It is highly desirable to develop industrially scalable methods to produce defect-free graphene to meet the requirement of graphene from lab to commercial applications. In this paper, a ball-milling ...in series with a shear-mixing exfoliation technique in supercritical CO2 was developed. Graphite was pretreated by ball-milling in supercritical CO2, and the exfoliated sheets with smaller lateral sizes and numerous crevices on their edges were elutriated into a shear-mixing vessel by supercritical CO2 simultaneously to inhibit over crushing. Whereafter, the freshly exfoliated sheets with crevices were further exfoliated into few-layer graphene without aggregation. 90% of the obtained graphene was less than five layers, and the processing capacity of 40 g for one batch increased 40–100 times compared with the previously reported method. The electrical conductivity of 3.25 × 105 S/m of the flexible graphene film on PVDF substrate demonstrates the excellent electrical performance of the obtained graphene.
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•Continuous graphene exfoliation system via ball-milling and shear-mixing in SC-CO2.•SC-CO2 ball-milling pretreatment producing numerous crevices on graphite edges.•CO2 elutriation separation inhibits over crushing and promoting exfoliation.•High-quality graphene was produced continuously with a single batch output of 40 g.•Obtained graphene showed excellent electrical conductivity of 3.25 × 105 S/m.
•A combined supercritical CO2 recompression and regenerative cycle for waste heat recovery of marine gas turbines is proposed.•The thermodynamic and economic model of the combined cycle are ...presented.•The influencing factors of the combined cycle are well discussed.•The effect of the combined cycle on the part-load performance of marine gas turbine is analyzed.
With the aim to recover the marine gas turbine exhaust heat, and improve the ship part-load thermal efficiency, a combined cycle coupling supercritical CO2 recompression and regenerative cycle is proposed. The proposed system adopts modular design. The application process can choose the module according to the ship's need. The cycle parameters, including the output power, exergy efficiency, the heat exchanger area per unit power output (APR) and the levelized energy cost (LEC), have been analyzed and optimized. The multi-objective optimization method based on genetic algorithm is selected as the optimization method to obtain the optimum system parameter. From the viewpoints of the output power, compactness and economics, the obtained result reveals the superiority of the proposed cycle compared to the common supercritical CO2 recompression cycle, the common supercritical CO2 regenerative cycle and the combined cycle coupling two supercritical CO2 regenerative cycle. What’s more, the proposed system can effectively improve the part-load performance of the ship. When the gas turbine fails, the combined cycle could meet 80% propulsion power of the ship by enabling the second combustion chamber, which could be used as the backup generator and improve the safety of the ship operation. The proposed cycle is suitable for marine gas turbine waste heat recovery, it has advantages of deep utilization of waste heat, high compactness and low cost.
•Neural Network based supercritical CO2 turbomachinery off-design model is developed.•Simple statistical analysis is performed to evaluate for the developed model.•Quasi-steady state analysis is ...performed to test turbomachinery off-design models.•Developed Neural Network based model more accurate than conventional methods.
Recently, supercritical CO2 (S-CO2) power system have received much attention due to their high efficiency and small size. S-CO2 exhibits a dramatic nonlinear property change near the critical point. Owing to this sensitivity, a bottleneck of S-CO2 system off-design analysis can be the turbomachinery off-design prediction. Conventionally, to reflect off-design performances of turbomachines within the system analysis, performance map with the correction method has been exploited. It is because computationally expensive to solve the Euler turbine equation for every iteration. However, due to the aforementioned behavior near the critical point, it is questionable if the method developed under air condition can still be valid for the S-CO2 system. The authors are proposing a method using Deep Neural Network (DNN) to build an S-CO2 turbomachinery off-design model. A statistical analysis revealed that the method showed 101 to 104 times better Mean Squared Error (MSE) and Mean Absolute Percentage Error (MAPE) indices than those of the existing correction methods. Analysis from the system point of view was also carried out. The results of the pre-trained DNN S-CO2 turbomachinery off-design model and the correction methods were compared by analyzing the off-design steady-state performance of an S-CO2 simple recuperated cycle. The results showed that system off-design performance predictions can be significantly distorted with the conventional correction methodologies, and that it can be avoided through the developed DNN based S-CO2 turbomachinery off-design model.
•Advanced effectiveness correlation for S-CO2 recuperator while considering inner pinch is developed.•Prediction of inner pinch and evaluation of S-CO2 cycle is progressed with applying ANN.•The ...developed methodology can provide fast and accurate results without iterative calculations.
Supercritical CO2 (S-CO2) power cycles have received much attention due to their desired advantages in various applications. Due to the substantial difference in specific heat of S-CO2 at different pressure, unique characteristics inside heat exchangers, especially in the recuperator, are observed and affect the cycle design. In this research, the problem of inner pinch occurring inside the S-CO2 recuperator is identified and resolved by suggesting a new framework for the definition of heat exchanger effectiveness using the point of zero inner pinch. The design methodology of S-CO2 cycles is improved using this definition by developing a module to calculate the zero inner pinch using artificial neural network (ANN) to undergo a learning process. As a result, the computation time required for cycle analysis is reduced by an order of 103 in the case of simple recuperated Brayton cycle, under the accuracy of 10-7 error bound. As the readers gain the access to the developed module for calculating the zero inner pinch, the procedure for S-CO2 cycle optimization will become far more manageable for researchers, and as a result, this result can allow the conceptualization of even further complex layouts in S-CO2 cycle research.
