Thermoelectric Generator Device Research Articles

Study of an LLC Converter for Thermoelectric Waste Heat Recovery Integration in Shipboard Microgrids

Static waste heat recovery, by means of thermoelectric generator (TEG) modules, constitutes a fast-growing energy harvesting technology on the way towards greener transportation. Many commercial solutions are already available for small internal combustion engine (ICE) vehicles, whereas further development and cost reductions of TEG devices expand their applicability at higher-power transportation means (i.e., ships and aircrafts). In this light, the integration of waste heat recovery based on TEG modules in a shipboard distribution network is studied in this work. Several voltage step-up techniques are considered, whereas the most suitable ones are assessed via the LTspice simulation platform. The design procedure of the selected LLC resonant converter is presented and analyzed in detail. Furthermore, a flexible control strategy is proposed, capable of either output voltage regulation (constant voltage) or maximum power point tracking (MPPT), according to the application demands. Finally, both simulations and experiments (on a suitable laboratory testbench) are performed. The obtained measurements indicate the high efficiency that can be achieved with the LLC converter for a wide operating area as well as the functionality and adequate performance of the control scheme in both operating conditions.

Stencil-Printed Scalable Radial Thermoelectric Device Using Sustainable Manufacturing Methods

In this study, we used n-chitosan-Bi2Te2.7Se0.3 and p-chitosan-Bi0.5Sb1.5Te3 composite inks to print a circular thermoelectric generator (TEG) device using a low-energy-input curing method. Thermoelectric (TE) composite films were fabricated using varying sizes of thermoelectric particles and a small chitosan binder (0.05 wt. %). The particles and binder were hot pressed at an applied pressure of 200 MPa and cured at 200 °C for 30 min. We achieved ZT of 0.35 for the n-type and 0.7 for the p-type TE composite films measured at room temperature. A radial TEG was fabricated using the best-performing n-type and p-type composite inks and achieved a power output of 87 µW and a power density of 727 µW/cm2 at a temperature difference of 35 K; these are among the best-reported values for printed TEG devices. Using a low-energy-input fabrication method, we eliminated the need for high-temperature and long-duration curing processes to fabricate printing devices. Thus, we envisage that the low-energy-input curing process and cost-effective printable strategy presented in this work pave the way for sustainable manufacturing of large-scale energy harvesting TEG devices.

Thermal properties of novel phase change materials based on protic ionic liquids containing ethanolamines and stearic acid for efficient thermal energy storage.

In the field of energy harvesting, phase change materials (PCMs) hold great promise. 2-hydroxyethylammonium stearate ([HEA]Ste), bis(2-hydroxyethyl)ammonium stearate ([DHEA]Ste), and tris(2-hydroxyethyl)ammonium stearate ([THEA]Ste) ionic liquids (ILs) demonstrate promising capabilities to enhance thermal energy storage (TES) performance within the 30-100 °C temperature range. This research presents these ILs as PCMs for the first time, emphasizing their environmentally friendly characteristics, safety profile, and cost-effectiveness. The chemical composition and microstructure of these PCMs were investigated using scanning electron microscopy (SEM), and fourier transform infrared spectroscopy (FT-IR), while differential scanning calorimetry (DSC) was employed to assess their latent heat of fusion and specific heat capacity. Furthermore, thermal gravimetric analysis (TGA) was utilized to evaluate the thermal stability of these ILs. In addition, valuable insights into the surface properties and behavior of PCMs at the nanoscale are provided using atomic force microscopy (AFM). Results show that the latent heats of fusion for [HEA]Ste, [DHEA]Ste, and [THEA]Ste are about 171.12, 152.58, and 136.55 kJ kg-1, respectively. Also, thermal stability analysis shows the maximum stability (99.5%) for [HEA]Ste. Ultimately, a custom-built setup featuring a cell containing a PCM derived from synthesized ILs and a commercially available thermoelectric generator (TEG) was employed to measure live voltage (V) in the conversion of heat energy into electrical power. On the other hand, specifically in this measurement we recorded the output voltage (open circuit case) of the TEG device versus time and demonstrated that after turning off the thermal energy source, the proposed system provides the electrical energy for a while (more than 2 hours).

