation of the condition satisfied by adiabatic processes. (The proof can be found in many introductory physics textbooks, I am using Principles of Physics HRW 9th ed.) At some point , they say 'For an ideal gas PV=nRT and if P,V T are allowed to...
  16. E

    Exploring Adiabatic Wind in the Rocky Mountains

    Homework Statement Adiabatic wind. The normal airflow over the Rocky Mountains is west to east. The air loses much of its moisture content and is chilled as it climbs the western side of the mountains. When it descends on the eastern side, the increase in pressure toward lower altitudes causes...
  17. I

    What is the power output of an adiabatic turbine with given parameters?

    An adiabatic turbine ,steam saturated vapour P1=1MPa P2= 100kPa. Mass flow rate is 10kgs-1 of steam. i need to work out how much power is produced help :(
  18. A

    Obtaining gamma (γ) in an adiabatic, reversible expansion

    PROBLEM: One mole of an ideal monatomic gas initially at 300 K (T1) and a pressure of 15.0 atm (P1) expands to a final pressure of 1.00 atm (P2). The expansion occurs via an adiabatic and reversible path. Calculate q, w, ΔU, and ΔH. SOLUTION: q = 0 (adiabatic; no heat exchange occurs)...
  19. brainpushups

    Adiabatic Free Expansion Question

    A typical free expansion scenario described in texts is that of a gas confined to a thermally insulated container with a removable membrane. When the membrane is removed the gas expands into vacuum. I understand that no work can be done because the gas does not exert a force. However, I am...
  20. K

    Reversible adiabatic expansion using Van der Waals' equation

    Homework Statement A real gas obeys Van der Waals‟ equation, which for one mole of gas is (p + A/V2)(V-B) = RT and its internal energy is given by U = CvT - A/V where the molar heat capacity at constant volume, Cv , is independent of the temperature and pressure. Show that the relation...
  21. N

    Numerical on adiabatic expansion

    An ideal gas with g =1.5 is expanded adiabatically. How many times has the gas to be expanded to reduce the rms velocity of molecules 2 times?
  22. D

    Need help finding temperature-volume relation in solving Adiabatic problem

    A monatomic ideal gas (γ = 5/3) is contained within a perfectly insulated cylinder that is fitted with a movable piston. The initial pressure of the gas is 1.31 × 105 Pa. The piston is pushed so as to compress the gas, with the result that the Kelvin temperature doubles. What is the final...
  23. S

    Thermodynamics: Vapor Compression Refrigeration that is Adiabatic?

    Consider a heat pump works on the vapor-compression refrigeration cycle with 0.2 kg/s of refrigerant-134a as the working fluid. The cycle is used to maintain a house at 26oC while absorbing heat from the outdoors at 3oC. R-134a enters the compressor at 200 kPa as a saturated vapor and leaves at...
  24. B

    Comparison b/w work done in adiabatic & isothermal processes

    Homework Statement In the graph attached, why is isothermal graph line higher than adiabatic one?? Homework Equations The Attempt at a Solution At first, i had thought that work done in an isothermal process is greater than in an adiabatic process...but for comparison we would...
  25. K

    Adiabatic Process: Derive Temp Change w/ Pressure

    Homework Statement Derive an expression for the change in temperature with pressure for an adiabatic process. If a dry air parcel is lifted adiabatically from 1000hPa to 800hPa what is the final temperature if it was initally at 20^{o}C?^{} Homework Equations PV^{k}=constant I derived an...
  26. M

    Thermodynamics: Proofs of work done on/by gas during adiabatic process

    Hello I'm really confused with this and would appreciate any help. Homework Statement a) Show that the work done on a gas during a quasistatic adiabatic compression is given by: W = \frac{P_f V_f - P_i V_i}{\gamma - 1} b) Show that the work done by a gas during a quasistatic...
  27. K

    Cooling that is both Adiabatic and Isochoric - possible?

