Numerical simulation of Rayleigh–Bénard convection with supercritical carbon dioxide in a shallow cavity

A numerical simulation of Rayleigh–Bénard convection with supercritical carbon dioxide is presented in this paper. A shallow cavity with an aspect ratio of 4 is selected as a container that is fully filled with supercritical carbon dioxide. The influences of the bottom heat flux on the flow stability, flow pattern evolution, and heat transfer ability of Rayleigh–Bénard convection are analyzed. Meanwhile, the transient and steady-state fluid behaviors are obtained. The results show that the bottom heat flux plays a dominating role in the stability of the convection. A transition from stable evolution to significant oscillation is found with the increase of the heat flux. The flow pattern evolution also strongly relies on the heat flux. A four-cell structure to a six-cell structure transformation accompanied by the orderly multicellular flow is observed with increasing heat flux. In addition, the local Nusselt number on the bottom wall is strongly related to the cell structure in the cavity

Development of a model for thermal-hydraulic analysis of helically coiled tube once-through steam generator based on Modelica

Abstract(#br)The Helically coiled tube Once-Through Steam Generator (H-OTSG) is a critical component for compact small reactors. The present study developed and verified a model in Modelica language and simulated steady-state and transient situations of the model. The Modelica model takes double-pipe heat exchanger as a prototype and adopts counter flow design. Different heat transfer correlations and pressure drop correlations for helically coiled tubes are reviewed and applied to the model. The model is verified by comparing the simulation results with the design parameters of the Marine Reactor X steam generator, and with the results performed by other dedicated programs. After verification, a 100 MW H-OTSG is proposed and steady-state conditions of the four main operating conditions, i.e. 100 MW, 75 MW, 50 MW, 25 MW, are simulated, and analyzed. Transient analysis is then performed in order to investigate the effects of different control strategies of the H-OTSG. The H-OTSG model developed with Modelica can be utilized for the safety analysis of small reactors in the future

Analysis of Density Wave Oscillations in Helically Coiled Tube Once-Through Steam Generator

Helically coiled tube Once-Through Steam Generator (H-OTSG) is one of the key equipment types for small modular reactors. The flow instability of the secondary side of the H-OTSG is particularly serious, because the working condition is in the range of low and medium pressure. This paper presents research on density wave oscillations (DWO) in a typical countercurrent H-OTSG. Based on the steady-state calculation, the mathematical model of single-channel system was established, and the transfer function was derived. Using Nyquist stability criterion of the single variable, the stability cases were studied with an in-house computer program. According to the analyses, the impact law of the geometrical parameters to the system stability was obtained. RELAP5/MOD3.2 code was also used to simulate DWO in H-OTSG. The theoretical analyses of the in-house program were compared to the simulation results of RELAP5. A correction factor was introduced to reduce the error of RELAP5 when modeling helical geometry. The comparison results agreed well which showed that the correction is effective

A seismic prediction method of reservoir brittleness based on mineral composition and pore structure

The Lucaogou Formation, a typical fine-grained mixed formation in the Jimusaer Sag of the Junggar Basin, exhibits considerable potential for hydrocarbon exploration. Accurate brittle prediction is a crucial factor in determining hydraulic fracturing effectiveness. However, the area features complex lithological characteristics, including carbonate rocks, clastic rocks, volcanic rocks, and gypsum interbeds, along with thin layering and sporadic sweet spots. Traditional prediction methods offer limited resolution and there is an urgent need for a seismic brittle prediction method tailored to this complex geological environment. This paper presents a multi-mineral composition equivalent model for complex lithologies that enables the accurate calculation of Vp and Vs These ratios serve as the foundation for pre-stack elastic parameter predictions, which include Poisson’s ratio and Young’s modulus. By comparing the predicted parameters with well-logging measurements, the prediction accuracy is improved to 82%, with particularly high conformity in intervals characterized by high organic matter and clay content. Additionally, a three-dimensional brittle modeling approach reveals that the brittleness of the reservoir exceeds that of the surrounding rock, showing a gradual improvement in brittleness with increasing burial depth from southeast to northwest. The central area exhibits relatively good brittleness, with a stable, blocky distribution pattern

Fulminant psittacosis complicated with multiple organ dysfunction syndrome: a case report

