Thermoelectric Cells Research Articles

Impact of moisture contents on the performance of organic bi-layer ITO/OD thermo-electric cells

We propose a bi-layer thermo-electric cell based on elastic indium tin oxide (ITO) substrate and organic semiconductor orange dye (OD). It is observed that thermo-electric voltages are ~30 % higher in bi-layer ITO/OD cell as compared to the single layer ITO cell. This improvement is caused by an obvious increase in Seebeck coefficient, which could be related to the appropriate electrical and thermal conductivities of the bi-layer organic thermo-electric cell. The effect of moisture contents on the Seebeck coefficient of the ITO/OD based bi-layer thermo-electric cell has also been investigated. The experimental results clearly show that with the increase of temperature Seebeck coefficient increases, whereas with increasing moisture contents the Seebeck coefficient of the ITO/OD thermo-electric cell significantly decreases. Our results point out the need for well-controlled environmental conditions, predominantly moisture level, in order to appraise the thermo-electric performance of organic semiconductor materials.

Challenges and Perspectives in Tandem Thermoelectric–Photovoltaic Solar Energy Conversion

This paper discusses enhancements of solar energy conversion by photovoltaic (PV) cells using thermoelectric (TE) generators harvesting the heat released by the PV cell. To optimize the TE–PV coupling, PV efficiency losses are analyzed by decoupling source- and absorber-dependent losses. This shows that the implementation of a tandem PV–TE device leads to a substantial increase of available power densities depending on the PV material. We further show that a major increase of the conversion efficiency can be achieved by adding an intermediate layer between the PV and the TE stage capable of absorbing the under-the-gap fraction of the solar spectrum. This increase of efficiency is discussed and commented upon also in view of the constraints PV–TE coupling imposes to the TE generator layout and to its material characteristics. The critical importance of effective heat dissipation will also be addressed. The conclusion is reached that not only could tandem PV–TE cells improve the conversion rate of existing solar cells but also that they could enable the use of lower cost PV materials, currently not considered because of their marginal PV efficiency.

Aspects of Protonic Ionic Liquid as Electrolyte in Thermoelectric Generators

The Seebeck coefficient (S E) or thermopower and power output have been measured in a series of 16 ionic liquids (ILs). Thermoelectric current extraction is assisted by a dissolved redox couple (I2/LiI) added to the IL. The experiments were carried out in a thermoelectric cell where the IL is packaged between two electrodes. A large range of Seebeck coefficients and power outputs could be observed. The highest S E was measured for protonic ILs, reaching a value of 968 μV/K. Moreover, the maximal power output of an IL-based thermoelectric generator and the polarity of its electrodes depend on the concentration of the redox-active species in the IL. The power output of the generator increased continuously with the redox concentration up to a maximum value (at 0.4 mol/L) but decayed for higher concentrations. We showed that an IL with high S E [linked to open-circuit voltage (V OC)] does not necessarily lead to high power output; rather, it is carrier transport and extraction that determine the generator power. Surprisingly, the carrier extraction is not highest at the maximum electrode temperature difference; the power output observed for a given electrode temperature difference can be further increased by heating up the cold electrode in spite of the consequent reduction in the total temperature difference between the electrodes.

Performance and reliability of commercially available thermoelectric cells for power generation

This paper presents performance and reliability study of commercially available Bi2Te3 thermoelectric cells (TEC1-12710T125) used as a thermoelectric generator (TEG). These TECs are tested in temperature regime from ambient temperature up to 250°C. This paper provides simple guide to estimate energy conversion efficiency of commercially available Bi2Te3 thermoelectric cells for power generation at a variety of operating conditions in low temperature regime. When these TECs were tested at hot side temperature of around 210°C continuously for 7h, their performance was seen to reduce by around 37% as compared to performance at lower temperatures. These cells when again tested at lower temperatures showed reduced efficiency and power output. This shows that the damage is irreversible although the process revert to lower hot side temperature (<100°C). Finally this paper presents performance of these TECs when subjected to thermal cycling and continuous operation at hot side temperature of about 160°C. It was observed that the open circuit voltage starts to jump beyond 300 cycles. This might be due to weakening of the soldered joints within the cell.

