Waste Heat Energy Harvesting Research Articles

Complete thermodynamic characterization of second-order phase transition magnetocaloric materials exclusively through magnetometry

To fully assess and improve the performance of near room-temperature magnetic refrigerants, it is crucial to measure and compare their three most relevant thermodynamic properties, and their dependence on temperature (T) and applied magnetic field (H): the isothermal entropy change, ∆Siso(T,H); the adiabatic temperature change, ∆Tad(T,H); and the heat capacity, Cp(T,H). Typically, each thermodynamic property requires its own specialized measurements, which are very time-demanding and can be challenging to setup. In this work, we report a complete thermomagnetic characterization of a benchmark magnetocaloric material, gadolinium, using a single and commercially available SQUID magnetometer. By improving a recently reported method with incremental field ramping steps for measuring temperature through magnetization, we obtained a ∆Tad(T) curve under a 1 T field change with its peak amplitude and maximizing temperature respectively within 2 % and 0.8 % of previously reported values for gadolinium. We were also able to estimate the temperature dependent heat capacity, Cp(T,μ0H=0.85T), using the ∆Tad(T) measurements from magnetometry combined with magnetization versus temperature curves at different field values. This estimate of Cp around the transition temperature of gadolinium is within a relative error of 11 % of the experimental and reported values. The reported methodology allows the complete characterization of a second-order magnetocaloric material (∆Siso(T,H), ∆Tad(T,H), Cp(T,H)) around its Curie temperature using a single and widely available device, which can accelerate studies of different magnetocaloric materials’ performance, and approximate their implementation in magnetic refrigeration and/or waste heat energy harvesting industries.

Co‐Fired Multilayer Thermoelectric Generators Based on Textured Calcium Cobaltite

AbstractThermoelectric generators are very attractive devices for waste heat energy harvesting as they transform a temperature difference into electrical power. However, commercially available generators show poor power density and limited operation temperatures. Research focuses on high‐temperature materials and innovative generator designs. Finding the optimal design for a given material system is challenging. Here, a theoretical framework is provided that allows appropriate generator design selection based on the particular material properties. For high‐temperature thermoelectric oxides, it can be clearly deduced that unileg multilayer generators have the highest potential for effective energy harvesting. Based on these considerations, prototype unileg multilayer generators from the currently best thermoelectric oxide Ca3Co4O9 are manufactured for the first time by industrially established ceramic multilayer technology. These generators exhibit a power density of 2.2 mW cm−2 at a temperature difference of 260 K, matching simulated values and confirming the suitability of the technology. Further design improvements increase the power density by a factor of 22 to facilitate practicable power output at temperature differences as low as 7 K. This work demonstrates that reasonable energy harvesting at elevated temperatures is possible with oxide materials and appropriate multilayer design.

First Principle Investigations on Structural, Mechanical, Electronic, And Thermoelectric Properties of XCoP (XTi, Zr, Hf) Half Heusler Alloys for Energy Recovery Application

AbstractXCoP (XTi, Zr, Hf) half Heusler alloys are investigated through density functional theory in stable non‐magnetic phase. The exchange‐correlation functional Generalized Gradient Approximation (GGA) is used to study these alloys. The equilibrium lattice constants and corresponding ground state energies of the studied alloys are calculated in stable γ‐phase. All these three reported alloys exhibit semiconducting behavior with corresponding bandgap values of 1.40, 1.29, and 1.38 eV for TiCoP, ZrCoP, and HfCoP, respectively. The studied alloys are mechanically stable and ductile in nature. The obtained thermoelectric figure of merit for p‐type TiCoP, ZrCoP and HfCoP are 0.5, 0.6, and 0.7 at 1200 K. Similarly, the figure of merit obtained for n‐type TiCoP, ZrCoP, HfCoP are 0.54, 0.37, and 0.31, respectively, at the same temperature. The investigated favorable transport properties of these alloys show that they are the potential candidates for waste heat energy harvesting application.

