Isothermal Process

5 Key excerpts on "Isothermal Process"

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  Advances in Thermodynamics and Thermal Engineering

  • (Author)
  • 2014(Publication Date)
  • Academic Studio

    (Publisher)

  It is also worth noting that, for many systems, if the temperature is held constant then the internal energy of the system also is constant, and so Δ U = 0. From First Law of Thermodynamics, Q = Δ U + W , so it follows that Q = W for this same Isothermal Process. Applications Isothermal Processes can occur in any kind of system, including highly-structured machines, and even living cells. Various parts of the cycles of some heat engines are carried out isothermally and may be approximated by a Carnot cycle. Phase changes, such as melting or evaporation, are also Isothermal Processes. Adiabatic process In thermodynamics, an adiabatic process or an isocaloric process is a thermodynamic process in which no heat is transferred to or from the working fluid. The term adiabatic literally means impassable, coming from the Greek roots ἀ - (not), δι ὰ - (through), and βα ῖ νειν (to pass); this etymology corresponds here to an absence of heat transfer. Conversely, a process that involves heat transfer (addition or loss of heat to the surroundings) is generally called diabatic . Although the terms adiabatic and isocaloric can often be interchanged, adiabatic processes may be considered a subset of isocaloric processes; the remaining complement subset of isocaloric processes being processes where net heat transfer does not diverge regionally such as in an idealized case with mediums of infinite thermal conductivity or non-existent thermal capacity. In an adiabatic irreversible process, dQ=0 is not equal to TdS (TdS>0). dQ=TdS=0 holds for reversible processes only. For example, an adiabatic boundary is a boundary that is impermeable to heat transfer and the system is said to be adiabatically (or thermally) insulated; an insulated wall approximates an adiabatic boundary. Another example is the adiabatic flame temperature, which is the temperature that would be achieved by a flame in the absence of heat loss to the surroundings.

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  eBook - ePub

  Thermodynamics Made Simple for Energy Engineers

  & Engineers in Other Disciplines

  • S. Bobby Rauf(Author)
  • 2023(Publication Date)
  • River Publishers

    (Publisher)

  8 Thermodynamic Processes

  Topics

  • Thermodynamic processes
  • Heat engine cycles
  • Steam turbines
  • Temperature-enthalpy diagrams
  • Pressure-enthalpy diagrams
  • Pressure-volume diagrams
  • Temperature-entropy diagrams
  • Practical examples and associated case study.

  8.1 Introduction

  This chapter explores some of the mainstream thermodynamic processes, heat engines and heat engine cycles. Fundamentals of thermodynamic processes, heat engines, heat engine cycles and associated systems are explained and illustrated through process flow diagrams, graphs, tables and pictures. Practical significance, application, analytical methods, and computational techniques associated with heat engine cycles and thermodynamic processes are demonstrated through case study, examples and self-assessment problems.

  8.2 Thermodynamic Processes

  Thermodynamic processes are processes that entail heat, internal energy, enthalpy, entropy, work, pressure, temperature and volume. In this section, we will explore the following thermodynamic processes and illustrate these processes with practical examples:

  1. Adiabatic Process
  2. Isenthalpic Process
  3. Isochoric Process
  4. Isothermal Process
  5. Isobaric Process
  6. Isentropic Process

  8.2.1 Adiabatic process

  Adiabatic process is a thermodynamic process in which no heat either enters or leaves the thermodynamic system boundary. An adiabatic process can also be explained through the following mathematical statements or equations:

  (8.1)

  Δ U = − W

  (8.2)

  Δ Q = 0

  Equations 8.1 and 8.2 essentially state that in an adiabatic process, wherein no heat is gained or lost, any work performed on the system or by the system is transformed into a net change in the internal energy of the system. As specifically stated above, Eq. 8.1

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  eBook - PDF

  Thermodynamics Made Simple for Energy Engineers

  • S. Bobby Rauf(Author)
  • 2021(Publication Date)
  • River Publishers

    (Publisher)

