Optimization of the Heat Exchangers of a Thermoelectric Generation System

The thermal resistances of the heat exchangers have a strong influence on the electric power produced by a thermoelectric generator. In this work, the heat exchangers of a thermoelectric generator have been optimized in order to maximize the electric power generated. This thermoelectric generator harnesses heat from the exhaust gas of a domestic gas boiler. Statistical design of experiments was used to assess the influence of five factors on both the electric power generated and the pressure drop in the chimney: height of the generator, number of modules per meter of generator height, length of the fins of the hot-side heat exchanger (HSHE), length of the gap between fins of the HSHE, and base thickness of the HSHE. The electric power has been calculated using a computational model, whereas Fluent computational fluid dynamics (CFD) has been used to obtain the thermal resistances of the heat exchangers and the pressure drop. Finally, the thermoelectric generator has been optimized, taking into account the restrictions on the pressure drop.     

Experimental Study and Optimization of Thermoelectricity-Driven Autonomous Sensors for the Chimney of a Biomass Power Plant

In the work discussed in this paper a thermoelectric generator was developed to harness waste heat from the exhaust gas of a boiler in a biomass power plant and thus generate electric power to operate a flowmeter installed in the chimney, to make it autonomous. The main objective was to conduct an experimental study to optimize a previous design obtained after computational work based on a simulation model for thermoelectric generators. First, several places inside and outside the chimney were considered as sites for the thermoelectricity-driven autonomous sensor. Second, the thermoelectric generator was built and tested to assess the effect of the cold-side heat exchanger on the electric power, power consumption by the flowmeter, and transmission frequency. These tests provided the best configuration for the heat exchanger, which met the transmission requirements for different working conditions. The final design is able to transmit every second and requires neither batteries nor electric wires. It is a promising application in the field of thermoelectric generation.     

Aircraft-Specific Thermoelectric Generator Module

Autonomous sensor nodes for wireless sensor networks are currently under discussion for aircraft structural health monitoring. Self-sufficient operation of a sensor node requires a positive power budget for sensing, processing, and communication tasks. Energy harvesting for autonomous powering by thermoelectric devices depends strongly on maintaining the temperature difference within the aircraft operation envelope. Aircraft pass through huge outside temperature variations and, in addition, provide heated cabin environments. To make use of these temperature differences most efficiently, additional effort for heat conduction and installation is required to maintain the temperature gradient. However, to keep the complexity of system implementation as low as possible we report in this paper on an aircraft-specific thermoelectric generator module which consists of a phase-change material attached to the thermoelectric generator at one side. If this module is exposed to the environmental conditions of an aircraft envelope, the phase transition and heat capacity of the attached material lead to unbalanced temperature levels on the two sides of the generator. Simulations with realistic aircraft parameters have been done and first tests of the breadboard in a climate chamber have shown promising results.     

A General Model for the Electric Power and Energy Efficiency of a Solar Thermoelectric Generator

A general model for the electric power and energy efficiency of a solar thermoelectric generator is discussed, considering the influences of the input energy, the thermal conductivity, the absorptivity and emissivity of the heat collector, and the cooling water. The influences of these factors on the performance of the thermoelectric device are discussed, considering the thermoelectric generator as a whole, including the heat collector, the thermoelectric device, and the cooling. Results show that high input energy, and high absorptivity and low emissivity of the heat collector, are helpful for obtaining a high-performance thermoelectric generator. A high thermal transfer coefficient of the cooling water can increase the temperature difference across the thermoelectric device but results in greater accessory power requirements if increased further.     

A Novel Optimization Method for the Electric Topology of Thermoelectric Modules Used in an Automobile Exhaust Thermoelectric Generator

Based on Bi₂Te₃ thermoelectric modules, a kind of automobile exhaust thermoelectric generator (AETEG) with a single-column cold-source structure was designed. To enhance its net power and efficiency, the output performance of all the thermoelectric modules was tested with a temperature monitoring unit and voltage monitoring unit, and modeled using a back-propagation (BP) neural network based on various hot-source temperatures, cold-source temperatures, load currents, and contact pressures according to the temperature distribution of the designed heat exchanger and cooling system. Then, their electric topology (series or parallel hybrid) was optimized using a genetic algorithm to achieve the maximum peak power of the AETEG. From the experimental results, compared with when all the thermoelectric modules were connected only in series or parallel at random, it is concluded that the AETEG performance is evidently affected by the electric topology of all the single thermoelectric modules. The optimized AETEG output power is greatly superior to the other two investigated designs, validating the proposed optimized electric topology as both feasible and practical.     

