Waste Heat Recovery Applications Research Articles

Understanding the High Thermoelectric Performance of Mg3Sb2‐Mg3Bi2 Alloys

n‐Type Mg3Sb2‐Mg3Bi2 alloys are some of the most promising thermoelectric materials in the low–mid temperature range. While discovered relatively recently, these materials have garnered intense attention, and numerous papers from the international thermoelectric community have been published in a relatively short period of time. As with all materials, detailed insights into the underlying mechanisms that contribute to these alloys’ distinguished thermoelectric properties are important for future researchers to push the performance of this material to new heights. Herein, experimental studies on the role defects, synthesis conditions, electronic band structure, and microstructure along with future prospects arecompiled to establish a guide for fully exploiting the potential of this material system. Considering the limited number of n‐type thermoelectric materials with this performance for low‐grade heat recovery and cooling technologies, further development of the Mg3Sb2‐Mg3Bi2 alloys is an important step toward commercial applications of thermoelectric materials, including cooling technologies and waste heat recovery applications.

Emergy and eco-exergy analysis of different scenarios in waste heat recovery applications for electricity and fresh water generation

Emergy and eco-exergy analysis of different scenarios in waste heat recovery applications for electricity and fresh water generation

Optimization of the Adsorption/Desorption Contribution from Metal-Organic-Heat-Carrier Nanoparticles in Waste Heat Recovery Applications: R245fa/MIL101 in Organic Rankine Cycles

The efficient recovery of low temperature waste heat, representing from 25% up to 55% of the energy losses in industrial processes, still remains a challenge and even Organic Rankine Cycles (ORCs) experience a strong efficiency decay in such a low temperature operating range (T < 150 °C). In similar heat transfer processes, several nanofluids have been proposed as a solution for increasing heat transfer efficiency, but they produced only moderate enhancements of the heat transfer efficiency in comparison with pure fluids. This paper aims at numerically assessing the potential gain in efficiency deriving from the application of an unconventional type of nanoparticles, the metal-organic heat carriers (MOHCs), in the ORC field. In comparison with standard nanoparticles, these MOHCs make it possible to extract additional heat from the endothermic enthalpy of desorption, with a theoretically high potential for boosting the heat transfer capacity of ORC systems. In this paper a numerical model was developed and customized for considering the adsorption/desorption processes of the pure fluid R245fa (pentafluoropropane) combined with a crystal structure for porous chromium terephthalate (MIL101). The R245fa/MIL101 nanofluid behavior was experimentally characterized, defining proper semi-emipirical correlations. Then, an optimization procedure was developed, combining the numerical model with a PSO algorithm, to optimize the thermodynamic conditions in the ORC so as to maximize the contribution of desorption/absorption processes. The results confirm the increase in net power output (+2.9% for 100 °C) and in expander efficiency (+2.4% for 100 °C) at very low heat source temperature. The relevance of tuning the operating cycle and the nanofluid properties is also demonstrated.

A recent review on waste heat recovery methodologies and applications: Comprehensive review, critical analysis and potential recommendations

Due to global warming and environmental issues in recent times, the world's concern is oriented nowadays toward discovering new renewable energy sources and energy management methods. Particularly, researchers are emphasizing on heat recovery technologies and applications in both residential and industrial sectors. While there are plenty of review papers in the literature on the subject matter, there is always a necessity to update the literature with the new advancements in the field. In this context, the purpose of this paper is to present a recent and complete systematic comprehensive review along with critical analysis and potential recommendations related to waste heat recovery (WHR) methodologies and applications. In methodologies, heat exchangers, Rankine cycle and thermoelectric generators are studied. Moreover, applications of WHR are discussed in automotive, and in both residential and industrial zones. Studies show that the optimization of heat recovery systems lead to significant magnitudes of energy savings. On the other hand, hybrid heat recovery systems prove to be the most trending research subject nowadays. For future work, the negative effect of backpressure should be taken into consideration when recovering energy from exhaust gases of engines and power generators, and more importance should be given to hybrid systems.