  Chapter 8 Thermodyna mic Processes INTRODUCTION This chapter explores some of the mainstream thermodynamic processes, heat engines and heat engine cycles. Fundamentals of ther-modynamic processes, heat engines, heat engine cycles and associated systems are explained and illustrated through process fow diagrams, graphs, tables and pictures. Practical signifcance, application, analyti-cal methods and computational techniques associated with heat engine cycles and thermodynamic processes are demonstrated through case study, examples and self-assessment problems. THERMODYNAMIC PROCESSES Thermodynamic processes are processes that entail heat, internal energy, enthalpy, entropy, work, pressure, temperature and volume. In this section, we will explore the following thermodynamic processes and illustrate these processes with practical examples: 1. Adiabatic Process 2. Isenthalpic Process 3. Isochoric Process 4. Isothermal Process 5. Isobaric Process 6. Isentropic Process Adiabatic Process Adiabatic process is a thermodynamic process in which no heat either enters or leaves the thermodynamic system boundary. An adia-batic process can also be explained through the following mathemati-cal statements or equations: 149 150 Thermodynamics Made Simple for Energy Engineers ΔU = -W Eq. 8-1 ΔQ = 0 Eq. 8-2 Equations 8-1 and 8-2 essentially state that in an adiabatic pro-cess, wherein no heat is gained or lost, any work performed on the sys-tem or by the system is transformed into a net change in the internal energy of the system. As specifcally stated above, Eq. 8-1 represents a scenario where negative work is involved. In other words, work is being performed by the surroundings onto the system. And, since no heat is transferred to or from the environment in an adiabatic process, the work performed by the surroundings onto the system, in this case, is converted into an equivalent amount of increase in the internal ener-gy of the system.

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  Thermodynamics and Heat Power

  • Irving Granet, Maurice Bluestein(Authors)
  • 2014(Publication Date)
  • CRC Press

    (Publisher)

  Most heat exchangers are well insulated and may be considered adiabatic. Thus,   mc T T mc T T ph pc ( ) ( ) 2 1 4 3 -= --where c ph is the specific heat of the hot fluid and c pc is the specific heat of the cold fluid. Note that the negative sign is needed because the heat transfers are going in opposite directions. Heat exchangers are discussed in more detail in Chapter 11. 6.7.3 Constant-Temperature Process Next, the isothermal steady-flow process for the ideal gas is considered. Here, the relation-ship pv = constant is substituted into Equation 6.92, which is then integrated to yield w p v p p = 1 1 1 2 ln (6.98) Using the ideal gas law, this relationship can also be written as w RT p p = ln 1 2 (6.99) Since the temperature is constant, there is no change in enthalpy for such processes. In prac-tice, reversible constant temperature processes are never realized but are a goal to shoot for as they represent the minimum work input for compression and the maximum work output for expansion (see Section 6.5.5). This is also what makes the Carnot cycle with its two constant temperature processes exist only in the ideal state. Note that even though the temperature may be constant, there can still be heat transfer equal to the work being done. 6.7.4 Isentropic Process Next, the isentropic steady-flow ideal gas process is considered. The general path equa-tion is given in Equation 6.67, which may be substituted into Equation 6.92 with n = k . The integration of this equation yields w k p v p v k = --( ) 2 2 1 1 1 (6.100) 298 Thermodynamics and Heat Power The ideal gas law may be used to find alternate expressions for Equation 6.98 that are more useful for the values given in a particular problem.

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  Lectures on Theoretical Physics

  Thermodynamics and Statistical Mechanics

  • Arnold Sommerfeld, F. Bopp, J. Meixner, J. Kestin(Authors)
  • 2012(Publication Date)
  • Academic Press

    (Publisher)

  The processes which we encounter in real life are always irreversible processes, processes during which disturbed equilibria are being equalized. Instead of using the term “reversible process” we can also speak of infinitely slow, quasi-static processes during which the system’s capacity for performing work is fully utilized and no energy is dissipated. In spite of their not being real, reversible processes are most important in thermo-dynamics because definite equations can be obtained only by considering reversible changes; irreversible changes can only be described with the aid of inequalities when equilibrium thermodynamics is used. The actual criterion for a process to be reversible states that during its course there are no lasting changes of any sort in the surroundings if the process is allowed to go forward and then back to the original state. 20 THERMODYNAMICS. GENERAL CONSIDERATIONS A. T he r e v e r s i b l e a d i a b a t i c p r o c e s s The term adiabatic implies: exclusion of heat transfer to and from the body; in this connection the thermos flask invented by Dewar may be thought of. The opposite case is that of an Isothermal Process; in order to maintain the temperature it is necessary to allow heat to be transferred; in this connection one may imagine a water bath in which our quantity of gas is immersed. Consider a unit mass of a perfect gas and substitute dq = 0 du = cv dT into (4.2), taking into account (4.4). We then have (1) cv d T = -p dv. In order to transform this into a relation between v and p we use the equation of state (3.11 a). Instead of (1) we may write °v ( P dv + v dp) + pdv = 0 K ic· + f): j cv -j -----J p dv — )— cv v dp ■ so that in view of (4.5) Cp p dv + cv v dp = 0, or, considering (4.14): dp dv (2) 7 + > Ί γ = ° We now assume γ to be a constant, see end of Sec. 4, so that we actually exceed the caloric assumption according to which u and hence cv, cp and y depend on T alone.

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