What is cyclic process: Definition and 12 Discussions

A thermodynamic cycle consists of linked sequences of thermodynamic processes that involve transfer of heat and work into and out of the system, while varying pressure, temperature, and other state variables within the system, and that eventually returns the system to its initial state. In the process of passing through a cycle, the working fluid (system) may convert heat from a warm source into useful work, and dispose of the remaining heat to a cold sink, thereby acting as a heat engine. Conversely, the cycle may be reversed and use work to move heat from a cold source and transfer it to a warm sink thereby acting as a heat pump. If at every point in the cycle the system is in thermodynamic equilibrium, the cycle is reversible. Whether carried out reversible or irreversibly, the net entropy change of the system is zero, as entropy is a state function.
During a closed cycle, the system returns to its original thermodynamic state of temperature and pressure. Process quantities (or path quantities), such as heat and work are process dependent. For a cycle for which the system returns to its initial state the first law of thermodynamics applies:







{\displaystyle \Delta U=E_{in}-E_{out}=0}
The above states that there is no change of the internal energy (


{\displaystyle U}
) of the system over the cycle.



{\displaystyle E_{in}}
represents the total work and heat input during the cycle and



{\displaystyle E_{out}}
would be the total work and heat output during the cycle. The repeating nature of the process path allows for continuous operation, making the cycle an important concept in thermodynamics. Thermodynamic cycles are often represented mathematically as quasistatic processes in the modeling of the workings of an actual device.

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  1. singularcell

    Efficiency and Temperature in Heat Engine Cycles: Approaching Parts B, C, and D

    I didn't have much trouble with part a but I'm struggling with b,c, and d. I considered the efficiency formula for a heat engine e = work done by engine/ qh but i am unsure of how to approach it. for part c) not sure how i can get to Tc without knowing Th for d) my gut is telling me 5/2 but i...
  2. E

    Cyclic Process for Ideal Gases

    Hello there, is my solution for part d logically correct? Here is my attempt at the solution : Part a : where : P1 = 3P2 Part b : Since P1=3P2, therefore, T1=3T, where T=300K. Thus, T1=900K Part c : Because the final pressure at the end of the cycle is exactly the same as the pressure at...
  3. S

    Entropy change for reversible and cyclic process

    Homework Statement An ideal diatomic gas is initially at temperature ##T## and volume ##V##. The gas is taken through three reversible processes in the following cycle: adiabatic expansion to the volume ##2V##, constant volume process to the temperature ##T##, isothermal compression to the...
  4. C

    Heat transferred in a cyclic process

    Homework Statement Assume that a gas obeys the VDW Virial expansion Pv = RT + (b-a/RT)P to first order in P and u = 3RT - aP/RT to first order in P, where v and u are molar quantities. In the following cycle (see attachment), the heat transferred to the gas is transferred by direct thermal...
  5. Saitama

    What is the Efficiency of a Cyclic Process?

    Homework Statement (see attachment, ignore the arrows made with the pen) Homework Equations The Attempt at a Solution Efficiency of a cycle is defined as ##\eta=\frac{W}{Q}## where W is work done and Q is heat input. W can be easily calculated by finding the area enclosed...
  6. H

    What is a reversible cyclic process?

    I know carnot's cycle is an example. but what is it exactly? a cycle in which ever part of process has a 'counter-process' please elaborate.
  7. R

    Calculate work and heat in a cyclic process ?

    Homework Statement Consider n moles of ideal gas kept in a cylinder with a piston. Two heat reservoirs 1 and 2 with the temperatures T1 < T2 are available, and at any given moment of time the heat exchange is established with only one of the reservoirs. In the initial equilibrium state the...
  8. C

    Work done by cyclic process (thermodynamics)

    Homework Statement http://s9.postimage.org/5iw5rixyl/image.jpg (sorry doesn't let me embed) Homework Equations P1V1=P2V2 and PV=nRT I know that Work done by gas from a --> b = (nRT)*Integral(V2/V1) My question is do i use PV=nRT to find N? and if T is constant (isothermal) what do I plug in...
  9. R

    Thermodynamics : Work in a Cyclic Process

    Homework Statement Three moles of an ideal gas are taken around the cycle abc. For this gas, Cp= 29.1 J/mol K. Process ac is at constant pressure, process ba is at constant volume, and process cb is adiabatic. The temperatures of the gas in states a, c, and b are Ta= 300K, Tb= 490K, Tc=...
  10. A

    Temprature-Entropy cyclic process

    Homework Statement There is a temperature-Entropy graph (T-S) (attachment),which illustrates a hypothetical cyclic process. a) Calculate the heat input or output along each of the paths. b) Find an expression for the efficiency η of the complete cycle in terms of T1 and T2 only...
  11. T

    Hypothetical cyclic process- does it violate the thermodynamic laws?

    Consider the following cyclic process: Each cycle 800J of Energy is transferred from a reservoir at 800K and 600J of energy from a reservoir at 600K. 400J of heat is rejected to a reservoir at 400K and 1000J of work is done. I think that the process doesn't violate the first or second laws...
  12. K

    How Do You Calculate Entropy Change in a Reversible Cyclic Process?

    An ideal gas undergoes a reversible, cycli process. First it expands isothermally from state A to state B. It is then compressed adiabatically to state C. Finally, it is cooled at constant volume to its original state, A. I have to calculate the change in entropy of the gas in each one of the...