Superheated Conditions Research Articles

New Opportunities for Organic Synthesis with Superheated Flow Chemistry.

ConspectusFlow chemistry has brought a fresh breeze with great promises for chemical manufacturing, yet critical deterrents persist. To remain economically viable at production scales, flow processes demand quick reactions, which are actually not that common. Superheated flow technology stands out as a promising alternative poised to confront modern chemistry challenges. While continuous micro- and mesofluidic reactors offer uniform heating and rapid cooling across different scales, operating above solvent boiling points (i.e., operating under superheated conditions) significantly enhances reaction rates. Despite the energy costs associated with high temperatures, superheated flow chemistry aligns with sustainability goals by improving productivity (process intensification), offering solvent flexibility, and enhancing safety.However, navigating the unconventional chemical space of superheated flow chemistry can be cumbersome, particularly for neophytes. Expanding the temperature/pressure process window beyond the conventional boiling point under the atmospheric pressure limit vastly increases the optimization space. When associated with conventional trial-and-error approaches, this can become exceedingly wasteful, resource-intensive, and discouraging. Over the years, flow chemists have developed various tools to mitigate these challenges, with an increased reliance on statistical models, artificial intelligence, and experimental (kinetics, preliminary test reactions under microwave irradiation) or theoretical (quantum mechanics) a priori knowledge. Yet, the rationale for using superheated conditions has been slow to emerge, despite the growing emphasis on predictive methodologies.To fill this gap, this Account provides a concise yet comprehensive overview of superheated flow chemistry. Key concepts are illustrated with examples from our laboratory's research, as well as other relevant examples from the literature. These examples have been thoroughly studied to answer the main questions Why? At what cost? How? For what? The answers we provide will encourage educated and widespread adoption. The discussion begins with a demonstration of the various advantages arising from superheated flow chemistry. Different reactor alternatives suitable for high temperatures and pressures are then presented. Next, a clear workflow toward strategic adoption of superheated conditions is resorted either using Design of Experiments (DoE), microwave test chemistry, kinetics data, or Quantum Mechanics (QM). We provide rationalization for chemistries that are well suited for superheated conditions (e.g., additions to carbonyl functions, aromatic substitutions, as well as C-Y [Y = N, O, S, C, Br, Cl] heterolytic cleavages). Lastly, we bring the reader to a rational decision analysis toward superheated flow conditions. We believe this Account will become a reference guide for exploring extended chemical spaces, accelerating organic synthesis, and advancing molecular sciences.

Catalytic aquathermolysis of contaminated polyolefin plastic waste over an in situ iron hydroxide/oxide nanocatalyst derived from an oil-soluble iron precursor

With the substantial increase in global plastic consumption over the past 50 y, society faces the challenges of managing and recovering resources from considerable amounts of plastic waste. A promising strategy for use in addressing this problem is to upcycle plastic waste into valuable materials via thermochemical conversion, and hydrothermal liquefaction, which uses low-cost and green H2O, has attracted attention as a sustainable technology. In this study, we introduced an aquathermolysis system using oil-soluble Fe-2-ethylhexanoate (Fe-2EH) as a catalyst precursor under superheated steam conditions to convert highly contaminated polyolefin plastic waste to liquid fuel. The excellent dispersibility and decomposition behavior of Fe-2EH facilitated the formation of highly dispersed in situ Fe-based catalysts, enabling their involvement in the early stages of aquathermolysis. The presence of H2O and the in situ catalyst significantly promoted the decomposition of C–X bonds (X = Cl, S, N, or O) rather than C–C bonds, and C–C cleavage was driven by thermal energy. Moreover, the presence of H2O with the catalysts reduced the proportion of non-paraffinic products, including olefins and aromatics that cause char/coke formation. During the reaction, the in situ catalyst particles comprised nanosized Fe oxide cores with Fe hydroxide-rich surfaces, preventing the accumulation of metal contaminants. Based on deuterium tracing studies, the H transfer index of the catalyst was closely related to the catalytic performance. These results indicated that catalytic aquathermolysis using Fe-2EH is an efficient system for use in improving product quality by effectively removing contaminants and suppressing char/coke formation.

