Band gap engineering in ruthenium‐based Heusler alloys for thermoelectric applications

In this work, systematic electronic structure calculations are performed on Ru₂TiZ alloys to examine their structural and thermoelectric related transport properties. The electronic structural properties are analyzed using the GGA and GGA+U as exchange correlational potential. The calculated lattice parameters agree very well with the existing experimental data, and the percentage of error is less than 1%. The electronic structural properties as analyzed, using the GGA exchange correlation scheme, reveal that these alloys can be semimetals. In the band structure, it is observed that ruthenium‐d and titanium‐d states are lying very close to the Fermi level. Hence, computations are performed again by including the Hubbard potential for d states of ruthenium and titanium. The calculated electronic structure in GGA+U reveals that all the 3 alloys are semiconductors with the indirect energy gap of 0.209, 0.175, and 0.259 eV, respectively, for Ru₂TiSi, Ru₂TiGe, and Ru₂TiSn. The electrical transport coefficients are calculated in both the GGA and GGA+U exchange correlational potential and reported. If experimentalists prove that these alloys are semiconductors, then all 3 alloys will be potential thermoelectric materials. If by experiment they are semimetals, only then Ru₂TiSn can be a good thermoelectric material. Doping of electron and hole for various concentrations is studied for Ru₂TiSn, and optimum doping level is reported.     

Understanding the origin of half‐metallicity and thermophysical properties of ductile La2CuMnO6 double perovskite

For first time, the magneto‐electronic structure with thermoelectric and mechanical properties of lanthanum‐based double perovskite La₂CuMnO₆ are investigated, using first‐principle methods. Generalized gradient approximation and modified Becke‐Jhonson potentials are integrated to figure out exchange‐correlation potential. The alloy stabilizes in cubic structure with ferromagnetic nature and determined structural parameters are consistent with experimental results. The band profile reveals the half‐metallic character, which is further confirmed by calculated electronic conductivities of up and down spin channels. The effect of pressure on the structural and electronic profile is demonstrated here. The analysis of the transport properties portrays that the highest value of 0.39 is achieved for figure of merit at higher temperatures. The mechanical stability of La₂CuMnO₆ is established, by determination of elastic constants. The calculated elastic parameters specify the ductile behavior of alloy with high melting temperature. The efficient thermoelectric parameters with half‐metallic and ductile character suggest the likelihood of applications of alloy to design hard spintronic devices or potential thermoelectric materials.     

Investigation of thermoelectric generators connected in different configurations for micro‐grid applications

This research work investigates the power‐current (P‐I) and voltage‐current (V‐I) characteristics of the thermoelectric modules (TEMs) in series‐parallel configurations under homogeneous and heterogeneous temperature difference (ΔT) condition. To study its performance, 5 different series‐parallel combinations were formed using 16 TEMs. The comparisons among the different configurations have been done to determine the optimal series‐parallel configuration. The total load power extracted from 16 individually connected TEMs was 18.2 W, which was placed as a reference load power. The optimal series‐parallel combination for maximizing the load power is square series‐parallel configuration, whose maximum load power is 95.5%, compared to the reference load power. Moreover, in square series‐parallel configuration, the total internal resistance value that remains constant is equal to the internal resistance of a single TEM, and the total open‐circuit voltage increases gradually on adding any number of TEMs. Thus, it produces higher load voltage and higher load current simultaneously, which is recommended to power DC micro‐grid applications. Furthermore, the series, parallel, and square series‐parallel configurations are connected as star to obtain 3 separate DC output to power the same application. The performance of TEMs under various configurations is analyzed, and the obtain results are verified experimentally.     