    I figure that it is possible for temperature to decline in a fixed volume system that is thermally insulated. The reason why is that, from what I understand, is that random kinetic energy may have angular momentum. If we were to subject a volume of such energy to a rotating force (torque), then...
  28. N

    Adiabatic approximation for joint probability distribution

    Hi group, I'm a theoretical ecologist with fairly adequate training in applied math (ODE, linear algebra, applied probability, some PDEs). In my current work, I've encountered the use of adiabatic approximation to a joint probability distribution of two ever-fluctuating spatial variables. A...
  29. A

    Carnot Cycle: Exploring Heat Efficiency and Adiabatic Processes

    I have some trouble understanding the carnot cycle and why you have to make it so complicated, i.e. this process involves 2 isothermal and 2 adiabatic processes. If you want an engine with maximum efficiency why can't you just have a system whose temperature is just a tiny inch above your hot...
  30. B

    Adiabatic Expansion: Solving for Pressure and Volume

    Homework Statement see attachment The Attempt at a Solution I'm having trouble where they multiply (101,000 by 1.5 m3)5/3 I get 151,500 Pa*m5 not 199,000 Pa*m5
  31. M

    Adiabatic Equation Derivation Troubleshooting

    I have been struggling to find my mistake for over 2 hours now and I still haven't exactly matched my answers with the books solution. I feel that my method should give the same answer the solution manual obtained however they are slightly off. I understand the book method completely. Can...
  32. R

    Calculating Enthalpy Change in Adiabatic Compression

    Homework Statement http://img29.imageshack.us/img29/4386/prob1p.jpg The Attempt at a Solution To answer the first question as to why the air needs to be refrigerated, I think it's because refrigerating the gas cause it to do work, so its enthalpy will decrease resulting in a decrease in...
  33. S

    Adiabatic, isobaric & isothermal expansions

    Homework Statement An ideal gas of N particles is reversibly expanded from V1 to V2 = 4V1. The starting temperature T1 is known and E_1 = \frac{3}{2} N k_B T_1. As of yet E_2 is unknown. a) Express \Delta E = E_1 - E_2 in terms of the added heat Q and work done on the gas W. b) Calculate...
  34. Rapier

    Entropy and Adiabatic Expansion

    Homework Statement Argon gas, initially at pressure 100 kPa and temperature 300 K, is allowed to expand adiabatically from 0.01 m3 to 0.029 m3 while doing work on a piston. In this problem you will calculate the contributions to the entropy change, as discussed in Moore, T7.4. a) What is...
  35. K

    Adiabatic compression of gas at two temperatures

    I have a system that looks like this: The top part is a piston, whereas the bottom is a displacer. I have looked at the Isothermal case for this system in a separate thread (https://www.physicsforums.com/showthread.php?t=553165) But in short, the result was that the pressure of the system...
  36. C

    Help with isotherms and adiabatic curves

    This is to help me understand a problem in the book, I don't want to state the question I'm attempting to solve though I would rather just get a nudge in the right direction conceptually. (I am analyzing an isotherm and adiabatic curve at the same point.) My book states that for an ideal gas...
  37. O

    Thermodynamics - Irreversible Adiabatic expansion

    Homework Statement Closed system made of a cylinder containing air, compressed by a piston with weights on top of it. The piston is frictionless and its weight can be neglected. The system contains initially 10 kg of air at 27 °C and a pressure of 10 ata. The weights are suddenly halved...
  38. K

    Understanding Adiabatic Compression

    Hi, I have a little problem understanding adiabatic compression. Let me start with the definition of adiabatic process from wikipedia, "In thermodynamics, an adiabatic process or an isocaloric process is a thermodynamic process in which the net heat transfer to or from the working fluid is...
  39. J

    Work input/output in adiabatic process

    I have to find the max cycle pressure, max temp, work input and output for an engine. I have been given the initial air pressure, temp and the volume of the cylinder. Fuel is added at 2.5MJ/kg For the air i have Cv, the index (1.4) and an R value of 287 J/kg K (not sure about this value) I...
  40. A

    How can I find the adiabatic equation for real gases?