Waste heat energy harvesting by using praseodymium, nickel codoped zinc oxide thermoelectric materials

Waste heat energy harvesting by using praseodymium, nickel codoped zinc oxide thermoelectric materials

Microfabrication Approaches on Magnetic Shape Memory Films

Magnetic shape memory alloys are emerging multifunctional materials that enable applications like high‐stroke actuation, solid‐state refrigeration, and energy harvesting of waste heat. Thin films of these alloys promise integration in microsystems to exploit their multifunctional properties at the microscale. However, the microfabrication process of these Heusler alloys is difficult. Herein, different etching techniques are investigated for the microfabrication of epitaxial Ni‐Mn‐Ga films, the encountered challenges are explained, and ways to overcome them are demonstrated. The results show that wet chemical etching is suitable for large patterned structures, while reactive ion etching of Ni‐Mn‐Ga films is unsuitable due to redeposition. For patterning structures below 10 μm with clean and sharp edges, the best results are obtained by ion beam etching with adjusted sample‐stage tilt. Finally, a microfabrication process using Si microtechnology to fabricate partially freestanding structures is demonstrated. These findings give guidelines for the fabrication and integration of these smart materials in Si‐based microsystems.

Development of Cu2Se/Ag2(S,Se)-Based Monolithic Thermoelectric Generators for Low-Grade Waste Heat Energy Harvesting.

With the ongoing climate and energy crises, thermoelectric conversion has slowly emerged as a clean and reliable alternative energy source for small Internet of Things (IoT) devices. Commercially available thermoelectric generators (TEGs) are typically composed of expensive and toxic Bi2Te3-based thermoelectric materials and require complicated and energy-intensive device assembly processes. As an alternative solution, we have developed a Ag- and Cu-chalcogenide-based monolithic TEG using simple, quick, and low-energy-cost device fabrication processes for low-grade waste heat recovery for energy harvesting. We used ductile Ag2S0.55Se0.45 and overstoichiometric Cu2.075Se, both possessing excellent transport properties around room temperature, with a zT value of ∼0.5 at 300 K. By optimizing the device fabrication process, we were successfully able to assemble the monolithic TEGs without any significant Ag- or Cu-ion migration and obtained a dense and robust device. Strategic optimization of the device structure was able to reduce the electrical contact resistance of the device, which resulted in increased power output. A maximum power density of 0.68 mW/cm2 at a ΔT = 30 K was obtained, which is comparable to a similar Bi2Te3-based monolithic TEG. These results show the potential of chalcogenide-based monolithic TEG as a simple and low-cost alternative to Bi2Te3-based TEGs for energy harvesting applications.

High-Performance Thermomagnetic Gd-Si-Ge Alloys.

Exploring low-grade waste heat energy harvesting is crucial to address increasing environmental concerns. Thermomagnetic materials are magnetic phase change materials that enable energy harvesting from low-temperature gradients. To achieve a high thermomagnetic conversion efficiency, there are three main material requirements: (i) magnetic phase transition near room temperature, (ii) substantial change in magnetization with temperature, and (iii) high thermal conductivity. Here, we demonstrate a high-performance Gd5Si2.4Ge1.6 thermomagnetic alloy that meets these three requirements. The magnetic phase transition temperature was successfully shifted to 306 K by introducing Ge doping in Gd5Si4, and a sharper and more symmetric magnetization behavior with saturation magnetization of Mmax = 70 emu/g at a 2 T magnetic field was achieved in the ferromagnetic state. The addition of SeS2, as a low-temperature sintering aid, to the Gd-Si-Ge alloy improved the material's density and thermal conductivity by ∼45 and ∼275%, respectively. Our results confirm that the (Gd5Si2.4Ge1.6)0.9(SeS2)0.1 alloy is a suitable composite material for low-grade waste heat recovery in thermomagnetic applications.

Non-planar dielectrics derived thermal and electrostatic field inhomogeneity for boosted weather-adaptive energy harvesting.