Possibility of Thermoelectric Oxide for Thermal Sensors

The thermoelectric effects in oxide materials are developed to the Seebeck effect for thermal sensing. Thermal sensors are the thermal converters, in which an electrical, magnetic, mechanical, radiation, chemical signal are measured by converting it into heat and measuring the resulting temperature changes in the device. This proposes an analysis the electrical converters and radiation sensors by using single−junction of p−Ca3Co4O9 and n−CaMnO3 materials are presented into possible thermal sensing. Several thermal converters are measured the signal electrical resistivity, and Seebeck coefficient depended on temperature. Thermal radiation sensors are included the sensitivity, electricity, and specific detectivity. For application, thermoelectric oxide cell can be fabricated crowbar circuit for protection an overvoltage condition of a power supply which it yield 1.2 s turn off switch.

Heat Transfer Analysis of an Engine Exhaust-Based Thermoelectric Evaporation System

Engine exhaust can be used by thermoelectric generators for improving thermal efficiency of internal combustion engines. In his paper, the performance of a thermoelectric evaporation system is investigated. First, the thermal characteristics of diesel engines are obtained according to the experiment data. Then, mathematical models are created based on the specified conditions of the coolant cycle and the evaporator geometric parameters. Finally, the heat transfer characteristics and power performance of the thermoelectric evaporation system are estimated, and a comparison with the system in which the heat exchanger operates with all-liquid coolant is investigated. The results show that the overall heat transfer rate of the thermoelectric evaporator system increases with engine power. At the rated condition, the two-phase zone with an area of 0.8689 m2 dominates the evaporator’s heat transfer area compared with the preheated zone area of 0.0055 m2, and for the thermoelectric module, the cold-side temperature is stable at 74°C while the hot-side temperature drops from 341.8°C to 304.9°C along the exhaust direction. For certain thermoelectric cells, the temperature difference between the cold side and hot side rises with the engine load, and the temperature difference drops from 266.9°C to 230.6°C along the exhaust direction. For two cold-side systems with the same heat transfer, coolant mass flow rate in the evaporator with two-phase state is much less, and the temperature difference along with equivalent heat transfer length L is significantly larger than in the all-liquid one. At rated power point, power generated by thermoelectric cells in the two-phase evaporation system is 508.4 W, while the other is only 328.8 W.

Seebeck coefficients of cells with lithium carbonate and gas electrodes

The Seebeck coefficient is reported for thermoelectric cells with gas electrodes and a molten electrolyte of one salt, lithium carbonate, at an average temperature of 750°C. We show that the coefficient, which is 0.88mVK−1, can be further increased by adding an inorganic oxide powder to the electrolyte. We interpret the measurements using the theory of irreversible thermodynamics and find that the increase in the Seebeck coefficient is due to a reduction in the transported entropy of the carbonate ion when adding solid particles to the alkali carbonate. Oxides of magnesium, cerium and lithium aluminate lead to a reduction in the transported entropy from 232±12 to around 200±4JK−1mol−1. This is of importance for design of thermoelectric converters.

Fast Switching in Thermoelectric Spin-Transfer Torque MRAM with Temperature Increase Caused by Peltier Effect

A new alternative data storage technology of nonvolatile memory, thermoelectric spin-transfer torque MRAM (TSTT-MRAM), is discussed in this paper. In principle, in the TSTT-MRAM mechanism the current is applied in the thermoelectric cell and the magnetic tunnel junction (MTJ) cell. The finite-element method and micromagnetic model were used to explore the magnetic degradation and switching mechanism in the TSTT-MRAM with temperature increases caused by a Peltier effect. The results showed that the temperature in the MTJ magnetic layers increased with increasing bias current into the thermoelectric device. For the switching process, the increased temperature affected the fluctuation of the saturation magnetization and lead to a decrease in the switching time when considering the same critical current. Thus, the fast switching process with TSTT-MRAM devices is interesting for the development of the future memory technology.