Phonon phase stability,structural, mechanical,electronic, and thermoelectric properties of two new semiconducting quaternary Heusler alloys CoCuZrZ (Z = Ge and Sn)

For meeting the energy demand, the development of new and novel thermoelectric (TE) materials for power generation is very vital. In this draft, we have theoretically investigated two new quaternary CoCuZrZ (Z = Ge and Sn) Heusler alloys for their structural, mechanical, electronic, and TE properties. In the energy minimization process, the alloys are found to be non-magnetic in the ground state. Based on calculated phonon dispersion curves, formation energy, and elastic constants, we propose that both CoCuZrGe and CoCuZrSn are stable. Furthermore, the mechanical properties indicate that CoCuZrGe (CoCuZrSn) has a brittle (ductile) nature. The electronic properties examined in Perdew-Burke-Ernzerhof (PBE), PBEsol, and modified Becke-Johnson (mBJ) potential, all predict that reported systems are narrow-gap semiconductors (SCs). In addition, the temperature dependent TE properties have been studied by calculating the electronic thermal conductivity (κ), Seebeck coefficient (S), power factor (PF) and electrical conductivity (σ/τ). The obtained positive value of S conveys the materials as p-type SCs, with a maximum value of 26.2 μV/K for CoCuZrGe and 28 μV/K for CoCuZrSn. The σ/τ, κ, and PF show increasing trends with rising temperature. The PF is found to be 1.55 × 10¹² WK⁻²m⁻¹s⁻¹ for CoCuZrGe and 1.38 × 10¹² WK⁻²m⁻¹s⁻¹ for CoCuZrSn. The proposed semiconducting Heusler alloys may receive attention for a range of TE and spintronic applications.     

Cross‐linked polymer electrolyte membrane based on a highly branched sulfonated polyimide with improved electrochemical properties for fuel cell applications

Sulfonated polyimides (SPIs) are extremely suitable as polymer electrolyte membranes (PEMs) for fuel cell applications, except for their poor water stability. Cross‐linking is a method that is commonly used to improve the weak hydrolytic stability of SPI membranes. However, this strategy significantly decreases the proton conductivity of the membrane, which leads to a lower fuel cell power density. In this work, a cross‐linked SPI membrane containing a highly branched polymer main chain was fabricated as a PEM. With a similar ion‐exchange capacity value, the cross‐linked membrane containing branched main chains showed an improved proton conductivity. Also, this membrane remained 92.3% of pristine weight after a hydrolytic stability test about 120 hours. In a single direct methanol fuel cell, the cross‐linked membrane containing a branched structure showed a higher power density (53.4 mW cm^?2) than the common cross‐linked membrane (43.0 mW cm^?2), indicating that branching is effective for improving the electrochemical properties of PEM‐based cross‐linked SPIs.     

Design and characterization of a cylindrical,water‐cooled heat sink for thermoelectric air‐conditioners

Thermoelectric air‐conditioners (TEACs) are becoming much concerned due to their many advantages, but the low COPs limit their broad applications. The two key factors to raise the COPs of TEACs are both the improvement of thermoelectric materials and the optimum design of hot side heat sinks. This paper provides a thermoelectric air‐conditioning system with a water‐cooled sleeve heat sink in the hot side of the thermoelectric pellets, and compares the overall heat transfer rates q_t, the total heat resistances R_t between the water‐cooled and air‐cooled heat sinks as well as the optimum fin length, the optimum fluid flow velocity and the optimum fin gap distance. The simulation results show that the overall heat transfer rate of water‐cooled heat sink is more than 20 times that of air‐cooled heat sink under the other same circumstances, as a result of the improvement of heat sink, the optimum COP of the thermoelectric air‐conditioning system with the water‐cooled heat sink proximately doubles that with the air‐cooled heat sink. This novel system could be simply installed and applied all the year round for cooling in summer and heating in winter. Copyright © 2005 John Wiley & Sons, Ltd.     

An investigation of thermoelectric cooling devices for small‐scale space conditioning applications in buildings

This paper presents the study of a thermoelectric cooler (TEC) designed for small‐scale space conditioning applications in buildings. A theoretical study was undertaken to find the optimum operating conditions, which were then applied in the laboratory testing work. A TEC unit was assembled and tested under laboratory conditions. Eight pieces of UltraTEC were shown to generate up to 220 W of cooling with a COP of 0.46 under the input current of 4.8 A for each module. Thermo‐economical analysis was carried out and results showed that a system with PV panel can compete with an equivalent system without a PV panel when PV costs fall down to or lower than £1.25 per Watt. For the cases without a PV panel, the system with a high level of TEC power input delivered a better performance in terms of the average cooling energy price than that system with a low level of TEC power input after critical interest rate (currently 4%). Copyright © 2009 John Wiley & Sons, Ltd.     

