Automobile Waste Heat Recovery Research Articles

A Review of Thermoelectric Generators in Automobile Waste Heat Recovery Systems for Improving Energy Utilization

With the progress of modern times, automobile technology has become integral to human society. At the same time, the need for energy has also grown. In parallel, the total amount of waste energy that is liberated from different parts of the automobile has also increased. In this ever-increasing energy demand pool, future energy shortages and environmental pollution are the primary concerns. A thermoelectric generator (TEG) is a promising technology that utilizes waste heat and converts it into useful electrical power, which can reduce fuel consumption to a significant extent. This paper comprehensively reviews automobile thermoelectric generators and their technological advancements. The review begins by classifying different waste heat technologies and discussing the superiority of TEGs over the other existing technologies. Then, we demonstrate the basic concept of and advancements in new high-performance TEG materials. Following that, improvements and associated challenges with various aspects, such as the heat exchanger design, including metal foam, extended body, intermediate fluid and heat pipe, leg geometry design, segmentation, and multi-staging, are discussed extensively. Finally, the present study highlights research guidelines for TEG design, research gaps, and future directions for innovative works in automobile TEG technologies.

Performance investigation of a thermoelectric generator system applied in automobile exhaust waste heat recovery

In this paper, a novel fluid-thermal-electric multiphysics numerical model is presented to predict the performance of a thermoelectric generator system applied in automobile waste heat recovery. The model considers the complete geometry, temperature-dependent material properties, topological connection among thermoelectric modules, and impedance matching, which can simulate the actual working conditions. Numerical simulations are carried out on the COMSOL platform combined with the exhaust temperature and exhaust mass flow rate under different vehicle speeds. In addition, the detailed physical field distribution characteristics of the automobile thermoelectric generator system, as well as the variations of output power, conversion efficiency, power losses, and net power with vehicle speed, are obtained. The position of thermoelectric modules on the hot side heat exchanger plays an important role in output uniformity, and the higher the vehicle speed is, the more uniform the output will be. At the vehicle speed of 120 km h−1, the output power and conversion efficiency of the automobile thermoelectric generator system are 38.07 W and 1.53% respectively. Considering the weight power loss and coolant pumping power loss, the net power is 23.66 W. This work fills the gap in evaluating the performance of automobile thermoelectric generator systems at different vehicle speeds comprehensively.

Performance analysis of a novel Two-stage automobile thermoelectric generator with the Temperature-dependent materials

In order to enhance the performance of the automobile waste heat recovery system, a novel two-stage automobile thermoelectric generator with a cascade configuration along the temperature gradient of exhaust gas was designed. The corresponding integrated one-dimensional numerical model considering temperature-dependent thermoelectric materials was developed to predict the performance accurately. The impedance matching condition for the maximum output power was derived for the novel two-stage automobile thermoelectric generator. The developed model was demonstrated through comparisons with the reported experimental data and simulation results. The results indicated significant discrepancies in output power, conversion efficiency, and the temperature difference between the cold/hot sides of thermocouples for single-stage and two-stage configurations. The designed thermoelectric generator with the two-stage configuration could capture the temperature change along the flow direction of exhaust gas and obtain better performance by adjusting the length of the two-stage module. Compared to the traditional single-stage thermoelectric generator, the designed two-stage configuration could achieve the output power increments by 13.5% under the same working conditions. The effects of working conditions (exhaust gas temperature and mass flow rate) and TEG geometry size on the output power are studied. This work could provide some guidance on the design and performance enhancement of automobile thermoelectric generators.

Automobile Waste Heat Recovery System Using Thermoelectric Generator

Energy crisis is major problem in this era. Thermoelectric generator is a promising solution for this problem. This research aims to recover waste heat energy from automobile by converting it into electrical energy using thermoelectric generator. Thermoelectric generator is applied at automobile exhaust system to produce electrical energy from heat energy directly with a phenomenon called see-beck effect. This work develops a heat exchanger model with thermoelectric generator for automobile waste heat recovery in which heat source and cold sink are actually modeled. Main emphasis is put on effective temperature difference across the TEGs to get better performance of the exhaust waste heat recovery system. This research shows that the model is able to produce up to 2.67 W energy using 3 Numbers of TEGs in this design.

Thermoelectric Analysis of Automobiles Exhaust Waste Heat Recovery Material – A Simulation Study

Abstract Alongside the improvements in renewable fuel technologies, there is also a tremendous increase in research in the field of automobile exhaust waste heat recovery. This is mainly done with the help of thermoelectric generators (TEGs) which use thermoelectric materials (TEMs) as their primary elements. Thermoelectric materials have extensive application in space vehicles. This experience led to its usage for terrestrial automobile waste heat recovery. Usage of TEMs could help in producing accessory power and for fuel savings. Practically the efficiency of system level of automobile exhaust applications is 33% lower than material conversion (device) level. Further the heat exchanger’s performance plays a vital role in the outcome from TEGs. We worked on a theoretical model of heat exchanger with three different profiles of parabolic fin. The fin material which are used to transfer the heat to thermoelectric material is Bismuth Telluride/Antimony Telluride (Bi2Te3/Sb2Te3) for automobile waste heat recovery. The dimensional characteristics of fins for finding the best model were found with the simulation study using ANSYS-Steady state thermal mode. A model of the double finned profile with 8 fins, 8cm length and 1.737cm breadth was proved effective and this profile was simulated using ANSYS-CFX for temperature profiles. Based on the data collected for Bi2Te3/Sb2Te3 super lattice thermoelectric material (TEM) the TEG’s performance was calculated. Double finned parabolic fins resulted in uniformity of temperature distribution. The TEM with a figure of merit (ZT) of 2.4 is showed extraordinary theoretical efficiency, which is of better device level rather than system level.

