How do you calculate exergetic efficiency?
How do you calculate exergetic efficiency?
(EEF) of Complex Systems 1988) that the exergy efficiency of the system on the whole can be calculated as the ratio of total useful exergy effect of the system (product) to available exergy (fuel).
What is second law efficiency?
Second Law Efficiency Second Law efficiency is a measure of how much of the theoretical maximum (Carnot) you achieve, or in other words, a comparison of the system’s thermal efficiency to the maximum possible efficiency. The Second Law efficiency will always be between the Carnot and First Law efficiencies. ηs = ηth.
How is exergy calculated?
The exergy destruction and entropy generation are related by the following expression: E x d = T 0 Δ S g e n , where T0 is the reference temperature. If E x d > 0 , then the process is irreversible; if E x d = 0 , then the process is reversible; if E x d < 0 , the process is impossible.
What is exergy in thermodynamics?
Exergy (Ex) is defined as the amount of work (=entropy-free energy) a system can perform when it is brought into thermodynamic equilibrium with its environment, i.e. lAmax l=Ex (Jørgensen et al., 1999).
What is the difference between exergy and entropy?
The entropy of a system is only related to the state of the system and is unrelated to the environment; in contrast, the exergy of a system is not only related to the state of the system but also related to the state of the environment, making it too complicated.
What is thermal efficiency formula?
The thermal efficiency, ηth, represents the fraction of heat, QH, converted to work. The air-standard Otto cycle thermal efficiency is a function of compression ratio and κ = cp/cv. The thermal efficiency, ηth, represents the fraction of heat, QH, converted to work.
What is 1st law efficiency?
First law efficiencies relate to the conversion of energy from one form to another and conservation of the overall quantity of energy, without direct consideration for the quality of energy.
What is first and second law efficiency?
The basic difference between both concepts is that while first law efficiency solely relates to the specific technology applied in order to satisfy certain tasks, for example, illumination and space heating, the concept of second law efficiency takes into account both the actual technology employed and the technology …
Can exergy be destroyed?
Energy changes from one form to another (see First Law of Thermodynamics). In contrast, exergy is always destroyed when a process is irreversible, for example loss of heat to the environment (see Second Law of Thermodynamics). The destroyed exergy has been called anergy.
What is an example of exergy?
For example, 100 Joules (100J) of heat would correspond to less exergy than would 100J of electricity. Exactly how much exergy is present within 100J of heat would depends upon the temperature, pressure, chemical composition, etc., of the system, as well as its surroundings (see point 3).
Is Exergy efficiency higher than energy efficiency?
So the input exergy is a fraction of input energy. Therefore, the exergy efficiency is higher than the energy efficiency.
What is the exergetic efficiency?
The exergetic efficiency η is defined as the ratio of dissipations due to output and input powers in oxidative phosphorylation, and from section 11.7.2 we have This equation suggests that the efficiency is a function of the state of the system, as both the forces and flows are state dependent.
What is the intrinsic efficiency of a heat exchanger?
In Eq. (38) the intrinsic efficiency is used. A heat exchanger network can be treated as a single heat transfer operation, which can be characterized by its minimum overall heat supply and withdrawal requirements. Those minimum requirements can be determined by pinch analysis.
How is the exergy load distributed in a heat exchanger network system?
In a heat exchanger network system, as seen in Fig. 4, to apply the exergy load distribution, the intrinsic exergy efficiency ηin, primary exergy Xp, and transformed exergy load Xtr are computed and used in Eq. (38). The exergy flow corresponding to the heat supplied to the process Xsq and the heat withdrawn Xwq are expressed as
What is the rate of exergy loss associated with heat loss?
The rate of exergy loss accompanying the heat loss ˙Ql is given as (1 − T o / T l)˙Ql, which is a measure of thermodynamic value of the heat loss, and depends significantly on the operating temperature. Exergetic efficiency expressions can take different forms, some of those for various engineering steady-state processes are:
