Challenges and progress on the modelling of entropy generation in porous media: a review

Depending upon the ultimate design, the use of porous media in thermal and chemical systems can provide significant operational advantages, including helping to maintain a uniform temperature distribution, increasing the heat transfer rate, controlling reaction rates, and improving heat flux absorption. For this reason, numerous experimental and numerical investigations have been performed on thermal and chemical systems that utilize various types of porous materials. Recently, previous thermal analyses of porous materials embedded in channels or cavities have been re-evaluated using a local thermal non-equilibrium (LTNE) modelling technique. Consequently, the second law analyses of these systems using the LTNE method have been a point of focus in a number of more recent investigations. This has resulted in a series of investigations in various porous systems, and comparisons of the results obtained from traditional local thermal equilibrium (LTE) and the more recent LTNE modelling approach. Moreover, the rapid development and deployment of micro-manufacturing techniques have resulted in an increase in manufacturing flexibility that has made the use of these materials much easier for many micro-thermal and chemical system applications, including emerging energy-related fields such as micro-reactors, micro-combustors, solar thermal collectors and many others. The result is a renewed interest in the thermal performance and the exergetic analysis of these porous thermochemical systems. This current investigation reviews the recent developments of the second law investigations and analyses in thermal and chemical problems in porous media. The effects of various parameters on the entropy generation in these systems are discussed, with particular attention given to the influence of local thermodynamic equilibrium and non-equilibrium upon the second law performance of these systems. This discussion is then followed by a review of the mathematical methods that have been used for simulations. Finally, conclusions and recommendations regarding the unexplored systems and the areas in the greatest need of further investigations are summarized

Overview on the hydrodynamic conditions found in industrial systems and its impact in (bio)fouling formation

Supplementary data to this article can be found online at https://doi.org/10.1016/j.cej.2021.129348.Biofouling is the unwanted accumulation of deposits on surfaces, composed by organic and inorganic particles and (micro)organisms. Its occurrence in industrial equipment is responsible for several drawbacks related to operation and maintenance costs, reduction of process safety and product quality, and putative outbreaks of pathogens. The understanding on the role of operating conditions in biofouling development highlights the hydrodynamic conditions as key parameter. In general, (bio)fouling occurs in a higher extension when laminar flow conditions are used. However, the characteristics and resilience of biofouling are highly dependent on the hydrodynamic conditions under which it is developed, with turbulent conditions being associated to recalcitrant biodeposits. In industrial settings like heat exchangers, fluid distribution networks and stirred tanks, hydrodynamics play a dual function, affecting the process effectiveness while favouring biofouling formation. This review summarizes the hydrodynamics played in conventional industrial settings and provides an overview on the relevance of hydrodynamic conditions in biofouling development as well as in the effectiveness of industrial processes.This work was financially supported by: Base Funding - UIDB/00511/2020 of LEPABE and UIDB/00081/2020 of CIQUP funded by national funds through the FCT/MCTES (PIDDAC); Project Bio cide_for_Biofilm - PTDC/BII-BTI/30219/2017 - POCI-01-0145-FEDER 030219, ABFISH – PTDC/ASP-PES/28397/2017 - POCI-01-0145- FEDER-028397 and ALGAVALOR - POCI-01-0247-FEDER-035234, fun ded by FEDER funds through COMPETE2020 – Programa Operacional Competitividade e Internacionalizaçao ˜ (POCI) and by national funds (PIDDAC) through FCT/MCTES; Portuguese Foundation for Science and Technology (FCT) under the scope of the strategic funding of UIDB/04469/2020 unit and BioTecNorte operation (NORTE-01-0145-FEDER 000004) funded by the European Regional Development Fund under the scope of Norte2020 - Programa Operacional Regional do Norte; FCT/ SFRH/BD/147276/2019 (Susana Fernandes) and SFRH/BSAB/150379/2019 (Manuel Simoes).info:eu-repo/semantics/publishedVersio

CFD Applications in Energy Engineering Research and Simulation: An Introduction to Published Reviews

