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Summary: In this work, a simulation model based on finite element analysis for a one‐dimensional p‐type segmented semiconductor element with different cross‐sectional areas is analyzed to predict transient thermal behavior for thermoelectric coolers (TECs). The proposed model considers all thermoelectric effects, including the Peltier effect, Thomson effect, Joule heating, and Fourier's heat conduction. The supercooling occurs when a pulse current higher than the steady‐state optimum current is applied to a TEC. Dynamic characteristics, such as minimum cold side temperature and holding time of transient state, which arise in transient supercooling are very important to be considered for the design and operation of TECs. In this study, we present a new approach of transient performance based on leg geometry shape, considering variable cross‐sectional areas, as well as individual element lengths of two different thermoelectric materials using a segmentation model proposed. A variety of model designs are analyzed, considering rectangular, trapezoidal, and inverse trapezoidal legs, where also optimum pulse current is found as a function of the element lengths. It is demonstrated that an improvement of 4.75% in the cooling is possible when using trapezoidal legs compared with conventional rectangular systems. Our presented model is mainly a new alternative in characterizing Peltier supercooling as a function of both pulse current ratio as well as the leg shape. [ABSTRACT FROM AUTHOR]

In this work, the influences of the Thomson effect and the geometry of the p-type segmented leg on the performance of a segmented thermoelectric microcooler (STEMC) were examined. The effects of geometry and the material configuration of the p-type segmented leg on the cooling power (Qc) and coefficient of performance (COP) were investigated. The influence of the cross-sectional area ratio of the two joined segments on the device performance was also evaluated. We analyzed a one-dimensional p-type segmented leg model composed of two different semiconductor materials, Bi2Te3 and (Bi0.5Sb0.5)2Te3. Considering the three most common p-type leg geometries, we studied both single-material systems (using the same material for both segments) and segmented systems (using different materials for each segment). The COP, Qc and temperature profile were evaluated for each of the modeled geometric configurations under a fixed temperature gradient of ΔT = 30 K. The performances of the STEMC were evaluated using two models, namely the constant-properties material (CPM) and temperature-dependent properties material (TDPM) models, considering the thermal conductivity (κ(T)), electrical conductivity (σ(T)) and Seebeck coefficient (α(T)). We considered the influence of the Thomson effect on COP and Qc using the TDPM model. The results revealed the optimal material configurations for use in each segment of the p-type leg. According to the proposed geometric models, the optimal leg geometry and electrical current for maximum performance were determined. After consideration of the Thomson effect, the STEMC system was found to deliver a maximum cooling power that was 5.10% higher than that of the single-material system. The results showed that the inverse system (where the material with a higher Seebeck coefficient is used for the first segment) delivered a higher performance than the direct system, with improvements in the COP and Qc of 6.67% and 29.25%, respectively. Finally, analysis of the relationship between the areas of the STEMC segments demonstrated that increasing the cross-sectional area in the second segment led to improvements in the COP and Qc of 16.67% and 8.03%, respectively. [ABSTRACT FROM AUTHOR]

This work shows a methodology for designing thermocouples of thermoelectric modules. The main quantities for design calculations are the geometric parameters: Cross-sectional area and leg length. Furthermore, the thickness of the ceramic material and the thickness of the metal bridge are considered. In addition, temperature-dependent thermoelectric properties are included in the analysis: Seebeck coefficient, thermal conductivity, electrical resistivity. An analysis of the entropy production is performed for two thermocouple geometries: Quadrangular and cylindrical. The proposed methodology allows determining the geometric conditions that the thermocouple must meet to minimize the entropy production and maximize efficiency. A conclusive result of this work is that the geometric conditions that minimize entropy production are the same that maximize the efficiency. [Display omitted] • A model for the thermal design of thermocouples for power generation. • Resource to the geometric dimensioning of thermocouples. • The model allows to analyze the performance of the developed designs. • The model can work with experimental data of any thermoelectric material. • The model presents realistic aspects for the design. [ABSTRACT FROM AUTHOR]