Optimal dynamic reconfiguration of thermoelectric generator array using RIME optimizer to maximize the generated power

The innovation of green and flexible sources of electricity is identified as one of the key enablers to a more electric-dependent world aiming at meeting the technology needs and promised sustainability goals. The thermoelectric generator device is one of these innovative sources as it directly converts the wasted heat to electric power with a cheap, silent, and no-emissions process. Yet, the power output of the thermoelectric generator is primarily based on the temperature distribution on its sides. Towards efficiently saving the wasted heat and maximizing the output power of the thermoelectric generator, optimizing the configuration for the thermoelectric generator array is paramount. In this regard, this paper proposes an optimal dynamic reconfiguration for several design options of the thermoelectric generator array, including series–parallel, total-cross-tied, bridge-linked, and honey-comp, to better enhance the thermoelectric generator array output power under nonuniform temperature distribution. The proposed dynamic reconfiguration approach is mathematically formulated as a maximization optimization problem for the thermoelectric generator array output power. The physics-based optimization of RIME is tailored to provide the optimal array reconfiguration layout that realizes the maximum power, upon which the overall power loss is potentially decreased, and the energy conversion efficiency is significantly improved. The efficacy and superiority of the proposed configuration types and optimal dynamic reconfiguration technique are assessed for two sizes of the thermoelectric generator array: a symmetric 9x9 array and an asymmetric 10x15 array. A detailed analysis is conducted to compare the thermoelectric generator output power of the studied configurations without and with the proposed dynamic reconfiguration technique. The results affirm that optimized dynamic reconfiguration significantly enhances the thermoelectric generator array-generated power. One of the key observations from the results is that employing a dynamic reconfiguration for the bridge-linked type yields up to a 10% increase in the output power of the thermoelectric generator array compared to the design options without reconfiguration. Also, the results show that the dynamically reconfigured bridge-linked type could yield about a 5% increase in the produced output power compared to other dynamically reconfigured design options.

Toward tiny high-power-density thermoelectric harvesters

Thermoelectric (TE) generators (TEGs) have recently attracted significant attention for harvesting ubiquitous heat energy to power industrial sensor nodes or wearable and implantable electronics. Such applications require that a small, fitted heat sink be incorporated into a tiny harvester to ensure conformal deployment and ease of use. Since the small heat sink will exhibit very poor heat rejection performance, the optimal structural design of the TEG device and the proper selection of its constituent TE materials are extremely important to ensure that sufficient electric power is provided to the connected post-stage circuits. Regrettably, the traditional forward design strategies, i.e., material-to-device and device-to-harvester, are often disconnected from one another and fail to form a complete chain, thereby presenting a fundamental challenge in achieving ultrahigh-power-density harvesters. Here we present a zero-dimensional model for a tiny harvester to establish a set of new metrics (not limited to the figure of merit zT) that can be used to determine the optimal TE material and to directly deduce the optimal configuration of the TEG for guaranteeing the maximum output power at various load conditions, making backward design strategy possible. Two tiny harvesters are accordingly fabricated and exhibit areal power densities 52 and 94 times that of a harvester incorporating a commercial TEG, with identical amounts of TE material used for each.

Experimental research on thermoelectric characteristics of a thermoelectric generator with external influencing factors optimization

The external influencing factors, the thermal interface material, load-bearing brick weight, and temperature difference, of a thermoelectric generator (TEG) device were experimentally examined. The micro heat pipe array (MHPA), as one novel thermal interface material, was investigated. The multi-variable coupling approach is used to analyze the intrinsic coupling correlation of the external influencing factors. The dimensionless synthesis economic factor index was proposed to analyze the improvement of thermoelectric characteristics, which can quickly assess the contact thermal resistance of different thermal interface materials. The results showed that the load power and load voltage generally increase with increased temperature differences. The contact thermal resistance decreases with increased load-bearing brick weight, but the decrement gradually decreases. The thermal interface material plays an important role in thermoelectric characteristics. The load-bearing brick weight performs little impact on the non-thermal interface material (NTIM) scheme. The two thermal conductive silicone grease schemes noticeably reveal better thermoelectric characteristics than those of the graphite paper schemes, although the thermal conductivity of thermal conductive silicone grease are much lower than that of graphite paper. The MHPA scheme exhibit the best thermoelectric characteristics, and its dimensionless synthesis economic factor index can be up to 371.81 %.

