Carbon Dioxide Flow Research Articles

Effect of equilibrium constant for carbon dioxide recombination in hypersonic flow analysis

An equilibrium constant is an important parameter in regard to determining the backward reaction rate constant in chemical kinetics modeling for a hypersonic flow. Three common approaches for the equilibrium constant determination are based on the partition function, Gibbs free energy, and the experimental reaction rate measurement. The present study conducted a computational fluid dynamics (CFD) analysis with different equilibrium constant formulations in a thermochemical nonequilibrium hypersonic flow in order to study the influence of the equilibrium constant in carbon dioxide flow during the Martian entry. The equilibrium constant for the carbon dioxide molecule dissociation differs from one method to another among the reactions that are considered in the carbon dioxide flow. Three different flow conditions, which are based on the experimental data that is provided in the literature, are considered in the detailed comparison analysis using CFD. The variation of the flow properties in terms of pressure, temperature, and mass fraction along the stagnation line is compared for different cases of the equilibrium constant computation. The results that are obtained from the present study confirm that the equilibrium constant influences the numerical computation in the thermochemical nonequilibrium flow especially for the non-catalytic wall boundary condition.

Thermal and hydraulic optimization of supercritical CO2 pillow plate heat exchanger with ellipse weld spots in CSP system

Pillow plate heat exchangers (PPHE) with compactness and high thermal performance are applying widely. In present article, PPHE with ellipse weld spots is first proposed, and turbulent flow and heat transfer of supercritical carbon dioxide (S-CO2) in PPHE channel is analyzed and optimized. The channel is made of many periodically overlapped metal plates, and the plate is a flat plate with many staggered convex-concave spots. Compared with channel section with concave spot, channel section with convex spot has higher flow velocity, lower flow fraction and higher heat transfer coefficient, so it dominates heat transfer process. Along flow direction, heat transfer coefficient in channel section with convex spot gradually increases to maximum in flat region, and then it drops to minimum in downstream region of convex spot, while friction factor has opposite tendency. A meaningful phenomenon is found that higher heat transfer coefficient (h) and lower friction factor (f) appear simultaneously in the same region. The flow and heat transfer behavior are significantly affected by weld spot geometries, and elliptic weld spot with larger ratio of spot length and width Ψ results in weaker vortices and fluid impingement, which remarkably reduces friction factor. The elliptic weld spot with Ψ = 1.4 is optimum geometry for maximum index of Nu/f1/3. In addition, correlations of f and Nusselt number (Nu) for Ψ = 0.6–1.4 and Re = 4132–6650 are developed.

Development of a Simple and Robust Kinetic Model for the Production of Succinic Acid from Glucose Depending on Different Operating Conditions

Succinic acid (SA) is one of the main identified biomass-derived chemical building blocks. In this work we approach the study of its production by Actinobacillus succinogenes DSM 22257 from glucose, focusing on the development and application of a simple kinetic model capable of representing the evolution of the process over time for a great diversity of process variables key to the production of this platform bio-based chemical: initial biomass concentration, yeast extract concentration, agitation speed, and carbon dioxide flow rate. All these variables were studied experimentally, determining the values of key fermentation parameters: titer (23.8–39.7 g·L−1), yield (0.59–0.72 gSA·gglu−1), productivity (0.48–0.96 gSA·L−1·h−1), and selectivity (0.61–0.69 gSA·gglu−1). Even with this wide diversity of operational conditions, a non-structured and non-segregated kinetic model was suitable for fitting to experimental data with high accuracy, considering the values of the goodness-of-fit statistical parameters. This model is based on the logistic equation for biomass growth and on potential kinetic equations to describe the evolution of SA and the sum of by-products as production events that are not associated with biomass growth. The application of the kinetic model to diverse operational conditions sheds light on their effect on SA production. It seems that nitrogen stress is a good condition for SA titer and selectivity, there is an optimal inoculum mass for this purpose, and hydrodynamic stress starts at 300 r.p.m. in the experimental set-up employed. Due to its practical importance, and to validate the developed kinetic model, a fed-batch fermentation was also carried out, verifying the goodness of the model proposed via the process simulation (stage or cycle 1) and application to further cycles of the fed-batch operation. The results showed that biomass inactivation started at cycle 3 after a grace period in cycle 2.

