Waste Heat Recovery Performance Research Articles

A novel thermal management system for a cylindrical battery based on tubular thermoelectric generator

This study introduces an innovative thermal management system tailored for cylindrical Lithium-ion batteries. It integrates a tubular thermoelectric generator (TTEG) to handle both battery thermal management and the utilization of waste heat for power generation. The main focus lies in evaluating the waste heat recovery capabilities of the TTEG to enhance effective thermal management. The research investigates key geometric and operational parameters such as battery discharge rate (C-rate), thermocouple count (NTC), heat transfer coefficient (HTC), and thermoelectric leg height (HL) to comprehensively assess the overall system performance. The results highlight that integrating the TTEG improves thermal management and waste heat recovery in lithium-ion batteries. It demonstrates temperature reductions of up to 21 °C at a discharge rate of 3C compared to batteries without the TTEG thermal management system. Additionally, increasing the NTC leads to a rise in the maximum battery temperature, thereby enhancing waste heat recovery performance. For instance, increasing the number of thermocouples from 100 to 144 results in a substantial up to 70 % increase in TTEG voltage.Furthermore, enhancing HTC and HL positively impacts thermal performance, showing a significant decrease in the maximum battery temperature. Elevated HTC and HL also contribute to improving thermoelectric voltage, power, and conversion efficiency, highlighting their dual role in enhancing waste heat recovery. For instance, at peak conditions, there is a notable reduction of 2.66 °C in the maximum battery temperature with an HL of 12 mm compared to 4 mm. Additionally, increasing HTC from 10 to 20, particularly at maximum discharge, leads to a surge of 15.87 % in voltage and a substantial 34.28 % increase in output power.

Design and Long-Term Performance of a Pilot Wastewater Heat Recovery System in a Commercial Kitchen in the Tourism Sector

This paper assesses the performance of waste heat recovery from commercial kitchen wastewater in practice. A pilot study of heat recovery from the kitchen at Penrhyn Castle, a tourist attraction in North Wales (UK), is outlined. The pilot heat recovery site was designed and installed, comprising a heat exchanger, recirculation pumps, buffer tank and an extensive temperature/flow monitoring system for performance monitoring of the waste heat recovery system. Continuous monitoring was conducted for a period of 8 months, covering the 2022 tourist season. The recovered heat from the kitchen wastewater preheats the incoming cold freshwater supply and consequently reduces the amount of energy consumed for subsequent water heating. Retrofitting the pilot heat recovery system to the kitchen drains resulted in a heat saving of 240 kWh per month on average, a reduction of 928.8 kg CO2e per year, and a payback period for the investment costs of approximately two years, depending on the cost of energy supply. The presented results illustrate the potential of this form of renewable heat in reducing the carbon footprint of water heating activities in buildings and the hospitality sector.

Organic-inorganic composite membrane-based transport membrane condenser: Performance of waste recovery from hot gas mixture of CO2 and water vapor

Recovering the waste heat from the stripped gas (i.e., the gas mixture of CO2 and water vapor) using the transport membrane condenser is an effective approach to reduce the regeneration heat consumption in CO2 chemical absorption process. To decrease the capital expenditure of transport membrane condenser, this study prepared an inexpensive organic–inorganic composite membrane through adding the hydroxylated boron nitride (BN-OH) into the polyvinylidene fluoride (PVDF) during membrane preparation via nonsolvent induced phase separation. Then the composite membrane was placed in a membrane cell as the transport membrane condenser to recovery the waste heat of simulated stripped gas. The results showed that when compared to the single PVDF membrane, the addition of BN-OH improves the pore uniformity, thermal conductivity, and porosity of membrane. Among all the prepared composite membranes, the composite membrane adding 5 wt% nano-sized BN-OH particles exhibits the best waste heat recovery performance. Furthermore, a decrease in the membrane thickness in addition to an increase in polyvinylpyrrolidone dosage during membrane preparation enhances the waste heat recovery performance, however deteriorates the mechanical strength of membrane. Moreover, the organic–inorganic composite membrane prepared in this study demonstrated a good stability of waste heat recovery performance during a long-term operation, showing a potential in the rich solvent-split modified carbon capture process to achieve a low capital expenditure and a high waste heat recovery performance.

