Effect Of Mixture Composition Research Articles

Ultra-lean hydrogen-air flames initiated by a hot surface

The benefits of using hydrogen as a fuel for rocket engines dictate the necessity of a deep understanding of possible scenarios of hydrogen ignition and subsequent combustion. Safety requirements on launch sites and hydrogen transportation and storage facilities should be elaborated based on a thorough investigation of hydrogen flame development. The paper aims to provide a detailed numerical analysis of the hot wall ignition of hydrogen-air mixtures with compositions near low flammability limits. It is shown that the development of ultra-lean flames initiated by a hot spot on the solid wall possesses several features compared to ultra-lean flames ignited by a point energy source. Three modes of flame development are observed: stable flame column with bow-shaped flame structure on top, individual flame kernel, and unstable flame column with multiple kernels generation. Effects of mixture composition, along with the impact of hot spot size, are analyzed. Column tip acceleration mechanism is determined. All of the combustion modes obtained are grouped in the diagram, providing information on the limits of various combustion modes depending on the mixture concentration and hot spot size.

The effect of mixture composition on the compressive strength and absorption of geopolymer paving blocks

The effect of mixture composition on the compressive strength and absorption of geopolymer paving blocks

Thermodynamic, economic and environmental assessment of a novel organic Rankine cycle-vapor compression refrigeration system using zeotropic mixture

The improvement of system configuration is an effective method to improve performance of the organic Rankine cycle-vapor compression refrigeration (ORC-VCR) system. A novel system with a recuperator on the ORC side and a flash tank on the VCR side is proposed. Firstly, the theoretical model of thermodynamic, economic and environmental performance is constructed. Then, the novel system is compared with the basic ORC-VCR system. Next, the effects of operating parameters on performance of the proposed system are investigated. Finally, a comparison of system performance in different positions of phase transition temperature is carried out. The results show that the coefficient of performance(COP), exergy efficiency, dynamic payback period(DPP), net present value(NPV) and annual emission reduction(AER) of the novel system are 0.38, 5.94 %, 8.89 years, 1.52 × 106 $ and 5.77 × 106 kg, respectively. Compared with the basic ORC-VCR system, the improvement in thermodynamic performance of the novel system is relatively preferable to the deterioration in economic performance. Moreover, the effect of mixture composition on system performance is distinct in different positions of phase transition temperature. It is shown that using zeotropic mixture is not appropriate in all cases. This paper can provide theoretical guidance to further improve performance of the ORC-VCR system.

A neutron radiography study on the drying of cement mortars: Effect of mixture composition and crack length

The drying process has a prominent impact on the volume changes, crack propagation and durability of concrete structures. This study is to quantify the moisture distribution in real-time drying cement mortars. Mortar prisms with different water-to-cement ratios (w/c) and superabsorbent polymers (SAP) amounts were cut into slices and prepared with distinct lengths of cut notches. They were subjected to accelerated drying during neutron radiography measurements. In mortars with higher w/c, the coarser pores accelerate water transport and lead to more rapid drying. The large voids and the SAP in the bulk of the specimens are emptied well before the exposed surface starts to dry out. The presence of notches enhances drying. However, the moisture loss through the notches is less efficient than through the external surfaces. The competition between evaporation from the surfaces and moisture transport within the material, in both liquid and gas forms, governs the moisture distribution evolution.

Properties of Palm Oil Ash Geopolymer Containing Alumina Powder and Field Para Rubber Latex

