Showing papers on "Thermoelectric effect published in 1997"

Thermoelectric Materials: New Approaches to an Old Problem

Abstract: Thermoelectrics is an old field. In 1823, Thomas Seebeck discovered that a voltage drop appears across a sample that has a temperature gradient. This phenomenon provided the basis for thermocouples used for measuring temperature and for thermoelectric power generators. In 1838, Heinrich Lenz placed a drop of water on the junction of metal wires made of bismuth and antimony. Passing an electric current through the junction in one direction caused the water to freeze, and reversing the current caused the ice to quickly melt; thus thermoelectric refrigeration was demonstrated (figure 1).

Thermoelectric properties of Al-doped ZnO as a promising oxide material for high-temperature thermoelectric conversion

Abstract: The thermoelectric properties of a mixed oxide (Zn 1-x Al x )O (x=0, 0.005, 0.01, 0.02, 0.05) are investigated in terms of materials for high-temperature thermoelectric conversion. The electrical conductivity, σ, of the oxide increases on Al-doping by more than three orders of magnitude up to ca. 10 3 S cm -1 at room temperature, showing metallic behaviour. The Seebeck coefficient, S, of (Zn 1-x Al x )O (x>0) shows a general trend in which the absolute value increases gradually from ca. -100 µV K -1 at room temperature to ca. -200 µV K -1 at 1000 °C. As a consequence, the power factor, S 2 σ, reaches ca. 15×10 -4 W m -1 K -2 , the largest value of all reported oxide materials. The thermal conductivity, κ, of the oxide decreases with increasing temperature, owing to a decrease in the lattice thermal conductivity which is revealed to be dominant in the overall κ. In spite of the considerably large values of κ, the figure of merit, Z=S 2 σ/κ, reaches 0.24×10 -3 K -1 for (Zn 0.98 Al 0.02 )O at 1000 °C. The extremely large power factor of (Zn 1-x Al x )O compared to other metal oxides can be attributed to the high carrier mobility revealed by the Hall measurements, presumably resulting from a relatively covalent character of the Zn–O bond owing to a fairly small difference of the electronegativities of Zn and O. The dimensionless figure of merit,ZT, of 0.30 attained by (Zn 0.98 Al 0.02 )O at 1000 °C demonstrates the potential usefulness of the oxide.

Low power thermoelectric generator-self-sufficient energy supply for micro systems

Abstract: New micro and sensor systems are being rapidly developed for their application in all technology events in future. The energy consumption of systems incorporated the latest technical advances decreases permanently to the range of only /spl mu/W. For the applications in this low power range (a few 10 /spl mu/W), DTS has developed a new self-sufficient power supply the low power thermoelectric generator. Whereas earlier with the help of MOS processing techniques manufactured thermoelectric generators reached only a /spl mu/W-output, it was now possible to open up the /spl mu/W-performance range on the basis of high effective thermoelectric compound semiconductor thin films, prepared by physical vapour deposition on polyimid substrates. The LPTG of DTS is a small compact thermoelectric device, full hybrid compatible with micro electronic and micro matched systems. Essential information about the LPTG device properties are given.

Thermoelectric response of an interacting two-dimensional electron gas in a quantizing magnetic field

Abstract: We present a discussion of the linear thermoelectric response of an interacting electron gas in a quantizing magnetic field. Boundary currents can carry a significant fraction of the net current passing through the system. We derive general expressions for the bulk and boundary components of the number and energy currents. We show that the local current density may be described in terms of ``transport'' and ``internal magnetization'' contributions. The latter carry no net current and are not observable in standard transport experiments. We show that although Onsager relations cannot be applied to the local current, they are valid for the transport currents and hence for the currents observed in standard transport experiments. We relate three of the four thermoelectric response coefficients of a disorder-free interacting two-dimensional electron gas to equilibrium thermodynamic quantities. In particular, we show that the diffusion thermopower is proportional to the entropy per particle, and we compare this result with recent experimental observations.