Thermo-economic and performance analysis of a novel tubular hybrid high-temperature proton exchange membrane fuel cell and thermoelectric generator

This paper proposes a novel tubular design for a hybrid high-temperature proton exchange membrane fuel cell (HT-PEMFC) and thermoelectric generator (TEG) system. The wasted heat from the fuel cell is captured by a thermoelectric generator to generate more electricity. Hence, the primary objective of the research is to determine the waste heat recovery performance of the TEG for thermal management of the tubular HT-PEMFC. A validated 3D numerical approach was employed to evaluate the performance of the tubular hybrid system with a tubular TEG integrated into the HT-PEMFC. A parametric study evaluates the impact of various TEG geometrical configurations and operational parameters on the system's performance. The results indicate that boosting the cell voltage improves the fuel cell efficiency, while decreasing the thermoelectric sizing has a notable impact on the TEG's performance. The TEG's conversion efficiency and output power are significantly impacted by changes in the angle ratio and the temperature of the cold side. Increasing the inlet temperature has a positive impact on thermoelectric power generation but leads to a reduction in fuel cell power and efficiency. Overall, the study highlights the importance of optimizing the operating conditions of hybrid tubular HT-PEMFC/TEG to achieve optimal performance and provides valuable insights for the design and development of hybrid energy systems that can potentially contribute to meet the increasing demand for sustainable energy solutions.

Numerical simulation of waste heat recovery process from the hot stripped gas in carbon capture process by using ceramic membrane

CO2 chemical absorption process suffers from the high CO2 regeneration heat requirement, so a rich solvent-split mechanism was put forward to recover the waste heat from the hot stripped gas for reducing the regeneration heat consumption. Ceramic membrane-based transport membrane condenser (TMC) can provide a higher heat transfer efficiency, therefore better meet the requirements for waste heat recovery from the hot stripped gas. The ceramic membrane structure is a key factor affecting the heat recovery performance, which has been neglected by previous studies. For investigating the effect of membrane structure, in this study, a condensation and mass transfer model was firstly constructed using the computational fluid dynamics approach to describe the process of waste heat recovery from the hot stripped gas. The errors between the simulated outlet temperature of stripped gas or CO2-rich solvent and the experimental ones are about 1.74 %, indicating the satisfactory accuracy of the model. Based on the model, the effects of ceramic membrane structure and physical parameters on the waste heat recovery performance were comprehensively investigated. The results showed that reducing the wall thickness or inner diameter of ceramic membrane contributes to improving the waste heat recovery efficiency of TMC. Notably, there may be an optimal membrane area beyond which the improvement of waste heat recovery is difficult. Additionally, when the thermal conductivity of ceramic membrane exceeds a critical value (∼10 W/(m K) in this study), the improvement of waste heat recovery performance may be difficult only by increasing the thermal conductivity. This study provides an important guidance for the selection of ceramic membranes for waste heat recovery process from the stripped gas in the future.

Simulation Analysis of High Radiant Heat Plant Cooling and Endothermic Screen Waste Heat Recovery Performance Based on FLUENT

In this article, we propose the endothermic screen model. The aim is to reduce the problems of the high temperature and low utilization of waste heat in industrial plants with high radiant heat. In this paper, the Rhino software is used to establish the model and import it into the FLUENT software, divide the mesh, set the boundary conditions and analyze the transient temperature field. Finally, the temperature change law in the plant and the waste heat recovery efficiency of the endothermic screen are obtained. The flow of cooling water in the endothermic screen is used to transform and transfer the high-radiation heat inside the plant to the outside. The simulation results show that after adding the endothermic screen, the average indoor temperature drops from 313.33 K to 305.66 K, which has a cooling effect. The waste heat recovery efficiency reaches up to 56%, and the waste heat recovery effect is obvious. The research results can provide a reference for the application of an endothermic screen in actual high radiant heat plants and provide a more comfortable working environment for the plant workers.