Most geopolymer binder is produced using raw materials comprising powder with high silica and alumina content. Additionally, fine aggregate is prepared with river sand for high bulk density. This research proposes using palm oil ash (POA) for the main binder and palm oil clinker (POC) for the fine aggregate. The chemical composition of POA has high levels of silica but low alumina, so it must undergo partial replacement with alumina powder (AP). POA and POC are waste by-products of electrical power plants. The properties to be investigated include compressive strength, bulk density, water absorption, and microstructure. The effect of mixture composition, i.e., POA and field Para rubber latex (FPRL), on those properties is of particular interest. POA was substituted by AP and FPRL at 2.5%, 5%, 7.5%, and 10%, and at 1%, 3%, 5%, and 10%, respectively. Geopolymer mortars were cured at ambient temperature for 24 hours and kept at ambient temperature until testing. The compressive strengths of the geopolymer mortars were tested at 1, 7, and 28 days. The results showed that the optimal mixture consisted of 5% AP in the case of AP only and 1% FPRL in the case of FPRL only, while the ternary optimal mixture of 1% FPRL and 7.5% AP achieved higher compressive strengths than the control (CT) sample at 28.16, 19.98, and 25.30 MPa, respectively, after 28 days of curing. Bulk density increased with the addition of AP and FPRL. The microstructures of the geopolymer samples investigated using SEM-EDX showed the presence of different elements with different mixtures and displayed a dense, compact geopolymer matrix with high compressive strength. Using large amounts of POA in combination with AP and FPRL improved the environmental aspects of landfill disposal. Doi: 10.28991/CEJ-2023-09-05-017 Full Text: PDF

Effects of mixture composition on oxidation and reactivity of DME/NH3/air mixtures examined by a micro flow reactor with a controlled temperature profile

Effects of mixture composition and equivalence ratios on oxidation and reactivity of dimethyl ether (DME)/ammonia (NH3) mixtures are investigated based on weak flame responses observed in a micro flow reactor with a controlled temperature profile (MFR). For observations, the NH3 fractions in fuel blends are varied as 0–50%. Three equivalence ratios (ϕ = 0.5, 1.0 and 1.2) are examined. A combined chemical reaction model for DME/NH3 mixtures is developed and used to simulate oxidation of DME/NH3 mixtures in MFR. Under the stoichiometric conditions, the DME oxidation is promoted and the mixture reactivity is enhanced as the NH3 fractions in fuel blends increase from 0 to 15%. As the NH3 fractions further increase from 15 to 50%, CO oxidation is inhibited; the mixture reactivities are suppressed strongly. Chemical reaction analyses indicate that NOx produced by the NH3 oxidation converts less-reactive radicals into more-reactive radicals (HO2→OH and CH3→CH3O) through the NO–NO2 catalytic loop at the intermediate temperatures of 800–1000 K. However, with larger NH3 fractions in fuel blends, the OH radical consumption by NH3 increases, thereby inhibiting CO oxidation. Moreover, when the equivalence ratios are varied, mixture reactivity is more inhibited as equivalence ratios increase, although they change only slightly irrespective of the equivalence ratios in neat DME cases. With richer equivalence ratios, more OH radicals are consumed by DME, CH2O, NH3, and H2. Moreover, the CO oxidation is inhibited in the intermediate temperature zone when NH3 is blended because CO has lower priority for OH radical consumption among these species as a result of its high activation energy. Results of this study demonstrate the strong potential of NH3 to control reactivity of hydrocarbon mixtures over a wide range by changing the mixture composition and equivalence ratios.

3D Printing of Biomass–Fungi Composite Material: Effects of Mixture Composition on Print Quality

It is known that 3D printing can facilitate greater design flexibility in the printing of custom shapes for packaging and construction applications using biomass–fungi composite materials. The feasibility of this new method was demonstrated by a preliminary experiment, the results of which were reported in a journal publication in 2020. As a follow-up, this paper reports on an experimental study on the relationship between the mixture composition (i.e., the psyllium husk powder content) and print quality using this new method. Four mixtures were prepared by varying the amounts of psyllium husk powder (in grams) added to 400 mL of water. The ratios (g/mL) of psyllium husk powder weight (wp) over volume of water (vw) for the mixtures were 0, 1:40, 2:40, and 3:40. Each mixture also contained 100 g of biomass–fungi material and 40 g of whole wheat flour. The print quality of the samples was evaluated based on the extrudability and shape stability. The results showed that mixtures without any psyllium husk powder were not extrudable. An increase in the ratio of psyllium husk powder to water from 1:40 to 2:40 resulted in improved print quality; however, when the psyllium husk powder to water ratio was increased to 3:40, the extrudability became worse. This phenomenon was explained by analyzing the rheological properties of the mixtures.