The bio-elastomer poly (L-lactide-co-ε-caprolactone) (PLCL) with linear random molecular chain structure exhibits low viscosity and melt strength, resulting in poor foamability, cell merging, or ...collapse during the foaming process. Consequently, PLCL foams have large cell sizes and low cell densities, limiting their use as biodegradable elastomeric foams. To enhance the foamability of PLCL, poly (D-lactic acid) (PDLA) was incorporated into the PLCL matrix. Stereocomplex crystals (Sc-crystals) formed between the L-LA segments of PLCL and the molecular segments of PDLA. The effects of varying PDLA content on the basic properties and foaming behavior of the blends were investigated. Results indicate that optimal Sc-crystal formation occurs in the PLCL/PDLA-10 blend. The presence of Sc-crystals enhances melt strength and facilitates cell nucleation, reducing cell size from 351.2 to 11.8 μm and increasing cell density from 1.4 × 104 to 1.7 × 108 cells/cm³. Consequently, the mechanical properties of the foam are significantly improved. The Sc-crystal formation between PLCL and PDLA provides an effective method to enhance the processability of linear chain copolymers containing L-lactide.
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•PDLA is introduced into PLCL to form stereocomplex (Sc) crystallization of PLA through the interaction between DLA segments of PDLA and LLA segments in the PLCL molecular chains. PDLA forms stereocomplex (Sc) crystallization with PLCL via DLA-LLA interaction•Sc crystallites in PLCL/PDLA blend boost melt strength and elastic modulus of PLCL.•Incorporating Sc crystallites into PLCL/PDLA blends significantly enhances PLCL's foamability.
•Supercritical CO2 heat transfer in lattice structure channel is numerically studied.•Effects of key parameters of lattice on flow and heat transfer are evaluated.•Buoyancy effect and flow ...acceleration affected by lattice structure is analyzed.•Vortices induced by lattice structure can suppress the heat transfer deterioration.
This study numerically explores the fluid flow and heat transfer features of supercritical carbon dioxide (CO2) in lattice structure array channel. The mitigation mechanism of the miniature cylindrical lattice structure array on heat transfer deterioration (HTD) of supercritical CO2 in vertically upward heated channel is studied. This paper evaluates the effect of several key influential parameters (length, diameter, pitch and number) of cylindrical lattice structure array on fluid flow field involving vortex structures, heat transfer coefficient, buoyancy effect and accelerated effect. The results indicate that the lattice structure can effectively suppress the HTD by generating the vortex structure which promoting the turbulent mixing effect and enhancing the turbulent kinetic energy (TKE) of the fluid. Compared with the smooth channel, the peak wall temperature of the lattice structure channel is reduced by about 50 °C, with a corresponding increase in the heat transfer coefficient of about 140 %. The average heat transfer coefficient of the channel is increased by more than 1/3. Furthermore, by increasing lattice length can reduce flow layer stratification and by increasing lattice diameter can creating a composite vortex, which enhance flow mixing strength. The larger the lattice pitch, the worse the overall suppression effect. A denser lattice arrangement produces more temperature valleys, thereby increasing the heat transfer coefficient. The conclusions in this study could provide the main theory support for security and stability of supercritical CO2 heat exchangers in power system.
Supercritical CO2 (sCO2) corrosion is a persistent challenge in carbon capture, utilization, and storage (CCUS) that requires effective inhibition strategies. We present a systematic study using ...experimentation and modeling to investigate the inhibition behavior of a composite formulation containing Sodium Molybdate (SM), Triethanolamine Borate (TB), and L-Cysteine (LC) on X80 steel. Our in situ electrochemical studies confirm the superior performance of this ternary system, achieving a composite inhibition efficiency of over 99.86%. Surface profilometry measurements showed a roughness value as low as 33.51μm, indicating enhanced corrosion resistance and uniformity. Atomistic simulations provided mechanistic insights, revealing that LC coordinates SM and TB through favorable S-mediated interactions, optimizing the interfacial ligand network. Chemical bonding analysis indicated that this designed interface effectively suppresses corrosion through cooperative interactions, exceeding the performance of individual inhibitors. Overall, the synergistic effects of the optimized multicomponent system surpassed the efficacy expected from simply combining the individual components.
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•LC acts as a molecular scaffold, aiding the cooperative assembly of SM and TB on the Fe surface.•AIMD simulations revealed optimized multi-component structures with LC linking SM and TB via its desulfurized S atom.•Experimental tests validated the composite formulation exhibits an inhibition efficiency of up to 99.86%.•The calculations have demonstrated that the S atom facilitates the assembly of other inhibitors through covalent adsorption.