Influence and comprehensive evaluation of porous metal foam filled fins on the performance of power cable surface waste heat recovery thermoelectric power generation device

Cables are essential components in power systems. Certain amount of heat is generated during the energy transfer process. Effective recovery and utilization of waste heat generated by cables is a helpful proposition. In this study, a cable waste heat recovery thermoelectric generation device (CTEG) is proposed. By installing cooling fins and thermoelectric generation devices on the cable surface, the waste heat on the cable surface is converted into electric energy. To improve the power generation efficiency of the device, a method of filling porous metal foam material in the fin teeth gap is used. The results demonstrate that filling the fin teeth gap with porous metal foam material with high porosity and low pore density (PPI) can significantly increase heat transfer efficiency and benefit the output power of the thermoelectric generation device. The flow field in the pipeline of thermoelectric generation device is also analyzed in this study. A comprehensive evaluation method is proposed to consider the power generation efficiency and heat transfer efficiency of the thermoelectric generation device. It is shown that filling porous metal foam material with high porosity and low pore density can maximize the power generation efficiency of the thermoelectric generation device, and at the same time, the pipe pressure drop loss can be compensated by the improvement of heat transfer. This research is significant because it provides useful information for enhancing the energy conversion efficiency of thermoelectric generation devices that recover waste heat from cable surfaces and generate electrical power.

Numerical and experimental study of a non-frosting thermoelectric generation device for low temperature waste heat recovery

Liquefied natural gas (LNG) has great potential for power generation using thermoelectric generators (TEG) due to the large amount of cold energy released during LNG gasification, but frosting is a major issue which slows the heat transfer between the TEG and the environment and reduces the power generation efficiency. This study describes a non-frosting cryogenic thermoelectric generator for cold energy recovery. This device uses natural gas vapor on the hot side of the TEG to avoid frosting caused by direct contact of the TEG with air. The device characteristics were modeled using a thermodynamic analysis with the predictions verified by experiments to predict the output characteristics. The results show an optimal channel length for the selected design conditions that maximizes the power generation. Increasing the flow rate and enhancing the heat transfer on the hot side significantly increases the power output. For the design conditions of 1000 Nm3/h gasification capacity and 0.4 MPa working pressure, the optimum channel length is 9.8 m with 350 pairs of thermoelectric modules that gives the maximum power generation of 593.94 W with a 1.36% efficiency.

Performance analysis of compact thermoelectric generation device for harvesting waste heat

In order to save energy and to effectively utilize the waste heat from diesel engines, a compact thermoelectric power generation (TEG) device with two heat collectors and three water coolers was designed. A three-dimensional steady-state fluid–solid coupling simulation was carried out for the structure formed by the heat collector-thermoelectric modules (TEMs)-water coolers of the device. The heat transfer characteristics, temperature and flow fields of the heat collector-TEMs-water coolers were analyzed. The output voltage and power of the device were experimentally investigated on a TEG test bench. The results show that the average temperature difference on both sides of each layer of TEMs ranges from 43 to 48 K. The temperature differences in the upper TEMs are slightly greater than those in the lower TEMs. There is small difference among the heat transfer coefficients of each TEM module with an average of about 82.6 W/(m2·K). The device generates the maximum output power of 15.8 W with a 560 K inlet air temperature and a hot air volume flow of 171 L/min. It is shown that more studies are required to perform cooperative the optimization of multiphysics simulation and comprehensive evaluation of heat transfer and power generation performance.

Examining the feasibility of a bi-evaporator cooling/electricity cycle: A comprehensive analysis of thermodynamic, economic, and environmental aspects, and bi-objective optimization