Weather-adaptive energy harvesting of omnipresent waste heat and rain droplets, though promising in the field of environmental energy sustainability, is still far from practice due to its low electrical output owing to dielectric structure irrationality and unscalability. Here we present atypical upcycling of ambient heat and raindrop energy via an all-in-one non-planar energy harvester, simultaneously increasing solar pyroelectricity and droplet-based triboelectricity by two-fold, in contrast to conventional counterparts. The delivered non-planar dielectric with high transmittance confines the solar irradiance onto a focal hotspot, offering transverse thermal field propagation towards boosted inhomogeneous polarization with a generated power density of 6.1mW m-2 at 0.2 sun. Moreover, the enlarged lateral surface area of curved architecture promotes droplet spreading/separation, thus travelling the electrostatic field towards increased triboelectricity. These enhanced pyroelectric and triboelectric outputs, upgraded with advanced manufacturing, demonstrate applicability in adaptive sustainable energy harvesting on sunny, cloudy, night, and rainy days. Our findings highlight a facile yet efficient strategy, not only for weather-adaptive environmental energy recovery but also in providing key insights for spatial thermal/electrostatic field manipulation in thermoelectrics and ferroelectrics.

Thermoelectric generator based on anisotropic wood aerogel for low-grade heat energy harvesting

• A CNT/PEDOT-decorated thermoelectric network is constructed from wood-based framework. • The anisotropic structure is advantageous to convert low-grade heat energy. • Ordered porous structure and energy filtering effect enhance the TE performance. • Successful application as a device for waste heat energy harvesting and conversion. Thermoelectric generators (TEGs) have received increasing attention due to their potential to harvest low-grade heat energy (<100 °C) and provide power for the Internet of Things (IoT) and wearable electronic devices. Herein, a wood-based ordered framework is used to fabricate carbon nanotube/poly(3, 4-ethylenedioxythiophene) (CNT/PEDOT) wood aerogel for TEG. The prepared CNT/PEDOT wood aerogel with an anisotropic structure exhibits a low thermal conductivity of 0.17 W m −1 K −1 and is advantageous to develop a sufficient temperature gradient. Meanwhile, CNT/PEDOT composites effectively decouple the relationship between the Seebeck coefficient and electrical conductivity by energy filtering effect to enhance thermoelectric (TE) output properties. The vertical TEG assembled by the CNT/PEDOT wood aerogels reveals an output power of 1.5 μW and a mass-specific power of 15.48 μW g −1 at a temperature difference of 39.4 K. Moreover, the layered structure renders high compressibility and fatigue resistance. The anisotropic structure, high mechanical performance, and rapid thermoelectric response, enabling the TEG based on CNT/PEDOT wood aerogel offer opportunities for continuous power supply to low-power electronic devices.

Multi-objective optimization of pyroelectric thermal–electrical cycles

Pyroelectric thermal–electrical cycles enable a class of solid-state heat engines that convert waste heat to electrical energy. This article numerically investigates thermal-to-electrical energy conversion in a PbZr0.52Ti0.48O3 (PZT) pyroelectric layer near room temperature and optimizes operating parameters to maximize the electrical energy output. A general thermodynamic cycle is modeled after the prototypical pyroelectric Ericsson cycle—implemented based on the Ginzburg–Landau–Devonshire theory—with variable operating temperature range, and heating/cooling and charging/discharging time intervals. We used a Pareto optimization approach to simultaneously maximize electrical energy density and power density for different PZT sample and cycle parameters. The evaluated Pareto optimal fronts showcase the possibility of achieving multiple optimal solutions and highlight the trade-off between output energy density and power density in pyroelectric energy conversion. Specifically, we demonstrate that a 4× enhancement in power density is achievable with a less than 10% reduction in energy density for the same sample and operating conditions primarily by optimizing heat transfer. The multi-objective optimization approach and results presented in this study could provide a framework to facilitate the design and operation of pyroelectric cycles for waste heat energy harvesting systems.