The cases of fulminant psittacosis complicated with multiple organ dysfunction syndrome （MODS） have been rarely reported in China. In this article， clinical manifestations and treatment of a patient with fulminant psittacosis complicated with MODS were summarized and analyzed. The 80-year-old male patient developed respiratory failure in Emergency Department and received mechanical ventilation， which rapidly progressed into acute respiratory distress syndrome （ARDS） complicated with MODS. Metagenomic next-generation sequencing （mNGS） using bronchoalveolar lavage fluid （BALF） samples confirmed the pathogen of Chlamydia psittaci. Then， moxifloxacin， doxycycline and omadacycline were given， which yielded favorable efficacy and prognosis. The diagnosis and treatment of this patient suggests that fulminant psittacosis can be manifested with respiratory failure， severe pneumonia with rapid progression and MODS. Imaging manifestations consist of pneumonia， bronchial inflation sign and pleural effusion. mNGS can be performed to identify the rare pathogens during early stage and confirm the diagnosis. Tetracyclines， macrolides and quinolones can be delivered as antibacterial drugs

Electro-Superplastic Solid State Welding of 40Cr/QCr0.5

Hot-squeezed chrome bronze QCr0.5 and ultra-fine treated 40Cr steel have been successfully welded using an electro-superplastic solid-state welding technique. Results have shown that the tensile strength of a 40Cr/QCr0.5 weld joint can be greatly increased, up to or exceeding that of QCr0.5 base metal. The weld interface between 40Cr and QCr0.5 has achieved metallurgical bonding and there are less micro-gaps, thicker transition regions and more copper convexes and dimples on the fracture surface of the 40Cr side when applying an external electrical field of E = 3 kV/cm, as well as with other welding parameters, including no vacuum, no shield gas, a pre-pressure of 56.6 MPa, an initial strain rate of 1.5 × 10−4 s−1, a pressure welding temperature of 710–800 °C, and a pressure welding time of 0–8 min

Study on Regional Agro-ecological Risk and Pressure Supported by City Expansion Model and SERA Model -A Case Study of Selangor, Malaysia

Abstract. This study revealed the influence of city expansion on the agroecological risks through the analysis and prediction of city expansion in different periods and study on the change of risk and pressure on the regional agricultural eco-environment. The city expansion of Selangor, Malaysia (as a case) was predicted based on relevant spatial and attribute data as well as simulation prediction models of city expansion. Subsequently, the ecological risk and pressure in the study area as well as on regional agricultural land use was assessed through the realization of factors of SERA Model. The results showed that the risk and pressure on agricultural land use was consistent with the level of the urbanization. With the expansion of urban area, the ecological risk on agricultural land use in the study area became greater. The risk and pressure on agricultural land use with city expansion was well analyzed with SERA model

Induced Wood-Inorganic Composites in Standing Trees via Slow-Release Drip

It is a novel idea to fabricate wood-inorganic composites by utilizing the transpiration of bionic trees to realize the self-assembly of inorganic precursors in wood formation. We selected a 10-year-old poplar and diffused the solvent or sol containing SiO2 precursor into the xylem via the slow-release drip method. In combination with the moisture in xylem, reactions such as hydrolysis, polycondensation and self-assembly were induced in order to form wood inorganic composites. It was found, through microscopic observation, that such inorganic substances were yellowish brown and widely existed in vessels, wood fibers and ray cells. For the new grown wood, the fiber–tissue ratio and cell wall thickness underwent an increase, while the vessel diameter and tissue ratio experienced a decline. Moreover, such change was related to the concentration of precursors. EDS analysis proved that the elemental composition of sediments in wood cells was C, O, Si, K and Ca. XPS confirmed that the newly formed wood contained silicon oxide, illustrating that the standing tree slow-release drip technology could induce wood to fabricate inorganic composites

Development of a computer code for thermal–hydraulic design and analysis of helically coiled tube once-through steam generator

The Helically coiled tube Once-Through Steam Generator (H-OTSG) is a key piece of equipment for compact small reactors. The present study developed and verified a thermal–hydraulic design and performance analysis computer code for a countercurrent H-OTSG installed in a small pressurized water reactor. The H-OTSG is represented by one characteristic tube in the model. The secondary side of the H-OTSG is divided into single-phase liquid region, nucleate boiling region, postdryout region, and single-phase vapor region. Different heat transfer correlations and pressure drop correlations are reviewed and applied. To benchmark the developed physical models and the computer code, H-OTSGs developed in Marine Reactor X and System-integrated Modular Advanced ReacTor are simulated by the code, and the results are compared with the design data. The overall characteristics of heat transfer area, temperature distributions, and pressure drops calculated by the code showed general agreement with the published data. The thermal–hydraulic characteristics of a typical countercurrent H-OTSG are analyzed. It is demonstrated that the code can be utilized for design and performance analysis of an H-OTSG