Techno-economic performance of the 2-propanol/1-butanol zeotropic mixture and 2-propanol/water azeotropic mixture as a working fluid in Organic Rankine Cycles

The techno-economic performance of the novel 2-propanol/1-butanol zeotropic mixture and 2-propanol/water azeotropic mixture as a working fluid in Organic Rankine Cycles (ORC) for waste heat recovery applications is analyzed. The ORC with two different architectures is modeled in the Aspen Plus V.10 environment for heat recovery from hot gases at 250 and 350 °C with atmospheric and sub-atmospheric condensation scenarios. The effects of different heat source/sink conditions on the performance of zeotropic mixture are studied in detail to show under which condition the zeotropic mixtures may result in higher efficiencies. The propanol/butanol mixtures (P/B) rich in propanol and propanol/water mixtures (P/W) with composition near the azeotropic point can result in 15–75% higher overall efficiencies compared to toluene and MM. However, cyclopentane shows higher efficiencies than these mixtures when atmospheric condensation is considered. According to the economic assessment, the 55%P/45%W and 75%P/25%B mixtures lead to superior results for the atmospheric condensation scenario compared to other fluids. Also, it was found that only under a tailored boundary condition, the zeotropic mixture can perform superiorly compared to the most efficient component in the mixture.

Biomass-based shape-stable phase change materials supported by garlic peel-derived porous carbon for thermal energy storage

Phase change materials with low cost, good thermal stability, and excellent shape stability are urgent in energy storage. Herein, a novel shape-stable phase-change material (SSPCM) for thermal energy storage is developed based on activated garlic peel (AGP), derived from widespread and cheap garlic peels. The paraffin (PA)/AGP composite PCM is prepared via vacuum impregnation method. The scanning electron microscope results show that AGP has many grooves, and the pores of AGP are filled by paraffin wax. The specific surface area of AGP is up to 1309 m2/g. The phase change enthalpy in the melting and freezing process is 52.5 J/g and 51.9 J/g, respectively. Moreover, the prepared SSPCM exhibits satisfied shape stability, thermal stability, and waste heat storage ability. Also, the SSPCM has a low latent heat loss rate of about 1.5% after 200 thermal cycles. This work provides an economical and environmental method for synthesizing shape-stabilized phase-change materials based on biomass materials with potential applications in waste heat recovery and recycling.

A decision support model for waste heat recovery systems design in Data Center and High-Performance Computing clusters utilizing liquid cooling and Phase Change Materials

The Data Center (DC) and High-Performance Computing (HPC) sector is increasingly becoming one of the single largest energy consuming sectors in the energy system and the demand for new DCs is growing with the rising use of cloud-based services, social media and internet usage in general. DCs and HPC clusters employ energy intensive cooling in order to dissipate the generated heat from the Information Technology (IT) equipment. Conventionally, the cooling is almost exclusively done by air-based systems; however, the use of liquid based cooling has shown potential to increase computational efficiency of the systems and decrease cooling needs by operation above the free cooling limit. Furthermore, the liquid coolant can operate at higher temperatures allowing high temperature waste heat recovery. In addition, load shifting through Latent Thermal Energy Storage (LTES) will allow the non-controllable waste heat resource to be stored seasonally, thereby granting the ability to cover larger District Heating (DH) loads. In this work, a decision support model is developed that will take basic information regarding a HPC cluster or DC as inputs. The decision support model will provide a parameterized output that shows different configurations and design parameters that can be utilized for the system. The main outputs includes yearly energy savings, yearly cost savings and efficiency gains through the Power Usage Efficiency and the Energy Reuse Efficiency. The decision support model is demonstrated in a Danish case study. Electricity savings between 8.14 % and 10.8 % of the total cluster electricity consumption and a waste heat recovery potential of 85 MWh/year to 576 MWh/year are obtained. It is shown that if the DH covered is needed to be self-sufficient the configuration would require an LTES with PCM mass of 500 kg, but system configurations that operate as an addition to an existing local heating source shows increases in yearly energy savings of 332 % compared to self-sufficient configurations. The goal of the decision support model is to assist the design of future waste heat recovery applications through selection of system parameters including coolant temperatures, energy storage design parameters, DH supply temperatures and DH load coverage from the DC or HPC cluster.