Although geothermal energy is generally considered benign, it still has its share of problems, including the emission of greenhouse gases that harm the environment. To make informed decisions about geothermal systems, it is imperative to study their environmental impacts. This study uses six approaches to propose and analyze an innovative geothermal-driven bi-evaporator cooling/electricity plan. The proposed efficient design is made of a single-flash cycle and the integration of a modified vapor compression cycle and ejector cooling system assisted by a thermoelectric power generator device. Exergoenvironmental and extended-environmental assessments are performed to examine the environmental impacts of the current devised scheme, including calculating CO2 emissions rate and sustainability index. The suggested plan's performance in the basic design mode using 14 various working fluids showed that R143m had the highest exergetic efficiency, lowest exergoenvironmental index, and lowest cost of production at 35.9%, 0.6002, and 24.67$/GJ, respectively. This working fluid was used for parametric study and bi-objective optimization, which revealed that the vapor generator destroys 157.7 kW of exergy at the optimal point. Additionally, the vapor turbine is the most expensive component at 14.44$/h. Pareto frontier also indicates that the final chosen optimal mode (scenario C) has 27.02% energetic efficiency and 21.33$/GJ production cost, which are higher than the base scenario by 12.55% and 15.66%, respectively. In addition, the optimal scenario reduces the payback period to 8.64 years from 15.68 years in the base scenario.

A Review on Thermoelectric Generators: Structural Optimization and Economic Analysis

The interest in recovering waste heat has resurged in recent years due to growing concerns about the energy crisis and global warming. A thermoelectric generator (TEG) is regarded as an environmentally-friendly technology for capturing and recovering waste heat by directly converting heat to electrical energy via the Seebeck effect. The critical challenge in improving this technology is the low conversion efficiency of the TEG device, thus limiting its application to a niche area. The structural optimization of TEG has been the subject of extensive research over the past few years. Nonetheless, there is currently a lack of review studies focusing on TEG structural optimization, and to the best of our knowledge, only one review paper associated with this key area is available in the literature. This work presents an analysis of the ongoing research progress of TEG structural optimization with a focus on the thermoelectric leg length, leg cross-sectional area, angle of the legs, and leg shape. In addition, the economic analysis of the application of TEG in recovering waste heat is also presented to rationalize the economic feasibility of this technology compared to other existing technologies.

Quantum Interference and Contact Effects in the Thermoelectric Performance of Anthracene-Based Molecules.

We report on the single-molecule electronic and thermoelectric properties of strategically chosen anthracene-based molecules with anchor groups capable of binding to noble metal substrates, such as gold and platinum. Specifically, we study the effect of different anchor groups, as well as quantum interference, on the electric conductance and the thermopower of gold/single-molecule/gold junctions and generally find good agreement between theory and experiments. All molecular junctions display transport characteristics consistent with coherent transport and a Fermi alignment approximately in the middle of the highest occupied molecular orbital/lowest unoccupied molecular orbital gap. Single-molecule results are in agreement with previously reported thin-film data, further supporting the notion that molecular design considerations may be translated from the single- to many-molecule devices. For combinations of anchor groups where one binds significantly more strongly to the electrodes than the other, the stronger anchor group appears to dominate the thermoelectric behavior of the molecular junction. For other combinations, the choice of electrode material can determine the sign and magnitude of the thermopower. This finding has important implications for the design of thermoelectric generator devices, where both n- and p-type conductors are required for thermoelectric current generation.

Epitaxial tin selenide thin film thermoelectrics

To enable the realization of miniaturized thermoelectric energy generation (TEG) devices for autonomous wireless sensors, high-quality thin film architectures are required. Although tin selenide (SnSe) has been identified as a promising thermoelectric material exhibiting ZT values up to 2.6 at 923 K for single crystals, most thin film studies evaluated polycrystalline or textured SnSe samples. Here, we have explored for the first time the impact of epitaxial alignment of the orthorhombic SnSe crystal structure on an orthorhombic DyScO3 substrate, in strong contrast to the few previous studies on cubic substrates. The achieved (100)-oriented single crystalline SnSe thin films exhibit the formation of two SnSe domain types. The in-plane electrical conductivity along the (b,c)-plane shows an abrupt increase above 400 K instead of the typical steady increase. The in-plane Seebeck coefficients exhibit very similar values as single crystals, leading to a maximum power factor of about 6.0 μW·K−2·cm−1. For these SnSe thin films, exhibiting two domain variants with in-plane alignment of the (b,c)-plane, a typical low thermal conductivity is expected, demonstrating the effectiveness of epitaxial alignment to enhance thermoelectric performance and to enable the realization of miniaturized thermoelectric energy generation (TEG) devices for autonomous wireless sensors.

