Transmission mechanics of infectious pathogen in various environments are of great complexity and has always been attracting many researchers' attention. As a cost-effective and powerful method, Computational Fluid Dynamics (CFD) plays an important role in numerically solving environmental fluid mechanics. Besides, with the development of computer science, an increasing number of researchers start to analyze pathogen transmission by using CFD methods. Inspired by the impact of COVID-19, this review summarizes research works of pathogen transmission based on CFD methods with different models and algorithms. Defining the pathogen as the particle or gaseous in CFD simulation is a common method and epidemic models are used in some investigations to rise the authenticity of calculation. Although it is not so difficult to describe the physical characteristics of pathogens, how to describe the biological characteristics of it is still a big challenge in the CFD simulation. A series of investigations which analyzed pathogen transmission in different environments (hospital, teaching building, etc) demonstrated the effect of airflow on pathogen transmission and emphasized the importance of reasonable ventilation. Finally, this review presented three advanced methods: LBM method, Porous Media method, and Web-based forecasting method. Although CFD methods mentioned in this review may not alleviate the current pandemic situation, it helps researchers realize the transmission mechanisms of pathogens like viruses and bacteria and provides guidelines for reducing infection risk in epidemic or pandemic situations.

Trailing oil is the tail section of contamination in oil pipelines. It is generated in batch transportation, for which one fluid, such as diesel oil follows another fluid, such as gasoline, and it has an effect on the quality of oil. This paper describes our analysis of the formation mechanism of trailing oil in pipelines and our study of the influence of dead-legs on the formation of trailing oil. We found that the oil replacement rate in a dead-leg is exponentially related to the flow speed, and the length of the dead-leg is exponentially related to the replacement time of the oil. To reduce the amount of mixed oil, the main flow speed should be kept at about 1.6 m/s, and the length of the dead-leg should be less than five times the diameter of the main pipe. In our work, the Reynolds time-averaged method is used to simulate turbulence. To obtain contamination-related experimental data, computational fluid dynamics (CFD) software is used to simulate different flow rates and bypass lengths. MATLAB software was used to perform multi-nonlinear regression for the oil substitution time, the length of the bypass, and the flow speed. We determined an equation for calculating the length of the trailing oil contamination produced by the dead-leg. A modified equation for calculating the length of the contamination was obtained by combining the existing equation for calculating the length of the contamination with new factors based on our work. The amounts of contamination predicted by the new equation is closer to the actual contamination amounts than predicted values from other methods suggested by previous scholars.

Much less attention has been focused on the particle deposition in rectifying plate though it is a common problem in shale gas pipe systems. The effects of particle parameter and flow field on the deposition and distribution of particle in a new‐type rectifying plate system are investigated. Both the computational fluid dynamics (CFD) method and the experiment method are used in order to analyze the particle deposition under various conditions. The accuracy of simulation model is verified with measurements in the experiment and from analyzing, and it is found that the Boltzmann equation can well describe the relationship between gas Reynolds number and particle deposition in the rectifying plate system. It is also found from investigation that the particle deposition is greatly affected by the particle parameter. Deposition rate rises with the increase of the particle diameter; however, it reduces gradually with the decrease of particle shape factor. Moreover, the particle mass concentration is an essential dimension that can give a prediction of where the particle may deposit.

Erosion caused by sand particles in the pipe system is a major concern in the shale gas industry. In the rectifying plate system, the fluid with high Reynolds number is assumed to be the fully turbulent flow. To investigate particle erosion under the complex flow in the rectifying plate system, various erosion simulations are conducted in this study. Because the gas velocity, sand input, particles size, and particles shape can affect the erosion in rectifying system, the effect of gas velocities (5‐30 m/s), sand inputs (50‐400 kg/d), and particle parameters (various particle sizes and various particle shapes) on erosion is simulated. Moreover, the erosion experiment conducted in Tulsa University is used to verify the accuracy of simulation model. Through the calculation and analysis, it is obtained that different gas velocities will change the position where the max erosion rate appears. Various sand inputs lead to different max erosion rates. In addition, the effect of sand input on the distribution of erosion scars on rectifying plate is more obvious than that of on elbows. Finally, the effect of size and shape of particles on erosion is investigated. It is found that with the increase in particle diameter, the shape of erosion scar on elbow 1 changes gradually from an ellipse to the V‐shape.

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As a common nature gas measuring tool, ultrasonic flow meter is more and more put into use. Therefore, the accuracy of measurement is what we concern the most. The performance of ultrasonic flow meter is closely related to fluid state which flows through it. This article identified the evaluation method of rectification effect of gasotron and its implementation steps. It proposed an assessing index L min based on dichotomy. Computational fluid dynamics method is used to simulate the model of an upstream straight pipe section with a header and plate gasotron, which obtained the assessing index L min in five different transmission conditions. Finally, the feasibility of the gasotron is validated against comparing indication errors in different installation conditions: with a header, benchmark, with a header and gasotron.

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