Experimental study on flow and heat transfer of supercritical carbon dioxide in zigzag channels with bending angle 30° for advanced nuclear systems

Zigzag-channel printed circuit heat exchangers have a wide range of application prospects in Gen-IV nuclear systems related to supercritical carbon dioxide Brayton cycles. Experimental data and empirical correlations are the basis for the design of zigzag-channel printed circuit heat exchangers. In this study, experimental investigation on flow and heat transfer of supercritical carbon dioxide in zigzag channels is carried out. The dimensions of the tested zigzag channels are as follows, the channel diameter 1.95 mm, the bending angle 30°, the longitudinal pitch 7.24 mm, as well as the radius of the curvature at the bending corner 0.5 mm. The Reynolds number and Prandtl number of supercritical carbon dioxide in the experimental study range between 3201 and 43258 and 1.1–6.0, respectively. Based on the obtained local Fanning friction factors and local Nusselt numbers, the effect of zigzag angle on flow and heat transfer are analyzed. And new flow and heat transfer correlations for the tested zigzag channel are proposed. The predicted values by the new developed correlations agree with the experimental data well. Comparisons between the new developed correlations and the existing correlations developed for printed circuit heat exchangers are conducted. Heat transfer enhancement obviously occurs when comparing with straight channels. Result shows that the heat transfer coefficient in the tested zigzag channels is about twice that predicted by Dittus-Boelter correlation (under cooling condition). The Fanning friction factor in the tested zigzag channel is about seven to ten times that in straight channels within the scope of investigated.

Crude Oil Pyrolysis Studies: Application to In Situ Superheat Steam Enhanced Oil Recovery

This work focuses on the occurrence and composition of flammable pyrolysis gases which can be expected from stimulation of heavy oil with superheat steam. These gases can have commodity value or be used to fire a conventional boiler to generate steam vapor for superheater feed. Seven oil samples taken from different US locations were tested via thermogravimetric analysis (TGA) with off-gas analysis of light hydrocarbons via mass spectrometry (MS). The samples were heated up to 500 °C at 5 °C/min in a gas flow of moist carbon dioxide and held at 500 °C until no further mass loss was noted. Then, carbonaceous residue was exposed to air at 500 °C to determine enthalpy of combustion by differential scanning calorimetry (DSC). To demonstrate that pyrolysis was indeed occurring and not simple de-volatilization, a high-molecular-weight reagent-grade organic molecule, lactose, was first demonstrated to produce components of interest. After treatment under moist CO2 at 500 °C, all samples were found to lose around 90% of mass, and the follow-up combustion process with air further reduced the residual mass to between 2% and 12%, which is presumed to be mineral matter and char. The light hydrocarbons methane, ethane, and propane, as well as hydrogen, were detected through MS during pyrolysis of each oil sample. Heavier hydrocarbons were not monitored but are assumed to have evolved, especially during periods where additional mass loss was occurring in the isothermal process, with minimal light hydrocarbon evolution. These results correspond to a possible concept of subsequent in situ combustion drive with or without heat scavenging following high-temperature pyrolysis from in situ superheat steam injection.