Transport Properties of Bi2S3 and the Ternary Bismuth Sulfides KBi6.33S10 and K2Bi8S13

Abstract: We have studied transport properties (resistivity, Hall effect, thermopower, and thermal conductivity) of Bi2S3 and two new ternary bismuth sulfides, KBi6.33S10 and K2Bi8S13, to explore their potential for thermoelectric applications. While both Bi2S3 and K2Bi8S13 display an essentially metallic conduction, KBi6.33S10 has a distinctly semiconducting character. From the Hall measurements it follows that the dominant carriers in all three compounds are electrons and that the carrier density in K2Bi8S13 is almost 2 orders of magnitude larger than in Bi2S3 and KBi6.33S10 over the whole temperature range from 4 to 300 K. While the room temperature thermopowers of KBi6.33S10 and K2Bi8S13 are comparable (∼−100 μV/K), the thermopower of Bi2S3 is a factor of 3 larger. All three compounds are poor conductors of heat, in particular the thermal conductivity of KBi6.33S10 is some 25% lower than the thermal conductivity of Bi2Te3, the benchmark thermoelectric material. To make these materials useful thermoelectrics, wa...

Hybrid air conditioning system and a method therefor

Abstract: A system for conditioning the air within an enclosure which houses heat producing equipment. The system includes a passive heat removal system (12), for precooling the air, and a thermoelectric temperature control system (14) used in conjunction with the passive heat removal system (12) to achieve additional cooling, temperature control and heating. The passive heat removal system (12) includes a heat pipe system. A power control system (30) includes a programmable control means (56) which receives signals, from a temperature sensor (36), which are indicative of the temperature of the air in the enclosure (20). Based upon these signals, the power control system (30) controls the activation of thermoelectric devices in the thermoelectric temperature control system (14) and controls the activation of fans (38, 42) to remove a desired amount of heat from the air in the enclosure (20) and discharge the unwanted heat to the outside air. A switching device (58) operates to apply battery power (60) to the power control system (30) if the electrical power source for the thermoelectric temperature control system (14) fails. A polarity reversal circuit (50) reverses the DC polarity of the DC voltage applied to the thermoelectric devices to reverse the heat pumping of the thermoelectric devices in the situation where the air in the enclosure (20) needs to be heated. Circuitry and sensors are provided to monitor the speed of the fans to detect any failure of a fan. A current control circuit supplies power to and temperature control of thermoelectric cooling devices.

Device for producing cold therapy

Abstract: The present invention provides heat exchange devices for heating and/or cooling parts of the body for therapeutic treatment of injury. The heat exchange devices include a cooling module with a housing enclosing a cooling chamber. A thermoelectric Peltier unit has a cooled surface sealed against an opening in the housing and a pump is provided for pumping heat exchange fluid through the cooling chamber directly into contact with the cooled surface and through conduits to a patient blanket. A reservoir containing refrigerant is in flow communication with the chamber in the cooling module housing and refrigerant only flows into the housing when depleted from the recirculation flow path between the cooling module and the blanket. Another device uses a thermoelectric unit disposed between two water pumps each of which pumps water to different sections of a flexible water bag which is strapped to the affected area of the user. Water pumped over one side of the thermoelectric unit is heated and water pumped over the other side is cooled.

Improvement of the Efficiency of Thermoelectric Energy Conversion by Utilizing Potential Barriers.

Abstract: A method of improving the efficiency of thermoelectric energy conversion by utilizing potential barriers is considered. Since potential barriers act as carrier energy filters, elimination of lower energy carriers results in an improvement of the efficiency of thermoelectric energy conversion (energy filtering method). The optimal height of potential barriers and the distance between the barriers is estimated within a semiclassical framework, i.e. using Boltzmann equation. Our calculated results show that this method works effectively for materials, in which acoustic phonon scattering is dominant compared with other scattering processes.

Method for making advanced thermoelectric devices

Abstract: Semiconductor materials optimized for their electrical conductivity and thermal conductivity promise much higher thermoelectric cooling power. The materials can achieve the same cooling or power generation capacity in thermopiles with less electron current compared with present bulk materials. Because less electron current is required to accomplish the same task, total thermopile semiconductor material cross-sectional area normal to thermal and electron flow is greatly reduced and the element length-to-cross-sectional area aspect ratio is increased. The net result is a significant improvement in the figure of merit, ZT, and in the device Coefficient of Performance (COP).