Prospects and requirements for thermophotonic waste heat energy harvesting

Thermophotovoltaic (TPV) power generators offer great possibilities for thermal energy conversion when thermal sources with temperatures nearing or exceeding 1000 K are available. While the power density of conventional TPV systems is generally determined by Planck’s law in the far field, their fundamental performance is known to be dramatically affected by near field effects between the thermal emitter and the photovoltaic cell. Another potentially disruptive enhancement to the performance may be reached by transforming the thermal emitter to exploit electroluminescence. Taking advantage of an electroluminescent emitter as the source of radiation fundamentally alters the thermodynamics of the system. This allows boosting the achievable power densities by orders of magnitude, and also provides access to electroluminescent coolers, thermophotonic (TPX) heat pumps, and TPX power generation devices that can outperform both TPV and thermoelectric heat engines, especially at the low-grade waste heat (LGWH) temperature range (300–500 K) containing in total the majority of recoverable energy. In reality, functional TPX devices are yet to be demonstrated experimentally, due to several material and design bottlenecks. Here, we discuss the thermodynamics, ideal characteristics and advantages of TPX heat engines, and quantify how non-idealities such as non-radiative recombination, optical and resistive losses affect their performance. Our results suggest that, at LGWH temperatures, TPX heat engines start to outperform the best TPV systems when reaching quantum efficiencies of the order of 90%; beyond this threshold, TPX systems become increasingly efficient and powerful. • Showing the promise of thermophotonic (TPX) heat engines (HEs) for heat recovery. • Capturing TPX-HEs’ thermodynamics by developing and using a holistic model. • Quantifying the impact of non-radiative recombination, optical and resistive losses. • TPX-HEs outperform idealized thermophotovoltaic systems at low temperatures (<600 K). • Functional TPX-HEs are within reach with existing semiconductor technologies.

Extensive Analysis on the Thermoelectric Properties of Aqueous Zn-Doped Nickel Ferrite Nanofluids for Magnetically Tuned Thermoelectric Applications.

Because of the ever-increasing consumption of energy, higher-efficiency thermoelectric materials are in more demand. In this regard, initially, ZnxNi(1-x)Fe2O4 nanoparticles were synthesized using a co-precipitation technique and investigated using Rietveld refinement and Brunauer-Emmett-Teller (BET) analyses. Then, they were dispersed in water to obtain stable 1 vol % of aqueous ZnxNi(1-x)Fe2O4 nanofluids and their viscous, electrical, thermal, and thermoelectric properties were analyzed in the absence and presence of a magnetic field. The Rietveld refinement revealed the formation of single phase spinel ferrite structures and cationic distribution of ZnxNi(1-x)Fe2O4 nanoparticles, whereas BET analysis revealed the surface area of the nanoparticles. The viscosity studies proved the pseudo-plastic shear thinning behavior and dipole-dipole interactions of ZnxNi(1-x)Fe2O4 nanofluids. The electrical conductivity, thermal conductivity, and Seebeck coefficient studies revealed that the maximum enhancement was observed for the Zn0.2Ni0.8Fe2O4 nanofluid, which was attributed to the enhanced electrical double layer formation and Brownian motion of nanoparticles in the nanofluid. The enhancement in the properties of synthesized nanofluids in the presence of a magnetic field was attributed to the formation of chain-like structures, which was substantiated through the magneto-viscosity studies. The thermoelectric energy conversion efficiency of ZnxNi(1-x)Fe2O4 nanofluids was calculated which showed that the maximum enhancement of 27% was observed in the Zn0.2Ni0.8Fe2O4 nanofluid at 770 G. The observed results proved that the synthesized nanofluids are magnetically tunable thermoelectric materials which are suitable for waste heat energy harvesting applications.

