Output Power Of Thermoelectric Generator Research Articles

Wearable thermoelectric generators for human body heat harvesting

A thermoelectric generator (TEG) can be used to harvest electrical energy from human body heat for the purpose of powering wearable electronics. At the NSF Advanced Self-Powered Systems of Integrated Sensors and Technologies (ASSIST), TEGs are one of the enabling technologies being explored to advance the center’s mission of creating wearable, self-powered, health and environmental monitoring systems. As part of this effort, an exploration of the relevant parameters for maximizing the wearable TEG power output from the body heat and maintaining the body comfort is particularly important. For this purpose, the heat from the body must be directed into TEG with minimal loss, the generator must be designed for maintaining a high temperature differential across the thermoelectric material, and the generator must have a small form factor to maintain the body comfort. In order to address these requirements, an optimum TEG design was developed and experiments were conducted both on a temperature-controlled hot plate and on different body locations including the wrist, upper arm, and chest. The TEG was further fabricated into a T-shirt and the power was recorded for different human activities. Comparison of the experiments on various body locations and on the T-shirt yielded the highest to lowest power generated on the upper arm, wrist, chest and T-shirt, respectively. The prospect of powering a wearable electrocardiogram sensor by a TEG on the upper arm is discussed.

Waste heat recovery of a diesel engine using a thermoelectric generator equipped with customized thermoelectric modules

The waste heat recovery performance of a thermoelectric generator (TEG) was experimentally investigated. Forty customized thermoelectric modules (TEMs) were installed on the upper and lower sides of a rectangular exhaust gas channel in a 4×5 arrangement. Water at an ambient temperature of ∼293K was supplied from a cooling tower and was used to create a temperature difference across each TEM. The water flow rate was fixed at 8 SLPM. A turbocharged six-cylinder diesel engine was used as the heat source; the engine was operated under various conditions. Three engine rotation speeds—1000, 1500, and 2000rpm—were employed to determine the effect of the exhaust gas flow rate on the TEG power output. The temperature of the exhaust gas was varied by changing the engine load, i.e., the brake mean effective pressure (BMEP), at an interval of 0.2MPa. From the experimental results, a contour map showing the power output of the TEG as a function of the engine load and speed was obtained. From the contour map, we observed that the power output of the TEG increases with the engine load or speed. The maximum power output was ∼119W at 2000rpm with a BMEP of 0.6MPa; the maximum energy conversion efficiency was ∼2.8%. The pressure drop across the TEG was experimentally found to be 0.45–1.46kPa under all engine operation conditions.

Comparison of Segmented and Traditional Thermoelectric Generator for Waste Heat Recovery of Diesel Engine

This paper established a mathematic model of segmented thermoelectric generator (TEG) based on low-temperature thermoelectric material bismuth telluride and medium-temperature thermoelectric material skutterudite. The performance of segmented TEG and traditional TEG has been compared using this model under different conditions, such as heat source temperature, cold source temperature, heat transfer coefficient, and length and cross section area of thermocouple. The results show that the maximum output power and conversion efficiency of segmented TEG are higher significantly using exhaust of diesel engine (DE) as heat source and coolant as cold source. The results also show that the trends of maximum output power and conversion efficiency are contrary with increment of thermocouple length. The trends of maximum output power is linear with increment of cross section area, and the conversion efficiency is constant. Finally, the segmented TEG has a more potential to recover waste heat than tradition TEG. The performance of segmented TEG is decided by the ratio of materials, the optimum design of segmented TEG should base on the crossing point of ZT value for two materials.

Optimization of Thermoelectric Components for Automobile Waste Heat Recovery Systems

For a typical spark ignition engine approximately 40% of available thermal energy is lost as hot exhaust gas. To improve fuel economy, researchers are currently evaluating technology which exploits exhaust stream thermal power by use of thermoelectric generators (TEGs) that operate on the basis of the Seebeck effect. A 5% improvement in fuel economy, achieved by use of TEG output power, is a stated objective for light-duty trucks and personal automobiles. System modeling of thermoelectric (TE) components requires solution of coupled thermal and electric fluxes through the n and p-type semiconductor legs, given appropriate thermal boundary conditions at the junctions. Such applications have large thermal gradients along the semiconductor legs, and material properties are highly dependent on spatially varying temperature profiles. In this work, one-dimensional heat flux and temperature variations across thermoelectric legs were solved by using an iterative numerical approach to optimize both TE module and TEG designs. Design traits were investigated by assuming use of skutterudite as a thermoelectric material with potential for automotive applications in which exhaust gas and heat exchanger temperatures typically vary from 100°C to over 600°C. Dependence of leg efficiency, thermal fluxes and electric power generation on leg geometry, fill fractions, electric current, thermal boundary conditions, etc., were studied in detail. Optimum leg geometries were computed for a variety of automotive exhaust conditions.

