Premixed System Research Articles

Controllable preparation of graphene glass fiber fabric towards mass production and its application in self-adaptive thermal management

Direct synthesis of graphene on nonmetallic substrates via chemical vapor deposition (CVD) has become a frontier research realm targeting transfer-free applications of CVD graphene. However, the stable mass production of graphene with a favorable growth rate and quality remains a grand challenge. Herein, graphene glass fiber fabric (GGFF) was successfully developed through the controllable growth of graphene on non-catalytic glass fiber fabric, employing a synergistic binary-precursor CVD strategy to alleviate the dilemma between growth rate and quality. The binary precursors consisted of acetylene and acetone, where acetylene with high decomposition efficiency fed rapid graphene growth while oxygen-containing acetone was adopted for improving the layer uniformity and quality. Notably, the bifurcating introducing-confluent premixing (BI-CP) system was self-built for the controllable introduction of gas and liquid precursors, enabling the stable production of GGFF. GGFF features solar absorption and infrared emission properties, based on which the self-adaptive dual-mode thermal management film was developed. This film can automatically switch between heating and cooling modes by spontaneously perceiving the temperature, achieving excellent thermal management performances with heating and cooling power of ∼501.2 and ∼108.6 W m−2, respectively. These findings unlock a new strategy for the large-scale batch production of graphene materials and inspire advanced possibilities for further applications.

Study on the explosion characteristics and flame propagation of hydrogen-methane-air mixtures in a closed vessel

In this study, the examination of the explosion pressure and flame propagation characteristics were investigated for premixed CH4–H2-air mixtures, with varying equivalence ratios (φ = 0.8–1.5) and methane volume ratios (R = 0–100%). This investigation was conducted employing a 20 L explosion vessel and a high-speed ripple shadow meter, while maintaining ambient temperature and pressure. The most critical primitive reactions effecting the formation and consumption of OH* were obtained by normalisation through rate analysis. The result found that as the R increased at the same φ, the premixed system exhibited a gradually decreased in the Pmax, (dP/dt)max, and KG. The increase in the R caused the flame structure to stabilise, extending the flame front distance and the time to reach the wall. The reaction process was divided into three phases based on the R: 0 < R<40% (dominated by hydrogen combustion), 40% < R<80% (dominated by methane and hydrogen co-combustion), and 80% < R<100% (dominated by methane combustion). The analysis of OH* production rate showed that R84 and R38 were the most dominant reactions promoting the OH* production and consumption, respectively. As R was increased, both the production and consumption rates of OH* decreased resulting in a weakening of the explosive reaction's intensity.

Improving the biodiesel combustion and emission characteristics in the lean pre-vaporized premixed system using diethyl ether as a fuel additive

This paper is a lab-scale experimental study of the impact of employing diethyl ether (DEE) as an additive to waste cooking oil biodiesel with Jet A-1 on the combustion as well as emission features of a swirl-stabilized premixed flame. First, waste cooking oil biodiesel with a volume fraction of 20% was blended with Jet A-1 and symbolized as W20. Then, diethyl ether with a volume fraction of 20% was blended with 20% biodiesel and 60% Jet A-1, symbolized as W20D20. The three test fuels (W20, W20D20 blend, and pure Jet A-1) were premixed with preheated air and pre-vaporized before being admitted to the vertical cylindrical combustor having an inner diameter of 150 mm and a length of 500 mm via a swirl burner (radial type) of 0.55 swirl number and 8 straight vanes with an angle of 45°. Local flame temperatures and emissions were measured and recorded at 350 °C of preheated air with a constant equivalence ratio (φ) of 0.85. According to the findings, a relatively wide range of flame temperatures was observed in the flame of the W20 blend, while the W20D20 blend had a flame temperature distribution very close to that of the Jet A-1. The W20D20 blend reduced UHC emissions by 69.6%, CO emissions by 61.4%, and NOx emissions by 12.5% relative to Jet A-1 at the combustion chamber outlet. Overall, adding DEE to biodiesel significantly impacts both combustion and emission profiles.

