Thermoelectric Generator Structure Research Articles

Analyzing and optimizing the power generation performance of thermoelectric generators based on an industrial environment

The industrial production process consumes electricity and generates a lot of waste heat. Recycling waste heat for power generation can effectively improve energy efficiency. This study uses thermoelectric conversion technology to recover industrial waste heat and designs a high-performance thermoelectric generator (TEG). According to the characteristics of industrial environmental temperature, the power generation performance of the TEG of various sizes is analyzed by a numerical calculation method. The TEG's structure, cooling method, and heat collection method are optimized based on numerical calculation results. After completing the structural optimization of the TEG, we conducted a field test of the equipment at a steel company in China. The results show that the optimized TEG has good power generation performance and can operate efficiently in an industrial environment. The best power generation performance can be obtained when the optimized TEG adopts the structure of 20cm × 150 cm. The maximum output power is 80.5 W, which is 11.2% higher than the unoptimized TEG. The best economic benefits can be obtained when the optimized TEG adopts the structure of 20cm × 75 cm. The minimum power generation cost is 1.76$W−1, which is 15.4% higher than the unoptimized TEG.

Characteristics analysis and parameter optimization of a micro-combustion based thermoelectric generator

Micro combustion based thermoelectric generator (micro-CTEG) has great potential to provide reliable electricity for portable electronic devices. Previous works on micro-CTEG has focused on the micro combustion issue, here we explore the heat transfer and thermoelectric (TE) coupling mechanism and give the guidelines for optimizing the performance of micro-CTEG. An analytical model was derived considering heat exchange inside the combustor, TE generator structure and temperature dependent material properties. Based on the optimization results, the temperature drop across the TE leg remains nearly constant for filling fraction approaching 1.0 and decreases remarkably with decreasing input fuel power for filling fraction approaching 0.1 due to the excessive gap heat loss. High filling fraction and high input fuel power is preferred to balance the power density and total efficiency. With identical thermoelectric figure of merit (ZT), increasing power factor under low filling fraction and decreasing thermal conductivity under high filling fraction are preferred respectively. The optimal load resistance factor, which represents the ratio of load resistance to internal resistance of TE generator, shows a decreasing trend with increasing temperature drop across TE leg. The optimal leg length remains nearly unchanged as thermal resistance of the heat sink is lower than 1 K/W.

Numerical analysis of semiconductor thermoelectric generator

A thermoelectric generation model is proposed based on the structure of thermoelectric generator, working conditions, the effect of air heat transfer and contact resistance in thermoelectric components. In addition, the effect of the thermoelectric generator output performance under the condition of different temperature of the cold and heat source, contact resistance between the cold-end and hot-end, the load resistance and the contact resistance is calculated. The results show that the output voltage is linear associate with the temperature difference between hot and cold ends, however, the output power increase along with the increase of temperature of hot-end and decrease of cold-end. The output voltage reaches 5.76 V and the output power reaches 9.81 W when the temperature difference is 200?C. Assume that the contact resistance is ignored, the output voltage and power reach peak values of 3.61 V and 3.85 W. The output performance of thermoelectric generator decreases with the increase of thermal contact resistance at hot and cold ends, and the reduction is getting lower and lower. With the increase of the load resistance, the output power increases at the beginning and then decreases. The optimal output power is 3.69 W when the contact resistance is 0 ? and the optimal load resistance is 3.3 ?. The maximum output power corresponding to neglecting the contact resistance will be reduced by 13.5% when the contact resistance is 0.5 ?.

Power generation characteristics of a thermoelectric modules-based power generator assisted by fishbone-shaped fins: Part I – effects of hot inlet gas parameters

ABSTRACT Several researchers and manufacturers are paying attention to technologies of waste heat recovery due to its effectiveness in the conversion of the energy from exhaust gas into electric power. Therefore, the analysis of the effects of thermoelectric generator (TEG) design on the power generation characteristics is an essential issue to develop its applications to waste heat recovery technologies aiming at pollution environment reduction and improvement of efficiency for energy use. In this study, a TEG based on the thermoelectric module (TEM) with fishbone-shaped fins was built for experimental purposes. The comparison of power generation characteristics including voltage and power output, conversion efficiency, and pressure drop for the fabricated TEM-based TEG with fishbone-shaped fins and TEM-based TEG without fins under conditions of the hot inlet gas temperatures from 200-500°C along with the changes in mass flow rate of hot inlet gas was conducted. The results indicated that TEM with fishbone-shaped fins had a maximum increase by 30.7 V of voltage output, 17.54 W of power output, 3.68% of conversion efficiency compared to the case of TEM without fishbone-shaped fins. However, the average pressure drop for TEM with fishbone-shaped fins was 3.65 Pa higher than that of TEM without fishbone-shaped fins. The experimental study showed that TEM-based TEG system had achieved high conversion efficiency by attaching the fishbone-shaped fins to the surface of the hot side in the TEG structure.