Optimization of Power System Scheduling Based on Shuffled Complex Evolution Metropolis Algorithm

Due to the world’s increasingly serious energy crisis, shortage of resources, and environmental degradation, traditional power system analysis and scheduling optimization methods have faced new challenges. This article examines the features of optimal scheduling of power system containing cascade hydropower, and establishes a scheduling model based on the Shuffled Complex Evolution Metropolis (SCEM-UA) algorithm. This model takes the cost of power generation, emission of gaseous pollutants, and the characteristics of the generators fully into account. Constraints on the changes in thermoelectric generator power output were added to the set of constraint conditions, reducing the impact of thermal power fluctuations on the power system. Here, the SCEM-UA algorithm was used to solve the problem of optimal power system scheduling and render the model capable of global optimization searches. Analyses of simulated cases have demonstrated that the SCEM-UA algorithm can resolve the conflict between convergence speed and global search capability, increasing the global search capability of the model.

Effect of vehicle driving conditions on the performance of thermoelectric generator

Thermoelectric generators (TEGs) have become a promising technology for vehicle exhaust heat recovery. Although the complex vehicle driving conditions may lead to significant variation of TEG performance, such influence was rarely paid attention to. In this study, a numerical model of thermoelectric generator (TEG) based on vehicle waste heat recovery is developed. When the acceleration duration is short, the hot side temperature increases quickly at first with an overshoot phenomenon. When the acceleration durations increase or the acceleration range becomes smaller, the overshoot phenomenon becomes weaker. The change of the voltage and power generally follows the same trend. The performance variation of TEGs becomes more significant with faster acceleration or deceleration. The transient response of the hot and cold side temperatures, voltage and power in deceleration is less significant than acceleration, because in deceleration, the cold side temperature increases first due to the weakened heat convection. For the step change of vehicle speed, when the speed is low, the voltage and power curves and the speed curve are more consistent, and a longer step duration leads to better consistency. A higher road grade can increase the power output of TEG significantly, and lead to a faster transient response. The Japanese 10–15 cycle, New European Driving Cycle (NEDC) and Urban Driving Dynamometer Schedule (UDDS) are selected to evaluate the impact of different driving cycles. The results suggest that a highly frequent change of driving condition may have a negative effect on the TEG performance.

Thermodynamic studies and maximum power point tracking in thermoelectric generator–thermoelectric cooler combined system

Thermoelectric generator (TEG) operated thermoelectric cooler (TEC) is a highly compatible combination for low-cooling power application. The conventional TEG–TEC combined systems have low operating efficiency and low cooling power because maximum power output from the TEG is not fully utilized. This paper proposes and analyses the combined system with maximum power point tracking technique (MPPT) to maximize the cooling power and overall efficiency. This paper also presents the effect of TEG, TEC source temperature and the effect of heat transfer area in the performance of the combined system. The thermodynamic models of the combined system are developed in MATLAB simulink environment with temperature dependent material properties and analysed for variable operating temperatures. It has been found that, in the irreversible thermodynamic model of the combined system with MPPT, when the hot and cold side of TEG and TEC are kept at a temperature difference of 150K and 10K respectively, the power output of TEG increases from 20.49W to 43.92W, cooling power of TEC increases from 32.66W to 46.51W and the overall combined system efficiency increases from 2.606% to 4.375% respectively when compared with the irreversible combined system without MPPT. The characteristics improvements obtained by this practice in the combined system for the above mentioned operating conditions is also true for other range of operating temperatures. It is also been observed that the external irreversibilities decreases the cooling power and the overall system efficiency of the combined system by 36.49% and by 16.9% respectively.