Rapid and accurate genotyping of human SNP rs671 in aldehyde dehydrogenase 2 gene using one-step CRISPR/Cas12b assay without DNA amplification

BackgroundThe SNP rs671 of Human aldehyde dehydrogenase (ALDH) is G-A transition at 1510th nucleotides, which is an important clinical indicator of alcoholic liver disease, digestive tract cancer and some drug efficiency. The commonly used genotyping assay of this polymorphism is relatively time-consuming and costly.FindingThis study develops a rapid and accurate one-step CRISPR/Cas12b assay to distinguish the G1510A polymorphism of human ALDH2 free of DNA amplification. The method we established requires only one step of adding 1 μl genomic DNA sample to premixed system, and waiting for the acquisition of fluorescent signal, taking approximate 30 min.ConclusionsThis method provides a potential tool for more accurate and reliable nucleic acid detection with a single base difference and supports the relevant disease diagnosis and personalized medicine.

Combustion Characteristics of a Novel Ammonia Combustor equipped with Stratified Injection for Low Emissions

Ammonia – a carbon-free fuel- is being considered by various research groups and organizations as a potential alternative fuel to tackle some global warming issues of the 21st century. However, ammonia faces some challenges as a fuel, particularly, the production of unwanted NOx and unburned ammonia traces at the back end of combustion systems accompanied by unstable flame regimes. Therefore, new concepts are currently being developed to address these challenges whilst also providing stable, high-power operation. This work presents a newly designed stratified combustion system for gas turbines capable of operating with both premixed and stratified modes. The system has been initially evaluated using these two modes employing solely hydrogen and ammonia. Increase of hydrogen stratification resulted in the reduction of NO and NO2, while N2O slightly increased due to the reduction of fuel in the premixed system. Further tests were conducted to evaluate the potential of the systems to replace fossil fuels. Previous work done using methane as the fuel-to-be-replaced has shown interesting trends in terms of emissions and stability. Thus, to progress on the subject, the work conducted here attempted propane/ammonia/hydrogen using this innovative strategy. Results denoted how stratification has a strong impact on NOx production at the flame front, whilst the mechanism of flame stabilization of the new burner enables large operability regions under a great variety of fuel combinations. Strategic injection setups were identified, whilst the best propane/ammonia/hydrogen blends for stability and emissions reduction are also detailed for further implementation in larger systems.

Effect of diethyl ether addition to waste cooking oil biodiesel on the combustion and emission characteristics of a swirl-stabilized premixed flame

Waste cooking oil biodiesel is a promising alternative to diesel and jet fuels. However, the challenge of using waste cooking oil biodiesel is its higher viscosity and lower volatility than diesel fuel, which hinder its spray and atomization from achieving diesel levels. These drawbacks can be enhanced by adding a less viscous fuel like diethyl ether. Thus, an experimental approach has been performed to investigate the effect of diethyl ether addition to waste cooking oil biodiesel in the lean pre-vaporized premixed system. Test fuels considered in this study are B20 (20% biodiesel + 80% Jet A-1), B20D10 (20% biodiesel + 10% diethyl ether + 70% Jet A-1), B20D30 (20% biodiesel + 30% diethyl ether + 50% Jet A-1) as well as pure Jet A-1. These blends are applied in the lean pre-vaporized premixed system with preheated air at 350 ℃ at a fixed equivalence ratio of 0.85 (lean condition). Results showed a 68, 38.4, 14.5, and 43.4% decrease in CO, NOx, CO2, and UHC emissions, respectively, for the B20D30 blend, compared with pure Jet A-1 fuel at the combustor exit, while the B20D10 blend indicated a 15.8, 8.9, 6.17, and 51.4% drop in CO, NOx, CO2, and UHC levels, correspondingly. Jet A-1 achieved a higher maximum temperature than those for other blends. The B20 blend revealed a relative variation in flame temperature distribution, while diethyl ether blends shared a similar temperature distribution compared with Jet A-1. Generally, B20D10 and B20D30 blends had the ability to reduce emission levels. Overall, it can be concluded that the recommended diethyl ether blending ratio is 30%, regarding emission levels and flame temperature profile.

