1,153 research outputs found
The universal influence of contact resistance on the efficiency of a thermoelectric generator
The influence of electrical and thermal contact resistance on the efficiency
of a segmented thermoelectric generator is investigated. We consider 12
different segmented -legs and 12 different segmented -legs, using 8
different -type and 8 different -type thermoelectric materials. For all
systems a universal influence of both the electrical and thermal contact
resistance is observed on the leg's efficiency, when the systems are analyzed
in terms of the contribution of the contact resistance to the total resistance
of the leg. The results are compared with the analytical model of Min and Rowe
(1992). In order for the efficiency not to decrease more than 20%, the contact
electrical resistance should be less than 30% of the total leg resistance for
zero thermal contact resistance, while the thermal contact resistance should be
less than 20% for zero electrical contact resistance. The universal behavior
also allowed the maximum tolerable contact resistance for a segmented system to
be found, i.e. the resistance at which a leg of only the high temperature
thermoelectric material has the same efficiency as the segmented leg with a
contact resistance at the interface. If e.g. segmentation increases the
efficiency by 30% then an electrical contact resistance of 30% or a thermal
contact resistance of 20% can be tolerated.Comment: 8 pages, 8 figure
An analytical model for the influence of contact resistance on thermoelectric efficiency
An analytical model is presented that can account for both electrical and hot
and cold thermal contact resistances when calculating the efficiency of a
thermoelectric generator. The model is compared to a numerical model of a
thermoelectric leg, for 16 different thermoelectric materials, as well as the
analytical models of Ebling et. al. (2010) and Min \& Rowe (1992). The model
presented here is shown to accurately calculate the efficiency for all systems
and all contact resistances considered, with an average difference in
efficiency between the numerical model and the analytical model of
pp. This makes the model more accurate than previously published
models. The maximum absolute difference in efficiency between the analytical
model and the numerical model is 1.14 pp for all materials and all contact
resistances considered.Comment: 8 pages, 5 figure
The demagnetization factor for randomly packed spheroidal particles
We investigate if the demagnetization factor for a randomly packed powder of
magnetic spheroidal particles depend on the shape of the spheroidal particles
and what the internal variation in magnetization is within such a powder. A
spheroid is an ellipsoid of revolution, i.e. an ellipsoid with two semi-major
axis being equal. The demagnetization factor is calculated as function of
particle aspect ratio using two independent numerical models for several
different packings, and assuming a relative permeability of 2. The calculated
demagnetization factor is shown to depend on particle aspect ratio, not because
of direct magnetic interaction but because the particle packing depend on the
aspect ratio of the particles. The relative standard deviation of the
magnetization across the powder was 3\%-8\%, increasing as the particle shape
deviates from spherical, while the relative standard deviation within each
particle was relatively constant around 5\%.Comment: 7 pages, 9 figure
The performance of a combined solar photovoltaic (PV) and thermoelectric generator (TEG) system
The performance of a combined solar photovoltaic (PV) and thermoelectric
generator (TEG) system is examined using an analytical model for four different
types of commercial PVs and a commercial bismuth telluride TEG. The TEG is
applied directly on the back of the PV, so that the two devices have the same
temperature. The PVs considered are crystalline Si (c-Si), amorphous Si (a-Si),
copper indium gallium (di)selenide (CIGS) and cadmium telluride (CdTe) cells.
The degradation of PV performance with temperature is shown to dominate the
increase in power produced by the TEG, due to the low efficiency of the TEG.
For c-Si, CIGS and CdTe PV cells the combined system produces a lower power and
has a lower efficiency than the PV alone, whereas for an a-Si cell the total
system performance may be slightly increased by the TEG.Comment: 10 pages, 6 figure
The maximum theoretical performance of unconcentrated solar photovoltaic and thermoelectric generator systems
The maximum efficiency for photovoltaic (PV) and thermoelectric generator
(TEG) systems without concentration is investigated. Both a combined system
where the TEG is mounted directly on the back of the PV and a tandem system
where the incoming sunlight is split, and the short wavelength radiation is
sent to the PV and the long wavelength to the TEG, are considered. An
analytical model based on the Shockley-Queisser efficiency limit for PVs and
the TEG figure of merit parameter is presented. It is shown that for
non-concentrated sunlight, even if the TEG operates at the Carnot efficiency
and the PV performance is assumed independent of temperature, the maximum
increase in efficiency is 4.5 percentage points (pp.) for the combined case and
1.8 pp. for the tandem case compared to a stand alone PV. For a more realistic
case with a temperature dependent PV and a realistic TEG, the gain in
performance is much lower. For the combined PV and TEG system it is shown that
a minimum value is needed in order for the system to be more efficient
than a stand alone PV system.Comment: 6 pages, 5 figure
Modeling the microstructural evolution during constrained sintering
A numerical model able to simulate solid-state constrained sintering is
presented. The model couples an existing kinetic Monte Carlo (kMC) model for
free sintering with a finite element model (FEM) for calculating stresses on a
microstructural level. The microstructural response to the local stress as well
as the FEM calculation of the stress field from the microstructural evolution
is discussed. The sintering behavior of a sample constrained by a rigid
substrate is simulated. The constrained sintering results in a larger number of
pores near the substrate, as well as anisotropic sintering shrinkage, with
significantly enhanced strain in the central upper part of the sample surface,
and minimal strain at the edges near the substrate. All these features have
also previously been observed experimentally.Comment: 9 pages, 7 figure
The magnetic properties of the hollow cylindrical ideal remanence magnet
We consider the magnetic properties of the hollow cylindrical ideal remanence
magnet. This magnet is the cylindrical permanent magnet that generates a
uniform field in the cylinder bore, using the least amount of magnetic energy
to do so. The remanence distribution of this magnet is derived and the
generated field is compared to that of a Halbach cylinder of equal dimensions.
The ideal remanence magnet is shown in most cases to generate a significantly
lower field than the equivalent Halbach cylinder, although the field is
generated with higher efficiency. The most efficient Halbach cylinder is shown
to generate a field exactly twice as large as the equivalent ideal remanence
magnet.Comment: 5 pages, 3 figure
- …