Optimization of thermoelectric generator (TEG) integrated with three-way catalytic converter (TWC) for harvesting engine’s exhaust waste heat

The exhaust-based thermoelectric generator (TEG) is a promising way to recover the waste heat of internal combustion engines (ICEs). Integrating TEG with three-way catalytic converter (TWC) can improve the output power of TEG and reduce additional pressure drop in the exhaust system. In the present study, some optimization designs for the integration structure of TEG and TWC are carried out through a complete 3-D numerical model. Moreover, the overall performance improvement between the present TEG and a single TEG is illustrated. The results show that the uniform temperature distribution and high output power can be obtained with TWC placed in the rear of heat exchanger. Increasing the number of thermoelectric modules (TEMs) can’t always increase the maximum output power of TEG, but can reduce the conversion efficiency of TWC because more heat is absorbed from the exhaust gas. On the condition of maintaining high conversion efficiency of TWC, a moderate height of hollow center body contributes to higher maximum output power of TEG with reasonable pressure drop. Compared with a single TEG, the maximum output power of present TEG is increased by 16%, and the maximum net output power is increased by 37% with considering the power loss caused by the additional pressure drop and increased weight.

A novel design for a wearable thermoelectric generator based on 3D fabric structure

A flexible and wearable thermoelectric generator (TEG) could enable the conversion of human body heat into electrical power, which would help to realize a self-powered wearable electronic system. To overcome the difficulty of wearing existing flexible film TEGs, a novel 3D fabric TEG structure is designed in this study. By using a 3D fabric as the substrate and yarns coated with thermoelectric materials as legs, a wearable and flexible TEG can be realized. The designed generator has a sandwich structure, similar to the classical inorganic generator, which allows the generation of a temperature difference in the fabric thickness direction, thus making it wearable and showing promising application in body heat conversion. To verify the effectiveness of the designed generator structure, a prototype was fabricated, using a locknit spacer fabric as the substrate and yarns coated with waterborne polyurethane/carbon nanotube thermoelectric composites as legs. The results suggest that the fabricated spacer fabric TEG prototype could work successfully, although the performance of this prototype is of a low level. To further improve the efficiency of the 3D fabric generator and apply it in wearable electronics in the future, highly efficient inorganic thermoelectric materials can be applied, and modifications on the conductive connections can be made.

Study on the Influence of the Cold-End Cooling Water Thickness on the Generative Performance of TEG

At present, about 40% of the fuel energy is discharged into air with the exhaust gas when an automobile is working, which is a big waste of energy. A thermoelectric generator (TEG) has the ability to harvest the waste heat energy in the exhaust gas. The traditional TEG cold-end is cooled by the engine cooling system, and although its structure is compact, the TEG weight and the space occupied are important factors restricting its application. In this paper, under the premise of ensuring the TEG maximum net output power and reducing the TEG water consumption as much as possible, the optimization of the TEG water thickness in the normal direction of the cold-end surface (WTNCS) is studied, which results in lighter weight, less space occupied and better automobile fuel economy. First, the thermal characteristics of the target diesel vehicle exhaust gas are evaluated based on the experimental data. Then, according to the thermoelectric generation model and the cold-end heat transfer model, the effect of the WTNCS on the cold-end temperature control stability and the system flow resistance are studied. The results show that the WTNCS influences the TEG cold-end temperature. When the engine works in a stable condition, the cold-end temperature decreases with the decrease of the WTNCS. The optimal value of the WTNCS is 0.02 m and the TEG water consumption is 8.8 L. Comparin it with the traditional vehicle exhaust TEG structure, the power generation increased slightly, but the water consumption decreased by about 39.5%, which can save fuel at0.18 L/h when the vehicle works at the speed of 60 km/h.