Influence of change in obstacle blocking rate gradient on LPG explosion behavior

The aim of this study was to examine the propagation characteristics of liquified petroleum gas (LPG)/air explosion. As such, the flame propagation process and pressure parameters of LPG explosion with an equivalent ratio of 1 were obtained using horizontal, long straight pipes and a high-speed camera. The large eddy simulation and power-law flame model were used to reproduce the simulation results, and the morphological evolution of the flame front during the explosion process was analyzed. The results showed that as the blockage ratio gradient increased, the time required for the flame to propagate from the electrode to the end of the pipe increased. Meanwhile, a flocculent flame formed at the end of the pipeline with a blockage ratio of 91%. Additionally, the maximum flame propagation speed changed in the same way as the blockage ratio. The gradient change of the barrier blockage ratio considerably influenced the pressure kinetics characteristics of LPG explosion: the maximum explosion pressure increased first and then decreased, the time to reach the maximum explosion pressure increased, and the deflagration index increased first and then decreased. The chemical kinetics analysis of premixed gas showed that when propane, n-butane, and isobutane were present in the premixed system, some of the elemental reactions that promote n-butane consumption inhibited propane and isobutane consumption. Meanwhile, the formation and consumption rate of H*, O*, and OH* from LPG during the explosion process was less than that of single-component combustible gas except propane.

Effect of a Perforated Polyethylene Material on Propane-Air Explosion in a Confined Space.

In this study, the effect of polyethylene barriers with different blockage ratios on the explosion behavior of a propane–air premixed gas in a confined space is investigated. The maximum explosion pressure (Pmax), the deflagration index (KG), and the flame propagation process of the propane–air premixed gas with different barrier thicknesses are examined by using a horizontal closed tube with a length of 0.5 m and a diameter of 0.1 m and a high-speed camera. The atmospheric pressure and temperature of the premixed gas were 101.3 kPa and 18 °C, respectively. Based on the Canny operator, the position of the flame front at different times and the shape of the barriers before and after the explosion are determined, and the propagation speed of the premixed flame and the deformation rate of the barriers are obtained. The results indicate that the barriers change the flow field structure of the unburned gas and increase the folding degree of the flame front. With the increase in the blockage ratio, the explosion of a premixed system becomes more rapid and violent. Under the action of Rayleigh–Taylor instability, the variation in the flame propagation speed induces a change in the tube pressure. In addition, the deformation of a barrier causes a change in the maximum explosion pressure. The greater the deformation ratio of the barrier after the explosion, the larger the maximum explosion pressure.

Study on Combustion Processes of a Premixed Charge Compression Ignition (PCCI) Engine Fueled with DME/Diesel

A dimethyl ether (DME) pre-mixing system was installed on a 2105 diesel engine for realizing pre-mixed charge compression ignition combustion mode. Combustion processes of a PCCI engine fueled with DME/diesel under various DME pre-mixing ratios were investigated in this paper. The results showed that the heat release process showed three stages with port induction of DME. As the DME pre-mixing ratio (PR) increased, the peak value of cylinder temperature and pressure raised and the corresponding crank angles advanced. The start of combustion (SOC) moved forward obviously and the duration of combustion extended; the peak value of the pressure rise rate reduced first and then raised. The results in this paper provided a reference for the combustion process optimization of DME/diesel PCCI engine.

Stanica za doziranje supstrata u postojeće digestore - PreMix

In this paper the analysis and description of the operation of the Premix station for dosing the substrate into existing digesters whose location is in the system of the device for processing of liquid waste are described. Apart from the capacity and other entry parameters, the necessary diameter of the pipeline with the length of the section for supplying the devices of the PreMix system is calculated, as it is given in the appropriate tables, the connection of the existing equipment and digesters is presented. The appropriate dependence of the volume flow, the velocity of circulation and power at constant pressure as well as the dependence of the volume flow, pressure and power at constant velocity of circulation are presented by diagrams.