Co‐gasification performance of coal and petroleum coke blends in a pilot‐scale pressurized entrained‐flow gasifier

Co‐gasification performance of coal and petroleum coke (petcoke) blends in a pilot‐scale pressurized entrained‐flow gasifier was studied experimentally. Two different coals, including a subbituminous coal (Coal A) and a bituminous coal (Coal B), individually blended with a petcoke in the gasifier were considered. The experimental results suggested that, when the petcoke was mixed with Coal A over 70%, the slagging problem, which could shorten the operational period due to high ash content in the coal, was improved. It was found that increasing O₂/C tended to decrease the syngas concentration and better operational conditions of O₂/C were between 0.6 and 0.65 Nm³ kg^?1. For the blends of Coal B and the petcoke, the slagging problem was encountered no more, as a result of low ash content in both Coal B and the petcoke. The better co‐gasification performance could be achieved if the blending ratio of the two fuels was 50%, perhaps resulting from the synergistic effect of the blends. With the aforementioned blending ratio, the optimal condition of O₂/C was located at around 0.65 Nm³ kg^?1. The co‐gasification was also simulated using Aspen Plus. It revealed that the simulation could provide a useful insight into the practical operation of co‐gasification. Copyright © 2011 John Wiley & Sons, Ltd.     

3D electro‐thermal modelling and experimental validation of lithium polymer‐based batteries for automotive applications

This article presents an electro‐thermal model of a stack of three lithium ion batteries for automotive applications. This tool can help to predict thermal behaviour of battery cells inside a stack. The open source software OpenFOAM provides the possibility to add heat generation because of Joule losses in a CFD model. Heat sources are introduced at the connectors and are calculated as a function of battery discharge current and internal resistance. The internal resistance is described in function of temperature. Simulation results are validated against experimental results with regard to cooling air flow field characteristic and thermal behaviour of the cell surface. The validation shows that the simulation is capable to anticipate air flow field characteristics inside the battery box. It also predicts correctly the thermal behaviour of the battery cells for various discharge rates and different cooling system conditions. The simulation supports the observation that batteries have a higher temperature close to the connectors and that the temperature increase depends highly on discharge rate and cooling system conditions. Copyright © 2016 John Wiley & Sons, Ltd.     

Multi‐objective genetic algorithm optimization of thermoelectric heat exchanger for waste heat recovery

A model is developed to simulate a cross‐flow heat exchanger, including fins, in the wall of which thermoelectric generators are sandwiched. Such a system could be used for waste heat recovery. The model is used to optimize the device based on several objective functions: total volume, total number of thermoelectric modules, power output, and pumping power. The design variables are the local distribution of modules and of current, the shape of the fins, and the division of the heat exchanger in sub‐channels. Pareto fronts are achieved with a multi‐objective genetic algorithm, and are presented here. The results show that the number of sub‐channels in the heat exchanger has a larger impact on the overall performance than the fin geometry for this particular problem. Also, the net power output is mostly correlated to the number of thermoelectric modules, and less to the heat exchanger volume. Various relations between the different competing objectives are shown and analyzed. Copyright © 2011 John Wiley & Sons, Ltd.     

