Materials For Waste Heat Recovery Research Articles

Band convergence strategy to improve thermoelectric performance in Ti-Doped AgSbTe2

AgSbTe2 is one of promising material for waste heat recovery in the lower-medium (450–600 K) temperature range. However, its development is hindered by the formation of Ag2Te. In this study, we employed a mechanical alloying method to synthesize samples, significantly reducing the Ag2Te. Density functional theory (DFT) confirms that Ti doping in AgSbTe2 samples leads to the involvement of multiple valence bands in transport and decrease the energy offset between the light valence band and the primary valence band. Therefore, the Seebeck coefficient (S) increases from the value of 245 μV/K in Ag1.05SbTe2 to 270 μV/K in the Ag1.05Sb0.98Ti0.02Te2 samples at 473 K. A maximum ZT value of ∼1.28 at 523 K and an average ZT value of ∼0.97 within 323–548 K are obtained in Ag1.05Sb0.99Ti0.01Te2.

Recent advances, challenges, and perspective of copper‐based liquid‐like thermoelectric chalcogenides: A review

AbstractAs a group of emerging liquid‐like thermoelectric materials for waste heat recovery into useful energy, di‐chalcogenides Cu2(S, Se, Te) have been considered as superionic thermoelectric materials. Due to their highly disordered degree of Cu‐ion in the crystal lattice, Cu2(S, Se, Te) compounds can exhibit ultralow thermal conductivity, and in the meantime, their rigid sublattice can decently maintain the electrical performance, making them distinct from other state‐of‐the‐art thermoelectric materials. This review summarizes the well‐designed strategies to realize the impressive performance in thermoelectric materials and their modules by linking the adopted approaches such as defect engineering, interfaces, nano‐porous inclusions, thin films, dislocations, nano‐inclusions, and polycrystalline bulks etc., with the moderate design of the device. Some recent reports are selected to outline the fundamentals, underlined challenges, outlooks, and future development of Cu2(S, Se, Te) liquid‐like thermoelectric materials. We expect that this review covers the needs of future researchers in choosing some potential materials to explore thermoelectricity and other efficient energy conversion technologies.image

Preparation and characterisation of sodium nitrate/stone-sawing mud shape-stabilized phase change materials for medium-high temperature thermal energy storage

Stone-sawing mud (SSM) is a solid waste generated during stone processing, with a presently estimated global production of 30 million m3. SSM is usually disposed of in the stone yard, occupying a large area of land and causing serious dust and water pollution. In this study, a novel shape-stabilized composite phase change material (ss-CPCM) containing SSM loaded with NaNO3 was prepared using the mixing and sintering method for medium-high temperature thermal energy-storage applications. The ss-CPCM retained 50 wt% NaNO3 without leakage. X-ray diffraction analysis showed good chemical compatibility between the SSM and NaNO3, and microscopy analysis demonstrated that NaNO3 was uniformly distributed within the SSM structure. The compressive strength of the ss-CPCM reached 23.14 MPa. The melting temperature and latent heat of the ss-CPCM are approximately 306.78 °C and 79.86 J·g−1, respectively, and no significant variations are observed after thermal cycling. The energy storage density of the material is 444.86 J·g−1 in the range of 50–400 °C, and its thermal conductivity is 0.696 W (m·K)−1. Furthermore, the thermal conductivity of the composites reached 2.421 W (m·K)−1 with the addition of 10 wt% of graphite. Hence, the NaNO3/SSM ss-CPCM is considered a promising material for waste heat recovery, thereby providing a valorisation method for the resource utilisation of SSM.