Assessment of chemical concentration accuracy and mixture uniformity of premixing in-line injection system

A premixing in-line injection system was developed and attached as a retrofit to a laser-guided variable-rate orchard sprayer. Chemical concentration accuracy and spray mixture uniformity produced from the premixing system was investigated with various viscosities of simulated pesticides and duty cycles of pulse-width-modulated (PWM) nozzles at different positions on the sprayer. The chemical concentration accuracy was accessed by calculating the relative error (RE) between measured and target concentrations, and mixture uniformity was evaluated by the coefficient of variation (CV) of the mixture concentration. Test results showed that the measured concentration was consistent across different nozzle positions, and RE and CV were observed within desirable ranges (<5.0%) for all nozzle positions and target concentrations. The average measured concentration slightly decreased as the viscosity of simulated pesticides increased. This phenomenon was more obvious under higher target concentrations. In addition, effects of PWM duty cycle combinations on the chemical concentration accuracy and mixture uniformity varied with number of active nozzles. It was found that RE and CV were larger than the desirable level (greater than5.0%) but were lower than the acceptable level (<10.0%) under conditions that nozzles were partly activated. For other treatments which all nozzles were activated, RE and CV were under the desirable level (<5.0%) for all target concentrations and nozzle positions. Laboratory tests demonstrated that the premixing in-line injection system was able to adequately mix the simulated pesticides with water, and could provide accurate and consistent uniformity of spray mixtures for the variable-rate spray nozzles to discharge different viscosities of simulated pesticides at different duty cycle combinations.

Microstructure of biopolymer-modified aerial lime mortars

Cellulose-based viscosity-modifying admixtures are used on daily basis in a wide range of building materials, dominantly in pre-mixed mortar systems. Lately, alternative admixtures such as different “gums” have emerged. In building materials, the gums have similar viscosity-enhancingeffects as cellulose ethers with different efficiency. Various ways of production, as well as diverse working mechanisms of the biopolymers are to be considered while choosing the most suitable admixture for the intended use. Influence of alternative admixtures in several doses on the microstructure of lime mortars was studied in this paper. Mortars were prepared with the same workability and the air content in fresh mortar was determined, for it can have notable impact on microstructure of hardened mortar. Hydroxypropyl derivative of chitosan showed air entraining ability, while the carboxymethyl derivative reported slight decrease in amount of air entrained into the mixture. In the case of diutan gum, the most water-demanding admixture, the percentage of entrained air dropped with growing dose. Admixture addition increased the volume of pores in diameter lower than 0.1 μm, and in region of pores around 10 μm. Only the diutan gum affected the distribution of capillary pores, which are typical for lime mortars. Hygric properties were in correlation with air content values.

Second law analysis of premixed and non-premixed oxy-fuel combustion cycles utilizing oxygen separation membranes

Two basic oxy-combustion cycles were investigated under premixed and non-premixed combustion conditions and the results were compared in terms of exergy destruction and first and second law efficiencies. An air separation unit (ASU) was used for oxygen separation from the feeding air in the premixed combustion cycle. In the non-premixed combustion cycle, CO2/H2O splitting membrane reactors were utilized, where oxygen separation and in situ oxy-combustion processes occur within the reactor. A gas turbine cycle, working on conventional air combustion of methane, was selected as the reference base case. Commercial process simulator Aspen Hysys V7.3 was used to model and simulate the different systems. The work proposed novel cycle designs for higher cycle efficiency under oxy-combustion conditions. Cycle performance using ion transport membrane (ITM) and ASU was evaluated and compared. Losses in the ASU and the condenser were identified to be the main reason for lower efficiencies and, hence, the systems were modified to include heat recuperation cycles. Additional two modified oxy-combustion cycle designs were proposed. First law and second law efficiencies of the modified premixed cycle were found to be 34.1% and 47%, compared to 35.1% and 44% for the reference air-combustion cycle. The overall thermal and second law efficiencies of the modified non-premixed cycle were the highest among all cycles with 37.8% and 50.4% efficiencies. The effects of hydrogen addition on the efficiencies of the premixed system were evaluated. It was found that hydrogen addition results in increased first and second law efficiencies of the cycle; however, the increase is only marginal.