Experimental Characterization of an Adaptive Supersonic Micro Turbine for Waste Heat Recovery Applications

Micro turbines (<100 kWel) are commercially used as expansion machines in waste heat recovery (WHR) systems such as organic Rankine cycles (ORCs). These highly loaded turbines are generally designed for a specific parameter set, and their isentropic expansion efficiency significantly deteriorates when the mass flow rate of the WHR system deviates from the design point. However, in numerous industry processes that are potentially interesting for the implementation of a WHR process, the temperature, mass flow rate or both can fluctuate significantly, resulting in fluctuations in the WHR system as well. In such circumstances, the inlet pressure of the ORC turbine, and therefore the reversible cycle efficiency must be significantly reduced during these fluctuations. In this context, the authors developed an adaptive supersonic micro turbine for WHR applications. The variable geometry of the turbine nozzles enables an adjustment of the swallowing capacity in respect of the available mass flow rate in order to keep the upper cycle pressure constant. In this paper, an experimental test series of a WHR ORC test rig equipped with the developed adaptive supersonic micro turbine is analysed. The adaptive turbine is characterized concerning its off-design performance and the results are compared to a reference turbine with fixed geometry. To create a fair data basis for this comparison, a digital twin of the plant based on experimental data was built. In addition to the characterization of the turbine itself, the influence of the improved pressure ratio on the energy conversion chain of the entire ORC is analysed.

Non-dimensional design optimization of annular thermoelectric generators integrated in waste heat recovery applications

The annular thermoelectric generators design facilitates the integration into conventional tubular heat exchangers which could enable their large-scale implementation in waste heat recovery applications for power generation. An analytical model is developed to identify the critical design parameters of annular thermoelectric generators (A-TEGs) integrated in heat exchangers. These parameters are found to be the diameter ratio, the P-to-N thickness ratio, and the fill ratio. The diameter and fill ratios are found to have a significant impact on the performance of the A-TEG system while the power output nearly plateaued at thickness ratios higher than 1.1. A novel dimensionless design factor (β) is proposed to guide the design optimization of the A-TEG system for maximized power generation. This design factor combines the diameter and fill ratios of the A-TEG design to define the locus over which the power output from the A-TEG system is always maximized. A detailed analytical model is developed and validated to simulate an A-TEG integrated heat exchanger for the purpose of optimizing the A-TEG design using the design factor (β). A parametric case study shows that at the optimum design factor, the material volume of the A-TEGs can potentially be reduced by 75% by decreasing the diameter and fill ratios with a reduction in the maximum power of only 11%. The study findings provide a useful tool to guide the efficient and cost-effective design of A-TEGs for waste heat recovery applications.

Potential of transcritical recompression Rankine cycle operating with CO2-based binary mixtures

CO2 transcritical Rankine cycle (CO2-TRC) has a great potential for many applications like concentrating solar power (CSP) and waste heat recovery due to advantages of using low- or medium-temperature heat sources and compact structures. However, the relatively low critical temperature of CO2 and the simple regenerative cycle layout limit the applicability to hot arid environmental conditions. In this work, a transcritical recompression Rankine cycle (TRRC) applying CO2-based binary mixture as working fluid is proposed to improve thermal performances. A thermodynamic model is developed and applied to estimate the potential of the cycle for CSP or waste heat recovery applications with ambient temperature in the range of 0–35 ℃. The results show that adding gaseous media (i.e. propane, H2S, R32 and R161) into CO2 increases the critical temperature and thus extends the condensation temperature range. The decreasing condensation pressure mainly contributes to the improvement of the optimal thermal efficiency, exergy efficiency and specific work of TRRC. Among the selected working fluids, the TRRC applying CO2-R32 shows the greatest potential under the medium-temperature heat source (e.g. turbine inlet temperature of 400 ℃) and relatively high ambient temperature (e.g. 15 ∼ 35 ℃). When the ambient temperature is 35 ℃, the corresponding thermal efficiency, exergy efficiency and specific work of the TRRC applying CO2-R32 are 32.77%, 58.99% and 36.93 kJ/kg, respectively, which are comparable to those of the pure CO2 TRRC at a lower ambient temperature of 15 ℃.