•The co-use of supercritical CO2 and carbon results in the significant synergy in cellulose hydrolysis.•Supercritical CO2 and water form a Pickering emulsion, enhancing the cellulose-carbon ...contact.•The initial cellulose hydrolysis rate increases up to 3 × at the emulsion interface.•The in-situ formed carbonic acid (pH ∼ 3.1) helps to hydrolyze oligosaccharides to glucose.•The promoting role of supercritical CO2 in cellulose hydrolysis is more profound in the mix-milled cellulose.
Rapid depolymerization of cellulose into processable monomers (e.g., sugars) using solid acid catalysts is an important step for cost-effective biofuel and biochemical production, but has not yet been achieved due to the limited contact between solid cellulose and solid catalysts. Herein, the unique roles of supercritical CO2 (i.e., scCO2) as an in-situ acid catalyst and reaction solvent in achieving the ultra-fast full solid catalytic hydrolysis of cellulose are disclosed for the first time. When the ball-milling pretreated cellulose was hydrolyzed using oxidized carbon catalysts at 150 °C and 100–300 bar-CO2, the hydrolysis kinetics remarkably increased by 3× for conversion and 5× for glucose, resulting in ∼90% conversion and ∼85% total sugar selectivity at 20 min. The hydrolysis rate obtained with scCO2 here was higher than conventional ones with toxic and unrecyclable homogeneous catalysts (e.g., HCl) under harsh reaction conditions (i.e., 180–220 °C and pH of 1–2). A comprehensive reaction engineering study (e.g., temperature, CO2 pressure, stirring speed, catalyst acid properties) combined with the estimation of the solution pH by the CO2 phase equilibrium model and the in-situ and ex-situ monitoring of the phase behavior of the H2O/scCO2 solution were conducted to quantify the activity promotion by scCO2 and understand the acid-solvent roles of scCO2 toward the enhanced hydrolysis of cellulose. Specifically, the formation of the Pickering emulsions at the interface between scCO2 and water and their impact on the enhancement of the cellulose-carbon contact were proposed and verified in detail.
•The modification of starch with ionic liquids, both pros and cons, is summarized.•The application of supercritical CO2 in the modification of starch are presented.•Regioselective derivatization of ...starch is reviewed for the first time as far as we know.•Controlled grafting of starch via different techniques is summarized.
Starch is a polysaccharide widely present in nature and characterized by a wide range of applications. This often implies the necessity for various novel properties with respect to those of native starch, mainly achievable via chemical modification. During the last decades, products with new or enhanced properties were prepared from starch because of the adoption of “green” solvents (ionic liquids and supercritical CO2) and several new techniques (regioselective derivatization, atom transfer radical polymerization, etc.) that are characterized by controlled modification. However, reviews on these works seem very rare. In this article, the application of ionic liquids and supercritical CO2 in the modification and processing of starch is summarized. The development of regioselective derivatization and controlled grafting of starch are also reviewed in the second part of this article.
•Adaptive channels are effective at alleviating heat transfer deterioration.•Effect of structure on wall temperature is related to heat transfer deterioration.•Turbulence in adaptive channel is not ...inhibited which enhances heat transfer.•Average heat transfer coefficient rises as channel variation length increases.
Supercritical CO2 power cycles have promising applications in many fields, the heat transfer of supercritical CO2 is critical to the efficiency and safe operation of cycle system. The adaptive channel was previously proposed by our group to improve heat transfer of supercritical CO2, the performance of heat exchanger with adaptive channel was experimentally studied. Whereas the effect of adaptive channel on heat transfer deterioration of supercritical CO2 and the mechanism remain unclear. In this study, the effect of adaptive channel on heat transfer deterioration of supercritical CO2 and the mechanism are analyzed numerically based on a single channel, the effect of structure on heat transfer is analyzed through the maximum wall temperature and average heat transfer coefficient under the same length and heat transfer area. The results reveal adaptive channel is effective at alleviating heat transfer deterioration with no local peak in wall temperature distribution. The channel variation length of adaptive channel need to be increased from 0.4 to 0.8 with the aggravation of heat transfer deterioration in order to eliminate local wall temperature peak. For the heat transfer deterioration conditions, the maximum wall temperature lowers first and then increases as channel variation length increases, there is a length that makes the maximum wall temperature lowest, which is lowered by more than 40 °C compared with straight channel. The average heat transfer coefficient can be increased by 1.1 ∼ 1.5 times as channel variation length increases. For the no heat transfer deterioration conditions, the maximum wall temperature increases about 30 °C whereas average heat transfer coefficient can be increased by 58 %∼76 % with channel variation length increasing. The mechanism of adaptive channel alleviating heat transfer deterioration is as follows: the fluid velocity always presents an inverted U-shaped distribution along the radial direction in adaptive channel, the radial density difference is less and buoyancy effects heat transfer weakly. The turbulent kinetic energy is kept at high, so the heat near the wall is transferred to the main flow timely.
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