Computational Fluid Dynamics (CFD) has been firmly established as a fundamental discipline to advancing research on energy engineering. The major progresses achieved during the last two decades both on software modelling capabilities and hardware computing power have resulted in considerable and widespread CFD interest among scientist and engineers. Numerical modelling and simulation developments are increasingly contributing to the current state of the art in many energy engineering aspects, such as power generation, combustion, wind energy, concentrated solar power, hydro power, gas and steam turbines, fuel cells, and many others. This review intends to provide an overview of the CFD applications in energy and thermal engineering, as a presentation and background for the Special Issue “CFD Applications in Energy Engineering Research and Simulation” published by Processes in 2020. A brief introduction to the most significant reviews that have been published on the particular topics is provided. The objective is to provide an overview of the CFD applications in energy and thermal engineering, highlighting the review papers published on the different topics, so that readers can refer to the different review papers for a thorough revision of the state of the art and contributions into the particular field of interest

Performance of continuous-flow micro-reactors with curved geometries. Experimental and numerical analysis

One of the major challenges in the design of micro-devices, when very fast reactions are carried out, is to overcome the limited performance due to the poor mixing efficiency of the reactants. Here, we report a holistic analysis of reactants mixing and reaction rate in liquid phase flow micro-reactors with curved geometries. In this sense, a mathematical model that accounts for momentum and mass conservation equations, together with species transport and chemical reaction rate under isothermal conditions, has been developed using computational fluid dynamics techniques (CFD). To validate the predictive model, four micro-reactor geometries with different radius and curved length (straight reactor, two types of serpentines and an Archimedean spiral) have been evaluated. Simulated results proved that mixing is promoted through the formation of Dean vortices as a consequence of the reduction of the radius of curvature and at the same time of the extension of the curve. Thus, the overall performance of the micro-reactor is improved because mass transport limitations are minimized and the process kinetics are greatly enhanced. Accordingly, the spiral micro-reactor reported the best performance by reducing by half the time required to obtain 95 % conversion when compared with the straight reactor. Simulated findings have been confirmed with the experimental analysis of the reaction between aqueous ammonium and hypochlorite ions. Very good agreement between simulated and experimental results has been achieved with an error lower than 10 %. Therefore, the robust model herein reported is a novel and valuable tool to assist in the optimum design of micro-reactors for fluid-phase isothermal applications.Financial assistance from the project RTI2018-093310-B-I00 (MCI/AEI/FEDER,UE) is gratefully acknowledged

Preservation of a two-wing Lorenz-like attractor with stable equilibria

"In this paper, we present the preservation of a two-wing Lorenz-like attractor when in the Lorenz system a feedback control is applied, making two of its equilibria a sink. The forced system is capable of generating bistability and the trajectory settles down at one stable equilibrium point depending on the initial condition when the forced signal is zero. Due to a variation in the coupling strength of the control signal the symmetric equilibria of the Lorenz system move causing the basins of attraction to be the dynamic bounded regions that change accordingly. Thus, the preservation of a two-wing Lorenz-like attractor is possible using a switched control law between these dynamic basins of attraction. The forced switched systems also preserve multistability regarding the coupling strength and present multivalued synchronization according to the basin of attraction in which they were initialized. Bifurcations of the controlled system are used to exemplify the different basins generated by the forcing. An illustrative example is given to demonstrate the approach proposed.

Optimization of pretreatment/hydrolysis processes of agro-food wastes to support biorefinery developments