The influence of inner topology of exhaust heat exchanger and thermoelectric module distribution on the performance of automotive thermoelectric generator

The waste heat of automotive exhaust gas would be directly transferred into electricity by thermoelectric modules (TEM) because of the temperature difference between heat exchanger and water tank. For the vehicle thermoelectric generator (TEG), the electrical power generation was deeply influenced by temperature difference, temperature uniformity and topological structure of TEG. In previous works, increasing the difference of temperature would significantly enhance the power generation of TEG and inserted fins were always applied to enhance heat transfer in heat exchanger. However the fins would result in a large unwanted back pressure which went against to the efficiency of the engine. In current studies, in order to enhance heat transfer rates and to avoid back pressure increase, a heat exchanger containing cylindrical grooves (the depth-to-width ratio is 0.25) on the interior surface of heat exchanger was proposed. The cylindrical grooves could increase the heat transfer area and enhance the turbulence intensity, meanwhile there was no additional inserts in the fluid to block the flow. The surface temperatures of water tank and heat exchanger with three internal structures, such as grooved surface, flat surface and inserted fins, were studied by numerical simulation at each row of thermoelectric modules. The results showed that comparing to other structures, heat exchanger with cylindrical grooves could improve the TEG efficiency at a low back pressure. The influence of the channel height on the TEG performance was investigated and the TEG with a channel height of 8mm showed the best overall performance. It was also found that a portion of heat exchanger uncovered with thermoelectric modules at the downstream section could make the upstream section hotter and make full use of each TEM.

Nominal power density analysis of thermoelectric pins with non-constant cross sections

The investigation of the geometric structure of TEG (thermoelectric generator) pins is essential, as their geometry determines the performance of devices. In this study, nominal power density (NPD) is used to find a better geometric structure of thermoelectric pins of TEGs, since a comparison of maximum dimensionless efficiencies for different geometric pins cannot be used to identify the optimum geometry. The influence of shape parameter on NPD for TEG pins in linear, quadratic and exponential cross-sectional functions is studied. The NPD decreases when the shape parameter increases for different geometric pins, while the maximum values of NPD are the same. Then, the effects of dimensionless efficiency and the temperature ratio on the NPD are analyzed. The NPD decreases with the increase in dimensionless efficiency and temperature ratio. Pins with linear variation in cross section have the highest NPD among the three geometries of pins evaluated.

Interferometric Analysis of Thermomechanical Deformations in Thermoelectric Generators

In thermoelectric applications, optimized thermal contacts are essential to enable efficient and homogeneous flow of heat currents. Thermomechanical stresses may lead to surface deformation, which alters the thermal contact. As a result, the heat current density is reduced and no longer homogeneous. Also an undesired temperature gradient perpendicular to the heat flow develops, and hence this temperature gradient again causes thermomechanical stresses. The described thermomechanical problems are particularly important in applications where high operating temperatures and hence large temperature differences are used. Also, system durability is a crucial aspect, especially in applications where thermal cycles occur (i.e., in the field of waste heat regeneration of car combustion engines). We describe a measuring technique to detect and evaluate the influence of these deformations. To analyze the surface and external points of contact of a thermoelectric generator (TEG), a measurement setup based on speckle interferometry is used. Temperature gradients as well as small surface deflections in the μm range have to be measured simultaneously. Therefore, an optical as well as a thermography camera are used to create a holistic image of the deformation and to analyze the influence of this deformation on the TEG structure.

Development of a Flexible Thermopile Power Generator Utilizing BiTe-Cu Thin Films

In this paper, a thermoelectric generator with a flexible structure is presented. The thermoelectric generator consists of 1625 thermocouples made from two materials, i.e. n-type BiTe and Cu thin films, on a flexible polyimide sheet by utilizing micromachining technology. The prototype of the flexible thermoelectric generator has dimensions of 100mm × 80mm × 3mm (length × width × thickness). Theoretical calculations show an output voltage of 317mV/K and a power of 7.8μW/K2. Preliminary experimental results measured on the test thermocouple samples show an average Seebeck voltage of 58.8μV/K per one thermocouple was obtained. This thermoelectric generator structure can be bent flexibly, so it can be used on both flat and cylindrical surfaces, e.g. on the skin of human body.