Waste heat recovery enhancement in the CO2 chemical absorption process by hydrophobic-hydrophilic composite ceramic membranes

A novel ceramic composite membrane configuration was proposed to improve the waste heat recovery performance from stripped gas in the CO2 chemical absorption process. Tubular hydrophobic and hydrophilic ceramic membranes were serially assembled to form a single composite membrane. The stripped gas and bypassed CO2-rich solvent flowed countercurrent on both sides of the composite membrane. The waste heat recovery performance from the stripped gas was investigated under eight membrane configurations using: hydrophobic, hydrophilic, and Janus membranes (i.e., with hydrophilic inner-surface and hydrophobic outer-surface, and viceversa). Results showed that when the stripped gas enters the hydrophobic segment, the waste heat recovery performance increases to a plateau and then decreases with an increasing length of the hydrophobic segment. When the length ratio of the hydrophobic segment was 25%, a maximum waste heat recovery performance was achieved. Similarly, an increase in the hydrophobicity of the hydrophobic segment caused an increase in waste heat recovery performance, in which the optimal water contact angle (CA) was 137.35°. As a result of the abovementioned conditions, a 7.44%–25.15% higher waste heat recovery of the composite membrane was achieved compared to commercial hydrophilic membranes.

Thermodynamic analysis of exhaust heat recovery of marine ice using organic rankine cycle

The use of organic Rankine cycle power systems for waste heat recovery on marine internal combustion engines can help to mitigate the GHG and reduce the fuel consumption of the marine engine. In this paper, the internal combustion engine combined with an organic Rankine cycle system was developed to analyze the performance of waste heat recovery from the exhaust gas of a heavy-duty marine Diesel engine via five selected working fluids with low global warming potential and ozone depletion potential. The net output power and thermal efficiency for each of the selected working fluids were obtained. Results indicate that the working fluids of butane have the best performance among the selected working fluids with the power efficiency of the organic Rankine cycle subsystem of 12.27% under the power load of 100%. For the overall proposed system, the maximum net power output is 1048 kW and the power efficiency is 36.47%. Besides, the total thermal efficiency of the proposed system was 67.94% when considering the recovered waste energy from jacket water.

Complex coupling between surface charge and thermo-osmotic phenomena.

Thermo-osmotic flows, generated at liquid-solid interfaces by thermal gradients, can be used to produce electric currents from waste heat on charged surfaces. The two key parameters controlling the thermo-osmotic current are the surface charge and the interfacial enthalpy excess due to liquid-solid interactions. While it has been shown that the contribution from water to the enthalpy excess can be crucial, how this contribution is affected by surface charge remained to be understood. Here, we start by discussing how thermo-osmotic flows and induced electric currents are related to the interfacial enthalpy excess. We then use molecular dynamics simulations to investigate the impact of surface charge on the interfacial enthalpy excess, for different distributions of the surface charge, and two different wetting conditions. We observe that surface charge has a strong impact on enthalpy excess, and that the dependence of enthalpy excess on surface charge depends largely on its spatial distribution. In contrast, wetting has a very small impact on the charge-enthalpy coupling. We rationalize the results with simple analytical models, and explore their consequences for thermo-osmotic phenomena. Overall, this work provides guidelines to search for systems providing optimal waste heat recovery performance.

Winter performance analysis of multi-mode integrated thermal management system based on thermodynamics

The thermal management system plays a critical role in pure electric vehicles to ensure the comfort of cabin and the thermal safety of battery, motor and controller, but it consumes lots of energy at the same time. In order to improve the energy utilization efficiency of the whole vehicle, a topology of the multi-mode integrated thermal management system (MITMS) is constructed in this paper by combining heat pump, battery thermal management and motor waste heat recovery. Focusing on the winter condition, simulations via AMESim have been conducted for the MITMS to assess its performance working as series and parallel structures. The results show that the MITMS with a series structure (series system) has better thermodynamic performance than that of the parallel one (parallel system). To be specific, compared with the parallel system, the exergy efficiency of the series system is promoted by 23.9% on average, and the coefficient of performance (COP) is increased by 13.5% under the condition of optimal refrigerant charge. Moreover, the series system has better heating performance, and its battery temperature rising rate in winter is also significantly improved. Based on the MITMS winter mode switching strategy formulated in this work, the performance of waste heat recovery is tested. Under low-temperature conditions, the heating capacity is increased by 22.75% on average. The MITMS test is carried out under the CLTC-P driving cycle. The results show that, compared with the baseline system, the battery temperature increases significantly and the SOC recovers by 2.68%, which further verifies the practical feasibility of the present system.

