摘要 :
Real operating conditions of a thermoelectric cooling device are in the presence of thermal resistances between thermoelectric material and a heat medium or cooling object. They limit performance of a device and should be consider...
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Real operating conditions of a thermoelectric cooling device are in the presence of thermal resistances between thermoelectric material and a heat medium or cooling object. They limit performance of a device and should be considered when modeling. Here we propose a dimensionless mathematical steady state model, which takes them into account. Analytical equations for dimensionless cooling capacity, voltage, and coefficient of performance (COP) depending on dimensionless current are given. For improved accuracy a device can be modeled with use of numerical or combined analytical-numerical methods. The results of modeling are in acceptable accordance with experimental results. The case of zero temperature difference between hot and cold heat mediums at which the maximum cooling capacity mode appears is considered in detail. Optimal device parameters for maximal cooling capacity, such as fraction of thermal conductance on the cold side y, fraction of current relative to maximal j' are estimated in range of 0.38-0.44 and 0.48-0.95, respectively, for dimensionless conductance K' = 5-100. Also, a method for determination of thermal resistances of a thermoelectric cooling system is proposed.
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This paper presents implementations and verification of models of thermoelectric cooler and generator modules using Matlab/Simulink. The proposed models are designed with a user-friendly icon and a dialog box, like Simulink block ...
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This paper presents implementations and verification of models of thermoelectric cooler and generator modules using Matlab/Simulink. The proposed models are designed with a user-friendly icon and a dialog box, like Simulink block libraries, making them easy to use for simulation, analysis, and optimization of further applications.
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摘要 :
This paper presents implementations and verification of models of thermoelectric cooler and generator modules using Matlab/Simulink. The proposed models are designed with a user-friendly icon and a dialog box, like Simulink block ...
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This paper presents implementations and verification of models of thermoelectric cooler and generator modules using Matlab/Simulink. The proposed models are designed with a user-friendly icon and a dialog box, like Simulink block libraries, making them easy to use for simulation, analysis, and optimization of further applications.
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摘要 :
Established thermoelectric theory enables direct calculation of the power output and conversion efficiency if the temperature difference across a module is given. However, in some applications such as those using a radioisotope or...
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Established thermoelectric theory enables direct calculation of the power output and conversion efficiency if the temperature difference across a module is given. However, in some applications such as those using a radioisotope or solar radiation as a heat source, the thermal input remains constant while the temperature difference varies with the geometry of the thermoelectric module. In this paper, a theoretical framework for thermoelectric module design under a given thermal input is presented. It provides a convenient approach for module geometry optimization. The usefulness of the theory is demonstrated through a design study, in which an appropriate thermoelement length for a solar thermoelectric system is determined by considering conflicting requirements for a longer length to obtain a greater temperature difference and for a shorter length to produce a larger power output.
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Thermoelectric devices have potential energy conversion applications ranging from space exploration through to mass-market products. Standardised, accurate and repeatable high-throughput measurement of their properties is a key en...
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Thermoelectric devices have potential energy conversion applications ranging from space exploration through to mass-market products. Standardised, accurate and repeatable high-throughput measurement of their properties is a key enabling technology. Impedance spectroscopy has shown promise as a tool to parametrically characterise thermoelectric modules with one simple measurement. However, previously published models which attempt to characterise fundamental properties of a thermoelectric module have been found to rely on heavily simplified assumptions, leaving its validity in question. In this paper a new comprehensive impedance model is mathematically developed. The new model integrates all relevant transport phenomena: thermal convection, radiation, and spreading-constriction at junction interfaces. Additionally, non-adiabatic internal surface boundary conditions are introduced for the first time. These phenomena were found to significantly alter the low and high frequency response of Nyquist spectra, showing their necessity for accurate characterisation. To validate the model, impedance spectra of a commercial thermoelectric module was experimentally measured and parametrically fitted. Technique precision is investigated using a Monte-Carlo residual resampling approach. A complete characterisation of all key thermoelectric properties as a function of temperature is validated with material property data provided by the module manufacturer. Additionally, by firstly characterising the module in vacuum, the ability to characterise a heat transfer coefficient for free and forced convection is demonstrated. The model developed in this study is therefore a critical enabler to potentially allow impedance spectroscopy to characterise and monitor manufacturing and operational defects in practical thermoelectric modules across multiple sectors, as well as promote new sensor technologies.
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Thermoelectrics are candidate niche electrical generator devices for energy management. At present, scientists are more focused on thermoelectric (TE) material development, but the TE module design procedure is still in a relative...