Computational thermodynamics‐assisted design of nitrate‐based phase change materials for waste heat recovery

Computational thermodynamics‐assisted design of nitrate‐based phase change materials for waste heat recovery

Improving the oxidation resistance of thermoelectric Mg2Si leg with silica coating

Due to the volatile and oxidation nature of Mg, Mg2Si based thermoelectric legs degrade faster when exposed to ppm level of oxygen during mid-temperature range operation. Here, we have established a modified sol–gel technique to get an oxidation-resistant SiO2 coating on the Mg2Si thermoelectric legs. The cyclic thermal ageing stability, oxidation resistance, and thermoelectric properties of the SiO2 coated Mg2Si have been investigated. The SiO2 coated Mg2Si is stable after ageing for 200 h at 823 K in air, and there is no degradation in the thermoelectric properties due to atmospheric exposure. It is thus a promising technique to increase the life span of Mg2Si based thermoelectric materials for waste heat recovery in automobiles and heavy industries.

Phase change materials for waste heat recovery in internal combustion engines: A review

Since most of the energy consumed by an internal combustion engine (ICE) is wasted, heat recovery from the exhaust and coolant is considered as a promising technology for improving the engine efficiency. The systems that used for recovering wasted thermal energy are called waste heat recovery (WHR) systems. However, most WHR methods suffer from main drawbacks such as difficult implementation, low thermal controllability and poor thermal storability. These drawbacks could be overcome by integrating thermal energy storage (TES) systems with ICEs. TES relies on sensible heat, latent heat and thermochemical storage. Latent heat storage method with phase change materials (PCMs) is the most utilized in ICEs because of its good controllability and high storage capacity. Therefore, this review presents the applications of TES with PCMs for recovering waste energy in ICEs. The literature shows that PCMs could be incorporated into different ICEs systems including exhaust recovery systems, cooling recovery systems, catalytic converters, diesel generators, evaporator and pressure regulators, additional diesel heaters, and cylinder's body. The previous studies on these systems show the potential of TES with PCMs in storing and recovering waste heat. Moreover, it is shown that the recovered heat by PCMs is mainly used for purposes of engine pre-heating during cold-start, maintaining hot temperature of catalysts for better conversion efficiency, and heating domestic and industrial water. Finally, the problems of PCMs with ICEs such as bulky system problem, high initial cost, corrosion issues, and poor stability; are also discussed in this review.

Preparation, characterization and performance of paraffin/sepiolite composites as novel shape-stabilized phase change materials for thermal energy storage

In this paper, the paraffin/sepiolite composites were fabricated as novel shape-stable phase change materials (SSPCMs) by vacuum impregnation for thermal energy storage. The structure-property relationships and comprehensive performance of sepiolite-based composite SSPCMs prepared with/without treatment of sepiolite from three mineral deposits were investigated. Compared with the natural sepiolite (SEP), the sepiolite after the purification and acidification treatment (TSEP) is a more suitable supporting carrier for paraffin wax. The prepared paraffin/TSEP composite SSPCM exhibits a significant promotion in absorption mass of paraffin and phase change latent heat. The maximum increase in latent heat of melt and crystallization is 78.32 % and 77.47 %. Simultaneously, the prepared sepiolite-based SSPCMs can reach up to 35.18 % paraffin loading. Its highest latent heat of melting and freezing is 60.12 J/g and 57.09 J/g, respectively, and the relative enthalpy efficiency is as high as 94.45 %. In addition, the sepiolite-based composite SSPCMs show good thermal stability and chemical stability according to the thermal cycling test. Moreover, it is demonstrated that sepiolite-based SSPCMs can slow down the spread of heat by absorbing heat energy and have reliable energy storage and temperature regulation performance. Therefore, the inexpensive and abundant sepiolite can be applied in phase change materials for waste heat recovery and temperature regulation. • Paraffin/sepiolite phase change material was prepared by vacuum impregnation. • Sepiolite from three mineral deposits was utilized as support material. • The latent enthalpy of the PCM was improved by acid activation of sepiolite. • The PCM exhibits good phase transition performance and thermal stability.