Eicosane-based thermo-conductive phase change composite for efficient capture solar energy and using in real-environment as power source

With the increasing shortage of fossil energy, it is urgent to develop a phase change composite with exquisite thermal conductivity and excellent enthalpy for efficient capture solar energy and integrate with a thermoelectric generator (TEG) to achieve high power output density (>15 W m−2), so as to solve the global energy crisis. Therefore, it is necessary to put forward requirements for thermal conductive performance and latent heat in designing phase change materials (PCMs). In this study, a thermo-conductive phase change composite with thermal conductivity of 1.53 W m−1 K−1 and enthalpy of 203.5 J g−1 enabled by three-dimensional single crystal nanodiamond (3D-SCND) framework was constructed for the first time via ice-template assembly and vacuum impregnation strategy. Benefited from the elaborate structure, it can realize fast but uniform transfer of heat flux, which is great for accelerating the solar energy storage and further reducing the energy loss during the solar-thermal-electric conversion. Due to derive from high energy density and rapid heat energy output capability of our PCM composite, not only solar-thermal energy conversion efficiency reaches up 90.2%, but also generate an effective real-environment thermoelectric output power density of 22.7 W m−2 using with a TEG device. Our strategy is very effective for fabrication high-performance PCMs for efficient capture solar energy to solve the global fossil energy crisis.

Synergetic Enhancement of Seebeck Coefficients and Electrical Conductivity in Flexible Liquid Crystal Composites

The development of thermoelectric (TE) devices, which convert thermal gradient into energy, was motivated by the immense amount of heat wasted from solar radiation and industrial heat dissipation. Polymer-based organic thermoelectric (OTE) materials have garnered much interest owing to their distinctive advantages, including low thermal conductivity, minimal toxicities, low cost, and superior mechanical elasticity. However, the TE performance of these organic materials is mainly limited due to their low Seebeck coefficient and poor electrical conductivity. In this work, we simultaneously improve the Seebeck coefficients and electrical conductivity of polyvinylidene fluoride (PVDF) polymer and single-wall carbon nanotube (SWCNT)-based composites by incorporating a liquid crystal (LC). This is attributed to the thermodiffusion of ions and the formation of stable and efficient conductive channels with LC incorporation. The concentration of LC is suitably tuned, which results in an increment of ∼42% Seebeck coefficient and ∼72% electrical conductivity compared to the reference PVDF/SWCNT composite. The tensile strain curve shows that the durability of the composite samples has increased by incorporating the LC. Also, a flexible thermoelectric generator (TEG) device consisting of eight composite legs is constructed, which shows an open circuit voltage and output power of 35.7 mV and 46.1 nW, respectively, at a temperature difference of 60 K. The findings show that LC-based SWCNT/PVDF composites exhibit superior TE potential and provide a new route for fabricating flexible TE devices.

Application of Thermoelectric Generators for Low-Temperature-Gradient Energy Harvesting

Thermoelectric generators (TEGs) convert a temperature difference into useful direct current (DC) power. TEGs are solid-state semiconductor devices that are generating a lot of interest for energy harvesting purposes in Internet of Things (IoT) applications. This paper analyzes the behavior of state-of-the-art TEGs designed for low temperature gradient operation, with special emphasis on IoT systems for health monitoring for high-voltage alternating current (AC) and DC applications. In such applications, the energy harvesting unit plays a leading role in supplying wireless sensors (WSs). An application example is also presented with the aim to monitor the health condition of devices installed in the tubular busbars found in electrical substations. Since substation busbars heat up due to the Joule effect, there is a small thermal gradient between the busbar and the ambient, so the TEG can convert this heat flow into useful DC energy to supply low-power WSs. This paper assesses the performance of different TEG devices for this application, where very low temperature gradients are expected. The results presented show that with temperature gradients as low as 5 °C it is possible to supply WSs.