Experimental investigation of an improved exhaust recovery system for liquid petroleum gas fueled spark ignition engine

In this study, we have investigated the recovery of energy lost as waste heat from exhaust gas and engine coolant, using an improved thermoelectric generator (TEG) in a LPG fueled SI engine. For this purpose, we have designed and manufactured a 5-layer heat exchanger from aluminum sheet. Electrical energy generated by the TEG was then used to produce hydrogen in a PEM water electrolyzer. The experiment was conducted at a stoichiometric mixture ratio, 1/2 throttle position and six different engine speeds at 1800-4000 rpm. The results of this study show that the configuration of 5-layer counterflow produce a higher TEG output power than 5-layer parallel flow and 3-layer counterflow. The TEG produced a maximum power of 63.18 W when used in a 5-layer counter flow configuration. This resulted in an improved engine performance, reduced exhaust emission as well as an increased engine speed when LPG fueled SI engine is enriched with hydrogen produced by the PEM electrolyser supported by TEG. Also, the need to use an extra evaporator for the LPG fueled SI engine is eliminated as LPG heat exchangers are added to the fuel line. It can be concluded that an improved exhaust recovery system for automobiles can be developed by incorporating a PEM electrolyser, however at the expense of increasing costs.

Equivalent Circuit Analysis of Photovoltaic-Thermoelectric Hybrid Device with Different TE Module Structure

Combining two different types of solar cells with different absorption bands into a hybrid cell is a very useful method to improve the utilization efficiency of solar energy. The experimental data of dye-sensitized solar cells (DSSCs) and thermoelectric generators (TEG) was simulated by equivalent circuit method, and some parameters of DSSCs were obtained. Then, the equivalent circuit model with the obtained parameters was used to optimize the structure design of photovoltaic- (PV-) thermoelectric (TE) hybrid devices. The output power(Pout)first increases to a maximum and then decreases by increasing the TE prism size, and a smaller spacing between p-type prism and n-type prism of a TE p-n junction causes a higher output power of TEG and hybrid device. When the spacing between TE prisms is 15 μm and the optimal base side length of TE prism is 40 μm, the maximum theoretical efficiency reaches 24.6% according to the equivalent circuit analysis. This work would give some enlightenment for the development of high-performance PV-TE hybrid devices.

Power generation of a thermoelectric generator with phase change materials

In this paper, a thermoelectric generator that embeds phase change materials for wasted heat energy harvesting is proposed. The proposed thermoelectric generator embeds phase change materials in its device structure. The phase change materials store large amounts of heat energy using the latent heat of fusion. When the heat source contacts the thermoelectric generator, dissipated heat from the heat source is stored in the phase change materials. When the heat source is removed from the thermoelectric generator, the output power of the thermoelectric generator slowly decreases, while the output power of conventional thermoelectric generators decreases rapidly without the heat source. The additional air layer in the proposed thermoelectric generator disturbs the heat dissipation from the phase change materials, so the thermoelectric generator can maintain the power generation for longer without a heat source. The experimental results for the thermoelectric generator fabricated clearly show the latent heat effect of the phase change materials and the embedded air layer.

Optimized thermal coupling of micro thermoelectric generators for improved output performance

There is a significant push to increase the output power of thermoelectric generators (TEGs) in order to make them more competitive energy harvesters. The thermal coupling of TEGs has a major impact on the effective temperature gradient across the generator and therefore the power output achieved. The application of micro fluidic heat transfer systems (μHTS) can significantly reduce the thermal contact resistance and thus enhance the TEG's performance. This paper reports on the characterization and optimization of a μTEG integrated with a two layer μHTS. The main advantage of the presented system is the combination of very low heat transfer resistances with small pumping powers in a compact volume. The influence of the most relevant system parameters, i.e. microchannel width, applied flow rate and the μTEG thickness on the system's net output performance are investigated. The dimensions of the μHTS/μTEG system can be optimized for specific temperature application ranges, and the maximum net power can be tracked by adjusting the heat transfer resistance during operation. A system net output power of 126 mW/cm2 was achieved with a module ZT of 0.1 at a fluid flow rate of 0.07 l/min and an applied temperature difference of 95K.It was concluded that for systems with good thermal coupling, the thermoelectric material optimization should focus more on the power factor than on the figure of merit ZT itself, since the influence of the thermal resistance of the TE material is negligible.

Integration of Dye-Sensitized Solar Cells, Thermoelectric Modules and Electrical Storage Loop System to Constitute a Novel Photothermoelectric Generator

This study self-develops a novel type of photothermoelectric power generation modules. Dye-sensitized solar cells (DSSCs) serve as the photoelectric conversion system and a copper (Cu) heat-transfer nanofilm coating on both sides of the thermoelectric generator (TEG) acts as a thermoelectric conversion system. Thus module assembly absorbs light and generates electricity by DSSCs, and also recycles waste heat and generates power by the TEG. In addition, a set of pulsating heat pipes (PHP) filled with Cu nanofluid is placed on the cooling side to increase cooling effects and enhance the power generation efficiency. Results show that when the heat source of thermoelectric modules reaches 90 degrees C, TEG power output is increased by 85.7%. Besides, after thermoelectric modules are heated by additional heat source at 80 degrees C, the electrical energy generated by them can let a NiMH cell (1.25 V) be sufficiently charged in about 30 minutes. When photothermoelectric modules is illumined by simulated light, the temperature difference of two sides of TEG can reach 7 degrees C and the thermoelectric conversion efficiency is 2.17%. Furthermore, the power output of the thermoelectric modules is 11.48 mW/cm2, enhancing 1.4 % compared to merely using DSSCs module.

