Adiabatic Process
An adiabatic process is a thermodynamic process in which there is no heat transfer into or out of the system. This means that the change in internal energy of the system is solely due to work done on or by the system. In practical terms, adiabatic processes are often achieved by insulating the system to minimize heat exchange with the surroundings.
4 Key excerpts on "Adiabatic Process"
eBook - ePub- Richard Gentle, Peter Edwards, William Bolton(Authors)
- 2001(Publication Date)
- Newnes(Publisher)
...Usually, this heat energy is transferred out of the cylinder walls to the engine cooling water. The quantity of heat energy transferred affects the values of pressure and temperature achieved by the gas within the cylinder. Only in an Adiabatic Process is there no transfer of heat energy to or from the gas, and this situation is impossible to achieve in practice. In order to find how much heat energy has been transferred during a non-flow process, we use the non-flow energy equation (NFEE) (see page 17, ‘The non-flow energy equation’. In words, this means that the heat energy transferred through the cylinder walls is the work done during the process added to the change in internal energy during the process. Remember that the internal energy of the gas is the energy it has by virtue of its temperature, and that if the temperature of the gas increases, its internal energy increases, and vice versa. Using the NFEE is straightforward, in that we have already seen the equations for work done, and the change in internal energy for any process (see page 16, ‘Internal energy’) is given by We can calculate each and add them together. Applying the NFEE to each process gives, Constant volume Constant pressure It is useful to digress here to establish an important expression concerning the gas constant, R, and values of c p and c v. We know that the heat energy supplied in the constant pressure process is therefore, Substituting. from p.V = m.R.T), p (V 2 − V 1) = m.R (T 2 − T 1), and dividing by (T 2 − T 1), Adiabatic This is the definition of an Adiabatic Process. Note: if W and δ U were calculated and put in the formula, the answer would be 0. Polytropic Isothermal Q = W + (U 2 − U 1). No change in temperature, therefore no change in U. Note that the ‘ m.R.T ’ versions of the work done expressions could be used instead. Example 2.3.4 0.113 m 3 of air at 8.25 bar is expanded in a cylinder until the volume is 0.331 m 3...
eBook - ePub- H. W. Liepmann, A. Roshko(Authors)
- 2013(Publication Date)
- Dover Publications(Publisher)
...In any case the relations for a perfect gas are integrible. Thus, for example, in ; if γ is constant, the relations become very simple indeed: We shall later see that an adiabatic, reversible process is isentropic: i.e., a process for which the entropy S remains constant. These examples do not exhaust, of course, the applications of the first law to reversible processes. But they outline the general procedure. 1.8 The First Law Applied to Irreversible Processes The first typical irreversible process that we shall discuss is the adiabatic expansion of a gas. The system of interest consists of a vessel with heat-insulated, rigid walls. A diaphragm divides the vessel into two volumes V 1 and V 2 (Fig. 1.3). Both volumes are filled with the same gas at the same temperature T. The pressures p 1 and p 2, however, are different. The theory of the flow under such conditions will occupy us in later chapters; here we are interested only in the thermodynamics of the setup. F IG. 1.3 Heat-insulated vessel with dividing diaphragm. Let the diaphragm be ruptured at a time t = 0. A violent flow of the gas ensues; a shock wave propagates into the low-pressure side, an expansion wave into the high-pressure side, and by reflection and refraction a complicated wave system is set up. This subsides under the action of viscosity and internal heat conductivity, and eventually the gas is at rest again, in a new state of thermodynamic equilibrium. We now apply the first law to the change from the initial state to the final one. No heat has left the surroundings, and no work has been performed by the surroundings. Hence from Eq. 1.5 we have The internal energy in an expansion process is conserved. If the gas can be approximated by a perfect gas, then E = E (T) and hence Eq. 1.32 yields: In the adiabatic, irreversible expansion of a perfect gas, initial and final state have the same temperature...
eBook - ePubStirling Cycle Engines
Inner Workings and Design
- Allan J. Organ(Author)
- 2013(Publication Date)
- Wiley(Publisher)
...Charles’ Law was proposed considerably later in the 1780s, but remained obscure until Gay-Lussac’s exposition of 1802. It is hard to see how the notion of the ‘isothermal’ process could have enjoyed currency prior to awareness of the concept of adiabatic. Rankine’s 1845 account of the cycle was argued graphically, and was in terms of process paths, including ‘isodiabatic’ paths. Such a path is not necessarily adiabatic, but the usage suggest awareness of ‘adiabatic’ as a limiting case. Had the variable-volume processes been treated from the outset as Rankine’s ‘diabatic’ – and other cycle phases evaluated accordingly – it is possible that the Stirling engine might have progressed differently towards commercial exploitation. A high price since has been paid for the burdensome – and inappropriate – association with isothermal phases, with the Carnot cycle and for the resulting epidemic of shattered illusions. 1. Things known or assumed as facts, and made the basis of reasoning or calculation. Shorter Oxford Dictionary, 1993....
eBook - ePub- Mike Pauken(Author)
- 2011(Publication Date)
- For Dummies(Publisher)
...The following units are equivalent: 1 kJ = 1 kPa · m 3. A constant-temperature process: Suppose you push on the piston shown in Figure 4-4 to compress the gas. If you don’t remove any heat, the gas temperature will rise. But you can maintain a constant temperature in the gas by removing just the right amount of heat as the gas is compressed. The gas pressure changes in the cylinder in this process. The process works in reverse by heating gas during expansion. For a constant-temperature process with an ideal gas, you can substitute the ideal-gas relationship, PV = mRT, into the preceding equation that defines boundary work. I discuss the ideal-gas relationship in Chapter 3. Completing the integration gives the following set of equations that are equal to each other for the boundary work: A reversible-Adiabatic Process: You can make the piston-cylinder device shown in Figure 4-4 adiabatic by putting perfect insulation around the cylinder. Adiabatic means no heat is transferred across the system boundary between the gas inside the cylinder and the environment. (For this case, the piston-cylinder device becomes part of the system.) Reversible means the process can go in the reverse direction to return to the initial state without creating a change in the system or the surroundings (see Chapter 9). As you push or pull on the piston, both the gas temperature and pressure in the cylinder change in this process. If the process is both adiabatic and reversible, the pressure-volume relationship is PV k = C, where k is the specific heat ratio (k = c p / c v) and C is a constant...