Effect of Mixture Composition on Electrophysical Parameters and Emission Spectra of Dichlorodifluoromethane Plasma with Oxygen and Helium

Effect of Mixture Composition on Electrophysical Parameters and Emission Spectra of Dichlorodifluoromethane Plasma with Oxygen and Helium

Recycling of plastic waste using flash pyrolysis – Effect of mixture composition

Recovery of plastic waste is becoming crucial since the amount of such waste increases continuously. The objective of this study is to investigate the potential of the pyrolysis technique for the recovery of plastic waste. In that frame, the influence of temperature (550°C or 600°C) on the pyrolysis of pure polypropylene (PP), polyethylene (PE), polystyrene (PS) and polyethylene terephthalate (PET) was first studied. It is shown that whatever the type of polymer, aromatic compounds are mainly formed and could reach 55wt.-% of the oil fraction for PP and 31wt.-% for PE at 550°C. In a second step, a PP/PE mixture and a model mixture representative of the packaging plastic waste stream were pyrolyzed to investigate the influence of a combination of polymers on the proportions and composition of the different fractions. The pyrolysis of the polymer mixtures shows that, even if the aromatic compounds formed are similar to those obtained for the virgin polymers, the proportion of aromatic compounds is much more important than when the polymers are pyrolyzed alone. Indeed, mixing PE with PP at a 50/50 ratio does not affect the amount of liquid, gas and solid fractions but leads to the formation of a higher quantity of xylene (39 wt-%) at 550°C. The combination of the plastics in the model mixture has also led to a decrease of the amount of waxy compounds. Furthermore, it was shown that a higher amount of aromatics than expected was formed. As a conclusion, this study demonstrates that pyrolysis is an effective technique to recover plastic waste as aromatic compounds for the petroleum industry. In the specific conditions used in this study (proposed model mixture and pyrolysis conditions), it will favor the idea that sorting is not needed to recover plastic waste through pyrolysis since aromatics formation is favored when the stream is composed of a mixture of polymers.

Influence of mix composition on the properties of recycled aggregate concrete

AbstractThere is an increasing trend towards using recycled aggregate (RA) in concrete due to the shortage of high quality natural aggregates. The use of RA in concrete results in the conservation of natural resources, protects the environment and encourages sustainable construction. Though some studies have been conducted on the use of recycled aggregate concrete (RAC), the effect of mixture composition on its properties has not been well addressed. In the reported study, the effect of mixture composition, namely cement content and water/cement ratio and the proportion of RA on the mechanical properties of RAC was evaluated, with the intention of developing varying grades of RAC. As reported in earlier studies, the properties of RAC were generally inferior to that of normal aggregate concrete (NAC). Notwithstanding this, RAC with acceptable mechanical properties can be produced utilizing RA, for example RAC with low strength can be used in non‐structural applications. The construction industry should be encouraged to use RAC in building construction; as its use will lead to technical, economic and environmental benefits. Further, the use of RAC will lead to a sustainable development of the construction industry, particularly in regions that lack good quality natural aggregates. Based on the data developed in the reported study, the following quantities of RA are recommended to produce RAC: (i) 20% to produce low strength (20–30 MPa) concrete, (ii) 40% to produce medium (30–50 MPa) concrete and high strength (more than 50 MPa) concrete. Mathematical correlations between the mechanical properties of RAC with varying mix design parameters, such as cement content and water cement ratio and the quantity of RA, are also reported. These correlations can be used to predict the properties of RAC prepared with other proportions of RA and mix design parameters.