Preparation of highly efficient thermoelectric Bi-doped Mg2Si0.55-xSn0.4Gex (x = 0 and 0.05) materials with a scalable mechanical alloying method

Mg2Si-type compounds are highly promising materials for use in thermoelectric devices for waste heat energy harvesting. These compounds have great potential because they exhibit high thermoelectric performance, but the scalability of their synthesis is a major issue for applications. In this study, Bi-doped Mg2Si0.55-xSn0.4Gex (x = 0 and 0.05) materials were prepared by mechanical alloying combined with hot press sintering in order to increase the mass capabilities of their synthetic route compared with the typical solid state reaction. The optimum thermoelectric properties were achieved for the best Mg2Si0.57Sn0.4Bi0.03 and Mg2Si0.53Sn0.4Ge0.05Bi0.02 compositions by ball milling for 32 h and the maximum figure of merit (ZT) values were 1.07 and 1.2, respectively.

High thermoelectric properties achieved in environmentally friendly sulfide compound Bi2SeS2 by nanoenginnering

The sulfide compound Bi2SeS2 is an environmentally friendly thermoelectric material, which is as an analogy of the traditional compound Bi2S3. Here, a high ZT value of 1.04 at 773 K is obtained through synergistically tuning the electrical transport properties by using Cu and I as the dual carrier providers and suppressing the lattice thermal conductivity by forming the Cu-rich nano-precipitates. The dual carrier providers lead to exclusively high electrical conductivity and hence a large power factor over 650 μWm−1K−2 at 773 K. The atomic resolved annular dark field STEM reveals the interstitial Cu and S deficiency would result into the formation of BiCuS2 or Cu2S nano-precipitates and embed in the lattice of Bi2SeS2, serving as strong phonon scattering. This work suggested that nanostructured Bi2SeS2 is very promising for waste heat energy harvesting in the future.

A Traveling Wave Thermoacoustic Engine—Design and Test

Abstract The demand for clean, sustainable, and cost-effective energy continues to increase due to global population growth and the corresponding use of consumer products. The provision of heat to a thermoacoustic prime mover results in the generation of an acoustic wave that can be converted into electrical power. Thermoacoustic devices offer highly reliable and transportable power generation with low environmental impact using a variety of fuel sources. This paper focuses on the design and testing of a single-stage, traveling-wave, thermoacoustic engine. The system configuration, component design, and integration of sensors will be described. Performance testing and system analysis show that for a 300 W heat source, the thermoacoustic machine generates a 54 Hz acoustic wave with a thermal efficiency of 7.8%. The system’s acoustic power output may be increased by 84% through improved heat exchanger design. Tuning of the acoustic system and optimization of the bi-directional turbine merit attention to realize an applicable waste heat energy harvesting system.

Enhancement of power generation of thermoelectric generator using phase change material

This paper demonstrates a thermoelectric generator (TEG) that embeds phase change material (PCM) for waste heat energy harvesting. In this TEG module, a volume of molten carbonate salt is encapsulated in a cuboid polydimethylsiloxane (PDMS) body. In order to study the effect of embedded PCM on the TEG performance, we compared the performance of TEGs with and without PCM. The results show that a higher output voltage and a longer energy harvesting time can be reached in TEG with PCM in compared with the corresponding values in the TEG without PCM once the heat source stops supplying heat. Especially, the relative increase of the total electricity by adopting the PCM is as large as 25%. Our work proposes an effective and feasible way to enhance the performance of the TEG system by application of the PCM.

Electricity from thermal sources

Applied Physics It is desirable to harvest as much energy as possible from processes that produce useful amounts of heat and convert it from waste into electrical power. Thermoelectrics and thermophotovoltaics can harness and convert heat waste but tend to operate at high temperatures. Davids et al. designed and fabricated a complementary metal-oxide semiconductor infrared photonic device that can harvest and recover energy from low-temperature thermal sources (see the Perspective by Raman). Using a new conversion mechanism, they experimentally demonstrate large thermal-to-electrical power generation in a bipolar grating-coupled tunneling device, rivaling the best thermoelectric devices. The device design could be used for energy harvesting of waste heat and the development of compact thermal batteries. Science , this issue p. [1341][1]; see also p. [1301][2] [1]: /lookup/doi/10.1126/science.aba2089 [2]: /lookup/doi/10.1126/science.aba8976

