By using the Seebeck effect to produce electrical voltage, thermoelectric as a highly scalable, stationary and silent heat engine has undergone a state of vigorous research. Starting with the review ...on thermoelectric generators, it shows that thermoelectric is gaining more attention since the past decade. Generally, the research conducted on the thermoelectric generators concentrate on the material development, mathematical and numerical model development as well as the application of thermoelectric generators. For this article, attention is given to the application research of the thermoelectric generators. From the survey conducted, most of the application research carried out is based on intermittent electrical power generation (e.g. the direct use of solar energy available or waste heat recovery). Hence, it opens an opportunity for the research on the application of thermoelectric generators by utilising a heat source that is continuously ready for thermal-electrical energy conversion, such as phase change material, geothermal heat or solar pond. In the later section, the review is continued by introducing solar pond, a facility that has been used as a supply of low-grade heat source at the remote area or industrial process heating. The research on the fundamentals of solar pond and its applications, but not limited to, the power generation has also been summarised. The ultimate idea of this review is to provide an insight that a thermal-storage based heat source (e.g. in this review, the solar pond) could be useful for small-scale electric power generation, despite its ordinary function as low-grade heat source provider via heat extraction.
•A review of the recent research of thermoelectric generators is presented.•The research on the solar pond as a heat source is discussed.•Power generation with thermoelectric generators and solar ponds is possible.
•A multi-aspect analysis is performed to assess the sustainability of biomass gasification.•A systematic guideline is demonstrated for numerical modeling of biomass gasification.•An in-depth analysis ...of different models is provided to choose an appropriate modeling scenario for gasification.•Comprehensive application of thermal models along with their influential parameters are demonstrated.
Sustainable energy production through conversion of biomass has recently found growing interest. Among thermochemical conversion techniques, gasification is of interest to replace direct combustion emitting air pollutants that threaten our environment. However, gasification process is still far from being efficient since most of the research studies have only focused on experimental implementation of the methods while numerical modeling has been limited to pilot scales, ignoring the performance optimization required for scaling up the gasification process. Gasification is a highly complex process, which involves the coupling of thermochemical equilibrium, kinetics, heat and mass transfer, and computational fluid dynamics. This complexity has currently prevented the proposed theoretical/computational models in the literature from achieving the required accuracy for optimizing the gasification process. Herein, we offer a comprehensive guideline to improve the numerical models which can be implemented in future sustainable biorefineries to improve their efficiency. The present study pursues two principal objectives: (1) Introducing the fundamental knowledge required for theoretical/computational modeling and (2) Reviewing alternative numerical models for gasification process. First, a brief overview of the knowledge needed to make a systematic model is gathered. The theory of gasification, the various types of gasifiers and their differences are reviewed. Furthermore, we discuss the importance of the type of biomass feedstock with concentration on advanced biofuels and focus on wood pellets for the modeling section. Second, CFD is introduced and chemical equilibrium, kinetics, and heat and mass transfer models are discussed in depth and the variation of different parameters with respect to the change of temperature within a gasifier is elaborated. The results of this study make a clear pathway for modeling of gasification process by anticipating the expected outputs from the model by using the existing experimental data. Finally, comprehensive application of these models is demonstrated and substantial parameters affecting the gasification process are introduced. This paper provides a framework for numerical modeling of the gasification process of biomass to optimize the efficiency of the conversion process.
Due to inherent uncertainties in measurement and analysis, groundwater quality assessment is a difficult task. Artificial intelligence techniques, specifically fuzzy inference systems, have proven ...useful in evaluating groundwater quality in uncertain and complex hydrogeological systems. In the present study, a Mamdani fuzzy-logic-based decision-making approach was developed to assess groundwater quality based on relevant indices. In an effort to develop a set of new hybrid fuzzy indices for groundwater quality assessment, a Mamdani fuzzy inference model was developed with widely-accepted groundwater quality indices: the Groundwater Quality Index (GQI), the Water Quality Index (WQI), and the Ground Water Quality Index (GWQI). In an effort to present generalized hybrid fuzzy indices a significant effort was made to employ well-known groundwater quality index acceptability ranges as fuzzy model output ranges rather than employing expert knowledge in the fuzzification of output parameters. The proposed approach was evaluated for its ability to assess the drinking water quality of 49 samples collected seasonally from groundwater resources in Iran's Sarab Plain during 2013–2014. Input membership functions were defined as “desirable”, “acceptable” and “unacceptable” based on expert knowledge and the standard and permissible limits prescribed by the World Health Organization. Output data were categorized into multiple categories based on the GQI (5 categories), WQI (5 categories), and GWQI (3 categories). Given the potential of fuzzy models to minimize uncertainties, hybrid fuzzy-based indices produce significantly more accurate assessments of groundwater quality than traditional indices. The developed models' accuracy was assessed and a comparison of the performance indices demonstrated the Fuzzy Groundwater Quality Index model to be more accurate than both the Fuzzy Water Quality Index and Fuzzy Ground Water Quality Index models. This suggests that the new hybrid fuzzy indices developed in this research are reliable and flexible when used in groundwater quality assessment for drinking purposes.