Macro- and Micro-Properties of Engineered Cementitious Composites (ECCs) Incorporating Industrial Waste Materials: A Review

Engineered cementitious composites (ECCs) possessing strain-hardening behavior have been developed utilizing supplementary cementitious materials and fibers. The developed ECCs exhibit excellent performance in terms of mechanical and thermal properties and are highly durable. However, the latest trend is to use industrial waste materials (IWMs), as alkali-activated materials, in the development of ECCs. In this paper, a state-of-the-art review on the development of sustainable-ECCs utilizing IWMs is presented. The formulations of binders and fibers, used in the production of ECCs, are described. The effect of mixture composition on the mechanical properties, such as compressive and tensile strength, and durability of ECCs is discussed. In addition, the importance of micromechanics modeling for producing a strain-hardened ECC is presented. Further, the engineering applications of ECCs in structural and repair fields are discussed along with suggestions for future research.

Accelerated carbonation technology granulation of industrial waste: Effects of mixture composition on product properties.

The use of accelerated carbonation technology in combination with a granulation process was employed to produce aggregates from a variety of industrial wastes, which included municipal solid waste incineration fly ash and air pollution control residue, oil shale ash, cement kiln dust, and quarry fines that have been produced in Estonia. Focusing mainly on the effects produced by the content of municipal solid waste incineration ash in the admixtures, the granule compositions were varied in order to tailor granule properties on the basis of CO2 uptake, strength development, leaching behaviour, microstructure, and morphology. All the steps involved in the accelerated carbonation technology granulation process, from mixing with additives to granulation and carbonation treatment, were carried out in the same apparatus - an Eirich EL1 intensive mixer/granulator. The amount of CO2 that was bound ranged from 23 to 108 kg per tonne of waste. The granules that included the optimised mixture of municipal solid waste incineration air pollution control residue, oil shale ash, cement kiln dust, and ordinary Portland cement were characterised by the highest compressive strength (4.03 MPa) and water durability for the size range of 4-10 mm. In addition, the process was found to be effective in reducing alkalinity (pH < 11.5) and immobilising heavy metals (especially zinc) and chloride. The composition and properties of the respective waste materials and mechanisms associated with the characteristics of the resulting granules were also addressed.

Effect of mixture composition on the mechanical behaviour of cold recycled asphalt mixtures

ABSTRACT Cold recycled asphalt mixtures (CRAMs) are generally comprised by reclaimed asphalt pavement, virgin aggregates, bitumen stabilising agents (asphalt emulsion or foamed asphalt) and active filler (Portland cement or hydrated lime). Depending on the type and content of each mixture constituent, the CRAM may exhibit different mechanical behaviours. The aim of this study is to evaluate the influence of mixture composition on the mechanical behaviour of CRAMs. The materials used were collected during the construction of an experimental test section and were used as base course mixtures. From triaxial resilient modulus test and dynamic modulus test, it was found that the type and content of bitumen stabilising agent and active filler substantially influence the behaviour of the CRAM. From triaxial resilient modulus tests, it was observed that the mixtures with cement addition behaved similarly to cementitious materials (independent of the confining pressure), while the ones with hydrated lime resembled a granular material (dependent of the stress-state). The dynamic modulus test results indicated that the CRAMs also exhibit viscoelastic properties. Besides, the test provided a clear difference between mixtures stabilised with either asphalt emulsion or foamed asphalt.

Mixing Characteristics of Binary Mixture with Biomass in a Gas-Solid Rectangular Fluidized Bed

Aiming to better understand the biomass pyrolysis and gasification processes, a detailed experimental study of the mixing characteristics is conducted in a fluidized bed with binary mixtures. Rapeseed is used as biomass, and silica sand or resin as inert material. The effect of mixture composition, initial packing manner, and superficial gas velocity on the concentration distribution is investigated in a rectangular fluidized bed by means of photography and sampling methods. The results show that the mixture composition plays an important role in the axial solids profile of binary mixtures. The mixing behavior of binary mixture is dominated by the bubble movement. The axial distribution of binary mixtures becomes uniform with increasing superficial gas velocity, whilst no obvious effect of initial packing manner is observed in this study.

