That Exergy?

The system, as they say, is in the dead state, when he is in thermodynamic equilibrium with its environment. The dead condition of the system temperature and pressure of the environment (thermal and mechanical equilibrium); it has no kinetic or potential energy relative to the environment (zero speed and zero above the control level); and it does not react with the environment (chemically inert). Moreover, there is no unbalanced magnetic, electric, and surface tension effects between the system and its environment if they are relevant to the situation at hand. System properties off are denoted by subscript zero, for example, P0, T0, h0, u0, and s0. Unless otherwise specified, the dead-state pressure and temperature are accepted T0 = 25 C (77 F) and P0 = 1 ATM (101,325 kPa or 14.7 psi). The system has a zero exergy the dead.

The notion that the system should go to the impasse at the end of the process to maximize performance may be explained as follows: if the temperature of the system in the final state, more (or less) ambient temperature, we can always make more work, running a heat engine between these two levels of temperature. If the final pressure more (or less) ambient pressure, we can still get the job done, enabling you to extend the system to the pressure of the environment. If the ultimate speed of the system is not equal to zero, we can catch more kinetic energy turbines and convert it to the rotating shaft work, and so forth. No work can be produced from a system that initially dead. The atmosphere around us contains a huge amount of energy. Nevertheless, the atmosphere in the dead state, and energy has the potential to work.

Thus, we conclude that the system provides the highest possible work as she is subjected to irreversible process from a given initial state to the state of the environment, that is, the dead state. It is important to understand that the exergy can't imagine the amount of work, work on the production unit will supply installation. Rather, it represents an upper limit on the amount of the device can deliver, without violating the laws of thermodynamics. There will always be a difference, large or small, between exergy and actual work performed by the device. This difference represents the available number of engineers for improvement, especially for greener buildings and more sustainable buildings in ASHRAE Sustainability " road map".

Please note that the exergy of the system in a given state depends on the environmental conditions (off), as well as the properties of the system. Therefore, exergy is a property of the system (environment combination and not the system itself. Environmental change is another way to increase the exergy, but he is definitely not an easy alternative.

Work capacity or exergy kinetic energy of the system is equal to the kinetic energy because it can be converted to work entirely. Similarly, the exergy of the potential energy is equal to the potential energy itself. On the other hand, the internal energy and enthalpy of the system is not fully available to work, and only part of the thermal energy of the system can be converted to work. In other words, the exergy of the heat energy is less than the amount of heat energy.