Review of recent advances in anaerobic packed-bed biogas reactors

Biogas digesters have captured many imaginations because they can turn organic wastes from our farms, factories and cities into a valuable source of renewable energy. In addition, the potential of this technology to reduce odors and other environmental concerns of animal feedlots has resulted in much recent interest from researchers and scientists all over the globe.Despite its numerous advantages, the potential of biogas technology could not be fully harnessed or tapped, as certain constraints are also associated with it. Researchers have tried different techniques to enhance gas production. This paper reviews the use of fixed-bed reactors in various fields reported by different researchers using variety of substrates.     

Comparative analysis of corrugation effect on thermohydraulic performance of double-pipe heat exchangers

Heat transfer augmentation in heat exchangers has been a key research topic in recent times. Over the years, many methods have been proposed for heat transfer enhancement, such as providing fins, changing the cross-sectional area of tubes, vortex generator, twisted tape inserts, and so forth. In addition to the above-mentioned techniques, corrugation of tubes was also proposed by a few authors who demonstrated that this method could effectively increase the heat transfer rate. To address the same in this study, the different corrugation profiles have been created with the help of CATIA software for the study. The simulations were performed using ANSYS R19.2. The results so obtained were used to calculate the various thermal and hydraulic perfoallrmance parameters of the heat exchanger with the help of macros created in MS Excel. The result shows that the use of corrugation on the inner tube of the heat exchanger increased the heat transfer coefficient, fanning friction factor, and rate of cooling by 5%–21%, 90%–355%, and 25.67%–157.40%, respectively, in case of the plain double-pipe heat exchanger for the mass flow rate variation of 5–25 kg/min. It is also observed that the smooth tube has more thermohydraulic performance as 1.2152.     

Patent-based trend analysis for advanced thermal energy storage technologies and their applications

Today, the world is moving towards sustainable and renewable energy resources. In order to ensure sustainable and steady power supply, thermal energy storage (TES) is playing a vital role. Most parts of the literature focus on different techniques and new energy storage materials. There is a scarcity of data on technological inventions in the form of patents to provide information to new researchers and investors before starting their new projects on TES. So this research work seeks to address this gap by concentrating on the patent analysis of various technologies with respect to their global publication trend in TES research field. The proposed research work also elaborates the technological evolution in domestic and industrial applications of TES. This analysis is carried out using patent database search tools IncoPat and Espacenet. Patent documents are retrieved between the time span ranging from 2006 to 2018. According to research findings, the number of published patents related to different TES technologies increase every year. China, the United States, Japan, and South Korea are categorized as main depositor countries. Moreover, technology-based applications and their inventing organizations from different countries are also ranked in current research work.     

Numerical study of nanofluid heat transfer for different tube geometries – A comprehensive review on performance

The heat transfer performance of a system can be improved using a combination of passive methods, namely nanofluids and various types of tube geometries. These methods can help enhance the heat transfer coefficient and consequently reduce the weight of the system. In this paper, the effect of tube geometry and nanofluids towards the heat transfer performance in the numerical system is reviewed. The forced convective heat transfer performance, friction factor and wall shear stress are studied for nanofluid flow in different tube geometries. The thermo-physical properties such as density, specific heat, viscosity and thermal conductivity are reviewed for the determination of nanofluid heat transfer numerically. Various researchers had measured and modelled for the determination of thermal conductivity and viscosity of nanofluids. However, the density and specific heat of nanofluids can be estimated with the mixture relations. The different tube geometries in simulation work are analyzed namely circular tube, circular tube with insert, flat tube and horizontal tube. It was observed that the circular tube with insert provides the highest heat transfer coefficient and wall shear stress. Meanwhile, the flat tube has greater heat transfer coefficient with a higher friction factor compared to the circular tube.     

