193 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
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
Topology optimized permanent magnet systems
Topology optimization of permanent magnet systems consisting of permanent
magnets, high permeability iron and air is presented. An implementation of
topology optimization for magnetostatics is discussed and three examples are
considered. First, the Halbach cylinder is topology optimized with iron and an
increase of 15% in magnetic efficiency is shown, albeit with an increase of 3.8
pp. in field inhomogeneity - a value compared to the inhomogeneity in a 16
segmented Halbach cylinder. Following this a topology optimized structure to
concentrate a homogeneous field is shown to increase the magnitude of the field
by 111% for the chosen dimensions. Finally, a permanent magnet with alternating
high and low field regions is considered. Here a figure
of merit of 0.472 is reached, which is an increase of 100% compared to a
previous optimized design.Comment: 10 pages, 10 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 lifetime cost of a magnetic refrigerator
The total cost of a 25 W average load magnetic refrigerator using commercial
grade Gd is calculated using a numerical model. The price of magnetocaloric
material, magnet material and cost of operation are considered, and all
influence the total cost. The lowest combined total cost with a device lifetime
of 15 years is found to be in the range \^{+++}$ refrigeration unit. In a
rough life time cost comparison between the magnetic refrigeration device and
such a unit we find similar costs, the former being slightly cheaper, assuming
the cost of the magnet can be recuperated at end of life.Comment: 17 pages, 17 figure
A thermoelectric power generating heat exchanger: Part I - Experimental realization
An experimental realization of a heat exchanger with commercial
thermoelectric generators (TEGs) is presented. The power producing capabilities
as a function of flow rate and temperature span are characterized for two
different commercial heat transfer fluids and for three different thermal
interface materials. The device is shown to produce 2 W per TEG or 0.22 W
cm at a fluid temperature difference of 175 C and a flow rate
per fluid channel of 5 L min. One experimentally realized design
produced 200 W in total from 100 TEGs. For the design considered here, the
power production is shown to depend more critically on the fluid temperature
span than on the fluid flow rate. Finally, the temperature span across the TEG
is shown to be 55% to 75% of the temperature span between the hot and cold
fluids.Comment: 9 pages, 11 figure
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