Performance review of a novel combined thermoelectric power generation and water desalination system

A novel combined thermoelectric power generation and water desalination system is described with a system schematic. The proposed system utilises low grade thermal energy to heat thermoelectric generators for power generation and water desalination. A theoretical analysis presents the governing equations to estimate the systems performance characteristics combined with experimental validation. Experimental set-up consists of an electric heat source, thermoelectric modules, heat pipes, a heat sink and an evaporator vessel. Four heat pipes are embedded in a heat spreader block to passively cool the bottom side of the thermoelectric cells. The condenser of these four heat pipes is immersed in a pool of saline water stored in an evaporation vessel which is maintained at sub-atmospheric pressure. The liquid to vapour phase change cooling method achieve low saturation temperature and offers a high heat transfer coefficient for the cooling of the thermoelectric generators. At the same time this method utilises the low temperature heat extracted from the cold side of the thermoelectric generator for water desalination. It was observed that at low saturation temperatures greater heat flux could be supplied to the thermoelectric generators with less heat losses to the atmosphere.

A Review on the Performance of the Nanofluid Based Solar Collectors – Solar Energy

Using nanofluids as an innovative kind of liquid blend with a trivial volume fraction (in percent) of nanometer-sized solid particles in suspension is a fairly a novel arena or idea. The objective of this presented review paper is to inspect the performance of the nanofluid-based solar collector (NBSC). In past few years for a number of experimental and industrial thermal engineering systems solar energy has proven to be the best input energy source. The scarcity of fossil fuels and environmental contemplations motivated the researchers to utilize alternative energy sources such as solar energy, wind energy, tidal energy etc. Therefore, it is essential to boost the performance of the solar thermal engineering systems. Because of better rheological properties nanofluids are utilized to build up the performance of conventional solar thermal engineering systems. Therefore, major part of this presented review paper lays a main emphasis to investigate the effects of nanofluids on the performance of solar collectors. Some proposals are also given to use the nanofluids for future work in different solar thermal engineering systems such as parabolic trough systems (PTS), solar thermoelectric cells and finally, the challenges of using nanofluids in solar energy devices are reviewed in brief.

The Further Improvement of the Ionic Thermoelectric Generator

The power conversion efficiency of the proton-conductive thermoelectric cell is improved by the unidirectional orientation of ionic conductivity in the electrospun Nafion cell. The thermoelectric performance of nanofibers is experimentally demonstrated.

Effect of ceramic coating in combustion and cogeneration performance of Al2O3 porous medium

In this work, the effect of SiC-, Ni-, and Cr-based coating on the performance of porous medium burner are evaluated. A dip-coating technique was used to coat SiC, Ni, and Cr powders on a pre-sintered porous Al2O3 substrate. The morphological properties of the sintered Al2O3 plain substrates and coating layer were observed using a light microscope and scanning electron microscopy. The combustion analyzer has been calibrated and used to measure the emissions during the experiment. Thermoelectric cells were used in the cogeneration system to generate electricity from the porous medium burner. The results show a significant improvement in the maximum surface flame temperature and combustion emissions over the plain substrate. The highest recorded surface flame temperature at flow rate of 0.25 L/min was 750 °C for SiC-coated, 741 °C for Cr-coated, 739 °C for Ni-coated and plain substrate registered a temperature of only 634 °C. An 18% increase in flame temperature was recorded for SiC-coated substrate when compared to the plain substrate. Moreover, the coated substrate reduced the emissions CO, COu and NOx. It was also found that; SiC-coated substrate reported the best overall power output when compared to the plain substrate.

Designing a Cold Plate Used in Rapid Freeze Prototyping Technology

The rapid prototyping with ice is a new manufacturing technology that can generate three-dimensional objects from ice by depositing and rapidly freezing water layer by layer. In order to freeze the water droplets, the plate must meet certain conditions, among those it is worth to be mentioned, the surface temperature, which should not surpass 0°C. The equipment presented in the paper is a part of rapid freeze prototyping equipment, designed and built by the authors. The authors analysed various freezing systems and they discovered that the classical cooling systems are not appropriate to be used in rapid freeze prototyping technology. The unique solution is the utilisation of thermoelectric cells, generic named as Peltier cells. The modern technology can be used in obtaining Peltier cells, with a high degree of reliability, electrical consumption and yield. This can be successfully used as heat pumps in industry. The author developed an original system that permitted to implement the Peltier cells. The cold plate was designed by using CAD software. In addition, the cold plate was produced and tested. The equipment obtained, has a greater power in comparison with the classical ones, even if it has smaller dimensions. The electrical power supply has to be well filtered in order to generate a higher efficiency. Through the main advantages of the Peltier cells can be mentioned: no maintenance have to be performed as this type of cells have no moving parts, thus having a major advantage; no CFC or other consumables parts have to be used, thus proving to be more economical than other systems; the heat regulation can be performed easier compared with the classical systems offering a better control and precision; it can be used in severe environments where conventional cooling systems can fail, being successfully used in the presence of liquid nitrogen; it can perform in various positions and is reversible similar to heat pumps. The main drawback of this system is that it uses a great amount of electrical energy, consequently can have a low yield.