Modeling for predicting frosting behavior of a fin–tube heat exchanger

A mathematical model is proposed to evaluate the frosting behavior of a fin–tube heat exchanger under frosting conditions. Empirical correlations of the heat transfer coefficients for the plate and tube surfaces and a diffusion equation for the frost layer are used to establish the model. The correlations for the heat transfer coefficients, derived from various experimental data, were obtained as functions of the Reynolds number and Prandtl number. The proposed model is validated by comparing the numerical results with experimental data for the frost thickness, frost accumulation, and heat transfer rate. The numerical results agree well with the experimental data. It is also found that this model can be applied to evaluate the thermal performance of a common fin–tube heat exchanger under frosting conditions.     

连续型与锯齿型螺旋翅片管翅片效率计算与分析

介绍了烟气换热领域常用的两类高频焊钢质螺旋翅片管.指出目前存在多种连续型与锯齿型高频焊螺旋翅片管翅片效率计算方法,不便于同类换热实验结果的相互比较.通过深入分析与计算比较,对连续型与锯齿型高频焊螺旋翅片管分别给出了建议的翅片效率计算方法,供相关的工程设计及实验研究选用.两种管型的翅片效率比较表明,锯齿翅片的翅片效率较高,提高的幅度随翅片高度增大而增大.     

An overview of the methanol reforming process: Comparison of fuels,catalysts, reformers,and systems

One of the main challenges facing power generation by fuel cells involves the difficulties related to hydrogen storage. Several methods have been suggested and studied by researchers to overcome this problem. Among these methods, using fuel reformers as a component of the fuel cell system is a practical and promising alternative to hydrogen storage. Among many hydrogen carrier fuels used in reformers, methanol is one of the most attractive ones because of its distinctive properties. To design and improve of the methanol reformate gas fuel cell systems, different aspects such as promising market applications for reformate gas–fueled fuel cell systems, and catalysts for methanol reforming should be considered. Therefore, our goal in this paper is to provide a comprehensive overview on the past and recent studies regarding methanol reforming technologies, while considering different aspects of this topic. Firstly, different fuel reforming processes are briefly explained in the first section of the paper. Then properties of various fuels and reforming of these fuels are compared, and the characteristics of commercial reformate gas–fueled systems are presented. The main objective of the first section of the paper is to give information about studies and market applications related to reformation of various fuels to understand advantages and disadvantages of using various fuels for different practical applications. In the next sections of the paper, advancements in the methanol reforming technology are explained. The methanol reforming catalysts and reaction kinetics studies by various researchers are reviewed, and the advantages and disadvantages of each catalyst are discussed, followed by presenting the studies accomplished on different types of reformers. The effects of operating parameters on methanol reforming are also discussed. In the last section of this paper, methanol reformate gas–fueled fuel cell systems are reviewed. Overall, this review paper provides insight to researchers on what has been accomplished so far in the field of methanol reforming for fuel cell power generation applications to better plan the next stage of studies in this field.     

Simple method for estimation of effectiveness in one tube pass and one shell pass counter-flow heat exchangers

In one tube pass and one shell pass counter-flow heat exchangers, when both streams change temperature by different amounts, the effectiveness is defined as the temperature change for the stream with lower capacity divided by the maximum possible change and the effectiveness depends on the number of transfer units and the thermal capacity ratio. In this paper, an attempt has been made to formulate a simple-to-use method which is easier than existing approaches, less complicated and with fewer computations for accurate and rapid estimation of effectiveness in one tube pass and one shell pass counter-flow heat exchangers as a function of number of transfer units and the thermal capacity ratio. The proposed method permits estimating the exit temperature for a one tube pass and one shell pass counter-flow heat exchanger without a trial-and-error calculation. The average absolute deviations between the reported data and the proposed correlations are found to be less than 2% demonstrating the excellent performance of proposed correlation. The tool developed in this study can be of immense practical value for engineers and scientists to have a quick check on the effectiveness in one tube pass and one shell pass counter-flow heat exchangers at various conditions without opting for any experimental measurements. In particular, practice engineers would find the predictive tool to be user-friendly with transparent calculations involving no complex expressions.     