Performance analysis of thermoelectric power-generation system with natural convection cooling

Nowadays, high-performance electronic devices release large amounts of heat throughout their operation. Thermoelectric passive cooling systems can offer a cost-efficient and straightforward solution for the thermal management of such devices based on a passive heatsink and a thermoelectric generator (TEG). TEG can transform a part of the heat generated by the electronic chip into electricity for the power supply of microelectronic systems. The thermoelectric system investigated here contains a 12 W Positive Temperature Coefficient (PTC) heating element placed on a 4 × 4 cm2 aluminium plate, a commercial SP1848-27145 TEG device and a finned plate heatsink recycled from a desktop PC. Two types of tests were performed here. An energy efficiency test was initiated at different load resistance values RL between 1 and 40 Ω by directly connecting TEG output to a direct current (DC) electronic load. The second test was developed for electrical power generation at 3.3 V–5 V by integrating a DC–DC boost converter between the TEG output and the electronic load set at RL of 600–900 Ω. It was registered a maximum energy conversion efficiency of 1.17 % for RL=2Ω, close to the internal resistance value of the TEG module. The second test revealed the generation of output electrical powers with minimum values of 15–17.5 mW at a temperature difference between TEG plates of about 20 K.

The effect of channel dimensions and configuration of thermoelectric elements on the performance of thermoelectric generator module for waste heat recovery

The use of thermoelectric modules can be effective in recovering waste heat in combustion gasses due to their special properties. In this study, due to the low efficiency of thermoelectric generators, the effects of channel dimensions and configuration of thermoelectric element pairs on heat transfer between a working fluid and a pair of PN elements were studied horizontally and vertically. To develop the simulation of the present model, temperature dependence of generator properties, variations in the convective heat transfer coefficient, temperature gradient, and pressure drop in both hot and cold working fluids along the channel were considered simultaneously. Additionally, it was found that geometric dimensions of rectangular channels affected the four main factors of temperature difference between the two sides of generators, pumped power, number of generators, and type of flow regime. Besides, the findings revealed that the increase in each dimension of the channel reduced the temperature difference between the two sides of elements. This factor was found to play a major role in the efficiency of the thermoelectric generator device, production of power peak, optimal module, channel area, and optimal channel height. In addition, the flow regime changed from turbulent to laminar at cold channel widths greater than 0.11 m. As a result, the total power dropped. Furthermore, the configuration model of PN elements affected the dimensions of the channel. At the length of 1.275 m of the channel, the power generation capacity of the vertical model was by 2.138 times greater than that of the horizontal model per 100 thermoelectric generators.

Experimental characterization of a commercial TEG device under mimicked operating conditions

A long-standing zT = 1 barrier is still present in commercial thermoelectric generator devices (TEG) and is typically not overcome. Although it is possible to accept the current limits of such devices, the performances reported on the datasheets are frequently not obtainable when these thermoelectric devices are arranged for use in the actual operating conditions. Despite this, the current primary energy prices and ongoing climate change make their use attractive for many industrial sectors. An experimental investigation is here proposed on a single type of TEG available on the market; the temperature relationships of the electrical resistivity, Seebeck coefficient, and thermal conductivity in a thermostatic chamber were first determined. A piece of apparatus was assembled to mimic the operating conditions of the TEG device and verify its performance, but some critical issues were highlighted regarding the heat transfer and its ability to maintain an adequate contact pressure on the hot and cold sides of the module. In order to extend the recovery of waste heat to a non-excessively high temperature in the hot forging process, the maximum temperature attained on the hot side of the TEG in the performed experiments was not allowed to exceed 180 °C. With temperatures of around 160 °C on the hot side and just over 40 °C on the cold side, the conversion efficiency was close to 3%. Considering this conversion efficiency and the operating conditions, the estimated order of magnitude of the electricity that could be produced by recovering heat waste in the Italian hot forging sector could be in the region of some hundreds of MWh per year.

Comparison of thermoelectric properties of sorted and unsorted semiconducting single-walled carbon nanotube free-standing sheets

Semiconducting single-walled carbon nanotubes (s-SWCNTs) are promising materials for thermoelectric generation (TEG) because of their large theoretical Seebeck coefficient (S). In this study, to discuss superiority of s-SWCNTs for TEG devices, thermoelectric properties of free-standing s-SWCNT sheets were compared with unsorted SWCNT sheets. To obtain the highest power density, the films were doped with triethyloxonium hexachloroantimonate and 2-(2-methoxyphenyl)-1,3-dimethyl-2,3-dihydro-1H-benzo[d]imidazole as the hole and electron dopants, respectively. The doped s-SWCNT sheets exhibited higher S but lower electrical conductivity than those of the unsorted SWCNT sheets. Consequently, the power factor of the s-SWCNT sheets was lower than that of the unsorted SWCNT sheets.