The study carried out during the present Ph.D. program aimed at investigating the use of agro-food processing wastes (AFWs) to produce fermentable sugars and/or value-added bioproducts according to the biorefinery approach. The work was carried out at the Dipartimento di Ingegneria Chimica, dei Materiale e della Produzione Industriale of the Università degli Studi di Napoli ‘Federico II’. The activities were focused on the release of sugars (pentoses and hexoses) from the AFWs investigated through different pretreatment processes, followed by enzymatic hydrolysis step. The fermentation of the produced sugar solutions was also carried out to produce biobutanol and succinic acid. Two AFWs were investigated: coffee silverskin and apple pomace. Coffee silverskin as feedstock for biorefinery applications: Coffee silverskin (CSS) are the residual thin teguments wrapping and protecting the external layer of green coffee beans. It is produced in large amount during the roasting phase of green coffee beans. It is mainly composed of carbohydrates (40% w/w) and lignin (30% w/w). The study of CSS was aimed at investigating the pretreatment, enzymatic hydrolysis and fermentation of this residue. A combination of mild alkaline solution and ultrasound (US) was applied to pretreat CSS. Biomass loading, sonication time, alkali concentration, residence time in autoclave were the parameters investigated and analysed according to a response surface methodology approach. The process was characterized in terms of sugar yield after the enzymatic hydrolysis of pretreated CSS. Alkali concentration and residence time in autoclave were the most significant parameters affecting the pretreatment process according to the statistical analysis. Under optimal operating conditions the maximum sugar yield was of 60% g/g. Moreover, the phenolic content assessed in the supernatant after CSS pretreatment was (25 mgGAE/graw_CSS) larger than that reported in the literature for similar works on CSS. The study about enzymatic hydrolysis of alkali-pretreated CSS highlighted that both biomass loading and cellulolytic enzymes loading affect sugars release. A sugar yield higher than 90% g/g was obtained with 10% w/v biomass loading and 80 FPU/gcellulose enzyme loading. The rich-in-sugars hydrolysate obtained after pretreatment and enzymatic hydrolysis of CSS was supplemented with some other nutrients and used as media for fermentation of C. acetobutylicum (ABE production) and A. succinogenes (succinic acid production). Concentration of 3.2 g/L ABE and 20.8 g/L succinic acid was obtained, at the end of each fermentation, respectively. With the proposed process (pretreatment, hydrolysis and fermentation), we were able to obtain fermentable sugars, lignin, solvents (ABE fermentation) and biochemicals (phenolic compounds and succinic acid) from CSS, stressing the potentialities of this residue to be used in biorefinery processes. Apple pomace as feedstock for biorefinery applications: Apple is a fruit widely produced and eaten all over the world. In Italy, more than 2.5 million tons of apple are produced every year. Worldwide, 20 % of fresh apple is processed into value added products: apple juice concentrate (65%), apple cider, wine, vermouth, purees, jams and dried apple products. The main residue of these processes is the apple pomace. This residue accounts for 25-35% of the dry mass of apple. The apple pomace is a good lignocellulosic candidate to be used in a biorefinery process, and it was already used as feedstock for production of butanol, ethanol and crude protein (or enzymes), citric acid, microbial colours, bio-hydrogen. Pretreatment of apple pomace was carried out by means of the ligninolytic enzyme “laccase”. The aim of this study was to investigate the possibility to carry out biological pretreatment and hydrolysis of apple pomace in a bubble column bioreactor. The proposed pretreatment/hydrolysis system aimed at the optimization of some parameters affecting the process in terms of amount of sugars released during the whole process. The enzymatic delignification was carried out using fungal laccases from Pleurotus ostreatus. Then the cellulose in the pretreated biomass was hydrolysed using Cellic CTec2® (Novozymes). The optimization of enzymatic pretreatment/hydrolysis process indicated that all the parameters investigated (biomass loading, laccase loading, gas (air) flow rate, cellulase loading) affect the performances of the process in terms of biomass composition and sugars release during the enzymatic hydrolysis. 15 %w/v biomass loading, 60 nL/h air flow rate, 30 U/gbiomass laccase concentration, and 20 FPU/gcellulose cellulase concentration were the optimal conditions for the sequential enzymatic pretreatment and hydrolysis process in the bubble column. All the experiments were carried out in a lab-scale bubble column. Under the operating conditions investigated, a maximum sugar yield of 0.34 gsugars/graw biomass was obtained, corresponding to 61% (gsugars/gsugars available) of the theoretical sugar yield obtainable from raw apple pomace. The high amount of sugars obtained, make AP one of the main feedstocks to be used in fermentative processes to produce solvents and biochemicals. Moreover, a solid residue of lignin that can be recovered and reused was obtained at the end of the process. ABE fermentation at University of Western Ontario (UWO) (Canada): The reasearch activity was focused on the ABE fermentation of an industrial product derived from corn: corn syrup. The objectives were: i) to screen four Clostridium species to identify the microorganism characterized by the best fermentative performance in terms of solvents production, yield and productivity; ii) to study the effects of substrate/product concentration on fermentation process (substrate/product inhibition effects); iii) to increase solvents production by means of a fed-batch process. The final aim of this project was to investigate the possibility of using corn syrup to produce solvents through ABE fermentation. The details regarding this activity are reported in the section Appendix. Regarding the main topic of my Ph.D. project, the work carried out at UWO have had a double purpose: 1) to improve my skills in anaerobic fermentative processes carried out by different Clostridium species in accordance to the final aim of the European project Waste2Fuels that is the bio-butanol production starting from agro-industrial residues; 2) to compare the fermentative performances of Clostridium spp. on agro-industrial products with various degrees of difficulty to ferment (in particular corn syrup and coffee silverskin)