Experimental Study on Performance Enhancement of Evacuated Tube by Constant Heat Flux Mode

The evacuated tube collector with U shape copper absorber tube is considered for the analysis. The experimental investigation is conducted on parabolic trough collector with U shape tube as absorber tube. The effect of the sudden fluctuations in the solar radiation on the performance of the collector is reduced by means of evacuated tube collector filled with thermic fluids. The analysis is performed with different thermic fluids such as dowtherm, therminol66, glycol water and ethylene glycol, are filled in the annular space between inner glass tube and U shape copper absorber tube. The experimentation is carried out at various mass flow rates from 20 to 100 LPH with the step-up flow rate of 20 LPH. A comparative study is carried out on various parameters such as effect of mass flow rate over instantaneous efficiency, useful heat gain and work input, etc. The characteristic curve of cylindrical parabolic trough collector (PTC) is also discussed. Experimental results show that, ethylene glycol gives better efficiency over mass flow rate and therminol66 gives best power heat ratio. Heat transfer mediums and its properties [specific heat capacity, thermal conductivity and dynamic viscosity] for all specified heat transfer fluids are also discussed. The results obtained with various specified heat transfer fluids filled in the annulus space of evacuated tube are compared with plain evacuated tube. It is observed that there is significant enhancement of overall instantaneous collection efficiency of the parabolic trough collector.     

疏浚底泥节能处理技术研究进展

总结了当今国内外疏浚底泥节能处理技术,重点介绍了底泥在生物处理、物化处理、环境保护方面的二次利用和能源回收等方面的研究进展,分析了各种底泥节能处理技术的优势和目前存在的问题.由于免烧结处理技术可降低重金属等污染物向环境释放的风险,可减少对环境的危害,因而受到众多研究者的关注,也是疏浚底泥节能处理研究的一个重点.对疏浚底泥的处理方式、方法及处理技术进行了展望,为底泥资源化的进一步研究提供参考.     

Recent advances in cleaner hydrogen productions via thermo-catalytic decomposition of methane: Admixture with hydrocarbon

A continuous increase in the greenhouse gases concentration due to combustion of fossil fuels for energy generation in the recent decades has sparked interest among the researchers to find a quick solution to this problem. One viable solution is to use hydrogen as a clean and effective source of energy. In this paper, an extensive review has been made on the effectiveness of metallic catalyst in hydrocarbon reforming for CO_X free hydrogen production via different techniques. Among all metallic catalyst, Ni-based materials impregnated with various transition metals as promoters exhibited prolonged stability, high methane conversions, better thermal resistance and improved coke resistance. This review also assesses the effect of reaction temperature, gas hour space velocity and metal loading on the sustainability of thermocatalytic decomposition TCD of methane. The practice of co-feeding of methane with other hydrocarbons specifically ethylene, propylene, hydrogen sulphide, and ethanol are classified in this paper with the detailed overview of TCD reaction kinetics over an empirical model based on power law that has been presented. In addition, it is also expected that the outlook of TCD of methane for green hydrogen production will provide researchers with an excellent platform to the future direction of the process over Ni-based catalysts.     

Effects of porosity and thickness of porous sheets on heat transfer enhancement in a cross flow over heated cylinder

An experimental study is carried out to investigate the thermal impact of wrapping an aluminum porous sheet over a circular tube in a heat convection configuration. The experimental apparatus consists of a heated horizontal cylinder with a constant heat flux. The cylinder is then covered with porous sheets of different thicknesses. The tube is exposed to a cross flow of air at different speeds which corresponds to different Reynolds numbers. The effect of the added porous layer on the pressure loss over the cylinder was also investigated. It is observed that heat transfer is greatly enhanced with the addition of the porous layer. Also, the addition of the porous layer doesn’t appear to increase the pressure loss.     

Correlating Isothermal Friction Factor Data for Micro-Fin Tubes Using Logistic Dose-Response Curve Fitting Method

Simultaneous heat transfer and friction factor experiments for plain and micro-fin tubes were conducted in our previous study. The results showed that the heat transfer characteristics of the micro-fin tubes were the same as for the plain tube. However, the friction factor characteristics of the micro-fin tubes in the transition region were different compared to the plain tube. This type of friction factor data cannot be easily correlated by the traditional regression method. Therefore, a logistic dose-response curve-fitting method is proposed in this study. This particular method has recently been used by other researchers in correlating the friction factor data in plain tubes. In this study, three sets of micro-fin tubes friction factor data with different inlets from our previous study were correlated by the logistic dose-response curve-fitting method. All the fully developed friction factor data for the entire flow regime were predicted by a composite logistic dose-response function within ±11% deviation. The majority of the data (over 85%) was predicted with less than ±5% deviation.     