•A new groundwater quality assessment method was developed.•The new method is based on a fuzzy inference system.•Widely accepted indices were also used and compared in this study.•The hybrid fuzzy based indices minimized uncertainties.•The new approaches were useful for groundwater quality assessment.
Exhaust heat recovery systems are used to make use of otherwise wasted heat from a car engine. The purpose of exhaust heat recovery systems is to potentially reduce the fuel consumption of the car ...and consequently reduce CO2 emissions and running costs. The system design described herein utilises thermoelectric generators (TEGs) and heat pipes with its key advantage being it is a passive solid state design. The use of heat pipes allows for more flexible designs as the TEG location is not limited to the exhaust pipe surface. Testing was undertaken on a car with a 3.0L V6 engine. In all test conditions the power loss due to pressure drop in the exhaust duct was always lower than the electrical power output. Repeat tests were conducted and the results were found to be consistent. When testing the system at different orientations, the bottom heat mode was found to be the best option. After all testing, the maximum power output of the system was 38W from the eight 62mm×62mm TEGs used. The rate of heat transfer in this case was 1541W with the resultant TEG efficiency being 2.46%. The calculated potential reduction in CO2 emissions, fuel consumption and fuel costs was 1.57%.
Many aquatic animals propel themselves by generating backward traveling waves over their body, which is thought to reattach the flow when the wave speed (
$C=\unicodeSTIX{x1D706}f$
, where
...$\unicodeSTIX{x1D706}$
is wavelength and
$f$
is frequency) is larger than the swimming speed (
$U$
). This has inspired the use of travelling waves, which have recently been generated at low amplitudes using smart materials, to reduce flow separation on an inclined plate. To see if low-amplitude travelling waves (amplitude approximately 0.01 of chord length
$L$
) can reduce the separation on an inclined plate, large-eddy simulations are performed. The simulations are carried out for Reynolds number (
$Re$
) 20 000 and an angle of attack of
$10^{\circ }$
with different wavelengths and frequencies. The travelling waves at a low reduced frequency (
$f^{\ast }=fL/U=6$
and
$\unicodeSTIX{x1D706}^{\ast }=\unicodeSTIX{x1D706}/L=0.2$
, where
$U$
is free-stream velocity) do not affect the flow separation and aerodynamic performance compared to the flat inclined plate. Nevertheless, increasing the wave speed by increasing the reduced frequency to 20 and 30 reduces flow separation. However, increasing the wave speed by increasing the wavelength, in contrast to the common belief, does not monotonically reduce the flow separation. In fact, increasing the wave speed by increasing the wavelength from 0.15 to 0.5 at constant frequency
$f^{\ast }=20$
increases the separation, but increasing from 0.5 to 1.0 and 2.0, interestingly, reduces flow separation. These observations indicate that the wave speed is not the only parameter for flow reattachment, but both wavelength and frequency individually impact flow separation by affecting two competing but interconnected mechanisms: the axial momentum, imparted onto the fluid by the undulations, tends to reattach the flow but the lateral velocity tends to detach it. In fact, increasing
$f^{\ast }$
and
$\unicodeSTIX{x1D706}^{\ast }$
increases both the axial momentum and the lateral velocity, which are competing to attach and detach the flow, respectively.
▶ High strain rate without considerable temperature rise accompanied by a high value of Zener-Hollomon parameter is achieved by ASB. ▶ An average grain thickness and length of 186 and 419
nm are ...developed accompanied by increase of the grain boundary misorientation by four cycles of ASB. ▶ While the hardness is increased from the inner regions to the outer ones, its homogeneity is increased with increase of the ASB cycles leading to decrease of the ratio of tensile strength to yield strength and consequently to decrease of the uniform elongation ▶ The yield and tensile strengths of the material are significantly increased up to the values of 194 and 235
MPa, respectively.