Improving the thermal energy storage capability of diatom-based biomass/polyethylene glycol composites phase change materials by artificial culture methods

We report a novel shape-stabilized phase change materials (SSPCMs) made from polyethylene glycol (PEG) and diatom-based biomass. The diatom materials were prepared by artificial culture and simple acid pickling and sintering. Scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FT-IR), X-ray diffractometry (XRD) and polarizing microscopy (POM) were used to characterize the prepared materials, such as their chemical composition, morphology, crystallization performance and so on. The results indicated that no chemical reaction occurred between PEG and diatom-based biomass during the preparation process, but the crystalline regions of PEG were decreased. Differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and thermal cycling tests showed that the SSPCMs with sintered diatom frustules as the supporting material have a good phase change performance and thermal stability in the PEG solid-liquid phase transition region. The maximum latent heat values in the melting and crystallization processes are around 121.54 J/g and 127.20 J/g respectively, and the relative enthalpy efficiency reaches up to ~98.1%. At the same time, the prepared SSPCMs have reliable heat storage and temperature-regulated performance. Our study demonstrates the great potential and significance for the practical application of artificially cultured diatom-based biomass in phase change materials for waste heat recovery and temperature regulation.

Multiple-Criteria Decision Analysis and characterisation of phase change materials for waste heat recovery at high temperature for sustainable energy-intensive industry

A latent heat storage system based on Phase Change Materials (PCMs) is proposed to increase the energy and environmental efficiency by recovering and storing waste heat from combustion gases or other surplus sources at in the energy-intensive industries (EII), currently unused. The final configuration design is specifically adapted to the plant operational requirements, by means of a methodology combining the search of the best conceptual design and a proper selection of core PCMs. To that end, a selection of suitable PCM is carried out by using characterisation techniques and thermal stability testing. Furthermore, relevant key factors are weighted by an in-house Multiple-Criteria Decision Analysis (MCDA) to define the most promising design options to be implemented in two plants belonging to the EII sector. For the ceramic sector, the design resulted in a shell-and-tube system with 1188 kg of a PCM melting at 885 °C and encapsulated in double concentric tubes, involving a storage capacity of 227 MJ. Similarly, 1606 kg of PCM, whose phase-change temperature is 509 °C, is selected for the steel sector providing a PCM-TES system capable to store 420 MJ.

Current Research and Future Prospective of Iron-Based Heusler Alloys as Thermoelectric Materials

In last two decades, Half Heusler (HH) alloys proved themselves as a potential candidate for thermoelectric devices. This is not only due to their structural capability for demonstrating and integrating various new concepts to enhance the thermoelectric figure of merit (ZT) but also high thermal stability which is advantageous for thermoelectric devices. However, most of the efficient HH alloys consist of expensive elements which resist their commercial application. This encouraged the development of highly efficient Fe-based Full Heusler (FH) alloys which have almost similar advantages of HH alloys along with the economical benefit. The main challenge in Fe-based FH as efficient thermoelectric as HH alloys is the reduction of lattice thermal conductivity and optimization of carrier concentration. This could be done through the use of concepts like bulk nanostructuring/bulk nanocomposite and more recently introduced Panoscopic approach or all scale hierarchical architecturing engineering and band structure engineering. In this review, we firstly discussed about the current progress on Fe-based FH alloys along with the challenges in enhancing the figure of merits. Herein, we also discussed various approaches adopted in bulk as well as nanostructured FH alloys to circumvent the interdependency of parameters in achieving higher ZT. It ends with discussion of the future trends for Fe-based FH thermoelectric materials for waste heat recovery. Through this review, we not only explain the probability of finding efficient thermoelectric in Fe-based FH alloys but also give a blueprint for enhancing ZT in many other thermoelectric materials.

Polycrystalline ZrTe5 Parametrized as a Narrow-Band-Gap Semiconductor for Thermoelectric Performance

The exotic transport physics of single-crystalline transition-metal pentatellurides has been debated for years. The authors discover that in fact polycrystalline samples show the same unusual properties, and that viewing these compounds as semiconductors with bipolar conduction explains their behavior. This insight allows for the prediction and optimization of their thermoelectric properties. Considering the dearth of work on materials for waste-heat recovery at lower temperatures, and on generators employing a single compound for both legs, this study could change the way we think about what is possible in thermoelectric applications.