    Hey! Maybe anyone knows, how to get real gas adiabatic equation. It's not a big deal, when you need to get ideal gas equation, but I haven't got any ideas about real gas. I'm wondering maybe it's something with Van der Waals equation, but in my opinion it can't be like this ...
  41. B

    Adiabatic Process: 1kg H2O from 220kPa, 200C to 50C

    Homework Statement 1 kg of H20 goes through a reversible adiabatic proces from 220kPa, 200C to 50C in the final state. What is the pressure final and volume final? Assume S1=s2 Homework Equations Conservation of Energy The Attempt at a Solution Found S to be 7.5080, was...
  42. C

    Calculating outlet temperature and heat transfer in an adiabatic spray cooler

    Question: In an adibatic Spray cooler, a fine mist of liquid water is used to cool hot air by evaporating all of the water. The liquid flows in at a rate of 90 g/s and 30°C. The input hot air is at 450°C and 900 torr. The dewpoint of the input air is 47°C and the flow rate is 1362 L/s...
  43. N

    Prove non adiabatic reversible expansion and ΔS

    Homework Statement One mole of a monatomic ideal gas is transformed from 0.00°C and 2.00 atm to -40.0°C and 0.400 atm. Show that this is NOT an adiabatic reversible expansion and calculate ΔS for the change. (Hint: you will need to consider a reversible path that includes a...
  44. S

    Can adiabatic process be isothermal process?

    i'm entirely confused with this. with analyzing each definition: adiabatic process : a thermodynamic process in which there is no transfer of heat if a system is in state (P1, V1, T1) → (P2, V2, T2) if it is adiabatic no heat transfer occurs, if no heat transfer occurs the two states must be...
  45. J

    Proof of work done by an ideal gas in a quasi-static adiabatic expansion

    Homework Statement Prove that the work done by an ideal gas with constant heat capacities during a quasi-static adiabatic expansion is equal to W= (PfVf)/(Y-1)[1 - (Pi/Pf)^((Y-1)/Y)] where Y = gamma, which is heat capacity at constant pressure over heat capacity at constant volume...
  46. L

    Adiabatic expansion at constant pressure.

    Homework Statement A sample of 4.00mol of oxygen is originally confined in a 20L vessel at 270K and then undergoes adiabatic expansion against a constant pressure of 600torr until the volume has tripled. Find q, W, dT, dU, dH. Homework Equations U=q+w H=U+PV The Attempt at a Solution q=0...
  47. V

    Adiabatic perturbations and Fermi's golden rule

    Hi all, I'm having some difficulty in my advanced QM class with adiabatic perturbations and Fermi's Golden Rule. I understand the physical reasons behind the conclusion of the adiabatic perturbation calculation (that a particle in the ground state will end up in the new Hamiltonian's ground...
  48. I

    Internal Energy and Work Done in an Adiabatic Process

    Homework Statement The question is as following: http://i56.tinypic.com/se547s.png Homework Equations W = F x distance or p d(v) . Potential energy : mgh , k.e : 1/2mv^2 The Attempt at a Solution Well I am stuck on part c, now I am aware that in adiabatic process Internal...
  49. I

    Adiabatic process - Diesel engine

    Homework Statement A diesel engine requires no spark plug. The air in a cylinder is compressed so highly that the fuel spontaneously ignites when sprayed into cylinder. If the air is initially at 20°C and is then compressed by a factor of 15 in volume, what final temperature is attained...
  50. J

    The work done by an adiabatic process?

    Homework Statement On my formula sheet I have this: W=(C/1-y)(Vf^(1-y)-Vi^(1-y)) y=Cp/Cv Homework Equations The Attempt at a Solution I am confused about what the C in C/1-y stands for. My textbook does not even have this formula and I realized that C is not Cp or Cv...
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