Performance of a supercritical carbon dioxide compressor using a streamline curvature based throughflow method

Supercritical carbon dioxide (sCO2) has emerged as a promising working fluid for the Brayton power cycle, offering enhanced efficiency due to its high density and low viscosity near the critical point. A critical component of the sCO2 Brayton cycle is the turbomachinery, namely the compressor. The pronounced sensitivity of the thermophysical properties of sCO2 in the vicinity of the critical point where the compressor operates can significantly impact the performance characteristics of sCO2 compressors. This study presents a two-dimensional (2D) streamline curvature-based throughflow method, considering real gas thermophysical properties, to analyze a centrifugal compressor operating with sCO2 at near-critical inlet conditions. The method’s validity is established through comparisons of the predicted performance characteristics with those of the Sandia National Laboratories compressor and by comparing the predicted flow field with the pitch-averaged flow field obtained from computational fluid dynamic (CFD) analysis. Moreover, various compressor intake conditions including subcritical vapor, supercritical vapor, supercritical liquid, and near-critical conditions are investigated to explore their impact on compressor performance. The streamline curvature-based throughflow method demonstrates its effectiveness by achieving significant agreement between the flow field and performance characteristics, both at design and off-design conditions where efficiency predictions were within 5.84% near the best efficiency point compared to CFD simulations. At near critical conditions, a maximum of 3201% increase the computational run-time required for CFD based computation was observed compared to superheated conditions while only a maximum of 164% increase in run-time was observed in the throughflow based computations as a result of the numerical under-relaxation required.

Perfect Conversion of Methylcyclohexane Dehydrogenation under Superheated Liquid-Film Conditions

Perfect Conversion of Methylcyclohexane Dehydrogenation under Superheated Liquid-Film Conditions

Characterization and corrosion behavior of plasma electrolytic oxidation coating on zirconium alloy in superheated steam condition

The plasma electrolytic oxidation (PEO) coating on Zirconium (Zr) alloy was employed and immersed under 400 °C/10.3 MPa steam conditions. The surface morphology, phase composition, microstructure, and element distribution of the PEO coating after corrosion were analyzed. The results indicate that the PEO coating presents lower corrosion weight gain because the compact oxide layer on the PEO coating presents few cracks and prevents the corrosion media from entering the substrate. The compact oxide layer is caused by the high compressive stress in PEO coating, which is helpful for the nucleation of t-ZrO2 grain and restricting the phase transformation from t-ZrO2 to m-ZrO2, thus reducing the volume expansion and defects. Based on the XRD, SEM, XPS, Raman mapping, and TEM results, the corrosion mechanism and phase transformation processes of the PEO coating under 400 °C/10.3 MPa conditions were summarized.

Copper-Catalyzed Racemization-Recycle of a Quaternary Center and Optimization Using a Combined Kinetics-DoE/MLR Modeling Approach.

The copper-catalyzed racemization of a complex, quaternary center of a key intermediate on route to lanabecestat has been identified. Optimization and mechanistic understanding were achieved through the use of an efficient, combined kinetic-multiple linear regression approach to experimental design and modeling. The use of a definitive screening design with mechanistically relevant factors and a mixture of fitted kinetic descriptors and empirical measurements facilitated the generation of a model that accurately predicted complex reaction time course behavior. The synergistic model was used to minimize the formation of dimer byproducts, determine optimal conditions for batch operation, and highlight superheated conditions that could be accessed in flow, leading to a further increase in yield which was predicted by the original model.