Reduction of Specimen Size for the Full Simultaneous Characterization of Thermoelectric Performance

The successful implementation of thermoelectric (TE) materials for waste heat recovery depends strongly on our ability to increase their performance. This challenge continues to generate a renewed interest in novel high TE performance compounds. The technological difficulties in producing homogeneous ingots of new compounds or alloys with regular shape and a size sufficiently large to prepare several samples that are usually needed for a separate measurement of all TE parameters are well known. It creates a situation whereby material performance could be critically over- or under-evaluated at the first stages of the research process of a new material. Both cases would equally lead to negative consequences. Thus, minimizing the specimen size yet keeping it adequate for accurate material characterization becomes extremely important. In this work we report the experimental validation of reliable simultaneous measurements of the four most relevant TE parameters on a single bismuth telluride alloy based specimen of 4 mm × 4 mm × 1.4 mm in size. This translates in roughly 140 mg in weight for one of the heaviest TE materials, as was used in this study, and <100 mg for most others. Our validation is based on comparative measurements performed by a Harman apparatus (ZT-Scanner) on a series of differently sized specimens of hot extruded bismuth telluride based alloys. The Seebeck coefficient, electrical resistivity, thermal conductivity and the figure of merit were simultaneously assessed from 300 K to 440 K with increments of 20 K, 15 K, 10 K, 5 K, and 1 K. Our choice of a well-known homogeneous material has been made to increase measurement reliability and accuracy, but the results are expected to be valid for the full TE characterization of any unknown material. These results show a way to significantly decrease specimen sizes which has the potential to accelerate investigation of novel TE materials for large scale waste heat recovery.

A Review on Electroactive Polymers for Waste Heat Recovery.

This paper reviews materials for thermoelectric waste heat recovery, and discusses selected industrial and distributed waste heat sources as well as recovery methods that are currently applied. Thermoelectric properties, especially electrical conductivity, thermopower, thermal conductivity and the thermoelectric figures of merit, are considered when evaluating thermoelectric materials for waste heat recovery. Alloys and oxides are briefly discussed as materials suitable for medium- and high-grade sources. Electroactive polymers are presented as a new group of materials for low-grade sources. Polyaniline is a particularly fitting polymer for these purposes. We also discuss types of modifiers and modification methods, and their influence on the thermoelectric performance of this class of polymers.

(Invited) Impact of Spark Plasma Sintering on the Thermoelectric Properties of Advanced Nanostructured Materials for Waste Heat Recovery

The rapid development of nanomaterials in the past decade has provided a possibility of directly converting waste heat back to electricity based on the thermoelectric Seebeck effect. In the past four years, we have developed a transformative approach to pioneered low cost and scalable solution-phase growth methods to mass produce thermoelectric nanowires and nanowire heterostructures to match the physical and economic magnitudes of energy use and economical entertainment in the manufacture/recycling. We have studied how spark plasma sintering can help to improve the density, mechanical strength, and electrical conductivity of these nanowires and nanowire heterostructures while minimizing the phase impurity and grain growth. These nanostructured thermoelectric materials show a significantly enhanced performance compared to the bulk crystals based on the quantum confinement and energy filtering.

Right sizes of nano- and microstructures for high-performance and rigid bulk thermoelectrics.

In this paper, we systematically investigate three different routes of synthesizing 2% Na-doped PbTe after melting the elements: (i) quenching followed by hot-pressing (QH), (ii) annealing followed by hot-pressing, and (iii) quenching and annealing followed by hot-pressing. We found that the thermoelectric figure of merit, zT, strongly depends on the synthesis condition and that its value can be enhanced to ∼ 2.0 at 773 K by optimizing the size distribution of the nanostructures in the material. Based on our theoretical analysis on both electron and thermal transport, this zT enhancement is attributed to the reduction of both the lattice and electronic thermal conductivities; the smallest sizes (2 ∼ 6 nm) of nanostructures in the QH sample are responsible for effectively scattering the wide range of phonon wavelengths to minimize the lattice thermal conductivity to ∼ 0.5 W/m K. The reduced electronic thermal conductivity associated with the suppressed electrical conductivity by nanostructures also helped reduce the total thermal conductivity. In addition to the high zT of the QH sample, the mechanical hardness is higher than the other samples by a factor of around 2 due to the smaller grain sizes. Overall, this paper suggests a guideline on how to achieve high zT and mechanical strength of a thermoelectric material by controlling nano- and microstructures of the material.