[Display omitted] • Develop of a new two-stage model design with phase change material for pulse operation. • New approach to find thermal characteristics for maximum temperature drop in thermoelectric coolers. • Analysis considering metal strips and the ceramic plates for more realistic results. • Thomson effect and phase change material impact on thermoelectric cooling performance. A novel physical model of a two-stage thermoelectric cooler (TEC) is developed, based on geometry factor (γ) analysis between stages under pulsed current conditions and with phase change material (PCM), to improve performance. A detailed investigation of a two-stage Peltier cooler based on a general thermodynamic formulation considering the Thomson effect is presented. The minimum cold side temperature, coefficient of performance (COP), and further the thermoelement's characteristic temperature profiles are discussed. The numerical analysis was carried out considering square pulse current, hot side heat transfer, metal strips, ceramic plates, and a PCM material volume in the heat sink. The investigation results proved that the geometry relation between both stages and the Thomson effect directly impacts supercooling, and a higher reduction in the cold side temperature can be achieved compared with conventional thermoelectric coolers. A reduction of 25.2 K in a two-stage over a single-stage TEC with PCM is achieved considering a large cross-sectional area in the first stage. It has been found that the holding time and the characteristic temperature profiles during and after pulse operation depends strongly on Thomson heat and geometry. A shorter holding time and maximum temperature drop are found for γ > 1 values due to the PCM's melting temperature and the higher pulse current. The characteristic cooling length reveals the part of the semiconductor element that is cooled during pulse operation. Results will guide the design or selection of a heat sink crucial to a solid-state cooling device's overall performance. [ABSTRACT FROM AUTHOR]

Thermoelectric coolers (TECs) can reach temperatures below that obtained with a steady-state current by applying an electrical current pulse which enables a transitory state in a Peltier device. This effect is known as supercooling. In this paper, we study characteristics parameters, such as the minimum cooling temperature and spatial temperature profile, in a TEC operated under current pulses and a cooling load (Q c) . Numerical analysis for a one-dimensional thermoelectric model of the cooling system is developed, and a novel MATLAB programming code is proposed for the transient state based on finite element analysis. We also investigate the influence of the thermoelement's length upon the cooling mechanism. A new parameter called the "characteristic cooling length" is proposed to describe the length in which the minimum cooling temperature occurs along the elements of a TEM. Results show the transient temperature profiles along the elements of the semiconductor P-type element, and a "characteristic cooling length" is characterized. We also propose a general principle, and the lowest cooling temperature values are obtained for a semiconductor's small length and variable pulse cooling load under current pulse operation. The present study will serve as guidance for the geometric design of TECs under current pulse operations. [ABSTRACT FROM AUTHOR]

In recent years the interest for the harvest of energy with micro thermoelectric generators (μ TEG) has increased, due to its advantages compared to technologies that use fossil fuels. There are three ways to improve the performance of the device, by modifying its structure, type of material and operation control. In this study, the role of the load resistance R L on the performance of a μ TEG with nanostructured materials is investigated. The interaction of the load resistance with the thermoelements exhibits interesting features, arising from the coupling of the temperature-dependent electrical and thermal transport properties at different temperature ranges and the architecture of nanostructured thermoelectric materials. This coupling results in inflections on the efficiency, i.e., maximum and minimum values of the efficiency at higher temperatures, 600–900 K. We show the explicit dependence of the performance of the μ TEG in terms of the load resistance and discuss the underlying physics. The unusual features of the efficiency of nanostructured thermoelectric materials are a result of the behavior of the power factor and the nonequilibrium properties of the system. We also analyze the effect of the geometric shape of the thermoelements on the device. We determine the performance of the μ TEG, evaluating the generation power and its efficiency. The results show that the efficiency of the device can decrease or increase depending on the value of R L , while the power decreases with an increase of the load resistance. [ABSTRACT FROM AUTHOR]