Thermoelectric Generator for a Stationary Diesel Plant

This paper describes the development and testing of a thermoelectric generator (TEG) using the exhaust heat of a 50-kW stationary diesel power plant. The generator consists of six units that represent primary generators for each diesel engine cylinder. Each primary generator comprises five sections with gas heat exchangers, thermoelectric modules, and liquid heat exchangers. The sections were optimized for the exhaust gas operating temperatures. The generator electric power was 2.1 kW at rated power of 2.2 kW, corresponding to 4.4% of the diesel plant electric power.     

Research on the Compatibility of the Cooling Unit in an Automotive Exhaust-based Thermoelectric Generator and Engine Cooling System

The temperature difference between the hot and cold sides of thermoelectric modules is a key factor affecting the conversion efficiency of an automotive exhaust-based thermoelectric generator (TEG). In the work discussed in this paper the compatibility of TEG cooling unit and engine cooling system was studied on the basis of the heat transfer characteristics of the TEG. A new engine-cooling system in which a TEG cooling unit was inserted was simulated at high power and high vehicle speed, and at high power and low vehicle speed, to obtain temperatures and flow rates of critical inlets and outlets. The results show that coolant temperature exceeds its boiling point at high power and low vehicle speed, so the new system cannot meet cooling requirements under these conditions. Measures for improvement to optimize the cooling system are proposed, and provide a basis for future research.     

Development of a mathematical model for optimizing the design of an automotive thermoelectric generator taking into account the influence of its hydraulic resistance on the engine power

A complex of models for optimizing the design and operation modes of an automotive thermoelectric generator is developed within the proposed approach taking into account the influence of hydraulic resistance of the generator on the internal combustion engine. Several designs of generators for converting the thermal energy of exhaust gases (EGs) of internal combustion engines into electricity due to the Seebeck effect in semiconductor elements, which have different geometries of the continuous-flow part of the generator with different hydraulic resistances, are considered. Models for calculating the thermoelectric elements, gas heat exchanger, and automotive engine are considered jointly. Simulation is performed using the example of a VAZ-21126 engine, which demonstrated that up to 500 W of electric power can be obtained using semiconductor thermoelectric elements based on germanium and lead tellurides.     

Theoretical and Experimental Study of Thermoelectric Generators for Vehicles

The general physical laws for reaching the maximum efficiency of a generator using vehicular exhaust heat have been studied. Based on the physical models of a generator with lumped and distributed parameters, the optimal gas temperature at the outlet of the thermoelectric generator (TEG) and the optimal distribution of gas temperature in the heat exchanger have been found. The basic generator parameters, namely the voltage, power, and efficiency, have been calculated in the steady-state and dynamic modes. The possibility of efficiency improvement by a factor of 1.5 through use of an exponential as compared with an isothermal distribution of heat exchanger temperature has been revealed. Calculations are confirmed by results from testing a prototype vehicular thermoelectric generator.     

Detailed Modeling and Irreversible Transfer Process Analysis of a Multi-Element Thermoelectric Generator System

Thermoelectric (TE) power generation technology, due to its several advantages, is becoming a noteworthy research direction. Many researchers conduct their performance analysis and optimization of TE devices and related applications based on the generalized thermoelectric energy balance equations. These generalized TE equations involve the internal irreversibility of Joule heating inside the thermoelectric device and heat leakage through the thermoelectric couple leg. However, it is assumed that the thermoelectric generator (TEG) is thermally isolated from the surroundings except for the heat flows at the cold and hot junctions. Since the thermoelectric generator is a multi-element device in practice, being composed of many fundamental TE couple legs, the effect of heat transfer between the TE couple leg and the ambient environment is not negligible. In this paper, based on basic theories of thermoelectric power generation and thermal science, detailed modeling of a thermoelectric generator taking account of the phenomenon of energy loss from the TE couple leg is reported. The revised generalized thermoelectric energy balance equations considering the effect of heat transfer between the TE couple leg and the ambient environment have been derived. Furthermore, characteristics of a multi-element thermoelectric generator with irreversibility have been investigated on the basis of the new derived TE equations. In the present investigation, second-law-based thermodynamic analysis (exergy analysis) has been applied to the irreversible heat transfer process in particular. It is found that the existence of the irreversible heat convection process causes a large loss of heat exergy in the TEG system, and using thermoelectric generators for low-grade waste heat recovery has promising potential. The results of irreversibility analysis, especially irreversible effects on generator system performance, based on the system model established in detail have guiding significance for the development and application of thermoelectric generators, particularly for the design and optimization of TE modules.     