Numerical study on the phase change and spray characteristics of liquid ammonia flash spray

Ammonia is regarded as one of the carbon-free alternative fuels for energy systems. The direct utilization of liquid ammonia in gas turbines can reduce the complexity and start-up time of the system. Liquid ammonia is susceptible to flash boiling because of its low boiling point, especially under standard conditions. The boiling point is 239.7 K under 1 atm, which is different from those of traditional hydrocarbon fuels and brings challenges for liquid ammonia spray and combustion simulation. However, the validity of phase-change models for liquid ammonia remains unclear and needs further exploration. Therefore, the present work aims to numerically evaluate the existing evaporation and boiling models for liquid ammonia flash spray. Large eddy simulations were conducted in the Euler-Lagrangian framework, considering droplet kinetics, evaporation, boiling, radiation, and gas-particle interactions. Specifically, five phase-change models were evaluated by comparing the simulation results with recently published experimental data for the vaporization of the ammonia flash spray in terms of the penetration length, spray morphology, and temperature-diameter distribution law. The results indicated that the combined model (the Zuo model combined with the Langmuir-Knudsen model) was more suitable under superheated conditions and agreed reasonably with the experimental results obtained under various temperature and pressure conditions. The evaporation rate tended to increase with decreasing pressure, leading to a significant reduction in the droplets and gas field temperatures. The interaction between the droplet and gas phases was significantly affected by pressure. The ammonia vapor mass fraction first decreased and then increased with an increase in temperature under low pressure, whereby it exhibited only a positive correlation at high ambient pressure. Finally, the effect of the particle diameter distribution was explored and discussed.

Thermal-hydraulic assessment of Once-Through Steam Generators for EU-DEMO WCLL Breeding Blanket primary cooling system application

Once-Through Steam Generators (OTSGs) were recently selected to be installed in the Primary Heat Transfer Systems (PHTS) related to EU-DEMO WCLL Breeding Blanket (BB). Referring to the Balance of Plant Direct Coupling Design (BoP-DCD) option, these components are used to deliver the thermal power removed from the two principal blanket subsystems, i.e. First Wall (FW) and Breeder Zone (BZ), to the Power Conversion System (PCS).OTSG design foresees a vertical component with primary water moving downward inside tube bundle and secondary fluid flowing throughout shell in counter current. The latter moves firstly downwards through the annular downcomer and then goes up in the central riser, where it boils up to super-heated steam conditions. Then, it is deflected by the upper tubesheet, flows again downwards along the steam downcomer and exits through the laterally connected steam nozzles.In the last years, as part of the research activities associated to the Work Package Balance of Plant (WPBoP), a detailed analysis of the steam generator, aimed at deeply understanding the main thermal-hydraulic aspects characterizing its performances during the pulsed regime of DEMO normal operations, was performed. To fulfil this scope, a complete model of the component was prepared by using the best-estimate system code RELAP5/MOD3.3, selected to be also the reference design verification tool.During operations, OTSG experiences full-load and low-load alternative phases with rapid transitions from one another. The steam generator capability to follow such load variations avoiding the occurrence of instabilities in the component was studied. The computational activity carried out was a preliminary thermal-hydraulic characterization of the component conceptual design during both pulse and dwell phases. The feedbacks of this analysis were also fundamental for the conceptualization of the steam generator mock-up to be installed in the planned STEAM facility that will be built at the ENEA Research center of Brasimone.

Drawbacks of phase change models in simulating flashing of steam with a subsaturation downstream boundary condition

AbstractThe development of phase change models applicable to a wide range of temperatures, pressures, and mass flow rates is primarily limited by the metastable or partially stable behaviour of the fluid. Due to this, the fluid does not change phase even after crossing saturation conditions. Most liquid–vapour phase change models have been developed primarily for the cavitation process where the phase change is not sustained, occurs in a very narrow region of space, or occurs under equilibrium conditions. In this paper, the mechanism of phase change is discussed along with the review of three different computational fluid dynamics (CFD)‐based phase change methods available in OpenFOAM, which are used to simulate flashing of steam, in applications related to steam assisted gravity drainage (SAGD) systems. The first method is based on barotropic compressibility (BC) used with the realizable turbulence model, the second combination is of mass transfer model (MTM) with the realizable turbulence model, and the third one is based on two fluid (TF) method along with a family of turbulence models. These methods are tested on a converging–diverging nozzle with pressure driven phase change. It is demonstrated that these methods are not able to adjust their physics to different depressurization rates, do not account for liquid to be in superheated conditions, and have significant discrepancies with experimental results. In the end, better approaches to model this category of phase change are discussed.