Enhanced thermal conductivity and shape stabilized LiNO3‐NaCl eutectic/exfoliated graphite composite for thermal energy storage applications

AbstractLiNO3 and NaCl salt mixtures are explored as phase change material (PCM) for thermal energy storage. We developed a process for synthesizing LiNO3 and NaCl eutectic mixture at room temperature and found that eutectic mixture consists of 88.8 wt% LiNO3 and 11.2 wt% NaCl salts. The latent heat and melting point of PCM are ~230°C and 302 kJ kg−1. Thermal conductivity of eutectic composition is measured with transient plane source (TPS) technique and value is 0.8 W m−1 K−1. We used thermochemically exfoliated graphite (ExG) in 5, 10, 15, and 20 wt% ratio with the developed eutectic to prepare PCM‐ExG composites to enhance thermal conductivity of pristine eutectic PCM. The maximum thermal conductivity of these PCM‐ExG composite PCMs is ~13.8 W m−1 K−1 for 20 wt% ExG and ~1400 kg m−3 density, ~16.5 times of pristine eutectic PCM. We observed that PCM‐ExG composite containing ExG ≥ 15 wt% retains liquid PCM inside the ExG pores, useful to reduce leakage problem of thermal energy storage vessel. The high thermal conductivity, high latent heat of fusion and suitable melting point of LiNO3‐NaCl eutectic PCM‐ExG composite PCM make it suitable for solar thermal energy storage and industrial waste heat recovery applications.

Analysis of Thermoelectric materials for heating applications in Automobiles

In today’s world with the technological advancements, all that has been considered as slags and waste can be utilized to its maximum therefore attaining sustainability. Thermoelectric devices are now being used in various applications including cooling and heating processes in electronics and automobiles. The choice of materials for these thermoelectric devices are essential in order to determine the parameters such as temperature gradient, thermo emf and total heat dissipated with the help of Seebeck, Peltier and Thomson co-efficients. The elements for the thermoelectric device are arranged by their thermo emf produced in the thermoelectric series. This has been taken into account for the selection of materials for the heating device, analyzed in this article. In certain cold countries, temperature can drop below 10°C, which is very much near its cloud point and pour point of petroleum fuels. Thermoelectric devices will thereby come to use in these places to maintain the temperature above the cloud point of the fuel. This study also focuses on another application of waste heat recovery in automobile engines to produce thermo emf, which can be utilized for small scale electronics in automobiles. In this study, materials are analyzed for the previously mentioned applications.

Direct integration of an organic Rankine cycle into an internal combustion engine cooling system for comprehensive and simplified waste heat recovery

Cogeneration systems based on internal combustion engines (ICE) provide decent efficiency and flexibility. In order to further improve the efficiency, organic Rankine cycle (ORC) can be used to convert high temperature (waste) heat from flue gas to electricity. There is a large amount of heat in jacket cooling at lower temperatures for which there is often no demand so it has to be rejected into the ambient. Previous systems trying to utilise this heat in the ORC cycle end up as too complex and expensive. This study introduces an innovative jacket cooling method. In the cooling system of an ICE, instead of typical water or oil-based heat transfer fluids, the working fluid of an ORC is used as the engine coolant, recovering the low-potential heat. Preheated organic fluid is then directly used in the bottoming ORC with further heat input from the flue gas. This concept allows utilising both low and high potential heat from the cooling of the ICE and from the flue gas recovery, while omitting the intermediate heat-transfer circuits commonly found in ORC waste heat recovery applications. Presented thermodynamic analysis shows a strong dependency of the ORC utilisation efficiency on cooling fluid allowed pressure in the ICE jacket and on the heat flow ratio between the coolant and the flue gas of the ICE. A baseline study with a specific 83 kWe ICE with the novel configuration provides an improvement of nearly 10 kW in comparison with 7 kW of an ORC utilising only flue gas. More general parametric analysis has shown the potential of the ORC power output improvement by more than 60% for specific ICE types and higher pressures and temperatures in the engine cooling circuit. In a cogeneration regime, these benefits in electrical power output come at the cost of a very slight decrease in overall efficiency.

