Theoretical investigation on the influence of Seebeck and Thomson effects in a thermoelectric generator

Four possible cases of modelling a thermoelectric generator (TEG) are presented in this paper. Case 1 models equal hot and cold junction Seebeck coefficient (SC) ignoring Thomson effect (TE), case 2 adopts equal hot and cold junction SC including TE, case 3 defines unequal hot and cold junction SC neglecting TE while case 4 represents unequal hot and cold junction SC with TE. The modified expressions for these cases are derived and employed in a comparative electric and geometric optimization of the TEG. The impact of the harmonious relationship between TE and SC on the optimum and maximum system performance parameters is studied and discussed. The results show that the systems performance can be enhanced or reduced depending on the operating temperature gradient and prevalent relationship between SC and TE. The results obtained from this work should be able to accurately predict the suitable TE and SC configuration for optimum and maximum system performance.

Textile-Integrated Thermocouples for Temperature Measurement

The integration of conductive materials in textiles is key for detecting temperature in the wearer´s environment. When integrating sensors into textiles, properties such as their flexibility, handle, and stretch must stay unaffected by the functionalization. Conductive materials are difficult to integrate into textiles, since wires are stiff, and coatings show low adhesion. This work shows that various substrates such as cotton, cellulose, polymeric, carbon, and optical fiber-based textiles are used as support materials for temperature sensors. Suitable measurement principles for use in textiles are based on resistance changes, optical interferences (fiber Bragg grating), or thermoelectric effects. This review deals with developments in the construction of temperature sensors and the production of thermocouples for use in textiles. The operating principle of thermocouples is based on temperature gradients building up between a heated and a cold junction of two conductors, which is converted to a voltage output signal. This work also summarizes integration methods for thermocouples and other temperature-sensing techniques as well as the manufacture of conductive materials in textiles. In addition, textile thermocouples are emphasized as suitable and indispensable elements in sensor concepts for smart textiles.

A CMOS-Based Thermopile Array Fabricated on a Single SiO2 Membrane

We present a novel thermopile-based infrared (IR) sensor array fabricated on a single CMOS dielectric membrane, comprising of poly-silicon p+ and n+ elements. Processing of the chip is simplified by fabricating the entire array on a single membrane and by using standard CMOS Al metal layers for thermopile cold junction heatsinking. On a chip area of 1.76 mm × 1.76 mm, with a membrane size of 1.2 mm × 1.2 mm, we fabricated IR sensor arrays with 8 × 8 to 100 × 100 pixels. The 8 × 8 pixel device has <2% thermal crosstalk, a responsivity of 36 V/W and enhanced optical absorption in the 8–14 µm waveband, making it particularly suitable for people presence sensing.

Fabrication and Thermoelectric Characterization of Transition Metal Silicide-Based Composite Thermocouples

Metal silicide-based thermocouples were fabricated by screen printing thick films of the powder compositions onto alumina tapes followed by lamination and sintering processes. The legs of the embedded thermocouples were composed of composite compositions consisting of MoSi2, WSi2, ZrSi2, or TaSi2 with an additional 10 vol % Al2O3 to form a silicide–oxide composite. The structural and high-temperature thermoelectric properties of the composite thermocouples were examined using X-ray diffraction, scanning electron microscopy and a typical hot–cold junction measurement technique. MoSi2-Al2O3 and WSi2-Al2O3 composites exhibited higher intrinsic Seebeck coefficients (22.2–30.0 µV/K) at high-temperature gradients, which were calculated from the thermoelectric data of composite//Pt thermocouples. The composite thermocouples generated a thermoelectric voltage up to 16.0 mV at high-temperature gradients. The MoSi2-Al2O3//TaSi2-Al2O3 thermocouple displayed a better performance at high temperatures. The Seebeck coefficients of composite thermocouples were found to range between 20.9 and 73.0 µV/K at a temperature gradient of 1000 °C. There was a significant difference between the calculated and measured Seebeck coefficients of these thermocouples, which indicated the significant influence of secondary silicide phases (e.g., Mo5Si3, Ta5Si3) and possible local compositional changes on the overall thermoelectric response. The thermoelectric performance, high sensitivity, and cost efficiency of metal silicide–alumina ceramic composite thermocouples showed promise for high-temperature and harsh-environment sensing applications.

