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At present, values adopted from specifications are mostly used to define the convective heat transfer coefficient ch in localized fire researches. In this paper, the specific scenario of the steel column surrounded by fire plume is selected as a typical case to explore the surface ch change rules of the steel column. This paper conducts a two-way coupling simulation analysis of the fire and the thermal models by means of CFD codes. First, the validity of this simulation methodology is verified. Following this, the distribution laws of the spatial velocity are analyzed, and the ch coefficient of the steel column surface is explored in detail using two different calculation formulas. The ch results obtained based on Newton's Law of Cooling is more likely to consider the temperature boundary layer situations above the column surface, which is lower at the bottom of the column and increases with height, with relative maximum value in the lower and middle parts of the column, reaching around 35 W/m2 K. In contrast, the c h distributions along the height obtained by the empirically based practical formula are similar to the distribution of fire plume velocity along the height. In other words, it considers mostly the effect of the velocity boundary layer, while the effect of significant changes in fluid temperature on convective heat transfer behavior is less considered.

A research idea of multi-physics field coupling can be used to solve the structural fire resistance problem. Most of the previous CFD-FEM numerical simulations in structural fire resistance studies apply adiabatic surface temperature (AST) to accurately describe the complex fire analysis boundary conditions, and this methodology belongs to the use of iterative coupling methods to achieve fluid-solid heat transfer coupling. However, there is less application for another direct two-way coupling method. In this paper, a 2.5-meter-high square steel tube column is selected to investigate the thermodynamic phenomena when surrounding by fire plume. Based on CFD code, the thermal-mechanical coupling in fluid domain is firstly realized, and then the fluid-solid thermal coupling is realized by using iterative coupling method (AST method) and direct coupling method (Conjugate heat transfer method, CHT method) respectively, and the accuracy of this two coupling methodology is verified by comparing with experimental data. The heat flux received at the column surface is analyzed in the CHT method while the characteristics of the AST parameters are analyzed in the AST method. Finally, the mechanical analysis is completed with the solid temperature as the boundary condition and the thermal-mechanical coupling in solid domain is realized.

Fire accidents constitute a significant safety concern for automotive lithium-ion battery packs and have impeded the development of electric vehicles (EVs). While fire safety concerns have been raised about EVs, their fire performance remains unknown, especially for plug-in hybrid electric vehicles (PHEVs). Hence, this paper conducted full-scale fire experiments of PHEVs to explore their fire behavior and characteristics. Two brand new PHEVs were employed, and their power battery packs were ignited as the origin of the fire to simulate the representative fire scenario. Results showed that visible flames appeared around the chassis after about 60 min of the experimental procedure. Around the fire emerged, the battery packs intermittently released plenty of white smoke, which induced gas-phase explosions. The main component of the smoke was combustible gases. The SUV-type PHEV test took 9 min 11 s for the chassis flames to evolve into a passenger compartment fire. Due to the slow propagation of the fire in sedan-type PHEV, it required 9 min 56 s for flames to engulf the rear part of the sedan. The maximum temperature of PHEV fires was 843.6°C, while the maximum height of the fire reached around 3 m. At a distance of 1 m, the radiative heat emitted from burning PHEVs peaked at 1.151 kW/m2. Moreover, some secondary hazards of PHEV fires were illustrated. These results stimulate future experiments seeking novel flame retardant materials for PHEVs and provide helpful guidance on screening reliable PHEV fire prediction and protection strategies.

El ahorro de energía en los edificios es una de las medidas importantes que se utilizan para reducir la escasez de energía y fomentar el desarrollo sostenible1- 3. El consumo de energía de los sistemas de conductos de ventilación y aire acondicionado (como, por ejemplo, los tipos de sistemas de transporte y distribución de aire) ha recibido considerable atención. El consumo de energía del ventilador causado por la resistencia de los sistemas de ventilación y aire acondicionado representa aproximadamente del 20% al 40% del consumo de energía de los edificios públicos; para algunos edificios, los niveles son incluso superiores a los de los sistemas de refrigeración acondicionados4, 5. Por lo tanto, determinar cómo optimizar el rendimiento de los sistemas de conductos de ventilación y aire acondicionado, reduciendo así la resistencia y disminuyendo el consumo de energía del ventilador, se ha convertido en un tema clave.