Energy optimization of multi-carrier energy systems to achieve a low carbon community

One of the most prominent concerns of human societies, especially in advanced countries, is how to manage and consume energy in a manner that not only energy demand would be supplied but also a minimum amount of pollution enters the environment. In this case, production and consumption resources of energy and carbon dioxides emission sources have to be identified. Optimizing the consumption schedule can reduce fossil fuel consumption and carbon dioxide emission. This project aims to design and plan a multi-energy carrier microgrid that facilitates reaching a low carbon society. In this manner, utilizing modeling techniques of carbon dioxide flow in energy systems offers a good estimation for the amount of carbon distributed in energy systems. This first step is one of the most fundamental aspects of implementing optimization studies with the purpose of carbon reduction. A proper optimization procedure for multiple energy carrier systems at the distribution system level is recommended by proposing suitable and comprehensive decision variables. The optimization studies, which are based on carbon flow in the distribution network, can assist the decision-makers of the energy field in evaluating the effectiveness of various solutions.

Flow and heat transfer investigation of supercritical carbon dioxide in a novel biomimetic honeycomb fractal gas cooler of transcritical CO2 heat pumps

Flow and heat transfer characteristics of gas coolers, one of the most significant components in transcritical CO 2 heat pumps, significantly influence the overall performance of the heat pumps. To ensure high heat transfer efficiency and increased structural stability of gas coolers, a novel biomimetic honeycomb fractal heat exchanger is proposed in this study. The conjugate heat transfer between supercritical CO 2 and water in this novel heat exchanger is then investigated by numerical methods under different operating and geometric parameters. The results indicated that the heat transfer coefficients of CO 2 were quite different in different flow channels and different locations in each flow channel, especially near the supercritical region, which was significantly influenced by the buoyancy effect. Based on the thermophysical parameters, buoyancy, and hydraulic diameter, a new correlation for supercritical CO 2 was developed. The relative errors between the data calculated by the correlation and the numerical results were mostly in the range of ±15% and the root mean square deviation of the ratio of the calculated data to the numerical results for the Nusselt number was 5.4%.

Investigation on the flow and heat transfer characteristics of supercritical CO2 in printed circuit heat exchanger with asymmetric airfoil fins

As an essential component of the supercritical CO2 recompression Brayton cycle, the recuperator has a significant impact on the efficiency and stability of the entire cycle system. The printed circuit heat exchanger is the most suitable heat exchanger for the recuperator in the supercritical CO2 recompression Brayton cycle. To investigate the effects of the structural parameters of the asymmetric AFF on the thermo-hydraulic performance of the printed circuit heat exchangers, simplified 3-D numerical simulation models for the printed circuit heat exchanger with National Advisory Committee for Aeronautics 85XX series asymmetric AFF were built. An optimization method combining an orthogonal experiment and a quadratic polynomial surrogate model with a multi-objective genetic algorithm was proposed to obtain the optimal structural parameters. The results show that the fin thickness, lb, has the most significant effect on the comprehensive performance and fluid-flow performance, and the transverse spacing, lc, has the highest influence on the thermal performance. The optimum structural parameters set are a combination of the transverse spacing of 3.9 mm, the longitudinal spacing of 11.5 mm, and the fin thickness of 0.77mm.

Atmospheric pressure discharge sustained by millimeter radiation in a waveguide plasmatron

In the developed waveguide plasmatron with combined gas influx, a nonequilibrium discharge maintained at atmospheric pressure by continuous microwave gyrotron radiation at 24 GHz was obtained and studied for the first time. It is shown that in the regime of argon discharge stabilization by carbon dioxide flow the temperature of electrons is 0.2-0.3 eV at gas temperature 1200-1500 K and the electron density does not exceed the cutoff value for the heating frequency in a wide power range. Keywords: microwave heating, atmospheric pressure discharge, nonequilibrium plasma, gyrotron.