Heat flow meter instruments

Abstract: An apparatus, such as, a heat flow meter instrument, for measuring thermal properties of a specimen includes a first thermoelectric device and a second thermoelectric device, each device being thermally coupled to a hot plate and a cold plate, and a heat flow transducer, thermally connectable to a specimen and constructed to measure heat flowing through the specimen. The heat flow transducer and the specimen are positionable in thermal contact between the hot plate of the first thermoelectric device and the cold plate of the second thermoelectric device. The apparatus also includes an electric power supply connected to provide controlled amounts of electric power to the first and second thermoelectric devices to maintain the plates at selected temperatures, and a processor connected to receive from the heat flow transducer a signal corresponding to the measured heat. The processor is programmed to calculate a thermal property of the specimen based on the temperatures and the measured heat. The apparatus includes a closed loop heat exchange system, thermally connecting the cold plate of the first thermoelectric device and the hot plate of the second thermoelectric device, constructed and arranged to transfer heat between the plates. The closed loop heat exchange system may include a fluid pump and a first set of conduits thermally connected to the cold plate of the first thermoelectric device and a second set of conduits thermally connected to the hot plate of the second thermoelectric device. The conduits convey a heat exchange fluid in a closed loop arrangement.

Thermoelectric transport in quantum well superlattices

Abstract: A full theory of thermoelectric transport in superlattices, including the well width and energy dependence of the optical and acoustic phonon scattering and the effects of confinement in raising valley degeneracy is developed It is shown that these features result in qualitatively significant modifications in the predicted figure of merit of superlattice systems Results are given for PbTe superlattices, and comments are made on recent experimental results for such systems

Tubular thermoelectric module

Abstract: A thermoelectric module having a high thermoelectric performance is shown and described. A flat thermoelectric module comprises a multi-layered body provided with a thermoelectric material layer having output take-out faces on two opposite sides, an electrode layer present on each output take-out faces, a metallic layer present on each electrode layer, and an electrical insulating outer layer covering the surface of the body. Adjacent layers are pressure-welded to be in close contact with each other. No solder is used in the construction of a module in accordance with the present invention, and it is therefore possible to improve the thermoelectric performance of the module by raising the operating temperature without being restricted by the melting point of solder.

Thermoelectric microcoolers for thermal management applications

Abstract: Due to the combined increase in circuit integration and chip power dissipation, there is a rapidly growing demand for solving the thermal management issues of power microelectronics. We are pursuing a novel thermal management approach that actively cools only the key high power devices by using a novel thermoelectric microcooler located under each of these power devices. In this way the device can operate at temperatures at or even below the ambient temperature of the heat sink, resulting in increased reliability and efficiency. To successfully handle the high heat flux densities generated at the back of the power chips, a microcooler with thin legs and low thermal resistance at the interfaces must be built. We are currently developing a thermoelectric microcooler combining thick films of Bi/sub 2/Te/sub 3/-based alloys and very high thermal conductivity substrates, such as CVD diamond or AlN. Electrochemical deposition is a very attractive process for depositing thick films of compound semiconductors on metallic surfaces. This paper presents recent results on the deposition of Bi/sub 2/Te/sub 3/ and related ternary solid solutions on a variety of metallic substrates. We also report on the development of Cu diffusion barriers for Bi/sub 2/Te/sub 3/ and stable metallizations and diffusion barriers for diamond and AlN substrates.

Optimization of Bi2Te3 thin films for microintegrated Peltier heat pumps

Abstract: Bismuth telluride films were deposited by coevaporation at various Te/Bi flux ratios to optimize their resistivity and their Seebeck coefficients for use in a thin film Peltier heat pump. Bismuth telluride films deposited at a flux ratio of Te/Bi=2.3 were found to possess optimal characteristics. Using these coatings, microintegrated Peltier heat pumps were fabricated on micromachined oxide bridges using standard semiconductor patterning and etching techniques. Chrome–gold and bismuth telluride metallizations were used to form the thermoelectric junctions. A maximum heat pumping rate of −30 μW was achieved by the device when operating in the cooling mode. A temperature reduction of 1.5 °C was attained, with an initial thermal response time in the cooling mode of 10 ms/°C.