RETRACTED: Computational Fluid Dynamics Modeling of the Catalytic Partial Oxidation of Methane in Microchannel Reactors for Synthesis Gas Production

This paper addresses the issues related to the favorable operating conditions for the small-scale production of synthesis gas from the catalytic partial oxidation of methane over rhodium. Numerical simulations were performed by means of computational fluid dynamics to explore the key factors influencing the yield of synthesis gas. The effect of mixture composition, pressure, preheating temperature, and reactor dimension was evaluated to identify conditions that favor a high yield of synthesis gas. The relative importance of heterogeneous and homogenous reaction pathways in determining the distribution of reaction products was investigated. The results indicated that there is competition between the partial and total oxidation reactions occurring in the system, which is responsible for the distribution of reaction products. The contribution of heterogeneous and homogeneous reaction pathways depends upon process conditions. The temperature and pressure play an important role in determining the fuel conversion and the synthesis gas yield. Undesired homogeneous reactions are favored in large reactors, and at high temperatures and pressures, whereas desired heterogeneous reactions are favored in small reactors, and at low temperatures and pressures. At atmospheric pressure, the selectivity to synthesis gas is higher than 98% at preheating temperatures above 900 K when oxygen is used as the oxidant. At pressures below 1.0 MPa, alteration of the dimension in the range of 0.3 and 1.5 mm does not result in significant difference in reactor performance, if made at constant inlet flow velocities. Air shows great promise as the oxidant, especially at industrially relevant pressure 3.0 MPa, thereby effectively inhibiting the initiation of undesired homogeneous reactions.

Low temperature Cu–Cu bonding by transient liquid phase sintering of mixed Cu nanoparticles and Sn–Bi eutectic powders

Fluxless bonding of plateless Cu–Cu substrates at processing temperature lower than 250 °C and low pressure of 0.1 MPa was achieved by transient liquid phase sintering (TLPS) of mixed Cu nanoparticles and Sn–Bi eutectic powders. The effects of mixture composition, and sintering temperature on the shear strength, microstructure, and remelting temperature were investigated. Lowering the sintering temperature of Cu mixed with 65 weight percentage of Sn–Bi (Cu–65SnBi) resulted in decreased shear strength, however, at 200 °C sintering temperature, the obtained highest shear strength was more than 20 MPa. It was found that it is essential to use Cu nanoparticles to accelerate the consumption so that no initial Sn–Bi phases remained after processing. The liquid phase generated at approximately 196 °C during sintering from the reaction between newly formed Cu6Sn5 and Bi-phase was expected to facilitate the densification and strengthening of the joints. Although this newly generated liquid phase was known to solidify as hypereutectic Sn–Bi, by controlling the sintering temperature at 200 °C, the remelting event at 139 °C was not observed by differential scanning calorimetry. It is assumed that the proportion of solidified Sn–Bi eutectic phases in Cu–65SnBi that was sintered at 200 °C were significantly small, hence, when reheated at 150 °C, the obtained shear strength was equivalent to that at room temperature.

Intensified Biobutanol Recovery by using Zeolites with Complementary Selectivity.

A vapor-phase adsorptive recovery process is proposed as an alternative way to isolate biobutanol from acetone-butanol-ethanol (ABE) fermentation media, offering several advantages compared to liquid phase separation. The effect of water, which is still present in large quantities in the vapor phase, on the adsorption of the organics could be minimized by using hydrophobic zeolites. Shape-selective all-silica zeolites CHA and LTA were prepared and evaluated with single-component isotherms and breakthrough experiments. These zeolites show opposite selectivities; adsorption of ethanol is favorable on all-silica CHA, whereas the LTA topology has a clear preference for butanol. The molecular sieving properties of both zeolites allow easy elimination of acetone from the mixture. The molecular interaction mechanisms are studied by density functional theory (DFT) simulations. The effects of mixture composition, humidity and total pressure of the vapor stream on the selectivity and separation behavior are investigated. Desorption profiles are studied to maximize butanol purity and recovery. The combination of LTA with CHA-type zeolites (Si-CHA or SAPO-34) in sequential adsorption columns with alternating adsorption and desorption steps allows butanol to be recovered in unpreceded purity and yield. A butanol purity of 99.7 mol % could be obtained at nearly complete butanol recovery, demonstrating the effectiveness of this technique for biobutanol separation processes.