Design of heat sink for improving the performance of thermoelectric generator using two-stage optimization

Thermoelectric (TE) devices can provide clean energy conversion and are environmentally friendly; however, little research has been published on the optimal design of air-cooling systems for thermoelectric generators (TEGs). The present study investigates the performance of a TEG combined with an air-cooling system designed using two-stage optimization. An analytical method is used to model the heat transfer of the heat sink and a numerical method with a finite element scheme is employed to predict the performance of the TEG. In the first-stage optimization, the optimal fin spacing for a given heat sink geometry is obtained in accordance with the analytical method. In the second-stage optimization, called compromise programming, decreasing the length of the heat sink by increasing its frontal area (WHSHf) is the recommended design approach. Using the obtained compromise point, though the heat sink efficiency is reduced by 20.93% compared to that without the optimal design, the TEG output power density is increased by 88.70%. It is thus recommended for the design of the heat sink. Moreover, the TEG power density can be further improved by scaling-down the TEG when the heat sink length is below 14.5 mm.

Analytical model of parallel thermoelectric generator

The paper studied the performances of parallel thermoelectric generator (TEG) by theoretical analysis and experimental test. An analytical model of parallel TEG was developed by theoretical analysis and calculation, based on thermodynamics theory, semiconductor thermoelectric theory and law of conservation of energy. Approximate expressions of output power and current of parallel TEG were deduced by the analytical model. An experimental system was built to verify the model. The results indicate that only when all of the thermoelectric modules (TE modules) in the parallel TEG have the same inherent parameters and working conditions, the parallel properties of the TEG are the same as that of common DC power. The existence of contact resistance is just like the increase of the TE module’s internal resistance, which leads to the deceases of output power. The thermal contact resistance reduces the output power by reducing the temperature difference between the two sides of the thermocouples. The results derived from the model are basically consistent with the experimental results, the model is suitable for the performance researching and designing of parallel TEG.

Conflict between internal combustion engine and thermoelectric generator during waste heat recovery in cars

It is shown that an internal combustion engine and a thermoelectric generator (TEG) arranged on the exhaust pipe of this engine come into the conflict of thermal machines that is related to using the same energy resource. The conflict grows with increasing useful electric power We of the TEG, which leads to the limitation of both the maximum TEG output power (Wemax) and the possibility of waste heat recovery in cars.

The influence of operating and device parameters on the maximum efficiency and the maximum output power of thermoelectric generator

Thermoelectric power generators are one of the promising green energy sources. The operating and the generator parameters influence the generator output performance. In the present study, the influence of the operating and the generator parameters on the maximum output power and the efficiency of the thermoelectric power generator are examined. The output power corresponding to the maximum efficiency and the maximum attainable output power of the generator are compared. It is found that the maximum power of the thermoelectric generator corresponding to the high Figure of Merit is very sensitive to the operating temperature. The maximum power attainable is larger than that its counterpart corresponding to the maximum generator efficiency. Copyright © 2010 John Wiley & Sons, Ltd.

Modeling a Thermoelectric Generator Applied to Diesel Automotive Heat Recovery

Thermoelectric generators (TEGs) are outstanding devices for automotive waste heat recovery. Their packaging, lack of moving parts, and direct heat to electrical conversion are the main benefits. Usually, TEGs are modeled with a constant hot-source temperature. However, energy in exhaust gases is limited, thus leading to a temperature decrease as heat is recovered. Therefore thermoelectric properties change along the TEG, affecting performance. A thermoelectric generator composed of Mg2Si/Zn4Sb3 for high temperatures followed by Bi2Te3 for low temperatures has been modeled using engineering equation solver (EES) software. The model uses the finite-difference method with a strip-fins convective heat transfer coefficient. It has been validated on a commercial module with well-known properties. The thermoelectric connection and the number of thermoelements have been addressed as well as the optimum proportion of high-temperature material for a given thermoelectric heat exchanger. TEG output power has been estimated for a typical commercial vehicle at 90°C coolant temperature.