SIMULATION OF AMMONIA SPRAY UNDER BOTH NORMAL EVAPORATING AND SUPERHEATED CONDITIONS

A predictive three-dimensional Eulerian-Lagrangian framework for ammonia spray is suggested, and its evolution characteristics under both normal evaporating and superheated conditions are unraveled. First, a simplified boundary model considering the effects of superheated fluid behaviors within the nozzle on the injection velocity and angle was proposed. The real vapor-liquid equilibrium theory is applied in the evaporation model to improve the prediction accuracy of the phase change. An explosion model with the homogenous nucleation theory was used to simulate the burst process. Then, the spray experiment for the liquid ammonia under varied conditions was conducted, and the high-speed diffused back illumination and schlieren approaches were adopted to measure the spray evolutions. Following that, the simulation results were verified against the experimental data under both normal evaporating and superheated conditions, and good agreements indicated that the suggested framework was feasible to accurately and efficiently simulate the evolutions and morphology of ammonia spray. Finally, the transient evolution characteristics of ammonia spray under various conditions were discussed. The heavy cooling effect of ammonia evaporation makes the initial fuel temperature have a notable effect on its spray penetration and expansion.

Flow Boiling Heat Transfer of R141b in Sintered Porous Tubes

In this paper, the high flux tubes of 25 mm outer diameter with the content of 8% and 12% nanoparticles were experimentally studied with the refrigerant R141b under atmospheric pressure. The liquid mass flux was controlled from 128.30 to 252.03 kg/m2·s, the maximum heat flux provided by the electric heating rod was 80 kW/m2, and the range of the superheated degree was from −7 to 4 °C. The results indicate that the porous media promotes the phase change at a low superheated degree, and the heat transfer capacity is 1.88 times that of the smooth tube. Additionally, the vapor quality increases significantly with the increase of nanoparticle concentration. Moreover, the heat transfer coefficient decreases as the outer wall temperature increases due to the formation of the gas film but increases with the increase of nano-powder content. Under the same superheated degree condition, the maximum heat transfer coefficient of the sintered porous tube with 12% nano-powder content is 1.3 times that of the tube with 8% nano-powder content.

Spray cyclic variations of multicomponent fuels under subcooled, transitional, and superheated conditions

The superheated spray has attracted attention due to itsenhanced atomization in gasoline direct injection (GDI) engines. Even though spray characteristics of multicomponent fuels under superheated conditions have been studied before, the connection between plume-to-plume interaction and spray cyclic variation (SCV) has not been adequately addressed. Moreover, the lack of physical understanding of SCV for multicomponent fuels hampers effort to reduce GDI engine cyclic variations. Thus, this work investigates the SCV of binary and ternary multicomponent fuel blends under superheated conditions. Three pure components of n-pentane, isooctane, and n-decane were analyzed and compared to their twelve binary and ternary blends. The experiments were conducted using the laser Mie-scattering technique in a spray chamber at a fuel temperature of 70 °C and ambient pressure of 50 kPa. This test condition facilitated the occurrence of subcooled, transitional, and superheated sprays for all 15 fuel blends. Five spray plume-to-plume interaction levels are defined to reveal the relationship between the SCV and plume-to-plume interaction. The results show that the spray structure is constrained by the blending ratio of n-pentane (high volatility component). The transitional spray exhibited higher plume-to-plume interaction with larger SCV on the variations of partially connected plumes. Both the non-collapsed spray (no plumes interaction) and totally collapsed spray (wholly merged plumes) showed less SCV. However, the total collapsed spray showed higher SCV compared to non-collapsed spray.

