System energy flow

At this point, it is useful to show how the second law can be related to the transformation of energy while making use of the "quality of the Joule" concept. Let us turn to Figure 6.7 in which the system is defined as contained within the rectangle and prevails in a steady state, that is, its properties do not change with time. Energy flows 1 and 2 enter the system, energy flows 3 and 4 leave the system and the first law requires that... 

System Energy Flow/Mass/Balance Analysis... 

Fig. 7. H2-system energy flow chart (lower heating values). Energy inputs in the right column are primary energy estimates for the system components.

In this text the same conventions apply to the flow of work. If the system does work on the surroundings (energy flows ouf of the system), w is negative. If the surroundings do work on the system (energy flows into the system), w is positive. We define work from the system s point of view to be consistent for all thermodynamic quantities. That is, in this convention the signs of both q and w reflect what happens to the system thus we use AE = q + w. 

AE (change in internal energy) + energy flows into the system - energy flows out of the system... 

Essentially this requirement means that, during die irreversible process, innnediately inside die boundary, i.e. on the system side, the pressure and/or the temperature are only infinitesimally different from that outside, although substantial pressure or temperature gradients may be found outside the vicinity of the boundary. Thus an infinitesimal change in p or T would instantly reverse the direction of the energy flow, i.e. the... 

From stochastic molecnlar dynamics calcnlations on the same system, in the viscosity regime covered by the experiment, it appears that intra- and intennolecnlar energy flow occur on comparable time scales, which leads to the conclnsion that cyclohexane isomerization in liquid CS2 is an activated process [99]. Classical molecnlar dynamics calcnlations [104] also reprodnce the observed non-monotonic viscosity dependence of ic. Furthennore, they also yield a solvent contribntion to the free energy of activation for tlie isomerization reaction which in liquid CS, increases by abont 0.4 kJ moC when the solvent density is increased from 1.3 to 1.5 g cm T Tims the molecnlar dynamics calcnlations support the conclnsion that the high-pressure limit of this unimolecular reaction is not attained in liquid solntion at ambient pressure. It has to be remembered, though, that the analysis of the measnred isomerization rates depends critically on the estimated valne of... 

One of the primary goals of current research in the area of tribology is to understand how it is that the kinetic energy of a sliding object is converted into internal energy. These dissipation mechanisms detennine the rate of energy flow from macroscopic motion into the microscopic modes of the system. Numerous mechanisms can be... 

Virst law. This is the law of conservation of energy which states that the flow of energy into a system must equal the flow of energy out of the same system minus the energy that remains inside the system boundary. For an open system in which the energy flows are not time dependent and in which there is no accumulation of energy in the system, the first law may be written as... 

Open steady-flow systems, which include almost all air conditioning processes, foUow this law. Examples include the energy flows in a cooling and dehurnidifying coil or an evaporative cooling system. 

Temperature becomes a quantity definable either in terms of macroscopic thermodynamic quantities, such as heat and work, or, with equal validity and identical results, in terms of a quantity, which characterized the energy distribution among the particles in a system. With this understanding of the concept of temperature, it is possible to explain how heat (thermal energy) flows from one body to another. 

The internal energy, E, of any system can change only if energy flows in or out of the system in the form of heat or work. For any process that converts one state (state 1) into another (state 2), the change in internal energy, AE, is given as... 

Energy flow into and out of the system takes two forms, work and heat. Prime energy source, Figure 12-37A, for the... 

According to the first law of thermodynamics, these four energy flows must always he in halance. For steady air flow through the system ... 

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