A novel SPD process for manufacturing of high strength tubes and cylinders by accumulative spin-bonding (ASB) is proposed. It is demonstrated that due to incremental deformation in this process, high strain rate without considerable temperature rise is achieved. This is accompanied with a high value of Zener–Hollomon parameter as a characteristic of this SPD process. ASB was applied to a commercially pure aluminum up to four cycles and its effects on the microstructure and mechanical properties were examined by optical microscopy, TEM, EBSD, microhardness and tension tests. The results show that ultra-fine grains are developed during the process by formation of subgrains at early stages followed by increase of the misorientations at later stages. This leads to a nanostructure with average grain thickness and length of 186 and 419
nm, respectively. It is indicated that while the hardness of outer regions is more than the inner ones, the hardness and its homogeneity is increased with the ASB cycles. Periodical presence of external layers within the thickness and consequent hardness saturation are responsible for this hardness evolution. As a result of grain refinement and the scheme of hardness development, the yield and tensile strength of material are significantly increased. Moreover, the ratio of the yield strength to the tensile strength and consequently the uniform elongation is decreased with the ASB cycles.
A first-principles-based effective Hamiltonian is used to investigate low-temperature properties of Ba(Zr,Ti)O(3) relaxor ferroelectrics under an increasing dc electric field. This system ...progressively develops an electric polarization that is highly nonlinear with the dc field. This development leads to a maximum of the static dielectric response at a critical field, E(th), and involves four different field regimes. Each of these regimes is associated with its own behavior of polar nanoregions, such as shrinking, flipping, and elongation of dipoles or change in morphology. The clusters propagating inside the whole sample, with dipoles being parallel to the field direction, begin to form at precisely the E(th) critical field. Such a result, and further analysis we perform, therefore, reveal that field-induced percolation of polar nanoregions is the driving mechanism for the transition from the relaxor to ferroelectric state.
The continual increases in energy demand and greenhouse gas emissions, call for efficient use of energy resources. Decentralized combined heat and power (CHP) technology provides an alternative for ...the world to meet and solve energy-related problems including energy shortages, energy supply security, emission control and conservation of energy. This paper presents the preliminary results of an experimental investigation of a natural gas-fired micro-CHP system for residential buildings based on an organic Rankine cycle (ORC). Isopentane was used as the ORC working fluid in consideration of several criteria including its environmentally-friendly characteristics. Experiments were conducted to evaluate the performance of the developed system at different heat source temperatures of nominally 85, 80, 75, 70, and 65 °C. The maximum electrical power output of 77.4 W was generated at heating water entry temperature of 84.1 °C, corresponding to net cycle electrical efficiency of 1.66%. Further work will be done with a view to increasing the cycle electrical efficiency by using more efficient components, in particular the expander and generator.
•A natural gas-fired ORC-based micro-scale CHP system has been developed and tested.•The good agreement between the mechanical and gross power validates the assumptions.•A vane expander suits a micro-CHP system based on an organic Rankine cycle.•A vane expander does not suit power generation by a Trilateral Flash Cycle (TFC).•Domestic gas-fired ORC systems may reduce reliance on central power stations.
In this paper, the magnetoelectroelastic responses of radially polarized and magnetized hollow and solid magnetoelectroelastic cylinders subjected to hygrothermal loading are obtained by a ...straightforward analytical method. The transversely isotropic and homogeneous cylinders are embedded with a Winkler-type elastic foundation on the inner and/or outer surfaces. The cylinders are assumed to be infinitely long. To obtain the temperature and moisture concentration distributions within the thicknesses of the cylinders, the steady state, axisymmetric heat conduction and moisture diffusion equations are solved. For uniform temperature and moisture concentration rise, the temperature and moisture dependence of the elastic stiffness coefficients are considered in the analysis. The coupled ordinary differential equations in terms of displacement, electric potential and magnetic potential are solved exactly by the successive decoupling method. Numerical results are shown to clarify the effects of hygrothermal loading, elastic foundation and temperature and moisture dependence of the elastic coefficients on the magnetoelectroelastic behavior of the cylinders. The results for magnetic, electrical and mechanical loadings are verified by those available in the literature.
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