HEAT TRANSFER CHARACTERISTICS OF SUPER CRITICAL CARBON DIOXIDE FLOW IN HORIZONTAL PIPES USING COMPUTATIONAL FLUID DYNAMICS AND ARTIFICIAL NEURAL NETWORKS

In the 21st century, the demand for eco-friendly, affordable energy is on the rise, and nuclear energy is one of the most practical methods of meeting this demand. Due to the high energy produced in the form of heat in these reactors, the design of the heat exchangers used is very important, as a failure can be catastrophic. Recently, heat exchangers using super critical fluids are gaining interest due to their drastic property variations near the pseudo critical point. In the present work, the validation of a computational fluid dynamics model is first carried out and compared against the available turbulence models in the software. Out of the six turbulence models used, <i>k-ε</i> Std model with the enhanced wall treatment is found to predict the wall temperature and Nusselt number with the average error of 12%. Later in the study, a detailed parametric analysis was carried out for a wide range of mass flux (20 kg/m<sup>2</sup>-s to 2900 kg/m<sup>2</sup>-s), heat flux (0.5 w/m<sup>2</sup> to 1000 w/m<sup>2</sup>) and operating pressure (7.5 MPa to 9.5 MPa). Total of 81414 data collected from this parametric study is processed by an Artificial Neural Network model, which is then trained to provide values for the top wall Nusselt number. An artificial Neural Network model created can predict the top wall Nusselt number for the entire range of operating parameters within the average deviation of 9%.

Assessment of carbon dioxide propagation in a pipeline emergency

One of the most important problems of our time is the annual growth of greenhouse gas emissions into the atmosphere. To combat this phenomenon, emission reductions or the development and application of technologies for capturing, storing, using and utilizing carbon dioxide are possible. The need to implement projects for the decarbonization of technological processes is also relevant in connection with the international climate agenda. To reduce emissions, one cannot do without measures aimed at carbon sequestration. Of great interest is the creation and implementation of industrial carbon sequestration technologies that use the existing oil and gas infrastructure and allow obtaining additional benefits by increasing oil and gas recovery. The implementation of this technology largely depends on the environmental and economic feasibility of the project, which is influenced by the selected technologies for capturing and cleaning gas from impurities, the length of the pipeline to the field, a reasonable injection technology, and many other factors. For this reason, scientific and practical research in this direction are of practical importance and are quite relevant. The article presents the results of an analysis of the consequences of a violation of the tightness of a pipeline for pumping carbon dioxide. The calculation of the distribution zone of the release, as well as changes in the concentration in the flow, was carried out. The conclusion is made about the possibility of estimating the time required for the distribution of the carbon dioxide flow in the air volume to reduce its concentration to acceptable values. The work performed is important in terms of profile planning, location and safety measures in the construction and operation of pipelines for carbon dioxide transfer.

Разряд атмосферного давления, поддерживаемый миллиметровым излучением в волноводном плазмотроне

In the developed waveguide plasmatron with combined gas influx, a nonequilibrium discharge maintained at atmospheric pressure by continuous microwave gyrotron radiation at 24 GHz was obtained and studied for the first time. It is shown that in the regime of argon discharge stabilization by carbon dioxide flow the temperature of electrons is 0.2-0.3 eV at gas temperature 1200-1500 K and the electron density does not exceed the cutoff value for the heating frequency in a wide power range.

Research on condensation characteristics of supercritical carbon dioxide in Laval nozzle considering working condition of power cycles

The supercritical carbon dioxide (sCO2) thermal power cycle is a solution for generation IV nuclear energy systems. The potential condensation in the key equipment of the power system poses a serious threat to the safe operation of the system. Aiming at the condensation that may occur inside the sCO2 compressor, this paper numerically simulates the condensation that occurs in a convergent-divergent nozzle. The wet steam model and the homogeneous equilibrium model (HEM) are present and compared with the experimental data. The HEM is used to calculate the influence of the inlet conditions of the fluid into the nozzle and the different expansion rates corresponding to different nozzle shapes on the condensation phenomenon. The results show that the HEM can represent the two-phase flow of carbon dioxide in the nozzle. The nozzle inlet boundary conditions and nozzle expansion rate have an important influence on the condensation characteristics, the former influences the condensation position, while the expansion rate has an influence on the outlet humidity and pressure drop.