Heat transfer of a Stirling engine for waste heat recovery application from internal combustion engines

This work analyzes the performances of a Stirling engine for waste heat recovery from the exhaust gas of internal combustion engines. Both experimental and numerical approaches were used. Experimental tests have been carried out on a research Stirling engine coupled to compression ignition engine by a thermally insulate pipe and a cap. Three configurations of coupling have been analyzed. Then, a three-dimensional numerical model has been developed by the authors to deepen the heat transfer between exhaust gas and working gas in the Stirling engine. The cap-heater system has been studied as a shell-and-tube heat exchanger. Experimental results have been set as boundary condition values for the cap, whereas for the heater, pressure and velocity have been evaluated using a 1D adiabatic model properly modified according to Stirling engine configuration. Velocity fields and temperature distribution inside the cap and heater have been analyzed, remarking that the layout of the heat exchanger becomes important for system efficiency. The method presented in this work could be useful to improve in wider terms the coupling between Stirling engine and internal combustion engines.

Application and Discussion of Flue Gas Waste Heat Recovery and Utilization Technology

Application and Discussion of Flue Gas Waste Heat Recovery and Utilization Technology

Conformal High-Power-Density Half-Heusler Thermoelectric Modules: A Pathway toward Practical Power Generators.

Thermoelectric generators (TEGs) exploiting the Seebeck effect provide a promising solution for waste heat recovery. Among the large number of thermoelectric (TE) materials, half-Heusler (hH) alloys are leading candidates for medium- to high-temperature power generation applications. However, the fundamental challenge in this field has been inhomogeneous material properties at large wafer diameters, insufficient power output from the modules, and rigid form factors of TE modules. This has restricted the transition of TEGs in practical applications for over three decades. Here, we successfully demonstrate large diameter wafers with uniform TE properties, high-power conformal hH TE modules for high-temperature application, and their direct integration on flue gas platforms, such as cylindrical tubes, to form large area flexible TEGs. This new conformal architecture design provides a breakthrough toward medium-/high-temperature TEGs over the conventional BiTe- and polymer-based flexible TEG design. A variable fill factor and greater flexibility due to the conformal design result in higher device performance as compared to conventional rigid TEG devices. Modules with 72-couple hH legs exhibit a device high-power-density of 3.13 W cm-2 and a total output power of 56.6 W under a temperature difference of 570 °C. These results provide a promising pathway toward widespread utilization of thermoelectric technology into the waste heat recovery application and will have a significant impact on the development of practical thermal to electrical converters.

Effect of carbon on the performance of red mud-molten salt composites for thermal management and waste heat recovery applications

• A novel composite material consisting of red mud, carbon and molten salt is investigated. • Carbon addition enhances the thermal conductivity by up to 13.45% (5 wt.%). • Energy density is only slightly reduced in a temperature range of 25-500 ℃. • However, the elastic modulus and coefficient of thermal expansion are affected. • These properties coupled with thermal cycling lead to progressive porosity increase. Red mud (RM) is a major waste of the aluminium industry with a present amount exceeding 4 billion tones, typically compacted in dams or dykes (stockpiles). This practice is highly problematic due to its high alkalinity and traces of heavy metals. Despite of many efforts, its present global utilization rate is only ∼15%. In this work, we attempt to enhance the thermal properties of previously reported novel composite phase change materials (CPCMs) based on RM, by adding graphite. The fabricated, carbon-containing, CPCMs demonstrate an overall good performance over the temperature range of 25 to 500 ℃. The latent heat ranges from 47.3 to 65.5 J/g, depending on salt and graphite contents. An optimal thermal conductivity is found to be up to 0.79 W/mK (25-500℃) on average. The specific heat capacity is on an average up to 1.23 J/(g ℃) when the PCM is in the solid phase (25-220 ℃) and 1.25 J/(g℃) when the PCM is in the liquid phase (220-500 ℃). No variations in the melting point or latent heat are observed after 96 cycles. Optimal energy storage density is calculated to be 1100 MJ/m 3 . Addition of graphite leads to a reduction in the coefficient of thermal expansion and the elastic modulus of the CPCM resulting in an increase in its porosity and thus a reduction in energy storage density. The working temperature of this novel CPCM makes it a cost-effective and compact solution for high-temperature heat storage/heat recovery applications.

