5,528 research outputs found
A Preliminary Exergy Analysis of the EU DEMO Fusion Reactor
Purpose of the present study is the exergy analysis of EU DEMO pulsed fusion power plant considering the Primary Heat Transfer Systems, the Intermediate Heat Transfer System (IHTS) including the Energy Storage System (ESS) as a first option to ensure the continuity of electric power released to the grid. A second option here considered is a methane fired auxiliary boiler replacing the ESS. The Power Conversion System (PCS) performance is evaluated as well in the overall balance. The performance analysis is based on the exergy method to specifically assess the amount of exergy destruction determined by irreversible phenomena along the whole cyclic process. The pulse and dwell phases of the reactor operation are evaluated considering the state of the art of the ESS adopting molten salts alternate heating and storage in a hot tank followed by a cooling and recovery of molten salt in a cold tank to ensure the continuity of power release to the electrical grid. The second option of the plant configuration is evaluated on the basis of an auxiliary boiler replacing the ESS with a 10% of the power produced by the reactor during both pulse and dwell modes
Maximum power, ecological function and efficiency of an irreversible Carnot cycle. A cost and effectiveness optimization
In this work we include, for the Carnot cycle, irreversibilities of linear
finite rate of heat transferences between the heat engine and its reservoirs,
heat leak between the reservoirs and internal dissipations of the working
fluid. A first optimization of the power output, the efficiency and ecological
function of an irreversible Carnot cycle, with respect to: internal temperature
ratio, time ratio for the heat exchange and the allocation ratio of the heat
exchangers; is performed. For the second and third optimizations, the optimum
values for the time ratio and internal temperature ratio are substituted into
the equation of power and, then, the optimizations with respect to the cost and
effectiveness ratio of the heat exchangers are performed. Finally, a criterion
of partial optimization for the class of irreversible Carnot engines is herein
presented.Comment: 17 pages, 4 figures. Submitted to Energy Convers. Manag
Energy conversion in isothermal nonlinear irreversible processes - struggling for higher efficiency
First we discuss some early work of Ulrike Feudel on structure formation in
nonlinear reactions including ions and the efficiency of the conversion of
chemical into electrical energy. Then we give some survey about energy
conversion from chemical to higher forms of energy like mechanical, electrical
and ecological energy. We consider examples of energy conversion in several
natural processes and in some devices like fuel cells. Further, as an example,
we study analytically the dynamics and efficiency of a simple "active circuit"
converting chemical into electrical energy and driving currents which is
roughly modeling fuel cells. Finally we investigate an analogous ecological
system of Lotka - Volterra type consisting of an "active species" consuming
some passive "chemical food". We show analytically for both these models that
the efficiency increases with the load, reaches values higher then 50 percent
in a narrow regime of optimal load and goes beyond some maximal load abrupt to
zero.Comment: 25 pages, 4 figure
Exergy efficiency optimization for gas turbine based cogeneration systems
Energy degradation
can be calculated
by
the
quantification
of
entropy and loss
of work
and
is a common approach in
power plant performance analysis. Information about the
location, amount and
sourc
es of system deficiencies are
determined by
the
exergy analysis, which
quantifies the
exergy
destruction.
Micro
-
gas turbines are
prime movers
that are
ideally suited for cogeneration applications due to their
flexibility in providing stable and reliable power. This paper
presents
an
exergy analysis
by means of a
numerical
simulation
of a
regenerative
micro
-
gas turbine
for cogeneration
applications
. The main objective is
to study
the best
configuration of each system component
,
considering the minimization of the
system irreversibilities
. Each component of
the system was evaluated
considering the quantitative exergy
balance
.
Subsequently the optimization
procedure
was applied
to the mathematical model that
describes the
full
system.
The rate of irreversibility, efficiency and flaws are
highlighted for each system component and for
the
whole
system.
The effect
of turbine inlet temperature
change
on plant
exergy destruction
was also evaluated
. The results disclose that
considerable exergy destruction occurs in the combustion
chamber. Also, it
was revealed that the exergy
efficiency is
expressively
dependent on the
changes
of
the turbine inlet
temperature
and increases with
the
latter
.The authors would like to express their acknowledgments for the support given by the Portuguese F01mdation for Science and Technology (FCT) through the PhD grant SFRH/BD/62287/2009. This work was financed by National Funds-Portuguese Foundation for Science and Technology, under Strategic Project and PEst-OE/EME/UI0252/2011 and also the PEst-C/EME/UI4077/2011
Stagnation Hugoniot Analysis for Steady Combustion Waves in Propulsion Systems
The combustion mode in a steady-flow propulsion system has a strong influence on the overall efficiency of the system. To evaluate the relative merits of different modes, we propose that it is most appropriate to keep the upstream stagnation state fixed and the wave stationary within the combustor. Because of the variable wave speed and upstream stagnation state, the conventional Hugoniot analysis of combustion waves is inappropriate for this purpose. To remedy this situation, we propose a new formulation of the analysis of stationary combustion waves for a fixed initial stagnation state, which we call the stagnation Hugoniot. For a given stagnation enthalpy, we find that stationary detonation waves generate a higher entropy rise than deflagration waves. The combustion process generating the lowest entropy increment is found to be constant-pressure combustion. These results clearly demonstrate that the minimum entropy property of detonations derived from the conventional Hugoniot analysis does not imply superior performance in all propulsion systems. This finding reconciles previous analysis of flowpath performance analysis of detonation-based ramjets with the thermodynamic cycle analysis of detonation-based propulsion systems. We conclude that the thermodynamic analysis of propulsion systems based on stationary detonation waves must be formulated differently than for propagating waves, and the two situations lead to very different results
Improving of Brayton cycle for aero gas turbine
Tato Prace je vyzkum o Braytonuv Obeh. Obsahuju ruzne metody, jak zvisit ucinnost obeh. Take vysvetluje jednu z techto metod presneji a popisuje ruzne moznosti, jako je IRA (Mezichladicem Recuperancni Aeroengine), coz je project z Technicke University v Mnichove. Vyvetluje ruzne studie o tepelnych vymeniku a jak tyto zmeny by mohly prispet ke slepseni spotreby paliva.This thesis is a research about Brayton cycle. It contains different methods on how to improve the efficiency of the cycle. Also it explains one of these methods more precisely and describes different options such as IRA (Intercooled Recuperative Aeroengine) which is a project from Munich Technical University. Besides it explains different studies about heat exchangers and how these modifications could help to improve fuel economy.
Energy and Exergy Investigations of a 972mw Based Steam Parameters Thermal Power Plant in Nigeria
The generation of electricity is critical to the expansion of the economy and the improvement of people's standard of living. Scientists from all over the world find themselves increasingly aware of the impact of power plants as a result of the expanding human population and the ever-increasing demand for dependable sources of energy. The construction of about 95% of power plants is carried out in accordance with energy performance requirements, which take into account only the first law of thermodynamics. It is not possible to use the first equation of thermodynamics to compute the actual effective energy loss since it does not differentiate between the quantity and quality of energy.Calculating energy and exergy based on the properties of the steam was at the focus of the investigation into the energy and exergy efficiency of the plant. According to the findings, an increase in the parameters governing the scalding steam caused an increase in both the system's efficiency and its enthalpy. The boiler has the highest exergy efficiency (59.66%), whereas the condenser has the highest energy efficiency (48.10%). The investigation proved beyond a shadow of a doubt that the boiler was the principal cause of the system's irreversibility.
 
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