Performance effect on the TEG system for waste heat recovery in automobiles using ZnO and SiO2 nanofluid coolants

AbstractEnhancement in heat transfer of the cold side is vital to amplify the performance of a thermoelectric generator (TEG). With enriched thermophysical properties of nanofluids, significant improvement in heat transfer process can be obtained. The current study concerns the performance comparison of an automobile waste heat recovery system with EG‐water (EG‐W) mixture, ZnO, and SiO2 nanofluid as coolants for the TEG system. The effects on performance parameters, that is, circuit voltage, conversion efficiency, and output power with exhaust inlet temperature, the total area of TEG, Reynolds number, and particle concentration of nanofluids for the TEG system have been investigated. A detailed performance analysis revealed an increase in voltage, power output, and conversion efficiency of the TEG system with SiO 2 nanofluid, followed by ZnO and EG‐W coolants. The electric power and conversion efficiency for SiO 2 nanofluid at an exhaust inlet temperature of 500K were enhanced by 11.80% and 11.39% respectively, in comparison with EG‐W coolants. Moreover, the model speculates that an optimal total area of TEGs exists for the maximum power output of the system. With SiO 2 nanofluid as a coolant, the total area of TEGs can be diminished by up to 34% as compared with EG‐W, which brings significant convenience for the placement of TEGs and reduces the cost of the TEG system.

Evaluation of metal foam based thermoelectric generators for automobile waste heat recovery

This paper focuses on harvesting heat emitted by exhaust systems efficiently using thermoelectric generators (TEGs) and converting it to electricity. In a TEG that employs gaseous working fluid, up to 80% of the thermal resistance is due to the gas side. Maximizing the energy transferred from the hot exhaust gas to the hot side of the thermoelectric modules by suitable enhancement techniques can result in an efficiency gain for the TEG. To this end, we have investigated the performance of metal foam-based heat exchangers for reducing thermal resistance of the hot side in TEGs. A computational model of the metal foam-enhanced TEG, solving for the coupled thermal and electrical energy transfer processes, was developed to investigate the enhancement in system performance for a range of metal foam porosities and pore densities, and mass flow rates of the exhaust gas. Skutterudites with multiple cofillers were selected as thermoelectric materials. The primary performance metrics that were analyzed include the electrical power output and the associated pressure drop for various inlet conditions of the exhaust gas. Based on the trade-off between the increased pumping power required to offset the increase in pressure drop, and the gain in heat transfer coefficient with increase in mass flow rate of the exhaust gas, an optimal mass flow rate that maximizes the net electric power produced by the metal foam-enhanced TEG was obtained. The results show a critical exhaust flow rate for different pore densities of metal foam beyond which the net electric power produced by the TEG is less than of the TEG with no metal foam. At this critical flow rate, the maximum net electric power produced from exhaust waste heat by metal foam enhanced TEG is 5.7 (20 PPI) to 7.8 (5 PPI) times higher than that generated by the configuration without metal foam.

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.

Effects of heat enhancement for exhaust heat exchanger on the performance of thermoelectric generator

It is critical that the exhaust heat exchanger of the thermoelectric generator (TEG) that is used in automobile waste heat recovery provides a high heat transfer performance while maintaining a low pressure drop. In this study, incorporating net power output as part of a main comparative parameter, simulations are used to investigate two types of heat transfer enhancements for an exhaust heat exchanger, rectangular offset-strip fins and metal foams. The results for the rectangular offset-strip fins show that there are optimal values of the fin transverse spacing and the fin thickness maximizes the net power output. The use of metal foams can significantly increase the total power output and the efficiency of the TEG, especially foam with low porosity and small pore density (PPI). However, metal foams also produce a high pressure drop and a low net power output. This problem may be solved by using a TEG that combines thermoelectric generation with catalytic conversion.

Studies on mechanical properties of thermoelectric materials by nanoindentation

In order to fabricate durable and efficient thermoelectric generators (TEG) for applications like automobile waste heat recovery, where thermal stress is a major concern, one needs to assess the mechanical performance of the TE materials. This work reports the hardness and elastic modulus of the moderate temperature range (200–1000 °C) TE materials, including half‐Heusler, skutterudites, bismuth telluride, silicon germanium alloys, and lead selenide, using nanoindentation and atomic force microscopy (AFM). The p‐type half‐Heusler exhibits considerably higher hardness and modulus values, and lower brittleness as compared with other materials, which may be indicative of its more robust mechanical performance.

Performance estimation of an adsorption cooling system for automobile waste heat recovery

This article presents a numerical study of the dynamic performance of an adsorption cooling system for automobile waste heat recovery. A new lumped parameter non-equilibrium model is developed and used to investigate and optimize the waste heat cooling system, which is estimated to be operated in quicker cycles when compared with the time needed to reach equilibrium. The effects of the operating temperatures and the overall heat transfer coefficient on the system performance are extensively investigated. It is found that the SCP is more sensitive to parameter changes than the COP. And improving the UA is the most effective way to obtain an increased SCP, but only in the ranges below the threshold value, which is determined by the overall mass transfer coefficient.