Vibration‐based piezoelectric,electromagnetic, and hybrid energy harvesters for microsystems applications: A contributed review

Wireless sensor nodes (WSNs) and embedded microsystems have recently gained tremendous traction from researchers due to their vast sensing and monitoring applications in various fields including healthcare, academic, finance, environment, military, agriculture, retail, and consumer electronics. An essential requirement for the sustainable operation of WSN is the presence of an uninterrupted power supply; which is currently obtained from electrochemical batteries that suffer from limited life cycles and are associated with serious environmental hazards. An alternative to replacing batteries of WSNs; either the direct replacement or to facilitate battery regular recharging, is by looking into energy harvesting for its sustainable drive. Energy harvesting is a technique by which ambient energy can be converted into useful electricity, particularly for low‐power WSNs and consumer electronics. In particular, vibration‐based energy harvesting has been a key focus area, due to the abundant availability of vibration‐based energy sources that can be easily harvested. In vibration‐based energy harvesters (VEHs), different optimization techniques and design considerations are taken in order to broaden the operation frequency range through multi‐resonant states, increase multi‐degree‐of‐freedom, provide nonlinear characteristics, and implement the hybrid conversion. This comprehensive review summarizes recent developments in VEHs with a focus on piezoelectric, electromagnetic, and hybrid piezoelectric‐electromagnetic energy harvesters. Various vibration and motion‐induced energy harvesting prototypes have been reviewed and discussed in detail with respect to device architecture, conversion mechanism, performance parameters, and implementation. Overall sizes of most of the reported piezoelectric energy harvesters are in the millimeter to centimeter scales, with resonant frequencies in the range of 2‐13 900 Hz. Maximum energy conversion for electromagnetic energy harvesters can potentially reach up to 778.01 μW/cm³. The power produced by the reported hybrid energy harvesters (HEHs) is in the range of 35.43‐4900 μW. Due to the combined piezoelectric‐electromagnetic energy conversion in HEHs, these systems are capable of producing the highest power densities.     

Adaptive post‐processing of short‐term wind forecasts for energy applications

We present a new method of reducing the error in predicted wind speed, thus enabling better management of wind energy facilities. A numerical weather prediction model, COSMO, was used to produce 48 h forecast data every day in 2008 at horizontal resolutions of 10 and 3 km. A new adaptive statistical method was applied to the model output to improve the forecast skill. The method applied corrective weights to a set of forecasts generated using several post‐processing methods. The weights were calculated based on the recent skill of the different forecasts. The resulting forecast data were compared with observed data, and skill scores were calculated to allow comparison between different post‐processing methods. The total root mean square error performance of the composite forecast is superior to that of any of the individual methods. Copyright © 2010 John Wiley & Sons, Ltd.     

Stability study of Bi‐2212 conductor based on perturbation spectrum for hybrid superconducting magnet

A hybrid superconducting central solenoid employs Bi‐2212 high‐temperature superconductors and Nb3Sn low‐temperature superconductors under the design of the Institute of Plasma Physics, Chinese Academy Of Science for further upgrade to CFETR, namely, the China Fusion Engineering Testing Reactor. The conductor type of both parts is cable‐in‐conduit conductors. This paper mainly focuses on stability study of the inner high‐temperature superconductors part whose conductor works under a peak magnetic field of 16.79 T, and the maximum operating current of each turn is 50 kA. The simulation based on a 1‐D simplified model is performed using the code THEA (thermal hydraulic and electric analysis of superconducting cable). Firstly, a brief analysis of stability considering the AC loss during current ramp‐up is studied. Then, the stability margins in cases of different perturbations with varied lengths and durations are calculated, and a qualitative explanation of the result is proposed. Besides, the inlet pressure and pressure drop crucially influence the convection heat transfer between strands and helium; thus, the effect of these two factors on stability margin is discussed. All these results will provide important references for further optimization of this hybrid magnet. Copyright © 2017 John Wiley & Sons, Ltd.     

A model‐based and data‐driven joint method for state‐of‐health estimation of lithium‐ion battery in electric vehicles

Lithium‐ion battery state‐of‐health estimation is one of the vital issues for electric vehicle safety. In this work, a joint model‐based and data‐driven estimator is developed to achieve accurate and reliable state‐of‐health estimation. In the estimator, an increase in ohmic resistance extracted from the Thevenin model is defined as the health indicator to quantify the capacity degradation. Then, a linear state‐space representation is constructed based on the data‐driven linear regression. Furthermore, the Kalman filter is introduced to trace capacity degradation based on the novel state space representation. A series of battery aging datasets with different dynamic loading profiles and temperatures are obtained to demonstrate the accuracy and robustness of the proposed method. Results show that the maximum error of the Kalman filter is 2.12% at different temperatures, which proves the effectiveness of the proposed method.     