Comparative Study of Conventional and Water Circulating-Heat Sink Cooling Base Thermoelectric Generator System for Optimum Solar Thermal Waste Heat Recovery

A novel technique for waste heat recovery in solar thermal power generation is investigated through experimentation and systematically presented. Power generation using Thermoelectric Generator (TEG) is a promising technique in waste heat recovery application. In this topology, TEG array is directly attached to the back of the solar Photovoltaic panel (model AP-AM15) to receive the transmitted heat at the back of the PV panel as waste heat. More so, a circulating water-heat sink is attached to the TEG cold side to improve the temperature gradient. Base on Seebeck effect, the TEG directly converts the temperature difference into electricity. The experimental result shows that efficiency between the range of 2.1% and 4.7% for the conventional cooling system while the output power approximately ranges between 0.05W and 0.47W, the circulating water-heat sink technique has efficiency ranging between 2.9% and 10.3% with output power between the range of 0.10W and 2.2W. The daily average increase in efficiency was found to be 263.76%. This shows that the daily average power is improved by a factor of 2.6376 with the water circulating water-heat sink technique. This is an indication of waste heat recovery from the solar thermal power generation.

Development of microdevices for the in-plane thermoelectric characterization of deposited films

Measuring the thermoelectric transport properties of a material is a prerequisite to determining its usefulness for application in waste heat recovery or cooling and the basis for devising improvement strategies. While well-established characterization methods exist for bulk samples, characterization of microscale samples remains challenging. This usually results in incomplete characterization such as restriction to study of the thermal transport properties, which can be misleading. While elaborate microdevices for complete thermoelectric characterization have been fabricated, a demanding transfer of the samples onto these devices is generally required and establishing sufficient electrical contact can be challenging in this case. Therefore a complete and transfer free in-plane characterization method for samples obtained by deposition processes was developed. The approach is based on expanding a well-established self-heating technique for the measurement of electrical and thermal conductivity to allow, in addition, for the measurement of the Seebeck coefficient. The fabrication exclusively involves photolithography and wet etching, with no need for other steps like electron-beam lithography and a lift-off process. The accuracy of the method is verified by numerical studies closely mimicking the actual measurement process, comparison to measurements on simultaneously deposited reference samples and results from literature.

Nearly isotropic transport properties in anisotropically structured n-type single-crystalline Mg3Sb2

As a top candidate for competing with the conventional n-Bi2Te3 thermoelectrics, Mg3Sb2-based materials have attracted increasing attentions for low-grade (<300 °C) waste heat recovery applications, due to the high thermoelectric performance, low cost, abundance and nontoxicity. Because of its anisotropic crystal structure as that of Bi2Te3, possible property anisotropy and the resultant similar requirement of texturing for preferential performance remain not entirely clear Mg3Sb2-thermoelectrics at working temperatures. This motivates the current work to focus on the transport-property anisotropy of n-type Mg3Sb2, centimeter-sized single crystals of which are successfully grown by a flux-assisted vertical Bridgman technique with a post-annealing under a Mg vapor pressure. This enables a revelation of nearly isotropic transport properties in this anisotropically structured material, guaranteeing reasonably high performances in polycrystalline materials achievable by cheap and scalable processing approaches such as powder-metallurgy. In addition, this work uncovers the strong lattice anharmonicity and large band degeneracy are respectively the origins for the low lattice thermal conductivity and superior electronic performance.