Experimental Investigations on Heat Transfer Deterioration for Vertical Flow of Supercritical Carbon-Dioxide Under Natural Circulation

Abstract Many upcoming designs of nuclear reactors conceptualize use of supercritical fluids (SCFs) due to certain associated advantages. Supercritical helium (SC-He), supercritical carbon-dioxide (SC-CO2), and supercritical water (SCW) find proposed applications in primary/secondary heat removal cycles in nuclear reactors. The knowledge of heat transfer characteristics of the working fluid is essential prerequisite for its actual application. Similarly, for SCF, heat transfer deterioration (HTD) is an area having much ambiguity and thus has attracted many researchers in the recent past. Still, conclusive guidelines for design applications of SCF are lacking due to dramatic variation of thermos-physical properties of SCF in the pseudo-critical region. In this paper, extensive experimental investigations are undertaken to study HTD of SC-CO2 under natural circulation (NC) system. Experiments conducted at pressures between 7.9 and 12.31 MPa for vertical heater horizontal cooler (VHHC) and vertical heater vertical cooler (VHVC) are reported. Effect of heat flux, operating pressure, and cooler orientation are discussed based on the experimental data generated. Methodologies available in literature for identification of HTD are also examined with the present experimental data. The experimental data are compared with the HTD criteria available in literature and a new criterion for onset of HTD is proposed for vertical flows under natural circulation. Role of buoyancy (Bu) and acceleration (Ac) parameters are also investigated. Noticeable HTD is observed for Bu > 3 × 10−6 whereas Ac is not found to affect the HTD in this study.

Energy and exergy analysis of combined power, methanol, and light olefin generation system fed with shale gas

Environmental problems and limitations of fossil fuel resources, especially crude oil, have intensified the importance of using cleaner and cheaper fuels besides enhancing energy conversion processes. Therefore, a novel power, methanol, and light olefin multi-generation system is designed and modeled in this paper. Chemical looping reforming, chemical looping combustion cycles, and Rankine power system are combined with methanol and light olefin production processes. The input fuel of the system is shale gas. The mass, energy, and exergy balance equations are applied for each system unit as a steady-state control volume to assess its thermodynamic operation. Then, the effects on the system performance of critical parameters are studied comprehensively. The results show that the necessary syngas can be supplied when 71.5% of the inlet shale gas is used in the steam reforming reactor of the chemical looping reforming cycle, and the steam to fuel ratio and carbon dioxide to fuel ratio are 0.61. Furthermore, if 31% of the produced methanol is consumed in the olefin production unit, the system energy and exergy efficiencies are achieved at 67.3% and 71.5%, respectively. In this case, the carbon dioxide flow rate is 800 kmol/hr, separated and stored in the chemical looping combustion cycle, leading to a clean thermodynamic system.

Numerical simulation of the supercritical carbon dioxide flow in converted marine pipelines

The article discusses the features of modeling the flow of supercritical carbon dioxide in offshore pipelines of complex geometry. The concept is based on the replacement of the initial oil and gas in field pipelines for the re-injection of carbon dioxide into the reservoir with the purpose of further disposal. Various variants of the component composition are considered depending on the origin of the fluid. Needed initial operating parameters for conversion are defined.

A Review of Flow and Heat Transfer Characteristics of Supercritical Carbon Dioxide under Cooling Conditions in Energy and Power Systems

Supercritical carbon dioxide (SCO2) is widely used in many fields of energy and power engineering, such as nuclear reactors, solar thermal power generation systems, and refrigeration systems. In practical applications, SCO2 undergoes a cooling process significantly when it is cooled near the pseudo–critical point. Because of the drastic variations in thermo–physical properties, the heat transfer characteristics fluctuate, affecting the heat exchange and overall cycle performance. This paper summarizes extensive experiments and numerical simulations on the cooling process of SCO2 in various application scenarios. The effects of various working conditions, such as mass flow, working pressure, pipe diameter, flow direction, and channel shapes, are reviewed. The applicability and computational results using different numerical methods under different working conditions are also summarized. Furthermore, empirical correlations obtained in experiments at different conditions are included. The present review can provide a helpful guideline for the design of effective cooling systems or condensers so that the accuracy of the design and efficiency of the system can be improved.