Experimental study of Thermoelectric Energy Harvesting

Waste heat energy harvesting aims to supply electricity to electric or electronic systems from different energy sources present in the environment without grid connection or utilization of batteries. These energy sources are solar (photovoltaic), movements (kinetic), radio-frequencies and thermal energy (thermoelectricity). The thermoelectric energy harvesting technology exploits the Seebeck effect. This effect describes the conversion of temperature gradient into electric power at the junctions of the thermoelectric elements of a thermoelectric generator (TEG) device. This device is a robust and highly reliable energy converter, which aims to generate electricity in applications in which the heat would be otherwise dissipated. The significant request for thermoelectric energy harvesting is justified by developing new thermoelectric materials and the design of new TEG devices. Potential TEG applications as energy harvesting modules are used in medical devices, sensors, buildings and consumer electronics. Present work is experimental study and analysis of thermoelectric energy harvesting and their low-power applications, and calculation of figure of merit which is dimensional less number for deciding harvesting efficiency.

Motorcycle Waste Heat Energy Harvesting Using Thermoelectric Generators

Meeting the increasing global demand for energy coupled with the depletion of fossil fuel sources has created breakthroughs in research on waste heat energy harvesting devices. By utilizing waste heat, energy consumption does not grow and is efficiently used instead. Harvesting energy from automobiles has promising outcomes for the application of thermoelectric generators (TEGs). Heavy duty diesel engines, pick-up trucks, sport bikes and model airplanes are involved in research attempting to do away with heavy batteries or alternators. For this study, a single cylinder, 100 cc Honda EX5 Dream, which is also known as ‘Kapcai’, was used to study the viability of installing TEGs for waste heat recovery in underbone of the motorcycle chassis. The natural convection passive cooling system of fin was used to dissipate heat for cold side of the TEGs to maintain temperature difference across TEGs of the motorcycle waste heat recovery system. Two currently commercially available TEG modules were used and were connected in series and parallel in order to obtain output power. Results for a single module of each of the two TEGs testing recorded a temperature gradient of 57.5 °C and 62.7 °C with open circuit voltage of 1.677 V and 1.704 V, respectively. The highest temperature difference and output voltage were recorded at 73.2 °C and 4.2 V in series arrangement for both the TEGs. In the same arrangement, the highest power output obtained was 551.0 mW. The outcomes from this field testing shows the applicability of waste heat recovery from the underbone chassis of a typical motorcycle in charging small portable devices such as smartphones or power banks for the rider of motorbike.

Energy harvesting from household heat sources using a thermoelectric generator module

Inefficiency in energy usage has led to the subject of energy harvesting which simply means recycling dissipated waste energy into another useful form of energy. This paper presents the harvesting of waste thermal energy from household heat sources (kerosene stove and generator exhaust pipe) as an electrical energy. Thermoelectric generator (TEG) modules (TGM-161-1.2-2.0) and aluminium heat sinks were constructed and placed close to the heat sources for waste heat harvesting. The hot and cold side temperatures of the TEG modules were measured along with the corresponding output voltages and currents, while the power and energy harvested were estimated. The harvesting of energy from the stove yielded means of 1.532 ± 0.091 V, 0.388 ± 0.003 A, 0.597 ± 0.039 W and 536.87 ± 34.98 J, subject to an average temperature difference of 84.59 ± 3.64 °C. For the generator exhaust pipe, average values of 1.28 ± 0.074 V, 0.285 ± 0.007 A, 0.367 ± 0.029 W and 330.62 ± 26.15 J with an average temperature difference of 62.31 ± 4.88 °C were achieved. The obtained results agreed with previous studies on energy harvesting using TEG modules. This work revealed the potential of waste heat energy harvesting using TEG technology.Keywords: Waste heat; temperature; thermoelectric generators; heat source; energy harvesting