Preparation of chitosan/tripolyphosphate nanoparticles with highly tunable size and low polydispersity

Nanoparticles prepared through the ionotropic gelation of chitosan with tripolyphosphate (TPP) have been extensively studied as vehicles for drug and gene delivery. Though a number of these works have focused on preparing particles with narrow size distributions, the monodisperse particles produced by these methods have been limited to narrow size ranges (where the average particle size was not varied by more than twofold). Here we show how, by tuning the NaCl concentration in the parent chitosan and TPP solutions, low-polydispersity particles with z-average diameters ranging between roughly 100 and 900nm can be prepared. Further, we explore how the size of these particles depends on the method by which the TPP is mixed into the chitosan solution, specifically comparing: (1) single-shot mixing; (2) dropwise addition; and (3) a dilution technique, where chitosan and TPP are codissolved at a high (gelation-inhibiting) ionic strength and then diluted to lower ionic strengths to trigger gelation. Though the particle size increases sigmoidally with the NaCl concentration for all three mixing methods, the dilution method delivers the most uniform/gradual size increase − i.e., it provides the most precise control. Also investigated are the effects of mixture composition and mixing procedure on the particle yield. These reveal the particle yield to increase with the chitosan/TPP concentration, decrease with the NaCl concentration, and vary only weakly with the mixing protocol; thus, at elevated NaCl concentrations, it may be beneficial to increase chitosan and TPP concentrations to ensure high particle yields. Finally, possible pitfalls of the salt-assisted size control strategy (and their solutions) are discussed. Taken together, these findings provide a simple and reliable method for extensively tuning chitosan/TPP particle size while maintaining narrow size distributions.

Experimental investigation on the performance of ORC power system using zeotropic mixture R601a/R600a

An experimental study on the practical performance of organic Rankine cycle (ORC) system using zeotropic mixture is performed by using a small scale ORC power generation experimental setup. R601a/R600a is selected as the working fluid. The effects of mixture composition, heat source temperature, and working fluid flow rate on the performance of ORC system are investigated. The experimental results indicate that the net power output first increases and then decreases as the R600a concentration increases. The optimal mixture composition with the maximum net power output is 0.6/0.4 (mass fraction) at the heat source temperature of 115°C. The net power output of R601a/R600a (0.6/0.4) is higher than that of R601a by 25%, indicating that the performance of ORC system can be clearly improved by using the zeotropic mixture. For a fixed working fluid flow rate, both net power output and thermal efficiency first decrease slowly and then drop sharply with the decrease of the heat source temperature. The appropriate superheat degree of R601a/R600a is in the range of 15 to 20°C when the heat source temperature has a small variation. In addition, the optimal working fluid volume flow rates yielding the maximum net power output are obtained for different compositions of R601a/R600a. The experimental results in the study can be of great significance for the design and operation of ORC power system using zeotropic mixture. Copyright © 2016 John Wiley & Sons, Ltd.

Effect of mixture composition on heat transfer characteristics of impinging methane-air flame jets of tube burners equipped with twisted tapes

Present study investigates the effect of the mixture equivalence ratio on the heat transfer characteristics of impinging premixed methane-air flame jets of tube burners equipped with twisted tape inserts. The induced swirl flow enhances the mixing process and improves the flame stability limits. The flame jet with mixture Reynolds number of 800 and burner to plate spacing of four times burner diameter is chosen based on the flame stability range. The heat transfer characteristics of non-swirling flame jet are compared with the swirling flame jets for various mixture compositions. Swirl flow is achieved with twisted tape inserts having twist ratios of 2, 3.2, 4.5 and 7.5. Twisted tape inserts resulted asymmetric flame. The flame shape is found to be highly influencing the heat transfer from the flame jet to the target surface. Better heat transfer distribution is achieved with stoichiometric mixture. However, the rich mixture produces more uniform heat flux distribution. Best thermal performance is observed for twisted tape with twist ratio of 7.5. The present study helps in better understanding and optimum design of the flame jet impingement heat transfer equipment.