Experimental investigation of the performance of a liquid fuel-fired porous burner operating on kerosene-vegetable cooking oil (VCO) blends for micro-cogeneration of thermoelectric power

Studies related to porous burner for thermoelectric (TE) power generation have mainly focused toward achieving a specific range of power output for various applications. However, detailed analyses on the performance and emission aspects of the porous burner are lacking. In addition, physical integration between the burner and TE modules has added further complexity in this research area. Thus, this work aims to comprehend the effects of fuel–air equivalence ratio on the performance and emission characteristics of a liquid fuel-fired porous burner for micro-cogeneration of TE power. A catalytically inert Al2O3 porous medium was incorporated into a liquid fuel-fired porous burner operating on four mixtures of kerosene-vegetable cooking oil (VCO) blends: 100 kerosene, 90/10 KVCO, 75/25 KVCO, and 50/50 KVCO. Ten bismuth-telluride TE cells were arranged in a ten-sided polygon that, together with finned dissipators, formed a TE module electrically connected in series but thermally connected in parallel. The performance aspects at various fuel–air equivalence ratios were thoroughly evaluated with the corresponding temperature profiles, voltage, current, power output, and electrical efficiency. Results indicated that the surface temperature of the porous media was generally higher than the developed and exit flame temperature of the burner. Varying the fuel-air equivalence ratio significantly affected the electrical efficiency, with a maximum and minimum value of 1.94% and 1.10%, respectively. The power output steadily increased in the lean region, but stabilized as the fuel–air equivalence ratio slowly increased beyond the stoichiometric ratio. The CO emission was relatively lower at the lean region; however, significant amount was recorded in the rich combustion region. Moreover, NOx fluctuated between 1 ppm and 4 ppm over the entire range of fuel–air equivalence ratio.

Silicon Based Thermoelectric Cells with Built in Solar Cells and CNT Composite Based Thermoelectric Cells for Measurement of Gradient of Temperature

Thermoelectric cells and Solar cells are source of harvesting energy from heat and light respectively. In this study both are fabricated on a single cell using n-Si and p-Si single crystal strips.Later, temperature gradient cells are also fabricated . The fabricated Phtoto-thermoelectric cells and Temperature gradient celss are investigated, showing improvement in seebeck effect.

Electricity generation from an exhaust heat recovery system utilising thermoelectric cells and heat pipes

The internal combustion engine used in majority of cars at the present time do not use their fuel input very efficiently. A majority of this energy is dissipated as heat in the exhaust. The related problems of global warming and dwindling fossil fuel supplies has led to improving the efficiency of the internal combustion engine being a priority. One method to improve the efficiency is to develop methods to utilise heat in car exhausts that is usually wasted. Two promising technologies that were found to be useful for this purpose were thermoelectric cells (TECs) and heat pipes. Therefore this project involved making a bench type, proof of concept model of power production by thermoelectric cells using heat pipes and hot engine exhaust gases. 8 cells were used and managed to produce 6.03 W when charging the battery. The system operated with a heat to electricity conversion efficiency of 1.43%. The discrepancy between the actual efficiency and the predicted efficiency of 2.31% is most likely due to the cells not operating at their optimum voltage. The predicted efficiency is approximately 1/9 of the Carnot efficiency and the actual efficiency is approximately 1/15 of the Carnot efficiency.