Computational analysis of experiments on shock detachment in hypersonic flow of nitrogen and carbon dioxide over a wedge

One of the most dramatic effects of vibrational and chemical non-equilibrium in hypersonic flows occurs in the bow-shock detachment process in flow over a wedge. This was shown theoretically and in reflected shock tunnel experiments by Hornung & Smith (J. Fluid Mech., vol. 93, 1979, pp. 225–239). In the present work, the effect is first demonstrated by computation of two-dimensional non-equilibrium flows. The effect of the finite transverse extent of the wedge is then studied by three-dimensional computations of non-relaxing flows. An analytical formula is obtained that gives the shock detachment distance of a finite wedge for ideal-gas and equilibrium flows. In the experiment, the finite transverse extent of the wedge competes with the non-equilibrium effects, as each introduces a new length scale. The carbon dioxide and nitrogen flows of the experiment are therefore computed in three dimensions and with two-temperature chemistry accounting for vibrational and chemical non-equilibrium. In the case of nitrogen flow, the agreement between experiment and computation is not good, the experimental detachment distance being larger. A number of possible reasons are quantitatively examined. A conclusive resolution of the discrepancy is considered to require a repeat of the experiment with more accurately characterized conditions. In the case of the carbon dioxide experiments, the computed results agree remarkably well with experiment. This is partially due to the fact that the condition is very close to equilibrium, where the sensitivity of the detachment process to relaxation effects is small. The analytical expression for the dimensionless detachment distance agrees very well with all the three-dimensional computations of non-relaxing flows.

Carbon Dioxide Flow Behavior through Nanopores: Implication for CO2 Sequestration in Unconventional Gas Reservoirs

Carbon Dioxide Flow Behavior through Nanopores: Implication for CO₂ Sequestration in Unconventional Gas Reservoirs

Single-stage microwave assisted coconut shell based activated carbon for removal of Zn(II) ions from aqueous solution – Optimization and batch studies

Health and environmental issues associated with heavy metal ions have received serious attention from communities worldwide. This work explores the potential of coconut shell as activated carbon (CSAC), in adsorbing zinc, Zn(II) ions. This adsorbent was prepared via a single-stage microwave irradiation technique under the flow of carbon dioxide, CO 2 gas. CSAC posed BET surface area of 625.61 m 2 /g, 513.25 m 2 /g of mesopores surface area, total pore volume of 0.42 cm 3 /g, and average pore diameter of 4.55 nm. Zeta potential distribution on CSAC was found to be −21 mV. Response surface methodology (RSM) had suggested that the optimum values of variables were 450 W and 3.17 min for radiation power and radiation time respectively, which resulted in 69.65% of Zn(II) removal and 44.32% of CSAC’s yield. Based on F-value, radiation power (473.62) and radiation time (140.50) posed major and moderate effects on Zn(II) removal, respectively. Meanwhile, CSAC’s removal was significantly affected by radiation power (78.84) and less affected by radiation time (7.06). In a batch study, when the initial concentration of Zn(II) was increased, Zn(II) uptakes increased as well. On contrary, Zn(II) removal percentage decreased with the increase of Zn(II)’s initial concentration. Multilayer adsorption of Zn(II) onto CSAC had occurred since this adsorption system followed Freundlich isotherm the best, and the monolayer adsorption capacity, Q m for Zn(II) was revealed to be 7.87 mg/g. The kinetic data of the Zn(II)-CSAC adsorption system was best described by pseudo-first-order (PFO) which indicated the role of physisorption. In the regeneration study, CSAC’s mass and Zn(II) adsorption uptakes had reduced from 100% to 37% and 77%, respectively, after 6 regeneration cycles.