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Fire is one of the most common disasters that threaten the safety of the crowd in metro stations. Due to the variations in the design of metro stations, the hazard posed by the spreading products of the fire can pose different risks. The typical structures of metro stations in Guangzhou and Washington, D.C., are very different from each other. In Washington, D.C., the "high-dome" structure is predominant in the construction of metro stations, while in Guangzhou, most metro stations have the "flat ceiling" structure. In this article, a numerical modeling for fire dynamic simulation is used to predict and compare the spreading characters of fire products (the smoke height change, the temperature distribution and the visibility change) when fires with 2.5 MW heat release rate occur in the platform center and at the platform end in the two kinds of metro stations. The results show that, in the same fire scenario, the lowest smoke heights monitored in the Guangzhou model is 0.6 m (fire at the platform end) and 0.8 m (fire in the platform center) above the safe smoke height in 360 s after a fire breaks out, while it is 6.15 m (fire in the platform center) and 6.2 m (fire at the platform end) above the smoke height in the Washington model. The temperature increment in the Guangzhou model is 23 °C (fire in the platform center) to 29 °C (fire at the platform end) in 360 s after the fire breaks out, while the temperature increment in the same period in the Washington model is 8.5 °C (fire at the platform end) to 9 °C (fire in the platform center). The visibility of most areas on the platform of the Guangzhou model is about 1 m no matter the fire is in the platform center or at the platform end at 360 s after the fire begins, while in the Washington model, the visibility of most areas is 1.5–13.5 mm (fire at the platform end) to 4–14 m (fire in the platform center) at the same moment. Based on the results, the environment is worse when the fire happens at the end of the platform than that when the fire happens in the platform center of the Guangzhou model. While the fire location has fewer impacts on the smoke height, temperature, and visibility in the Washington model, metro stations with a high-dome structure can be beneficial to fire evacuation safety; however, the construction cost can be high. Metro stations with flat ceiling are widely used in more cities for it has lower construction cost; to compensate for its weaker abilities under fire conditions, it is suggested that smoke exhaust systems should be carefully and fully considered. [ABSTRACT FROM AUTHOR]

We developed a longitudinal temperature acquisition system to address the inaccuracies in the determination of temperature fields in a large-scale artificial ground freezing project. The system can determine the temperature field distribution inside a freezing pipe. The results indicate the apparent temperature differences among different freezing pipes, and the brine temperature in the freezing pipes has an evident nonlinear distribution along the length of the freezing pipes. Therefore, using a single temperature boundary condition to obtain the freezing temperature field may not be sufficient to accurately reflect the freezing temperature of the different layers. The proposed system offers a new method to determine the heat flux function. Moreover, the dynamic heat flux boundary was built for numerical simulation to solve the temperature field. Through comparison, it is found that the dynamic heat flux boundary can be used to obtain the frozen curtain morphology and temperature field distribution more accurately. After adopting the new solution method in a large-scale freezing project in Guangzhou, China, the accuracy of determination of frozen wall thickness increased by approximately 53%. This study can provide a new way of thinking about temperature field calculation in practical engineering problems. [Display omitted] • A new longitudinal temperature acquisition system was developed. • There were apparent differences in the cooling efficiency between different freezing pipes and layers. • The method for calculating the temperature field by dynamic heat flux boundary conditions of freezing pipe was proposed. • Using dynamic heat flux boundary to calculate can more accurately reflect the irregularities of the frozen curtain. [ABSTRACT FROM AUTHOR]