A Study on Gas Transfer Characteristics of Porous Materials with Liquid Water by Considering Their Pore Size Distribution

In this study, the gas transfer characteristics for porous materials with liquid water are studied, and the methods for calculating relative permeability and relative diffusivity of gas in a porous material by considering its pore size distribution are proposed. The calculation results show not only that the saturation has an impact, but also that the pore size distribution of the gas diffusion layer should be considered when calculating the relative diffusivitiy of a porous material with liquid water. In addition, the relative diffusivity calculated by the simplified formula proposed in this paper is closer to the experimental result than that obtained by other researchers. Moreover, the formulas proposed in this paper explain why porous materials with different pore size distributions have similar relative diffusivity obtained through experments by other researchers.     

Improvement of hydrogen storage capacity on the palladium-decorated N-doped graphene sheets as a novel adsorbent: A hybrid MD-GCMC simulation study

A hybrid molecular simulation, as a combination of molecular dynamics and Grand Canonical Monte Carlo simulation, is performed to investigate the storage capacity of hydrogen in carbon nanostructure adsorbents. Pure graphene sheet, nitrogen-doped graphene sheet, palladium-decorated graphene sheet and nitrogen-doped graphene sheet decorated with palladium atoms are selected for this purpose. Palladium is added to the structure in atomic and nanoparticle forms. Initially, all selected systems are optimized using density functional theory (DFT). The atomic charges of various structures are incorporated in the hybrid simulation. Then, hybrid simulations of hydrogen adsorption in different structures are performed at a temperature of 300 K in the pressure range of 1–40 bar. Simulation results show that among various structures, the simultaneous doping of graphene sheet with nitrogen atom and decoration of sheets by palladium atoms could increase the storage capacity by about 437% in comparison to pure graphene. In addition, the atomic form of palladium is more efficient than its nanoparticle form. Finally, comparing the adsorption capacity of the proposed structure with the target set by the US Department of Energy for 2020 indicates that proposed nanostructure can improve this target for hydrogen storage in comparison with previous carbon structure materials.     

Energy harvesting in wireless sensor networks: A taxonomic survey

Wireless sensor networks (WSNs) have aroused the conspectus attention of scholars due to their extensive deployment in the emerging fields of the Internet of Things (IoT's) and self‐driven devices. But WSNs technologies having a major bottleneck has been associated with limited energy. Mostly research in WSNs has been focused on minimizing energy usage to extend the survival time of limited power source in a network. Energy harvesting can be addressing its energy‐scarcity problem of WSNs, so it is giving popularity to Energy Harvesting in Wireless Sensor Networks (EH‐WSNs). The paper presents a comprehensive taxonomic survey on recently energy harvesting techniques and algorithms that proposed by various authors and also examined the work done by the various researchers in the field of EH‐WSNs. For the ready reference of the researchers, a concise summary and comparative analysis of various promising techniques for energy harvesting have also been included in the systematic survey. However, many equipment developed using the hybridization method in a singular package to get full advantages of available free energy, are explored in this review. The review on hybrid energy harvesting (HEH) systems can be considered as the originality of this article. However, the outdoor photovoltaics have been provided maximum power density about ≈100 mW/cm³, and the piezoelectric harvesters have been given maximum voltage about 325 V but the current in very minute amount. The thermoelectric, rectenna and hybrid energy harvesters (EHs) have been given high efficiency more than 80%. Additionally, hybrid EHs have location/time‐independent characteristics which harnessed power from more than one source that can be became more popular for upcoming leading technologies of self‐driven or autonomous devices shifting from battery operated devices. Finally, the survey also identifies often challenges and various significant issues that still essential to be addressed to develop a cost effective, efficient, long‐lasting, and almost maintenance‐free energy harvesting systems for WSNs along with trail to their possible solutions for future perspectives.     