New materials and devices for thermoelectric applications

Abstract: New high efficiency thermoelectric materials with ZT values substantially larger than 1.0 have been recently developed. The successful development of a segmented thermoelectric generator utilizing a combination of state-of-the-art thermoelectric materials and these novel thermoelectric materials could result in a high thermal-to-electric materials conversion efficiency over 19%. This is because the new thermoelectric materials have a higher average ZT value and the generator can be operated in a temperature range wider than possible with state-of-the-art (SOA) materials. Such improved power generators could be used for a variety of applications including waste heat recovery. This could also lead to the development of high performance thermoelectric generators operating in a relatively narrow temperature range for specific applications. However, there are also new low power and thermal management applications for small thermoelectric devices using SOA materials. If more efficient thermoelectric materials are incorporated, the performance of these new devices will be even higher.

A New Class of Materials with Promising Thermoelectric Properties: MNiSn (M = Ti, Zr, Hf)

Abstract: TiNiSn, ZrNiSn and HfNiSn are members of a large group of intermetallic compounds which crystallize in the cubic MgAgAs-type structure. Polycrystalline samples of these compounds have been prepared and investigated for their thermoelectric properties. With thermopowers of about −200 µV/K and resistivities of a few mΩcm, power factors S2/p as high as 38 ΩW/K2 cm were obtained at 700 K. These remarkably high power factors are, however, accompanied by a thermal conductivity which is too high for applications. In order to reduce the parasitic lattice thermal conductivity, solid solutions Zrl−xHfxNiSn, Zrl−xTixNiSn, and Hfl−xTixNiSn were formed. The figure of merit of Zr0.5Hf0.5NiSn at 700 K (ZT = 0.41) exceeds the end members ZrNiSn (ZT = 0.26) and HfNiSn (ZT = 0.22).

One dimensional simulation for Peltier current leads

Abstract: Current leads, which connect superconducting magnets at the liquid helium temperature and power supplies at the room temperature, are the major source of heat leaking into cryostats, and therefore largely determines the running cost of magnet systems. Heat leak can be reduced by using high-temperature superconductors as the low-temperature (4 K-77 K) segments of current leads. Another method to reduce heat leakage, recently proposed, uses Peltier thermoelectric elements as the high-temperature (200 K-300 K) segments of current leads. These thermoelements effectively pump heat out of cryostats without using separate sources of electricity. The authors carried out experiments and numerical calculations with such Peltier current leads and found out that they reduce heat leak at 77 K by 20-30 percent.

Controlled temperature cabinet system and method

Abstract: A temperature controlled cabinet system and method enables medical items associated with particular temperature ranges to be stored and maintained within their associated temperature ranges in cabinets disposed within ambulances and other medical vehicles. The system includes a temperature sensor for measuring the cabinet interior temperature, a controller assembly for controlling system operation and two heat pumps disposed in the cabinet walls to heat or cool the cabinet interior. Alternatively, a single heat pump may be utilized to heat or cool the cabinet interior. The controller assembly includes a control console for displaying the actual cabinet temperature and entering a desired temperature range into the system. The heat pumps include a pair of heat sinks disposed about a thermoelectric device (e.g., a Peltier chip) that heats one heat sink, while cooling the other heat sink based on voltage polarity or current flow direction applied to the device. The system controls voltage polarity applied to the thermoelectric device to enable the heat pumps to heat or cool the cabinet interior in response to a comparison of the measured temperature with the desired temperature range. The system utilizes D.C. power from the vehicle electrical system, and may be installed in new cabinets or retrofit into previously disposed cabinets lacking temperature control capability.