Weight Penalty Incurred in Thermoelectric Recovery of Automobile Exhaust Heat

Thermoelectric recovery of automobile waste exhaust heat has been identified as having potential for reducing fuel consumption and environmentally unfriendly emissions. Around 35% of combustion energy is discharged as heat through the exhaust system, at temperatures which depend upon the engine’s operation and range from 800°C to 900°C at the outlet port to less than 50°C at the tail-pipe. Beneficial reduction in fuel consumption of 5% to 10% is widely quoted in the literature. However, comparison between claims is difficult due to nonuniformity of driving conditions. In this paper the available waste exhaust heat energy produced by a 1.5 L family car when undergoing the new European drive cycle was measured and the potential thermoelectric output estimated. The work required to power the vehicle through the drive cycle was also determined and used to evaluate key parameters. This enabled an estimate to be made of the engine efficiency and additional work required by the engine to meet the load of a thermoelectric generating system. It is concluded that incorporating a thermoelectric generator would attract a penalty of around 12 W/kg. Employing thermoelectric modules fabricated from low-density material such as magnesium silicide would considerably reduce the generator weight penalty.     

Thermoelectric-Driven Autonomous Sensors for a Biomass Power Plant

This work presents the design and development of a thermoelectric generator intended to harness waste heat in a biomass power plant, and generate electric power to operate sensors and the required electronics for wireless communication. The first objective of the work is to design the optimum thermoelectric generator to harness heat from a hot surface, and generate electric power to operate a flowmeter and a wireless transmitter. The process is conducted by using a computational model, presented in previous papers, to determine the final design that meets the requirements of electric power consumption and number of transmissions per minute. Finally, the thermoelectric generator is simulated to evaluate its performance. The final device transmits information every 5 s. Moreover, it is completely autonomous and can be easily installed, since no electric wires are required.     

Update on the Design and Development of a TEG Cogenerator Device Integrated into Self-Standing Gas Heaters

Heating by gas combustion is widespread in residential and industrial environments, through the use of different types of systems and plants. A relevant case is that of gas stoves, where the heat-radiating unit operates autonomously with local gas feeding. A thermoelectric generator (TEG) can be integrated within this type of autonomous gas heater, for local production of electric power, so that devices requiring electric power can be added, where desired, without the need for any connection to the electrical grid. This approach can also lead to easier installation and operation, and eventually increases the overall efficiency. Following the development plan presented in a previous report, a new prototype of an autonomous gas heater for outdoor use has been implemented through the integration of an improved TEG device with a simple and robust design, which can be easily operated by the end-user. A small amount of heat is withdrawn and converted into electricity by the TEG, providing self-sustaining operation and, moreover, powering additional functions such as high-efficiency light-emitting diode lighting.     

Control Strategy for a 42-V Waste-Heat Thermoelectric Vehicle

A 42-V waste-heat thermoelectric vehicle is employed as a potential application of thermoelectric generators for fuel economy improvement and emissions reduction. The 42-V waste-heat thermoelectric vehicle currently in development employs an assemblage driving system consisting of a waste-heat thermoelectric generator, a 42-V powernet, and an integrated starter and generator (ISG). The waste-heat thermoelectric generator also functions as a power supply. To optimize the utilization of the waste-heat energy generated by the thermoelectric generator, an electric assist control strategy and a torque split control strategy are proposed herein. Through the development of relevant systems and strategies, including the thermoelectric generator and an electric bus system, two vehicle models are established and compared using the ADVISOR platform based on MATLAB/Simulink. The calculation results show improved fuel economy and emissions performance resulting from the integration of the torque split control strategy into the 42-V waste-heat thermoelectric vehicle.     

温差发电器的设计

温差发电器是一种利用大自然中广泛存在的温差进行发电的装置。温差发电器主要由半导体温差发电模块和控制器两部分组成,半导体温差发电模块将热能转化为电能,并通过充电电路将电能储存在蓄电池中;控制器主要完成限流、欠压保护功能。同时,还设计了升压电路,从而使温差发电器输出较高的电压。     

A Thermoelectric Generator Using Engine Coolant for Light-Duty Internal Combustion Engine-Powered Vehicles

We proposed and fabricated a thermoelectric generator (TEG) using the engine water coolant of passenger vehicles. The experimental results revealed that the maximum output power from the proposed thermoelectric generator was ~75 W, the calculated thermoelectric module efficiency of the TEG was ~2.1%, and the overall efficiency of electric power generation from the waste heat of the engine coolant was ~0.3% in the driving mode at 80 km/h. The conventional radiator can thus be replaced by the proposed TEG without additional devices or redesign of the engine water cooling system of the existing radiator.     