Atriums have recently been applied with increasing frequency for natural illumination, though they produce a harsh indoor thermal environment. Cooling energy consumption is extremely huge in atriums due to the hot summer in certain regions of China. Accordingly, this paper mainly focused on the ratio of skylight to atrium to optimize the thermal environment without compromising the natural lighting. The study quantitatively analyzed the impacts of two geometric parameters, the area ratio (AR) and section aspect ratio (SAR) of the skylight to the roof, on the lighting and thermal environments of atriums by simulation. These models are calibrated with the data measured in a library in Guangzhou, China, to obtain the most appropriate models and boundary conditions. The SAR range of models was set in SAR<4 to be universal through the investigation of buildings. From the results revealed, the AR is the critical factor affecting the diffuse skylight in atriums, whereas the SAR is not. It was when the AR≥1/5.5 that atriums with square plane can meet the natural lighting requirements. The atrium thermal environment was assessed comprehensively from the aspects of air temperature, surface temperature, and vertical temperature difference. It generally became better as the AR decreases and the SAR increases until to AR<1/5. Thus, the optimal nondimensional combination of the atrium configuration was AR = 1/5 and SAR = 4. The temperature distribution characteristics were explained by the theories of heat pressure and air flow, extending the application scope and prospects of this research. • The measured temperature distribution of one atrium was compared with CFD simulation. • The atrium scales conformed to natural lighting requirements were determined. • The thermal environment was optimized by changing ratios of skylight to atrium. • The rules of temperature distribution were explained via heat pressure and air flow. [ABSTRACT FROM AUTHOR]

When on-site tests are performed in artificial ground freezing projects, the conventional analytical method for determining the soil temperature field often presents significant error under certain conditions, particularly when the temperature-measuring pipe is far removed from the freezing front. This paper proposes a new method—called the undetermined coefficient method (UCM)—that more accurately predicts the actual soil temperature field and position of the freezing front. The UCM comprises a new mathematical formula developed based on a series of model tests performed under three different conditions—no seepage, constant seepage, and sudden seepage—and a multiple data regression analysis-based method for determining the coefficients in the developed formula. The proposed UCM was compared to a conventional analytical method based on the results from model tests and from the construction of the cross-channel of Guangzhou Metro Line 11. The results indicated that the UCM presented higher stability and practical value than conventional alternatives and could accurately predict the actual soil temperature field and position of the freezing front. Therefore, the UCM is expected to be of high practical value in artificial ground-freezing operations. • A novel analytical method—the undetermined coefficient method (UCM)—is proposed. • A model test about different seepage condition was carried out. • The UCM can be applied to real large-scale artificial ground freezing operations. • The optimal measurement point positions in UCM were determined. [ABSTRACT FROM AUTHOR]

• Full-scale experiments were applied in subway tunnels with different operation conditions. • Tunnel air and wall temperature were monitored for more than 1 year. Temperature features at day, month, and year levels were analyzed. • The phenomenon of temperature rising over time in newly built subway lines were identified. • The impact of train number, passenger flow and ventilation condition on tunnel thermal environment were pointed out. Tunnel thermal environment has a great impact on the energy consumption and safety in the subway system. Due to the complexity of subway network structure and the influence of piston effect, analytical and numerical methods are limited in showing the real situation. In comparison, full-scale experiments are effective in verifying models and presenting the real situation in subway tunnels. In this study, the experimental method was adopted. The tunnel wall and air temperature were monitored in 5 subway lines in Guangzhou, China for more than 1 year. These selected tunnels have different operation conditions; namely operation year, train density, passenger number, and ventilation form. Based on long-term and multipoint monitoring, the temperature profiles were obtained. In aspect of time-varying features, it was found that the daily temperature profiles present different shapes nder different heat sources and ventilation situations. The temperature profiles in a typical year show 60 and 30–60 days delayed effect compared to outdoor temperature in winter and summer, respectively. In regard to the temperature distribution features, it was revealed that the temperature distribution within a tunnel is not sensitive to the length of tunnel but susceptible to ventilation condition; the tunnel temperature differences between two ends are 0.1-0.8℃ and 1.4-1.6℃ in high-ventilation and low-ventilation tunnels, respectively. Moreover, the possible influencing factors, including operation year, train density, passenger flow, and ventilation condition were analyzed. It was discovered that the factors related to the heat source (train density and passenger flow) have the most important impact, and the ventilation condition takes second place, while the operation years almost have no impact on the thermal environment in subway tunnels. The monitoring data are useful for both analytical and numerical studies and this study provides first-hand research data for subway operators. [ABSTRACT FROM AUTHOR]