Three-dimensional solution for a hybrid cylindrical shell under axisymmetric thermoelectric load

Abstract: An exact axisymmetric piezothermoelastic solution is presented for a simply-supported hybrid cylindrical shell made of cross-ply composite laminate and piezoelectric layers. Numerical results for hybrid shells are presented for sinusoidal and central band thermal and electrical loads. The effect of the loading, the radius-to-thickness ratio, the span-to-radius ratio and the number of layers of the substrate on the response is investigated. The interface between the substrate and the actuated piezoelectric layer has been found to be subjected to high shear stress. It has been shown that the maximum values of the deflection and the stresses, due to thermal load, can be appreciably reduced by appropriate application of actuation potential.

Composite thermoelectric material

Abstract: A composition of matter is disclosed in which nanophase metal particles are effectively dispersed in a polymer matrix so that hitherto unattainable thermoelectric properties are attained. Preferred polymers and metals are taught. A method of making the composition of matter useful as a themoelectric composite material using a conducting polymer matrix is disclosed as is a thermoelectric cooling/heating device which uses that composition.

Thermoelectric semiconductor material, manufacture process therefor, and method of hot forging thermoelectric module using the same

Abstract: A thermoelectric semiconductor material having sufficient strength and performance and high production yield. The thermoelectric semiconductor material is characterized in that a sintered powder material of a thermoelectric semiconductor having a rhombohedral structure (or hexagonal structure) is hot-forged and plastically deformed to direct either the crystals of the sintered powder structure or the subcrystals constructing the crystals in a crystal orientation having an excellent figure of merit.

Method of pumping a fluid through a micromechanical valve having N-type and P-type thermoelectric elements for heating and cooling a fluid between an inlet and an outlet

Abstract: A pumping method is used for pumping a fluid from an inlet to an outlet of a pump having a plurality of micromechanical valves. Each micromechanical valve is for communicating a fluid and constructed from n-type and p-type materials forming a peltier junction interface which can be selectively cooled to freeze the fluid into a plug to obstruct the flow of fluid, or selectively heated to melt the plug to communicate the fluid in a tube extending through the junctions. A plurality of valves connected in series can be used together as a pump to pump the fluid from the inlet through the valves to the outlet. Selective heating and cooling of the junctions provides varying fluid pressures and plugs along the tube to pump the fluid through the tube.

Thermoelectric materials -- New directions and approaches. Materials Research Society symposium proceedings, Volume 478

Abstract: Thermoelectric materials are utilized in a wide variety of applications related to solid-state refrigeration or small-scale power generation. Thermoelectric cooling is an environmentally friendly method of small-scale cooling in specific applications such as cooling computer chips and laser diodes. Thermoelectric materials are used in a wide range of applications from beverage coolers to power generation for deep-space probes such as the Voyager missions. Over the past thirty years, alloys based on the Bi-Te systems {l{underscore}brace}(Bi{sub 1{minus}x}Sb{sub x}){sub 2} (Te{sub 1{minus}x}Se{sub x}){sub 3}{r{underscore}brace} and Si{sub 1{minus}x}Ge{sub x} systems have been extensively studied and optimized for their use as thermoelectric materials to perform a variety of solid-state thermoelectric refrigeration and power generation tasks. Despite this extensive investigation of the traditional thermoelectric materials, there is still a substantial need and room for improvement, and thus, entirely new classes of compounds will have to be investigated. Over the past two-to-three years, research in the field of thermoelectric materials has been undergoing a rapid rebirth. The enhanced interest in better thermoelectric materials has been driven by the need for much higher performance and new temperature regimes for thermoelectric devices in many applications. The essence of a good thermoelectric is given by the determination of themore » material's dimensionless figure of merit, ZT = ({alpha}{sup 2}{sigma}/{lambda})T, where {alpha} is the Seebeck coefficient, {sigma} the electrical conductivity and {lambda} the total thermal conductivity. The best thermoelectric materials have a value of ZT = 1. This ZT = 1 has been an upper limit for more than 30 years, yet no theoretical or thermodynamic reason exits for why it can not be larger. The focus of the symposium is embodied in the title, Thermoelectric Materials: New Directions and Approaches. Many of the researchers in the field believe that future advances in thermoelectric applications will come through research in new materials. The authors have many new methods of materials synthesis and much more rapid characterization of these materials than were available 20--30 years ago. They have tried to focus the symposium on new directions and new materials such as skutterudites, quantum well and superlattice structures, new metal chalcogenides, rare earth systems, and quasicrystals. Other new materials are also presented in these proceedings. Separate abstracts were prepared for all the papers in this volume.« less