Experimental study on the deflagration characteristics of methane-ethane mixtures in a closed duct

For the study of premixed methane/ethane/air explosion propagation characteristics, the explosion overpressure parameters and flame propagation process images of premixed methane/ethane at different initial stoichiometric and volume ratios were obtained by using a horizontal closed duct and a high-speed camera. The numerical simulation method was used to study the evolution characteristics of the flow field inside the duct during explosion propagation. Parameters such as the maximum explosion pressure (Pmax), maximum pressure rise rate (dP/dt)max and combustion time tc of the premixed system were acquired. The premixed system flame front position was detected based on a self-written program of the Canny operator, and the variations in the premixed flame propagation speed were obtained. The results show that with increasing ethane volume fraction, the premixed system explosion process is more rapid and drastic. Each premixed system can be divided into three combustion stages according to the different ethane volume fractions: the methane-dominant combustion stage (I), transition stage (II) and ethane-dominant combustion stage (III). When a tulip flame is generated, a vortex is created inside the duct. After a plane flame is formed by the flame front, the pressure rise rate (dp/dt) sharply oscillates. Based on the GRI-Mech3.0 mechanism, the chemical kinetics analysis of the premixed gas showed that the production rate of key free radicals (H*,O* and OH*) gradually increased with the increase of ethane volume fraction, thus enhancing the explosion reaction intensity.

Performance and emissions of pre-mixed and post-mixed combustion systems with a casting aluminum-silicon alloy (CASA) condensing gas boiler

Condensing gas boilers are widely employed for their high heat efficiency, which attributes to their ability to use the recoverable sensible heat and latent heat in flue gas. In this paper, the optimal excess air rate of a novel condensing gas boiler is investigated experimentally. With the change of excess air rate, the pre-mixed and post-mixed systems were used to study the performance, the thermal efficiency and emissions of the boiler. The CO emission reduces firstly then increases regardless of which premixed system, when the excess air rate is from 1.15 to 1.4. The NOx emission decrease from 64 ppm to 10 ppm and the efficiency decreases from 64 ppm to 19 ppm as the excess air rate increases from 1.15 to 1.4. The efficiency decreases from 102.05% to 98.7% and the efficiency decreases from 100.9% to 97.6% as the excess air rate increases from 1.15 to 1.35. Considering both NOx emission and thermal efficiency, the optimum excess air rate is 1.23. With the change of heat load, the emission, the fan speed and the thermal efficiency of the two system were compared. The concentration of CO increases from 7.5 ppm to 65.5 ppm when the pre-mixed system heat load changes from 8 kW to 24 kW. The efficiency of post-mixed system decreases from 106.5% to 97.5% and the efficiency of pre-mixed system decreases from 106.9% to 96.8% as the heat load increases from 9 to 26 kW. The variation of thermal efficiency and condensate volume with various heat load in the post-mixed system with different return water temperature are also studied. The efficiency decreases from 107% to 98.5% as the heat load increases from 9 to 24 kW at the inlet of return water is 30 °C. And the vapor condensation ratio ω decreases from 105% to 97.5% as the heat load increases from 9 to 24 kW at the inlet of return water is 40 °C. In summary, post-mixed system is more suitable for the development of small condensing boilers. The lower the return water temperature and heat load, the higher the thermal efficiency of boiler.

Studying demulsification mechanisms of water-in-crude oil emulsions using a modified thin liquid film technique

The thin liquid film (TLF) technique equipped with Scheludko-Exerowa cell has been demonstrated to be a valuable tool for studying stability of dispersed systems of soft matter such as emulsions and foams. Many industrial applications involve the addition of various chemical aids to obtain desired properties or resolve technical problems. One of the examples is the use of chemical demulsifiers to remove emulsified water from petroleum emulsions. To study the role of chemicals in this process, a TLF technique with a dosing system is required to add demulsifiers into already formed thin liquid films stabilized by interfacial layers formed from indigenous surface active molecules. Herein, we present a modified design of the Scheludko-Exerowa cell with a dosing mechanism which allows for addition of desired chemicals to the intervening organic liquid film that is already formed. The stability of the water-in-oil emulsions and the mechanisms of their chemical destabilization were studied by determining the thinning process of intervening thin oil films before and after dosing a controlled amount of demulsifiers into the film. Dosing of a biodegradable polymer demulsifier (EC300) into the intervening oil film converted a stable film formed by asphaltene-in-heptol solutions into an unstable film with lifetimes of less than 20 s. The observed change in the film drainage rate and stability is related to the disruption of asphaltene network formed at the oil-water interface by EC300 demulsifiers. The experiments with the modified TLF cell also revealed the overdosing effect of EC300 demulsifier, forming more stable films at high EC300 concentrations. A comparison of the experimental results between a dosed system and a premixed system confirmed the value of the modification in the current TLF technique to study the stabilization/destabilization processes of water-in-oil emulsions that mimic more closely the real petroleum emulsions. The modified TLF technique allows for a better understanding of the underlying demulsification mechanisms.