Silica scaling and boiling effect on corrosion behaviour of nickel-based alloys associated with superheated hydrothermal fluids containing HCl, H2S and CO2

The effect of amorphous silica (AM-silica) surface deposits on the corrosion behaviour of two nickel-based alloys associated with superheated hydrothermal fluid containing sour gases (HCl, H2S and CO2) was investigated experimentally at 350 °C at 10 barG. The results demonstrate that the AM-silica scales do not promote localized corrosion damage whereas some corrosion products were detected in non-scale samples due to fluid boiling from sub- to superheated conditions. This study contributes to more understanding of the effect of amorphous silica scaling and boiling on corrosion behaviour and the selection of materials for future application in superheated geothermal systems.

The Effect of Superheated Water Extraction Conditions on Properties of Quinoa-Barley Malt Extract

Background: Superheated water extraction (SWE), is a novel method, used to extract proteins or other bioactive component from agriculture products. Methods: In this study, the extract from quinoa-barley malt (in a proportion of 30:70) was treated by SWE method. The effect of extraction time (15, 30, and 45 min) on physicochemical and functional properties of the extract was determined at 120 ºC. Results: The result showed that by increasing the extraction time the amount of protein increased. The maximum protein (%) was obtained in 45 min of SWE. The results revealed that increasing the extraction time had a significant effect on the turbidity and pH. In addition, increasing the extraction time had a positive effect on the functional properties. The highest protein isolate (PI) solubility was at 120 °C. Conclusions: Although SWE method appears to be a useful extraction method for producing valuable materials from cereal and pseudocereal, this method has only been used at pre-commercial scale and more investigation is required to study the quantity, quality, and stability of the extracted valuable materials to scale it up for industrial means.

Performance analysis and working fluid selection of an Organic Rankine Cycle Power Plant coupled to an Enhanced Geothermal System

This paper presents a coupled Wellbore-Reservoir-Organic Rankine Cycle (ORC) power plant model for sustainable and efficient use of multiple-fractures Enhanced Geothermal System with simulations conducted over 40 years of operation time. A multi-objective optimization of the ORC under off-design conditions was conducted using constrained NSGA-II technique considering specific investment cost, energy and exergy efficiencies as objective functions. Twenty working fluids were considered to select the best one based on the turbine inlet superheated vapor condition, the lowest specific investment cost, the best energy and exergy efficiencies. Optimal operations conditions were determined for each working fluid considering turbine inlet temperature, turbine inlet pressure, condenser temperature, refrigerant mass flow rate, and length, tubes number, inner diameter and outer diameter of evaporator and condenser, isentropic turbine efficiency, isentropic pump efficiency as decision variables. The results show that the working fluids have a significant effect on the reinjection geofluid temperature and slight effect on the production temperature. The best performing working fluid was R1233zd(E) providing an energy efficiency of 19.2–19.32% and the exergy efficiency found is between 56.4% and 58.44% over the 40 years of production in off-design conditions and optimal operation conditions. The energy efficiency and the exergy efficiency decrease with increasing condenser temperature.

Optimization of superheated steam treatment conditions for wheat aleurone layer flour

Although, wheat aleurone layer flour (WALF) is a good source of nutrients, it has certain disadvantages due relatively high levels of lipids and various of microorganisms and enzymes. Therefore, in the current study, the effect of superheated steam (SS) treatment on stabilization of WALF was investigated. This study aims to explore the effects of SS treatment on the degradation of free fatty acids of WALF under different conditions. The optimal process was obtained by an orthogonal optimization experiment, including optimized SS temperature, material moisture and treatment time. Results showed that the free fatty acids content of WALF significantly were decreased with SS treatment as the increase of treatment temperature, material moisture content and treatment times (p<0.05). Therefore, the optimum treatment conditions were selected during SS treatment. Compared with raw WALF, the activity of enzymes, total number of microbial colonies and phytate content in WALF were notably reduced after the SS of optimal condition. Nevertheless, its total dietary fiber content, insoluble dietary fiber content, pentosan content, total phenol content and total antioxidant capacity presented a remarkable increase (p<0.05).