Techno‐economic analysis of biomass/coal Co‐gasification IGCC systems with supercritical steam bottom cycle and carbon capture

In recent years, integrated gasification combined cycle technology has been gaining steady popularity for use in clean coal power operations with carbon capture and sequestration (CCS). This study focuses on investigating two approaches to improve efficiency and further reduce the greenhouse gas (GHG) emissions. First, replace the traditional subcritical Rankine steam cycle portion of the overall plant with a supercritical steam cycle. Second, add different amounts of biomass as feedstock to reduce emissions. Employing biomass as a feedstock has the advantage of being carbon neutral or even carbon negative if CCS is implemented. However, due to limited feedstock supply, such plants are usually small (2–50 MW), which results in lower efficiency and higher capital and production costs. Considering these challenges, it is more economically attractive and less technically challenging to co‐combust or co‐gasify biomass wastes with low‐rank coals. Using the commercial software, Thermoflow®, this study analyzes the baseline plants around 235 MW and 267 MW for the subcritical and supercritical designs, respectively. Both post‐combustion and pre‐combustion CCS conditions are considered. The results clearly show that utilizing a certain type of biomass with low‐rank coals up to 50% (wt.) can, in most cases, not only improve the efficiency and reduce overall emissions but may be economically advantageous, as well. Beyond a 10% Biomass Ratio, however, the efficiency begins to drop due to the rising pretreatment costs, but the system itself still remains more efficient than from using coal alone (between 0.2 and 0.3 points on average). The CO₂ emissions decrease by about 7000 tons/MW‐year compared to the baseline (no biomass), making the plant carbon negative with only 10% biomass in the feedstock. In addition, implementing a supercritical steam cycle raises the efficiency (1.6 percentage points) and lowers the capital costs ($300/kW), regardless of plant layout. Implementing post‐combustion CCS consistently causes a drop in efficiency (at least 7–8 points) from the baseline and increases the costs by $3000–$4000/kW and In recent years, integrated gasification combined cycle technology has been gaining steady popularity for use in clean coal power operations with carbon capture and sequestration (CCS). This study focuses on investigating two approaches to improve efficiency and further reduce the greenhouse gas (GHG) emissions. First, replace the traditional subcritical Rankine steam cycle portion of the overall plant with a supercritical steam cycle. Second, add different amounts of biomass as feedstock to reduce emissions. Employing biomass as a feedstock has the advantage of being carbon neutral or even carbon negative if CCS is implemented. However, due to limited feedstock supply, such plants are usually small (2–50 MW), which results in lower efficiency and higher capital and production costs. Considering these challenges, it is more economically attractive and less technically challenging to co‐combust or co‐gasify biomass wastes with low‐rank coals. Using the commercial software, Thermoflow®, this study analyzes the baseline plants around 235 MW and 267 MW for the subcritical and supercritical designs, respectively. Both post‐combustion and pre‐combustion CCS conditions are considered. The results clearly show that utilizing a certain type of biomass with low‐rank coals up to 50% (wt.) can, in most cases, not only improve the efficiency and reduce overall emissions but may be economically advantageous, as well. Beyond a 10% Biomass Ratio, however, the efficiency begins to drop due to the rising pretreatment costs, but the system itself still remains more efficient than from using coal alone (between 0.2 and 0.3 points on average). The CO₂ emissions decrease by about 7000 tons/MW‐year compared to the baseline (no biomass), making the plant carbon negative with only 10% biomass in the feedstock. In addition, implementing a supercritical steam cycle raises the efficiency (1.6 percentage points) and lowers the capital costs ($300/kW), regardless of plant layout. Implementing post‐combustion CCS consistently causes a drop in efficiency (at least 7–8 points) from the baseline and increases the costs by $3000–$4000/kW and $0.06–$0.07/kW‐h. The SO_x emissions also decrease by about 190 tons/year (7.6 × 10^?6 tons/MW‐year). Finally, the CCS cost is around $65–$72 per ton of CO₂. For pre‐combustion CCS, sour shift appears to be superior both economically and thermally to sweet shift in the current study. Sour shift is always cheaper, (by a difference of about $600/kW and $0.02‐$0.03/kW‐h), easier to implement, and also 2–3 percentage points more efficient. The economic difference is fairly marginal, but the trend is inversely proportional to the efficiency, with cost of electricity decreasing by 0.5 cents/kW‐h from 0% to 10% biomass ratio (BMR) and rising 2.5 cents/kW‐h from 10% to 50% BMR. Pre‐combustion CCS plants are smaller than post‐combustion ones and usually require 25% less energy for CCS due to their compact size for processing fuel flow only under higher pressure (450 psi), versus processing the combusted gases at near‐atmospheric pressure. Finally, the CO₂ removal cost for sour shift is around $20/ton, whereas sweet shift's cost is around $30/ton, which is much cheaper than that of post‐combustion CCS: about $60–$70/ton. Copyright © 2014 John Wiley & Sons, Ltd.     