Flow characteristics of refrigerants flowing through capillary tubes – A review

A comprehensive review of the literature on the flow of various refrigerants through the capillary tubes of different geometries viz. straight and coiled and flow configurations viz. adiabatic and diabatic, has been discussed in this paper. The paper presents in chronological order the experimental and numerical investigations systematically under different categories. Flow aspects like effect of coiling and effect of oil in the refrigerants on the mass flow rate through the capillary tube have been discussed. Furthermore, the phenomenon of metastability and the correlations to predict the underpressure of vaporization have also been discussed. The paper provides key information about the range of input parameters viz. tube diameter, tube length, surface roughness, coil pitch and coil diameter, inlet subcooling and condensing pressure or temperature. Other information includes type of refrigerants used, correlations proposed and methodology adopted in the analysis of flow through the capillary tubes of different geometries operating under adiabatic and diabatic flow conditions. It has been found from the review of the literature that there is a lot more to investigate for the flow of various refrigerants through different capillary tube geometries.     

Polymer-graphene hybride decorated Pt nanoparticles as highly efficient and reusable catalyst for the dehydrogenation of dimethylamine–borane at room temperature

Addressed herein, we report a reduced graphene oxide (rGO) nanosheet coupled with polyaniline (PANI) for platinum (Pt) nanoparticles as supporting materials. The PANI-coupled rGO (PANI@rGO) nanosheet is prepared by a simple one-step chemical assembly strategy, and Pt nanoparticles are anchored on the support of PANI@rGO through the reaction of PANI with a platinum salt. The designed PANI efficiently exposes the surface of rGO sheets and stabilizes metal nanoparticles. Consequently, the Pt@PANI-rGO catalyst exhibits good reusability, durability and high catalytic performance for dimethylamine–borane dehydrogenation reaction. The structure morphology and properties of Pt@PANI-rGO NPs were characterized by using several different techniques such as UV–Vis, XPS, TEM, XRD and HR-TEM-EDX analyses. This newly prepared catalyst can be reused again at low concentrations and temperature. They showed a high turnover frequency (42.94 h^?1) and low E_a value of 15.1 ± 2 kJ/mol for DMAB dehydrocoupling in the ambient conditions. The proposed nano architecture offers a new pathway to promote the performances of rGO in various applications; moreover, this work provides a powerful and universal synthetic strategy for such an architecture.     

Modeling and prediction of NOx emission in an LPG–diesel dual-fuel CI engine

Different alternative fuels have been proposed by various researchers in diesel engines in view of increased NO_x and particulate emissions. Out of the various methods proposed, dual fueling is one of the most important techniques that helps solve the different operational problems related to diesel engine combustion and emission. In the current study, modeling and predicting the formation of NO_x emission in a duel fuel liquefied petroleum gas (LPG)–diesel engine has been undertaken. Simulations have been conducted for various LPG flow rates at different engine loads and the predicted NO_x values are compared with the experimental values. The results found that there is a decent agreement between the forecasted and the investigational results, where the average difference is within 13.7%. Furthermore, it is found that minimum NO_x emission was observed for an LPG flow rate in the range of 0.4–0.6 kg/h and when the engine is running with 75% loading.     

Multi-objective opportunistic maintenance optimization of a wind farm considering limited number of maintenance groups

Several different models provided by researchers to maintain a wind turbine, but most of these models only focused on the case involved a single objective optimization problem. In practice, real cases of wind farms lead to multi-objective approach to optimize maintenance efforts. In this paper, based on an opportunistic approach, a multi-objective based model is proposed to optimize the maintenance of a farm involved several different types of wind turbines. The assumptions of stochastic behavior of wind velocity as well as the existence of a limited number for maintenance groups are also considered in this new approach. The proposed model considering imperfect maintenance, attempts (1) maximizing the expected rate of energy and (2) minimizing the total expected costs related to maintenance efforts. The opportunistic approach is also provided by the component's reliability threshold values. The comparative analysis addresses that the capability of the proposed model is more efficient compared to models addressed in literature.