Thermal Presentation of Two-Phase Congested Thermosyphon in Submission of Determined Thermoelectric Dominance Producer by Means of Phase Change Material Thermal Storage

With the growing energy command due to growing world people and industrialization, utilizing strenuous solar energy for thermal and electrical power production will be the future renewable power source to decrease the confidence on fossil fuel and reduce carbon dioxide discharge. Besides by means of determined Photovoltaic (CPV) system, Concentrated Thermoelectric generator (CTEG) will be another possible option for sustainable power generation. The CTEG system utilizes concentrated solar flux as a heat source to the thermoelectric generating (TEG) module in generating direct current thermoelectricity which can be easily converted to alternating power using an inverter. By maintaining a temperature difference between the hot and cold sides of the thermoelectric cells (Seebeck effect), thermoelectricity is generated where its magnitude is a function of temperature difference. The main challenge is the effectiveness of excess heat removal which accumulated at the cold side of the thermoelectric cell to achieve greater power generation. Using acting cooling mechanisms are not energy efficient proposal as it requires power in operating them and significantly reduces the total power output generated. They are planned in the paper for working CTEG system through passive cooling and achieving invariable cooling. Two-phase closed thermosyphon is implement as an helpful heat transporting device for transfer excess heat from heated TEG part to the frozen PCM storeroom reservoir for heat luggage compartment. This investigation is to evaluate the thermal presentation of the proposed system.. The working fluid used in the thermosyphon was Acetone and its filling ratio was designated at 40% of the evaporator volume. Paraffin wax was selected as PCM with melting point of 47oC and acceptably high latent heat storage was selected in the thermal storage. The passive cooling mechanisms consist of PCM storage tank, heat pipe-based heat transfer system for transporting heat from TEG modules to the PCM thermal storage during the daytime and a similar heat pipe-based system for discharging heat from PCM storage tank to the cooler ambient during the night time.

Numerical Simulation of n-CaMnO3/Bi and p-NaCo2O4/Ag Thermoelectric Cell by Finite Element Method

In the optimal design of thermoelectric cell, the electrical power, voltage and efficiency are interesting issues to investigate. We simulated thermoelectric cells to study the distribution temperature, voltage, current, electric power and efficiency by finite element method (FEM). The elements were used Brick 20 node 226 and tetrahedron 227 from the mesh tools element attributes mesh volume p-n type for hexagonal and copper for tetrahedron boundary condition to the thermoelectric cell. The calcium bismuth manganese oxide n-type (CaMnO3/Bi) leg and sodium cobalt oxide doping silver p-type (NaCo2O4/Ag) leg size of 2.5×2.5×10 mm3 was fabricated in FEM. copper plate size of 2.5×5.5×0.5 mm3. The electrical resistance of 17 Ω, voltage of 0.96 V, current of 3.68 mA, electric power of 3.53 mW and conversion efficiency of 1.76 % at temperature difference of 200 K.

Numerical assessment of the thermodynamic performance of thermoelectric cells via two-dimensional modelling

The present paper is aimed at putting forward a two-dimensional model for thermoelectric cells. The energy conservation equation was formulated in order to account for the Fourier (heat) conduction, the Thomson (thermoelectric) effect, and the Joule heating on the temperature distribution. The electric field was also modelled in order to come out with the current and voltage distributions. The governing equations were discretized by means of the finite-volume method, whereas the TDMA algorithm was adopted for solving the sets of linear equations. An explicit solution scheme was employed to address the temperature influence on the thermoelectric effect. The model results have been compared with experimental data, when a satisfactory agreement was achieved for both cooling capacity and COP, with errors within a 10% band. In addition, the model was employed to assess the effects of the thermophysical properties and the couple geometry on the thermodynamic performance of the thermoelectric cell.

Temperature gradient measurements by using thermoelectric effect in CNTs-silicone adhesive composite.

This work presents the fabrication and investigation of thermoelectric cells based on composite of carbon nanotubes (CNT) and silicone adhesive. The composite contains CNT and silicon adhesive 1∶1 by weight. The current-voltage characteristics and dependences of voltage, current and Seebeck coefficient on the temperature gradient of cell were studied. It was observed that with increase in temperature gradient the open circuit voltage, short circuit current and the Seebeck coefficient of the cells increase. Approximately 7 times increase in temperature gradient increases the open circuit voltage and short circuit current up to 40 and 5 times, respectively. The simulation of experimental results is also carried out; the simulated results are well matched with experimental results.