Parametric study on the performance of the earth‐to‐air heat exchanger for cooling and heating applications

To reduce energy consumption, the earth‐to‐air heat exchanger (EAHE) is a suitable technique for cooling and heating buildings. This paper studies numerically the effect of some design parameters (pipe diameter, inlet condition, pipe length, and outlet condition) on the overall performance of the EAHE system. Four diameters of the EAHE pipe (2, 3, 4, and 6 in) are studied and this numerical study has been done for summer and winter seasons for Nasiriyah city in southern Iraq. First, the built numerical model was validated against the experimental model, and the results of comparison showed a good consensus. After the validation and by using computational fluid dynamics modeling, the overall performance of the EAHE system with all pipe diameters was analyzed with ranges of air velocity, DBT or inlet temperature, and a pipe length of 50 m. The simulated results showed that the EAHE system with 6 in pipe diameter has the best values of overall performance, but from the thermal performance point of view, the 2 in pipe diameter is more suitable.     

Lignin‐derived heteroatom‐doped porous carbons for supercapacitor and CO2 capture applications

The present study reports the economic and sustainable syntheses of functional porous carbons for supercapacitor and CO₂ capture applications. Lignin, a byproduct of pulp and paper industry, was successfully converted into a series of heteroatom‐doped porous carbons (LHPCs) through a hydrothermal carbonization followed by a chemical activating treatment. The prepared carbons include in the range of 2.5 to 5.6 wt% nitrogen and 54 wt% oxygen in its structure. All the prepared carbons exhibit micro‐ and mesoporous structures with a high surface area in the range of 1788 to 2957 m² g^?1. As‐prepared LHPCs as an active electrode material and CO₂ adsorbents were investigated for supercapacitor and CO₂ capture applications. Lignin‐derived heteroatom‐doped porous carbon 850 shows an outstanding gravimetric specific capacitance of 372 F g^?1 and excellent cyclic stability over 30,000 cycles in 1 M KOH. Lignin‐derived heteroatom‐doped porous carbon 700 displays a remarkable CO₂ capture capacity of up to 4.8 mmol g^?1 (1 bar and 298 K). This study illustrates the effective transformation of a sustainable waste product into a highly functional carbon material for energy storage and CO₂ separation applications.     

Optimum fluid layer thickness for heat transfer effectiveness using water‐based nanofluids—A numerical estimation

Nanofluids are considered to be the novel method for heat transfer in heat pipes and heat exchangers. But its application in microlevel cooling systems is still limited because of the paradox that once convection onsets in the base fluid, the effectiveness of nanofluid as a heat transfer medium will be reduced. The onset of convection in the nanofluid occurs only after its onset in the base fluid which is mostly water. Hence, it is vital to estimate the fluid layer thickness of the base fluid at which convection will just onset. The problem is analyzed using the concept of the critical Rayleigh number. The study of velocity and temperature profiles in the fluid gap also gives an indication of convection in the fluid gap.