Perancangan Termokopel Berbahan Besi (Fe) dan Tembaga (Cu) Untuk Sensor Temperatur

The design of iron (Fe) and Copper (Cu) thermocouples has been carried out for temperature sensors. The sensor will be made of two different types of materials namely iron and copper. The reference temperature used is 10C. The data collection procedure is first of all a thermocouple with a hot junction is tied together with a solder as a heat source. Besides that, it is also tied to a factory thermocouple that functions as a calibrator. Then the other end of the thermocouple (cold junction) will be inserted into a container containing ice cubes. Then the ports for each thermocouple will be connected to a multimeter, each of which is used to measure temperature (0C) and voltage (mV). From the results of observations and analyzes, it was found that for iron and copper thermocouples had the following characteristics: Seebeck coefficient was 0.001, the mean temperature rises and falls respectively (106.17 ± 0.82) 0C and (118.67 ± 0.90) 0C. The sensitivity of the thermocouple is 0.5 mV / 0C with linearity of 0.9.

Thermodynamic Analysis of TEG-TEC Device Including Influence of Thomson Effect

A thermodynamic model of a thermoelectric cooler driven by thermoelectric generator (TEG-TEC) device is established considering Thomson effect. The performance is analyzed and optimized using numerical calculation based on non-equilibrium thermodynamic theory. The influence characteristics of Thomson effect on the optimal performance and variable selection are investigated by comparing the condition with and without Thomson effect. The results show that Thomson effect degrades the performance of TEG-TEC device, it decreases the cooling capacity by 27 %, decreases the coefficient of performance (COP) by 19 %, decreases the maximum cooling temperature difference by 11 % when the ratio of thermoelectric elements number is 0.6, the cold junction temperature of thermoelectric cooler (TEC) is 285 K and the hot junction temperature of thermoelectric generator (TEG) is 450 K. Thomson effect degrades the optimal performance of TEG-TEC device, it decreases the maximum cooling capacity by 28 % and decreases the maximum COP by 28 % under the same junction temperatures. Thomson effect narrows the optimal variable range and optimal working range. In the design of the devices, limited-number thermoelectric elements should be more allocated appropriately to TEG when consider Thomson effect. The results may provide some guidelines for the design of TEG-TEC devices.

Potential Sources of Errors in Estimating Plant Sap Flow Using Commercial Thermal Dissipation Probes

Thermal dissipation systems are a conventional technique to estimate sap velocity by determining the temperature difference between sap flow probes. The Thermal Dissipation Probe (TDP) method is commercially available and has been used by many researchers and professionals to estimate sap flow in plants. However, some errors and practical issues cause inaccuracy when evaluating plant sap velocity with this technique. Specifically, the sources of these errors are from the effect of the ambient thermal gradient (i.e., error caused by the cold junction location), the underestimation of nighttime sap flow, and the deficient thermal contact between the probe and tree body. This article focuses on errors associated with the traditional TDP, which effect on the thermal difference between the reference and heated probes. These errors vary as a nonlinear function of the transmitter length and the numbers of cold junctions which are affected by changes in the ambient temperature. Keywords: Ambient thermal gradient, Sap velocity, Thermal dissipation probe (TDP), Thermocouple cold junction.

Validation of discrete numerical model for thermoelectric generator used in a concentration solar system

In a concentration solar system, large temperature differences occur between the hot- and cold-junction of thermoelectric module due to concentration technology. Therefore, the nonlinear temperature dependence of the Seebeck coefficient, the electric conductivity, and the thermal conductivity of thermoelectric materials should not be neglected in performance evaluation of thermoelectric generator. Herein, a discrete numerical model, with advantage of low-computational expense, high accuracy, and broad application scope, is built to design the thermoelectric generator in a concentration solar system. Temperature-dependent material properties and contact resistance are both incorporated in the discrete numerical model. Besides, an experiment is carried out to measure the performance of Bi2Te3 thermoelectric generator operating under various temperature differences (Δ T). Finally, the discrete numerical model-calculated results are compared to the experimental data and the theoretical results computed by the commonly used constant properties model. Results show that the variation between the constant properties model-calculated output power and the measured one is less than 4% with Δ T lower than 59 K and rises to 12.6% with Δ T up to 251 K, while the error between the discrete numerical model-calculated output power and experiment remains lower than 2% even when Δ T is above 251 K.