627 research outputs found
Closed-loop approach to thermodynamics
We present the closed loop approach to linear nonequilibrium thermodynamics
considering a generic heat engine dissipatively connected to two temperature
baths. The system is usually quite generally characterized by two parameters:
the output power and the conversion efficiency , to which we add a
third one, the working frequency . We establish that a detailed
understanding of the effects of the dissipative coupling on the energy
conversion process, necessitates the knowledge of only two quantities: the
system's feedback factor and its open-loop gain , the product of
which, , characterizes the interplay between the efficiency, the
output power and the operating rate of the system. By placing thermodynamics
analysis on a higher level of abstraction, the feedback loop approach provides
a versatile and economical, hence a very efficient, tool for the study of
\emph{any} conversion engine operation for which a feedback factor may be
defined
The Vacuum Chamber of the GANIL SSC
http://accelconf.web.cern.ch/AccelConf/c78/papers/a-14.pdfInternational audienc
Tailoring strain in SrTiO3 compound by low energy He+ irradiation
The ability to generate a change of the lattice parameter in a near-surface
layer of a controllable thickness by ion implantation of strontium titanate is
reported here using low energy He+ ions. The induced strain follows a
distribution within a typical near-surface layer of 200 nm as obtained from
structural analysis. Due to clamping effect from the underlying layer, only
perpendicular expansion is observed. Maximum distortions up to 5-7% are
obtained with no evidence of amorphisation at fluences of 1E16 He+ ions/cm2 and
ion energies in the range 10-30 keV.Comment: 11 pages, 4 figures, Accepted for publication in Europhysics Letter
(http://iopscience.iop.org/0295-5075
Optimal working conditions for thermoelectric generators with realistic thermal coupling
We study how maximum output power can be obtained from a thermoelectric
generator(TEG) with nonideal heat exchangers. We demonstrate with an analytic
approach based on a force-flux formalism that the sole improvement of the
intrinsic characteristics of thermoelectric modules including the enhancement
of the figure of merit is of limited interest: the constraints imposed by the
working conditions of the TEG must be considered on the same footing.
Introducing an effective thermal conductance we derive the conditions which
permit maximization of both efficiency and power production of the TEG
dissipatively coupled to heat reservoirs. Thermal impedance matching must be
accounted for as well as electrical impedance matching in order to maximize the
output power. Our calculations also show that the thermal impedance does not
only depend on the thermal conductivity at zero electrical current: it also
depends on the TEG figure of merit. Our analysis thus yields both electrical
and thermal conditions permitting optimal use of a thermoelectric generator.Comment: 6 pages, 4 figures. accepted for publication in EP
Reply to the Comment on "Optimal working conditions for thermoelectric generators with realistic thermal coupling" by S. Su et al
We reply to the comment made by Su et al. on "Optimal working conditions for
thermoelectric generators with realistic thermal coupling". In particular we
justify the efficiency definition used in the main paper.Comment: 2 page
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