Hydrophobic–Hydrophilic Janus Ceramic Membrane for Enhancing the Waste Heat Recovery from the Stripped Gas in the Carbon Capture Process

A novel hydrophilic–hydrophobic ceramic membrane was developed in this study for the waste heat recovery from the hot stripped gas (i.e., CO2 balanced by water vapor) in the CO2-rich solvent-split modified carbon capture process. This Janus ceramic membrane contained a layer of hydrophobic fluoroalkylsilane (FAS) molecules grafted on a hydrophilic Al2O3 ceramic membrane support. With the increase of FAS concentration, the carbon chain length in FAS molecules in addition to the grafting time, the water and solvent contact angles (CAs) of the hydrophobic side of the Janus membrane improved. The hydrophobic side of the Janus membrane also exhibited a good thermal stability under the typical CO2 regeneration temperature. Furthermore, this Janus ceramic membrane improved the waste heat recovery performance when compared with the conventional hydrophilic ceramic membrane. The hydrophobic side of the Janus membrane should orient toward the stripped gas for achieving a high heat recovery performance. With an increase in the water CA of the hydrophobic side of the Janus membrane, the waste heat recovery performance of the Janus membrane first increased and then declined. The optimal water CA was about 106 ± 1.3° in this study. Moreover, once the water CA for the hydrophobic side of the Janus membrane was fixed, the waste heat recovery performance of the Janus membrane was almost fixed no matter what the grafting conditions were adopted. The novel Janus ceramic membrane developed in this study exhibited a great potential to improve the waste heat recovery performance in the carbon capture process.

Energy performance analysis and optimization of a coupled adsorption and absorption cascade refrigeration system

An energy cascade utilization system is an advanced technology that recoveries waste heat energy efficiently. However, research on cascade systems by utilizing waste hot water with 60–100 °C is still considerably lacking in the literature. Specifically, this paper investigates the waste heat recovery performance of a multistage coupled absorption chiller (ABC)-adsorption chiller (ADC) cascade system. The proposed ABC-ADC cascade system is capable of producing potable water and three streams of chilled water under different temperature settings. Firstly, the experimental analysis is judiciously carried out on a four-bed two-evaporator ADC subsystem prototype. Key results reveal that the ADC’s maximum specific daily water production is 10.5 m3/day/ton. Subsequently, the ABC-ADC cascade system’s performance is experimentally analysed and optimized. The achievable maximum cooling coefficient of performance (COPc) is obtained to be 0.55. Additionally, a general method is proposed to optimize the subsystem’s cooling capacity combination of the ABC-ADC cascade system in search of an optimal COPc. The results indicate that the optimized COPc can further be enhanced by around 20%. The performance efficiency of an optimized ABC-ADC cascade system incorporating a microturbine system is then investigated. Compared to the experimental ABC-ADC cascade system, the optimized system’ total coefficient of performance is demonstrated to improve by 18%. The primary energy saving ratio is also promoted from 9.8% to 18%. Moreover, 68.92% of the gas turbine’s dissipated energy is able to be recovered by the optimized ABC-ADC system. As far as application is concerned, this cascade system has been demonstrated to be superior to standalone heat-driven chillers with great commercial potential for implementation in industries where low-grade waste heat is readily available.

Three-zone numerical modeling method for predicting system-level waste heat recovery performance of thermoelectric generator with various electrical array configurations

In this study, an experimentally validated numerical model is formulated to accurately predict the energy harvesting performance of a thermoelectric generator (TEG) by reflecting the underlying physics of the thermoelectric energy conversion phenomena. The most advantageous feature of the modeling method employed herein is its high reliability because the system-level performance is predicted based on module-level power generation characteristics. A further benefit that the proposed physics-based model affords is that the effect of electrical array configurations (i.e., the particular manner by which the thermoelectric modules (TEMs) are electrically connected) on the waste heat recovery performance of the TEG can be accurately predicted. For this purpose, a three-zone modeling method, wherein each TEM is modeled into heat sink, heat generation, and heat conduction zones, is proposed. Moreover, user-defined functions are embedded into the numerical model to correlate the temperature fields obtained from the transport of momentum and energy with the Seebeck effect and Joule heating that appear as the thermoelectric output power and heat sink/heat generation near the TEM surface. The accuracy and reliability of the numerical model are validated by the experimental results of temperature and output power using a TEG prototype whose configurations and dimensions are identical to those of the proposed numerical model. Further comparisons between the numerical results obtained using eight different electrical array configurations and the corresponding experimental results ensure the robustness of the modeling method and numerical model formulated in this study. Finally, two correlations are derived as a function of the number of electrical array branches to predict the output voltage and current of a TEG whose branches consist of an identical number of TEMs for minimizing unexpected power losses.