Fundamental study on development of latent heat storage material for waste heat recovery of biomass gasification

Recently, latent heat thermal energy storage system (LHTES) has gained attention in order to utilize middle temperature (373~573 K) waste heat from biomass gasification. This paper has investigated thermo- physical properties of erythritol [CH₂OHCHOH CHOHCH₂OH], mannitol [CH₂OH (CHOH)₄CH₂OH] and their compounds as phase change materials (PCMs). The differential scanning calorimetry (DSC) was applied to measure the melting point and latent heat of these PCMs. Also the melting and solidification characteristics of these PCMs were observed in a glass tube with a digital camera. In the DSC measurement, when the amount of mannitol content was more than 40 mass%, the melting point of these compounds show two melting points. The experimental results showed that the velocity of melting and solidification were different for every mixture ratio of compounds. These compounds had the super-cooling phenomenon during the solidification process.

Modification of fly ash as a carrier of paraffin wax based phase change energy storage material for waste heat recovery

Modification of fly ash as a carrier of paraffin wax based phase change energy storage material for waste heat recovery

Large enhancement in the thermoelectric properties of Pb0.98Na0.02Te by optimizing the synthesis conditions

PbTe is known as a good thermoelectric material for waste heat recovery in the temperature range of 500 to 900 K. While various approaches such as nanostructuring for thermal conductivity reduction, resonant impurities, and band convergence by alloying for power factor enhancement have been proposed recently for enhancing the thermoelectric properties of PbTe, a systematic study on optimizing the synthesis conditions is also crucial to find a better base material, upon which those new approaches can be applied to further improve the material. In this paper, we systematically investigate the effect of various hot-press conditions on the thermoelectric properties of p-type 2% Na-doped PbTe, by varying the hot-press pressure from 70 to 130 MPa and the sintering time from 0.5 to 2 h. It is shown that the micro- and nano-scale structures in the hot-pressed material can be controlled by changing the sintering time and pressure. We demonstrate that by optimizing the hot-press conditions, the thermoelectric figure of merit of p-type 2% Na-doped PbTe can be enhanced up to zT = 1.74 at 774 K, which is about a 24% enhancement compared to the value of 1.4 presented by Pei et al. for the same material composition. Our electron transport modeling on bulk PbTe shows that this enhancement is due to the thermal conductivity reduction in both the electronic and lattice contributions. We believe that our findings can be accompanied with other recently-proposed techniques to further enhance the zT of this important thermoelectric material.

A copper-containing oxytelluride as a promising thermoelectric material for waste heat recovery

The new thermoelectric material BiOCuTe exhibits an electrical conductivity of 224 S cm−1 and a Seebeck coefficient of +186 μV K−1 at 373 K, together with an extremely low lattice thermal conductivity of ∼0.5 W m−1 K−1. This results in a ZT of 0.42 at 373 K, which increases to 0.66 at the maximum temperature investigated, 673 K.

Microstructure and thermal conductivity of surfactant-free NiO nanostructures

High purity, nanometer sized surfactant-free nickel oxide (NiO) particles were produced in gram scale using a solution combustion method and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), gas pycnometry and gas adsorption analysis (BET). The average particle size of the as-synthesized NiO increases significantly with the preheating temperature of the furnace, while the specific surface area decreases. A BET specific surface area of ∼100m2/g was obtained for NiO nanoparticles with size as small as 3nm synthesized at 300°C. The thermal conductivity (κ) of pressed pellets of the synthesized NiO nanoparticles obtained using spark plasma sintering (SPS) and uniaxial hot pressing is drastically decreased (∼60%) compared to that of NiO single crystal. This strong reduction in κ with particle size suggests the suitability of the synthesized surfactant-free NiO nanoparticles for use as nanoinclusions when designing high performance materials for waste heat recovery.