Ideal mechanical work

A closed system cannot perforin an isentropic process without performing work. Example (Fig. 3) A quantity of gas enclosed by an ideal, tfictionless, adiabatic piston in an adiabatic cylinder is maintained at a pressure p by a suitable ideal mechanism, so that Gl = pA (A being the area of piston). When the weight G is increased (or decreased) by an infinitesimal amount dG, the gas will undergo an isentropic compression (or expansion). In this case,... 

A possible objection could be that the surface tension is measurable and thus the Laplace equation assigns the location of the ideal interface. But this is not true. The only quantity that can be measured is mechanical work and the forces acting during the process. For curved surfaces it is not possible to divide volume and surface work. Therefore, it is not possible to measure only the surface tension. 

A work reservoir is similarly defined as any body or combination of bodies, used as part of the surroundings, whose only interaction with the system is one that may be described in terms of work. We may have a different type of reservoir for each mode of interaction other than thermal interaction. A work reservoir then is used to perform work across the boundary separating the reservoir and the thermodynamic system and to measure these quantities of work. In the following we are, in order to simplify the discussion, primarily concerned with mechanical work, but this limitation does not alter or limit the basic concepts. A reservoir for mechanical work may be a set of weights and pulleys in a gravitational field, an idealized spring, or a compressible fluid in a piston-and-cylinder arrangement. In any case the reservoir must... 

Adiabatic flow of a perfect gas without friction. An ideal frictionless process is represented where a gas is compressed, the area indicating the flow work, which is equal to the change in kinetic energy if no mechanical work in a machine is involved. Thus ... 

We recall from thermodynamics that a component s contribution to a mixture s ability to perform mechanical work (the Gibbs free energy) is called the chemical potential p. . The chemical potential increases with temperature, pressure, and concentration of the component in the mixture. For example, the chemical potential for an ideal gas component can be expressed as... 

In the case of an ideal gas and a large hole between the vessels—in other words, when the gas passes through the hole as a macroscopic flux—the components of the transfer energy E are both the internal energy U and mechanical work pV. Therefore, for ideal gas... 

This result, called the Carnot efficiency or the thermodynamic efficiency, places a fundamental limit on the efficiency with which heat can be converted to mechanical work. Only if the high temperature, T, were infinite or the low temperature, T , were zero would it be possible to have a heat engine operate with 100% efficiency. To maximize efficiency, the greatest possible temperature difference should be used. Although we derived this result specifically for the ideal gas, we will show later in this section that it applies to any reversible engine operating between two temperatures. For a real engine, which must operate irreversibly, the actual efficiency must be lower than the thermodynamic efficiency. 

To repeat, I am not advancing explanation by mechanisms as an ideal or a norm. Explanation by laws is better - but also more difficult often too difficult. (See also 1.8.) Moreover, as should be clear by now, I am not suggesting that mechanisms can be identified by formal conditions analogous to those that enter into the formulation of laws. "If p, then sometimes q" is a near-useless insight. Explanation by mechanisms works when and because we can identify a particular causal pattern that we can recognize across situations and that provides an intelligible answer to the question, "Why did he do that "... 

The temperature 9 of the second law, called the thermodynamic temperature, will be shown to be identical to the ideal-gas temperature T. To proceed, we consider the Carnot cycle to produce mechanical work from heat. The Carnot cycle is an idealized reversible cycle by which a working fluid is confined in a cylinder-piston device to (a) absorb heat from a high-temperature source while producing mechanical work and (b) reject heat to a low-temperature sink while being compressed toward the original state. The successive steps of a Carnot cycle are as follows ... 

When one talks about reversibility of the Rehbinder effect, the presence of a thermodynamically stable interface between mutually saturated solid phase and the liquid, as well as complete disappearance of these effects upon the removal of the medium (e.g. by evaporation) are implied. These features emphasize principal difference between the Rehbinder effect and corrosive action of the medium. At the same time, one has to realize that it is not possible to draw here a distinct border line. The term disintegration covers a broad range of processes from idealized cases of purely mechanical breaking to destruction by corrosion or dissolution. The Rehbinder effect, i.e. the lowering of strength due to adsorption and chemisorption, stress-caused corrosion, and corrosion fatigue, occupies some intermediate place between these extremes. All these phenomena represent a certain degree of combination between the mechanical work performed by external forces and chemical (physico-chemical) interaction with the medium. 

Under ideal, thermodynamically reversible conditions, this mechanical work is equal to the Gibbs free energy change (AG) for the process. The numbers obtained here cannot be compared directly with the values obtained for molecules in solution using bulk thermodynamic methods (Chapter 5) because they include the additional elastic work involved in stretching the unfolded polypeptide as the tethered ends are pulled further apart than they would normally be for an unfolded protein free in solution. 

In an adiabatic expansion of a gas, mechanical work is done by the gas as its volume increases and the gas temperature falls. For an ideal gas undergoing a reversible adiabatic change it can be shown that pvy=Ki V p -r=K2... 

An actuator is a functional element which connects the information processing part of an electronic control system in a technical of nontechnical process. Actuators can be used to control the flow of energy, mass or volume. The output quantity of an actuator is energy or power, often in the form of a mechanical working potential (force times displacement). The actuator control is always achieved using very low electrical power, ideally without any power consumption (Janocha 2004). 

The development of force under conditions of fixed length, as in an isometric contraction, involves the elastic deformation of a chain or chains within the protein-based machine. On relaxation, ideal elastic elements return the total energy of deformation to the protein-based machine for the performance of mechanical work. Thus, the approach toward high efficiency for the function of a protein-based linear motor, or even for the RIP domain movement in Complex III, depends on how nearly the extension of an elastomeric chain segment approaches ideal elasticity. 

If one makes a rough approximation that the gaseous products behave as an ideal gas, then the change of their internal energy (dE) is equal to the sum of the heat exchanged with the surroundings dQ) and the performed mechanical work dAy. 

Carnot cycle The idealized reversible cycle of four operations occurring in a perfect heat engine. These are the successive adiabatic compression, isothermal expansion, adiabatic expansion, and isothermal compression of the working substance. The cycle returns to its initial pressure, volume, and temperature, and transfers energy to or from mechanical work. The efficiency of the Carnot cycle is the maximum attainable in a heat engine. It was published in 1824 by the French physicist Nicolas L. S. Carnot (1796-1832). See Carnot s principle. 

Let us consider one step of the functional cycle of a mechanical entropic machine—expansion of an ideal gas confined to a cylinder with a movable piston (Fig. 3.1). The external load M applied to the top of the piston is assumed to be initially equilibrated by the gas pressure, p = nRT/V, where V is the initial volume of gas in the cylinder, T is the gas temperature in degrees Kelvin, R is the universal gas constant, and n is the number of moles of the gas. The system is assumed to be in contact with a thermostat. On gradually reducing the weight of the external load from to M2, gas will expand, lifting the load and thus performing mechanical work, AW. If the motion of a piston occurs slowly enough, the temperature of the gas will remain con-... 

Differential sorption heats were provided by Monte Carlo simulations of sorption processes, viz., from the slope of curves obtained by plotting values of total potential energy against sorption-phase concentration. The isosteric sorption heat can then be calculated by adding the mechanical-work term to the differential sorption heat assuming that the gas is ideal and the sorption phase is denser than the gas phase. 

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