Experimental and numerical studies on novel airfoil fins heat exchanger in flue gas heat recovery system

• The novel airfoil fins heat exchanger was studied experimentally and numerically. • The novel airfoil fins channel has the best thermal–hydraulic performance. • The enhancement mechanism could be explained with field synergy principle. • Thermal-hydraulic correlations of novel airfoil heat exchanger were proposed. To improve the performance of waste heat recovery, a novel airfoil fins heat exchanger was applied to flue gas waste heat recovery. Two groups of experimental conditions were installed to test the heat effectiveness of the novel airfoil fins heat exchanger. The results showed that the heat effectiveness of the novel airfoil fins heat exchanger could reach more than 96%, which is higher than the conventional heat exchanger. The thermal–hydraulic performances of the novel airfoil channel, NACA 0020 airfoil channel and zigzag channel were investigated with the first and second laws of thermodynamics, which showed that the novel airfoil channel has the best comprehensive thermal–hydraulic performance among the three channels. The correlations of Nusselt number and friction factor of the novel airfoil fins heat exchanger were proposed for flue gas, whose maximum deviations were within ±5.0% and ±7.1%, respectively. The present work could provide guidance for the application of the novel airfoil fins heat exchanger in waste heat recovery.

Experimental investigation of optimal location of flow straightener from the aspects of power output and pressure drop characteristics of a thermoelectric generator

This study addresses the combined effects of the location and porosity of a flow straightener on the waste heat recovery performance of a thermoelectric generator (TEG). An exhaust gas channel was built for the flexible placement of a flow straightener with varying porosity in the range of 0.121–0.516 at five different locations. Customized thermoelectric modules were placed between the exhaust gas channel and two coolant channels for waste heat recovery. A diesel engine releases the exhaust gas flow into the exhaust gas channel of the TEG placed in the middle of the tail pipe. Experimental results showed that a TEG design in which a flow straightener is positioned near the inlet of the TEG needs to be avoided because of a low power output to pressure loss ratio. The net power output, energy conversion efficiency, and pressure drop characteristics were enhanced as the location of flow straightener moved rearward of the TEG. A friction factor correlation was also proposed for predicting pressure drop characteristics of TEGs equipped with a flow straightener to improve their practicality in industry and engineering fields.

CO2 capture cost saving through waste heat recovery using transport membrane condenser in different solvent-based carbon capture processes

In this study, the waste heat from the hot stripping gas was recovered by adopting the transport membrane condenser (TMC) in the monoethanolamine (MEA)-, diethanolamine (DEA)-, piperazine (PZ)- and potassium glycinate (PG)-based rich-split modified carbon capture processes. A 220-h test showed that TMC can exhibit a good stability on the waste heat recovery performance. The PZ-based TMC-modified rich-split process (i.e., PZ-case) achieved a highest waste heat recovery performance, followed by the PG-case, MEA-case and DEA-case. A strong linear relationship between the heat and water fluxes was observed during the waste heat recovery. Three scenarios were considered for comparing the CO2 capture cost savings of 4 cases. When the TMC area was fixed meaning the same additional investment of rich-split modification, PZ-case gained the highest CO2 capture cost saving ($6.40/t-CO2), followed by PG-, MEA- and DEA-case. When a fixed waste heat recovery performance of 600 kJ/kg-CO2 was required for obtaining the same revenue after rich-split modification, PZ- and PG-case obtained the same CO2 capture cost saving of $4.22/t-CO2. Moreover, when the reboiler duty reduction potential was aimed at 15%, PG-case achieved the maximum CO2 capture cost saving ($4.56/t-CO2).

Exergy analysis of the multi-stage slag waste heat recovery system

Based on the black-box model, this paper analyzed the multi-stage slag waste heat recovery system. The exergy efficiency, the exergy loss coefficient and the exergy loss rate were adopted as evaluation indexes to investigate the energy consumption and the weakness of the system. Meanwhile, the performance of waste heat recovery was analyzed by comparing the comprehensive exergy efficiency between the system and other conventional waste heat recovery methods. The results showed that the comprehensive exergy efficiency of the system reached 75.75%, which was much higher than other methods, and the weakness of the system was the subsystem of waste heat boiler. In general, the system recovered the slag waste heat effectively and converted coal to clean syngas through gasification reaction, which had incredible potential in energy saving, emission reduction and consumption reduction.