Legume Protein Isolates for Stable Acidic Emulsions Prepared by Premix Membrane Emulsification

Proteins originating from dry legumes are not that much used in food formulations, yet, they are interesting components from a sustainability point of view, and could have interesting functional properties, e.g. for emulsion preparation. Therefore, this work focuses on the potential of the water soluble part of pea, chickpea and lentil protein isolates under acidic emulsions (pH 3.0) using a novel mild technique: premix membrane emulsification. Pea proteins (PP) and chickpea proteins (CP) lower the interfacial tension in the same way as whey protein isolate (WPI), which suggests that they could facilitate emulsion droplet formation similarly as WPI, while lentil proteins (LP) are slightly less effective. It is possible to make oil-in-water (O/W) emulsions with an average droplet diameter (d4,3) of ~5 μm after 5 cycles in the premix system. The droplet size distribution of the emulsions remained constant during one day of storage, indicating that legume proteins are able to form and kinetically stabilize O/W emulsions. CP and PP exhibited emulsifying properties comparable to those of WPI, whereas LP is slightly less efficient, therewith indicating the great potential and that pea and chickpea protein isolates hold as emulsifiers in acidic food formulations.

Study on Pre-Mixed Micro Abrasive Water Jet Machining System

This paper conducts a study on a pre-mixed micro abrasive water jet machining system. A new kind of abrasive mixing tank and the jet system are designed and tapped for the pre-mixed micro abrasive water jet machining system. The performances of the pre-mixed micro AWJ machining system are tested, and some polishing experiments are conducted for hard-brittle materials such as silicon nitride. The results show the feasibility and the advantage of the pre-mixed micro abrasive water jet machining system for polishing hard-brittle materials.

Development and field evaluation of a nested RT-PCR kit for detecting Japanese encephalitis virus in mosquitoes

A novel nested reverse transcription-polymerase chain reaction (RT-PCR)-based kit is described for detecting Japanese encephalitis virus (JEV), especially for genotype 1 and 3 strains. The assay consists of a first round RT-PCR and a subsequent nested PCR amplification. It has unique features such as the use of a premix system in which all reagents are lyophilized in reaction tubes and the inclusion of control RNA in each reaction to monitor false negative results. In addition, an automatic tissue homogenizer and a RNA extraction system are used concurrently for assay standardization and increasing throughput. The assay using the kit proved specific for JEV with no amplification of other JEV-related flaviviruses. The detection limits were approximately 0.1 PFU/ml and 1 PFU/ml for JEV genotypes 1 and 3, respectively. The assay protocol has been validated in large-scale field trials in South Korea during the 2008–2009 surveillance seasons. Nineteen of 1136 pools of mosquitoes (54,583 mosquitoes total) were identified as JEV positive. This nested RT-PCR kit combined with control RNA and an automatic RNA extraction system should be suitable for routine JEV surveillance programs.

A multi-objective design optimization strategy as applied to pre-mixed pre-vaporized injection systems for low emission combustors

This paper presents a multi-objective optimization procedure as applied to the design of the injection system of a Lean Pre-mixed Pre-vaporized combustion chamber. The optimizer drives an Artificial Neural Network in a repeated analysis scheme in order to simultaneously reduce NOX and CO pollutant emissions. The ANN is trained with a few three-dimensional high resolution reactive viscous flow simulations, carried out with a reliable and robust CFD code. Results, obtained in a four-dimensional state space, demonstrate the validity of the overall procedure with truly moderate computational costs.