Pure hydrogen production by chemical looping technology: use of iron as redox element and bioethanol as renewable reductant

The use of hydrogen as an alternative energy carrier is a promising solution to overcome the global warming issues. Hydrogen is light, storable, energy-dense, and when burned it produces no emissions of pollutants or greenhouse gases. However, since it is not naturally available, the environmental impact of hydrogen is closely linked to the type of source used for its production. The 96% of the commercial H2, mainly used in chemical and petrochemical sectors, is produced from fossil fuels, resulting globally in 900 Mt of CO2 per years. The study and optimization of alternative hydrogen production technologies based on renewable sources is therefore essential to make hydrogen a green fuel and to achieve the Zero-Net Emissions target of 2050. One of the most interesting applications of H2 as alternative and clean fuel is in the in the automotive sector, which up to now contribute for a large part to global CO2 emissions. The use of H2 in the sector of automotive is now possible thanks to the development of Fuel Cells zero-emission vehicles. Among them, Proton Exchange Membrane Fuel Cells (PEMFC) are the most promising one, able to converts the chemical energy of H2 directly into electricity already at low temperatures, with an efficiency value three times higher than internal combustion engine powered by gasoline. However, for their correct functioning, high purity hydrogen stream is required, with a strict limit on CO concentration (CO<10ppm), a poison of the Pt-based fuel cell catalyst. Chemical looping hydrogen (CLH) technology allows the direct production of pure hydrogen in a totally green way. The process is based on the ability of iron oxides to transfer oxygen atoms between a fuel and an oxidant, maintaining constant its activity for high number of redox cycles. The process is composed by two steps: the iron oxides is first reduced to the metal form by feeding a fuel and then Fe is oxidized by steam to produce pure hydrogen and to restore the iron oxides, which participate in a subsequent redox cycle. The absence of purification units makes the CLH process suitable for the decentralized small-scale hydrogen production, solving the issues of hydrogen transportation and storage. The main purpose of this work is to demonstrate the feasibility of producing pure and green H2 by a CLH process, suitable to be directly fed to PEMFC, using bioethanol as renewable fuel. The experimental work focused on the synthesis of Fe-based materials, having high activity and high resistance to deactivation, evaluating the process efficiency in a fixed bed bench-scale plant. The influence of the operative conditions on the process efficiency was investigated, focusing the attention on the effect of different redox temperature (675°-750°C) at constant pressure (1 bar) and different flow rate of reductant fuel, with the aim of identifying the optimal conditions. The thesis is structured into 10 chapters. The first part introduces the issues related to global warming and increased energy demand, mainly based on fossil fuel. Then, chemical looping process is presented as a promising solution to overcome the criticalities of the use of H2 as fuel. The second chapter reports the recent advances in scientific literature in the field of CLH technology. Then, in Chapter 3 the experimental set-up and the synthesis methods of the iron-based oxygen carrier are described in detail; the characterization of the synthesized particles is reported in Chapter 4. In Chapter 5 the decomposition of bioethanol is studied to evaluate the feasibility of using it as renewable source of reducing agents; furthermore, tests of CLH are performed on commercial Fe2O3 powders aimed at the production of pure hydrogen by monitoring the amount of ethanol fed in reduction. Then, the influence of MnO2 addition on enhancing the iron oxides reducibility and therefore on the maximization of pure hydrogen yields is studied. In Chapter 6 the experimental results on the use of structural promoters (Al2O3, MgO and CeO2) to improve Fe oxides thermal resistance is deeply investigated focusing the attention on the influence of promoter addition on iron oxide redox activity and on the sample morphology. In Chapter 7 a dedicated study of the couple Fe/Al is performed, evaluating the influence of temperature on the process efficiency values and on Fe/Al interaction. The effect of the addition of Mn oxide to enhance the Fe oxides reduction degree and to avoid the production of hydrogen contaminated by CO, when Al2O3 is present as a structural promoter, is investigated in Chapter 8. In Chapter 9 Temperature programmed reduction (TPR) profiles of the most active samples are reported aiming to deeply study the influence of promoters in kinetics of iron oxides reduction and on the iron oxides reduction mechanism. At the end, in Chapter 10, based on the promising results obtained with OCs powders, the use of Fe-based foam, a highly porous materials suitable to be used in fixed bed reactor by keeping low pressure drop is studied with the aim of process scalability