Ring droplet formation during evaporation of a sessile water droplet on a biphilic surface

Numerous studies have investigated droplet evaporation on surfaces with different roughness and wettability values. However, most studies have focused on droplet evaporation from homogeneous surfaces at low surface temperatures (below 100 °C). In this study, we conducted droplet evaporation experiments on biphilic surfaces with different ring pattern sizes fabricated by a hybrid method consisting of the sol-gel approach and a picosecond laser system. This study investigated the droplet evaporation boiling phenomenon on these biphilic surfaces under superheated conditions. Changes in droplet geometry and inner bubble dynamics during evaporation were analyzed using a high-speed camera. A ring-shaped droplet formed during the final evaporation period. The formation of the ring enhanced the droplet evaporation efficiency. Furthermore, the experimental results from this study work were compared with the theoretical model proposed in the literature.

Accelerated conversion of waste cooking oil into biodiesel by injecting 2-propanol and methanol under superheated conditions: A novel approach

Catalysed biodiesel production has issues such as high chemical costs, high reaction time and complex product separation which sometimes generate wastewater. However, superheated transesterification allows rapid conversion of reactants due to high operating temperatures with nearly uninterrupted operation. The present study discusses the semi-continuous production of biodiesel from waste cooking oil (WCO) through injection of (superheated) methanol and 2-propanol separately (for comparative assessment). Batch studies and central composite design (CCD) studies involved optimizing 4 parameters: initial oil mass, alcohol preheat temperature, reaction temperature and retention time. The optimization allowed for evaluation of the solitary and interactive influences of each reaction parameter on the biodiesel yield. From CCD experiments, the highest obtained biodiesel yields of 97.82% and 98.85% was obtained with methanol and 2-propanol at 235 °C and 250 °C reaction temperature, respectively, using 250 g of initial oil mass within 8 min retention time, when both alcohols were preheated to 130 °C. Obtained results show a higher biodiesel yield with 2-propanol compared to methanol. However, transesterification with methanol proceeds at a higher rate. Biodiesel from both methanol and 2-propanol have comparable physico-chemical properties, which are acceptable as per ASTM standards. Since product separation does not involve wet washing, wastewater is not a concern and the process can be scaled up with relative ease to obtain biodiesel of acceptable commercial purity.

Sensory Quality Evaluation of Superheated Steam-Treated Chicken Leg and Breast Meats with a Combination of Marination and Hot Smoking.

As the sensory qualities of meat processed using methods such as superheated steam, marination, and hot smoking have not been examined, this study analyzed the sensory quality of chicken meats (leg, breast) and its chemical correlation by determining optimal processing conditions (superheated steam treatment, marination, and hot smoking). Chicken meats were defrosted using room temperature, running tap water, or high-frequency defroster. Marinated meats with herbal extract solution were treated with superheated steam and then hot smoked with wood sawdust; sensory evaluations were performed at each processing step. The products were analyzed for fatty acids and nutrients, along with storage tests under different conditions. High-frequency defrosting showed the lowest drip loss and thawing time compared to other methods. Bay leaves and oak wood were selected as the best sub-materials for higher sensory scores. Optimal superheated steam conditions showed higher overall acceptance (8.86, 8.71) and were set as follows; leg meat (225 °C; 12 min 20 s), breast meat (223 °C; 8 min 40 s). The final meat products possessed good nutritional composition and no severe sensory spoilages were detected during storage despite microbial and chemical degradations. Thus, regular sensory evaluations at each processing step and storage condition were effective for developing superior chicken meat products.

過熱液膜方式・テトラリン脱水素触媒反応の熱解析と活性要因

過熱液膜方式・テトラリン脱水素触媒反応の熱解析と活性要因