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Thermoelectrics are candidate niche electrical generator devices for energy management. At present, scientists are more focused on thermoelectric (TE) material development, but the TE module design procedure is still in a relatively virgin state. One of the most well-known methods is the reduced current approach (RCA) for TE module design, where the same current is induced through the p and n legs of the thermoelectric generator (TEG). The current density of each element is manipulated by changing the area of both legs. This teehnique leads to a TE module architecture based on the most efficient configuration of both p and n legs. In the current paper, we apply an extended version of this technique, to show how a TE module with a higher volumetric power density can be designed, compared to the original RCA. Our studies indicate that for some combinations of p and n material properties, optima yielding significant material savings without compromising power output can be determined. The current study has been directed towards obtaining high power output from high-temperature TEGs, rather than focusing on efficiency enhancement.
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Interest in thermoelectrics for waste-heat recovery and localized cooling has flourished in recent years, but questions about cost and scalability remain unanswered. This work investigates the fabrication costs and coupled thermal...
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Interest in thermoelectrics for waste-heat recovery and localized cooling has flourished in recent years, but questions about cost and scalability remain unanswered. This work investigates the fabrication costs and coupled thermal and electrical transport factors that govern device efficiency and commercial feasibility of the most promising thermoelectric materials. For 30 bulk and thin film thermoelectric materials, we quantify the tradeoff between efficiency and cost considering electrical and thermal transport at the system level, raw material prices, system component costs, and estimated manufacturing costs. This work neglects the cost of heat, as appropriate for most waste-heat recovery applications, and applies a power generation cost metric in $/W and a cooling operating cost metric in $/kWh. The results indicate material costs are too high for typical thermoelectric power generation applications at mean temperatures below 135 ℃. Above 275 ℃, many bulk thermoelectric materials can achieve costs below $1/W. The major barrier to economical thermoelectric power generation at these higher temperatures results from system costs for heat exchangers and ceramic plates. For cooling applications, we find that several thermoelectric materials can be cost competitive and commercially promising.
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Nanostructured thermoelectric materials generally exhibit enhanced properties. PbTe－CoSb_3 thermoelectric composites (0－8 wt% of PbTe) have been successfully prepared by freeze-drying nanoparticles of PbTe (6 nm in diameter, syn...
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Nanostructured thermoelectric materials generally exhibit enhanced properties. PbTe－CoSb_3 thermoelectric composites (0－8 wt% of PbTe) have been successfully prepared by freeze-drying nanoparticles of PbTe (6 nm in diameter, synthesized by laser fragmentation of micron-sized particles in water) with micron-sized skutterudite CoSb_3 powders (*5 lm in diameter, synthesized by powder metallurgy), followed by spark plasma sintering. X-ray diffraction analyses and scanning electron microscopy observations have been performed. Microstructures reveal an agglomeration of the PbTe particles at the grain boundaries of CoSb_3. Electrical resistivity, thermopower, and thermal conductivity measurements have been performed in the 300－800 K temperature range. The composites exhibit n-type conduction whereas the reference CoSb_3 skutterudite is p-type. This change of conduction mode is attributed to substitution of Sb for a minute amount of Te in the composites. The influence of both PbTe nanoparticules and Te on the thermoelectric properties is discussed in detail.
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A new type of thermoelectric transport is described, consisting of pulses of charge carriers that "fly" periodically through the external circuit from the hot end of the sample to the cold end, with a determined duration of the "o...
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A new type of thermoelectric transport is described, consisting of pulses of charge carriers that "fly" periodically through the external circuit from the hot end of the sample to the cold end, with a determined duration of the "on" and "off' times of the electric contacts, while maintaining continuously the thermal contacts. It is shown that such a non-equilibrium ideal thermal "machine" works cyclically with improved efficiency compared with efficiencies of the thermoelectric devices operated in an equilibrium transport regime, but the electric flow and power are increased, as a consequence of concentrating the charge carriers on pulses of a small spatial extent. The machine is reversible, in the sense that it can operate either as a thermoelectric generator or as an electro-thermal cooler. So, it is described special designing a new thermoelectric generator to fulfill the needs of pulse operating, and a setup able to measure the thermoelectric parameters of Non Steady-State (pulse) operated generators. Preliminary measurements show a minimum two times increase of delivered electrical power, using the same heat power input when we are working in the pulse operation. It is confirmed existence of a lower limit of frequency where the electrical power starts to increase comparing with the DC operation, and a superior limit of frequency where the increase is too low to be taken into consideration. All these results are strong confirmation of the theory of "pulsed thermoelectricity".
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Non-standardized forms of performance data is an issue designers encounter when dealing with thermoelectric module manufacturers. To assess a product's performance, experimental methods can be used as well as analytical modeling b...
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Non-standardized forms of performance data is an issue designers encounter when dealing with thermoelectric module manufacturers. To assess a product's performance, experimental methods can be used as well as analytical modeling by using the material properties that are not usually revealed. The latter investigates theories using the guidelines given by the manufacturers. After analyzing the theories, the values are used to assess the performances of the thermoelectric modules. The samples then go through experimental testing to insure their validity. Finally, the analytical, experimental, and manufacturer-provided results are compared to find a common ground. The results shows good agreement where the most of the errors are less than 1%.
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