Semiconductor thermal conditioning apparatus and method

Abstract: An apparatus for thermally conditioning a semiconductor unit is provided which includes a surface plate for receiving the semiconductor unit thereon which is connected to a thermoelectric device and a closed loop heat exchanger. At least one temperature sensor is disposed adjacent the surface plate for sensing the temperature of the surface plate. The thermoelectric device has first and second sides with the first side disposed against the surface plate. The closed loop heat exchanger is coupled to the second side of the thermoelectric device. The closed loop heat exchanger includes a chamber or cavity having an inlet and an outlet with the chamber disposed adjacent the second side of the thermoelectric device. The closed loop heat exchanger further includes conduit connected to the inlet and outlet of the chamber and a heat transfer unit connected to the conduit opposite the chamber. Heat transfer fluid is contained within the closed loop heat exchanger and a pump is provided for pumping the heat transfer fluid through the closed loop heat exchanger wherein the heat transfer unit transfers heat to or from the heat transfer fluid to control the temperature of the heat transfer fluid. The thermoelectric device transfers heat to or from the surface plate to thermally condition the semiconductor unit disposed on the surface plate while the closed loop heat exchanger transfers heat to or from the second side of the thermoelectric device which increases the range of temperature under which the semiconductor unit may be thermally conditioned.

Effect of porosity on the thermal-electric properties of Al-doped SiC ceramics

Abstract: Silicon carbide has being used in many practical applications because of its many excellent properties, such as extreme hardness, excellent thermal and mechanical properties and high thermal shock resistance. There are many reports in the literature on silicon carbide. Recently, as high-temerature thermoelectric materials, silicon carbide ceramics have attracted much attention in the literature [1±6]. Koumoto et al. [1] reported that porous SiC ceramics showed high ®gures of merit for thermoelectric energy conversion. Since then, the thermoelectric properties of porous SiC ceramics fabricated by using different starting SiC powders (e.g. synthesized by carbothermal reduction of silica contained in rice hull ash [2] and the gas-phase reaction method [3]) and different processing routes (e.g. sintering in nitrogen or argon atmosphere [4] and reaction sintering [5]) have been investigated. Despite efforts to investigate the porous SiC thermoelectric ceramics, the effect of porosity on the thermoelectric properties is still unclear. In this letter, the effect of porosity on the thermal-electric properties of porous Al-doped SiC ceramics by hot pressing and pressureless sintering methods is reported. Commercial a-SiC powders (grain size ,10 im, purity .98.5%) were ball milled with different contents of Al powder (400 mesh, purity .99%) for 24 h. The samples were prepared in two different ways: (i), pressureless sintering (PS) under argon for 1 h at 1770 8C after the mixtures were cold isostatic pressed at 200 MPa and (ii) hot-pressing (HP) under argon at 20 MPa and 1900 8C for 0 h or 1 h in highstrength graphite dies. During the sintering, graphite end-caps were bonded to the silicon carbide cylinders, which facilitated attachment of thermocouples and electrical leads for Seebeck coef®cient and electrical conductivity measurements. The relative density of the ceramic samples, measured by the liquid displacement method, is shown in Fig. 1. The porosity of the samples decreased with Al dopant concentration, which is supported by scanning electron microscope (SEM) observation. X-ray diffraction (XRD) analyses showed that there existed only a single SiC phase and no other new phase. The average grain size was around 8 im from SEM. Electrical conductivity measurements were carried out under argon by a two-probe a.c. method. Two platinum lines were sealed on two platinum slices, which were pressed to ®rmly attach to the polished graphite electrodes on the two ends of the samples. The electrical conductivity was obtained from two resistance values measured under two opposite current directions (biased at about 0.2 V a.c. voltage). Fig. 2 shows the electrical conductivity of the 4 wt % Al-doped SiC ceramics with different densities. It is clear that the electrical conductivity increases with the decrease of porosity, as expected. The thermal conductivity was measured using a