Electric Power Generation from Thermoelectric Cells Using a Solar Dish Concentrator

In this paper, design details, theoretical analysis, and outcomes of a preliminary experimental investigation on a concentrator thermoelectric generator (CTEG) utilizing solar thermal energy are presented. The designed CTEG system consisted of a parabolic dish collector with an aperture diameter of 1.8 m used to concentrate sunlight onto a copper receiver plate with 260 mm diameter. Four BiTe-based thermoelectric cells (TEC) installed on the receiver plate were used to convert the concentrated solar thermal energy directly into electric energy. A microchannel heat sink was used to remove waste heat from the TEC cold side, and a two-axis tracking system was used to track the sun continuously. Experimental tests were conducted on individual cells and on the overall CTEG system under different heating rates. Under maximum heat flux, a single TEC generator was able to produce 4.9 W for a temperature difference of 109°C, corresponding to 2.9% electrical efficiency. The overall CTEG system was able to produce electric power of up to 5.9 W for a 35°C temperature difference with a hot-side temperature of 68°C. The results of the investigation help to estimate the potential of the CTEG system and show concentrated thermoelectric generation to be one of the potential options for production of electric power from renewable energy sources.     

Cost–Performance Analysis and Optimization of Fuel-Burning Thermoelectric Power Generators

Energy cost analysis and optimization of thermoelectric (TE) power generators burning fossil fuel show a lower initial cost compared with commercialized micro gas turbines but higher operating cost per energy due to moderate efficiency. The quantitative benefit of the thermoelectric system on a price-per-energy ($/J) basis lies in its scalability, especially at a smaller scale (<10 kW), where mechanical thermodynamic systems are inefficient. This study is based on propane as a chemical energy source for combustion. The produced heat generates electric power. Unlike waste heat recovery systems, the maximum power output from the TE generator is not necessarily equal to the economic optimum (lowest $/kWh). The lowest cost is achieved when the TE module is optimized between the maximum power output and the maximum efficiency, dependent on the fuel price and operation time duration. The initial investment ($/W) for TE systems is much lower than for micro gas turbines when considering a low fractional area for the TE elements, e.g., 5% to 10% inside the module. Although the initial cost of the TE system is much less, the micro gas turbine has a lower energy price for longer-term operation due to its higher efficiency. For very long-term operation, operating cost dominates, thus efficiency and material ZT become the key cost factors.     

Design and Numerical Simulation of a Symbiotic Thermoelectric Power Generation System Fed by a Low-Grade Heat Source

All liquid heating systems, including solar thermal collectors and fossil-fueled heaters, are designed to convert low-temperature liquid to high-temperature liquid. In the presence of low- and high-temperature fluids, temperature differences can be created across thermoelectric devices to produce electricity so that the heat dissipated from the hot side of a thermoelectric device will be absorbed by the cold liquid and this preheated liquid enters the heating cycle and increases the efficiency of the heater. Consequently, because of the avoidance of waste heat on the thermoelectric hot side, the efficiency of heat-to-electricity conversion with this configuration is better than that of conventional thermoelectric power generation systems. This research aims to design and analyze a thermoelectric power generation system based on the concept described above and using a low-grade heat source. This system may be used to generate electricity either in direct conjunction with any renewable energy source which produces hot water (solar thermal collectors) or using waste hot water from industry. The concept of this system is designated “ELEGANT,” an acronym from “Efficient Liquid-based Electricity Generation Apparatus iNside Thermoelectrics.” The first design of ELEGANT comprised three rectangular aluminum channels, used to conduct warm and cold fluids over the surfaces of several commercially available thermoelectric generator (TEG) modules sandwiched between the channels. In this study, an ELEGANT with 24 TEG modules, referred to as ELEGANT-24, has been designed. Twenty-four modules was the best match to the specific geometry of the proposed ELEGANT. The thermoelectric modules in ELEGANT-24 were electrically connected in series, and the maximum output power was modeled. A numerical model has been developed, which provides steady-state forecasts of the electrical output of ELEGANT-24 for different inlet fluid temperatures.     

Enhancement in Performance of the Tubular Thermoelectric Generator (TTEG)

For use in a tubular thermoelectric generator (TTEG), we fabricated tubular Bi_0.5Sb_1.5Te₃/Ni composite using a melt-spinning technique combined with the spark plasma sintering (SPS) process. With this method, powder sintering, joining of two different materials, and tubular shaping can be achieved simultaneously. The tilted laminate structure which is crucial for the transverse thermoelectric effect was successfully achieved in the sample after SPS densification. The sintered samples showed better mechanical stability and thermoelectric properties compared with the previously studied melt-cast sample. We confirmed larger open-circuit voltage of 240 mV and generating power of 2.5 W with a 100-mm-long TTEG under the small temperature difference of 83 K, and the corresponding power density for a unit heat transfer surface area was approximately 800 W m^?2.