MEMBRANE BIOREACTOR FOR ENHANCED ENZYMATIC HYDROLYSIS OF CELLULOSE

With the rising environmental concerns related to fossil fuels utilization and the depletion of these resources, interest in bioethanol from lignocellulosic waste as an alternative, sustainable energy source has been increasing. Date palm waste is considered a good feedstock for bioethanol production, especially in countries of large date palm plantations, such as the United Arab Emirates. In the lignocellulose to bioethanol process, the enzymatic hydrolysis of celluloses to produce simple sugars that can be converted to bioethanol by fermentation is the most challenging step, and enhancing it is essential for efficient and feasible operation. Enzyme inhibition by the products is one of the several problems that hinders the cellulose bioconversion. To resolve this problem, a novel membrane bioreactor (MBR) was designed with an inverted dead-end filtration concept for simultaneous removal of the product during the reaction. Polyethersulfone membranes (PES) were used, and their selectivity in allowing only product permeation was proven. The effects of water flowrate and initial substrate concentration were investigated, and a mathematical kinetic model that was based on the mechanistic steps was developed to predict the dynamic behavior of the system, and the kinetic parameters were estimated by fitting the experimental data. The experimental results were also used to develop a statistical non-linear interactive model. Using standard cellulose, the glucose production yield increased from 7% without product separation to 45% with product separation. Both kinetic and statistical models showed good agreement (R2: 0.96 and 0.97, respectively). The process was optimized, and the optimal conditions were determined to be at substrate concentration of 2.67 g/L and a water flowrate of 0.8 mL/min, at which a maximum yield of 86.7% was achieved.To increase the efficiency of the process by increasing solids loading and mixing quality, another novel tubular radial-flow MBR was designed. The effectiveness of the inverted dead-end MBR versus radial-flow MBR designs was assessed using real, complex lignocellulose biomass, namely date seeds (DSs). The tubular radial-flow MBR used here had more than a 10-fold higher membrane surface area than the flat-sheet MBR design. With simultaneous product separation using the flat-sheet inverted dead-end filtration MBR, a total reducing sugars yield of 10.8% from pretreated DSs was achieved within 8 h of reaction, which was three times higher than the yield without product separation, which was only 3.5% within the same time and under the same conditions. The superiority of the tubular radial-flow MBR to hydrolyze pretreated DSs was confirmed with a total reducing sugars yield of 29% within 8 h. A detailed kinetic model was developed to predict the dynamic behavior of the tubular radial-flow MBR, and the kinetic parameters were estimated from the experimental data. The novel reactor was proved to successfully operate at high solids loading, and with a developed statistical non-linear interactive model the total reducing sugars production was optimized with optimal conditions of substrate concertation of 28.9 g/L and water flowrate of 1.2 mL/min resulting in a maximum glucose production of 8.7 g. In addition, the effects of different glucose concentrations, water flowrates, and membrane cut-offs on glucose diffusion were studied. The promising results obtained by this research could pave the way for an economic lignocellulose-to-bioethanol process

Biodiesel Production From Rubber Seeds (Hevea brasiliensis) with In Situ and Acid Catalyst Method by Using Ultrasonic Assisted

Biodiesel production from the non-edible raw materials become very important because will not collide with human needs. Furthermore, this research studies to biodiesel production with ultrasonic assisted by in situ method. The raw material uses rubber seed and ultrasonic process use ultrasonic cleaner. The objective of this research was to study the influence of catalyst concentration and ratio of raw materials to methanol. The process was done at 60oC for 30 minutes reaction time. The results showed that maximum yield of Fatty Acid Methyl Ester (FAME) was 34.74% by using sulphuric acid 0.1% as catalyst and rubber seed ratio to methanol 1:1.75 (w/v)