Parametric optimization of H-type finned tube with longitudinal vortex generators by response surface model and genetic algorithm

Low-low temperature electrostatic precipitator technology is one of the important ways for energy saving and emission reduction of coal-fired power plants. In order to further improve the dust removal efficiency and enhance waste heat recovery performance, a novel H-type finned elliptical tube heat exchanger with longitudinal vortex generators is proposed. To achieve the maximum heat transfer enhancement with the minimum friction factor augmentation, the response surface model and multi-objective genetic algorithm are adopted to optimize the design parameters. Firstly, combined with the finite volume method and the central composite design method, the second-order response surface model between the design parameters (the length, height, angle, and position of longitudinal vortex generators) and the objective functions (Nusselt number and friction factor) is established. Then, based on the response surface model, the Pareto optimal solution set is obtained by the multi-objective genetic algorithm. Finally, by comprehensively comparing Nusselt number, friction factor and performance evaluation criteria of Pareto optimal solutions, the optimal combination is determined. Compared with the H-type finned tube heat exchanger, the performance evaluation criteria of the optimized novel heat exchanger is improved by 48–55%, which contributes to improve the overall performance of low-low temperature electrostatic precipitator system. The findings of this paper may provide practical guidelines for researchers and designers to develop efficient heat exchangers.

Highly enhanced thermoelectric energy harvesting from a high-temperature heat source by boosting thermal interface conduction

Thermoelectricity is regarded as one of the promising waste heat recovery candidates. A fundamental but effective method for the best use of thermoelectric generators (TEGs) is to maximize the heat flow crossing thermoelectric materials. The main focus of the present study was to develop a thermal interface material (TIM) with high thermal conductivity and temperature resistance as the key to minimizing the overall thermal resistance of the heat flow path of a TEG module operating under high-temperature conditions. In combination with a polyimide matrix and a multi-dimensional filler compound, a new TIM having stable heat conduction behavior at high temperatures was produced. The developed TIM was stable without losing mass up to ∼500 °C, and its thermal conductivity reached 81.4 W/m·K. It was applied to the interface between a TEG and a heat source whose temperature ranged from 100 to 300 °C and, the effect of the thermal conductivity and interface thermal resistance of the TIM on thermoelectric power generation performance during onsite curing of the TIM was investigated. Reduction of the interface thermal resistance by the new TIM improved the power generation by, at most, 132.3 and 38.6% compared to cases without a TIM and with a conventional graphite foil TIM, respectively. In terms of energy conversion efficiency, the TEG with the new TIM showed maximum improvements of 73.2 and 20.9% over the cases without a TIM and with a graphite TIM for the same temperature difference across the TEG, respectively. In addition, thermal cyclic testing confirmed the long-lasting heat-conducting feature of the developed TIM. The present work clearly shows the potentially significant influence that TIMs have on the waste heat recovery performance of TEGs.

Energy harvesting performance of hexagonal shaped thermoelectric generator for passenger vehicle applications: An experimental approach

In this study, the waste heat recovery performance of a hexagonal thermoelectric generator (TEG) was investigated experimentally. Based on the system configuration and dimensions, a total of 18 thermoelectric modules (TEMs) were used for thermal energy harvesting. The internal finned structures of the hexagonal TEG were placed on the inner surface of the exhaust gas channel, in consideration of the thermal resistance and friction factor, in order to augment the heat transfer from the exhaust gas to the thermoelectric modules (TEMs), under various operating conditions. The surface of the TEMs was positioned on the hexagonal-shaped exhaust gas channel surface, whereas the other surface of the TEMs was maintained cool by a set of coolers through which the engine coolant flowed. The coolant line was modified in order to induce a total coolant flow of 10 LPM at 353 K from a coolant controller to the hexagonal TEG. In this study, the assembled hexagonal TEG was installed in the middle of the exhaust gas pipe of the internal combustion engine manufactured for hybrid electric vehicles, and was used as the heat source. The waste heat recovery performance of the hexagonal TEG was evaluated by considering eight engine-operating conditions under which the automotive vehicles were most frequently driven. The output power of the hexagonal TEG tended to increase with the increase in engine speed and load, and ranged between 21.2 and 98.8 W, which corresponded to a conversion efficiency of ∼1.3–2.6%. An acceptable maximum pressure drop across the hexagonal TEG of ∼2.1 kPa was observed for the maximum exhaust gas flow rate condition.